120 files changed, 13197 insertions, 3816 deletions

diff --git a/.flake8 b/.flake8
index 45ab6562..6b824e97 100644
--- a/.flake8
+++ b/.flake8
@@ -1,3 +1,15 @@
 [flake8]
-max-line-length=80
-ignore=E111,E114,E402
+max-line-length=100
+ignore=
+    # E111: Indentation is not a multiple of four
+    E111,
+    # E114: Indentation is not a multiple of four (comment)
+    E114,
+    # E402: Module level import not at top of file
+    E402,
+    # E731: do not assign a lambda expression, use a def
+    E731,
+    # W503: Line break before binary operator
+    W503,
+    # W504: Line break after binary operator
+    W504
diff --git a/.github/workflows/test-ci.yml b/.github/workflows/test-ci.yml
new file mode 100644
index 00000000..19881858
--- /dev/null
+++ b/.github/workflows/test-ci.yml
@@ -0,0 +1,31 @@
+# GitHub actions workflow.
+# https://help.github.com/en/actions/automating-your-workflow-with-github-actions/workflow-syntax-for-github-actions
+
+name: Test CI
+
+on:
+  push:
+    branches: [main, repo-1, stable, maint]
+    tags: [v*]
+
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        python-version: [3.6, 3.7, 3.8, 3.9]
+    runs-on: ${{ matrix.os }}
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v1
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install tox tox-gh-actions
+    - name: Test with tox
+      run: tox
diff --git a/.gitignore b/.gitignore
index 37962447..4e91be94 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
+*.asc
 *.egg-info/
 *.log
 *.pyc
@@ -6,6 +7,7 @@ __pycache__
 .repopickle_*
 /repoc
 /.tox
+/.venv
 
 # PyCharm related
 /.idea/
diff --git a/.mailmap b/.mailmap
index 905139d5..caf1c98f 100644
--- a/.mailmap
+++ b/.mailmap
@@ -4,6 +4,7 @@ Hu Xiuyun <xiuyun.hu@hisilicon.com>           Hu xiuyun <xiuyun.hu@hisilicon.com
 Hu Xiuyun <xiuyun.hu@hisilicon.com>           Hu Xiuyun <clouds08@qq.com>
 Jelly Chen <chenguodong@huawei.com>           chenguodong <chenguodong@huawei.com>
 Jia Bi <bijia@xiaomi.com>                     bijia <bijia@xiaomi.com>
+Jiri Tyr <jiri.tyr@gmail.com>                 Jiri tyr <jiri.tyr@gmail.com>
 JoonCheol Park <jooncheol@gmail.com>          Jooncheol Park <jooncheol@gmail.com>
 Sergii Pylypenko <x.pelya.x@gmail.com>        pelya <x.pelya.x@gmail.com>
 Shawn Pearce <sop@google.com>                 Shawn O. Pearce <sop@google.com>
diff --git a/README.md b/README.md
index 5c886359..5519e9aa 100644
--- a/README.md
+++ b/README.md
@@ -6,15 +6,29 @@ development workflow.  Repo is not meant to replace Git, only to make it
 easier to work with Git.  The repo command is an executable Python script
 that you can put anywhere in your path.
 
-* Homepage: https://gerrit.googlesource.com/git-repo/
-* Bug reports: https://bugs.chromium.org/p/gerrit/issues/list?q=component:repo
-* Source: https://gerrit.googlesource.com/git-repo/
-* Overview: https://source.android.com/source/developing.html
-* Docs: https://source.android.com/source/using-repo.html
+* Homepage: <https://gerrit.googlesource.com/git-repo/>
+* Mailing list: [repo-discuss on Google Groups][repo-discuss]
+* Bug reports: <https://bugs.chromium.org/p/gerrit/issues/list?q=component:repo>
+* Source: <https://gerrit.googlesource.com/git-repo/>
+* Overview: <https://source.android.com/source/developing.html>
+* Docs: <https://source.android.com/source/using-repo.html>
 * [repo Manifest Format](./docs/manifest-format.md)
 * [repo Hooks](./docs/repo-hooks.md)
 * [Submitting patches](./SUBMITTING_PATCHES.md)
 * Running Repo in [Microsoft Windows](./docs/windows.md)
+* GitHub mirror: <https://github.com/GerritCodeReview/git-repo>
+* Postsubmit tests: <https://github.com/GerritCodeReview/git-repo/actions>
+
+## Contact
+
+Please use the [repo-discuss] mailing list or [issue tracker] for questions.
+
+You can [file a new bug report][new-bug] under the "repo" component.
+
+Please do not e-mail individual developers for support.
+They do not have the bandwidth for it, and often times questions have already
+been asked on [repo-discuss] or bugs posted to the [issue tracker].
+So please search those sites first.
 
 ## Install
 
@@ -34,3 +48,8 @@ $ PATH="${HOME}/.bin:${PATH}"
 $ curl https://storage.googleapis.com/git-repo-downloads/repo > ~/.bin/repo
 $ chmod a+rx ~/.bin/repo
 ```
+
+
+[new-bug]: https://bugs.chromium.org/p/gerrit/issues/entry?template=Repo+tool+issue
+[issue tracker]: https://bugs.chromium.org/p/gerrit/issues/list?q=component:repo
+[repo-discuss]: https://groups.google.com/forum/#!forum/repo-discuss
diff --git a/SUBMITTING_PATCHES.md b/SUBMITTING_PATCHES.md
index 5021e7ee..0c189247 100644
--- a/SUBMITTING_PATCHES.md
+++ b/SUBMITTING_PATCHES.md
@@ -4,13 +4,13 @@
 
  - Make small logical changes.
  - Provide a meaningful commit message.
- - Check for coding errors and style nits with pyflakes and flake8
+ - Check for coding errors and style nits with flake8.
  - Make sure all code is under the Apache License, 2.0.
  - Publish your changes for review.
  - Make corrections if requested.
  - Verify your changes on gerrit so they can be submitted.
 
-   `git push https://gerrit-review.googlesource.com/git-repo HEAD:refs/for/master`
+   `git push https://gerrit-review.googlesource.com/git-repo HEAD:refs/for/main`
 
 
 # Long Version
@@ -38,34 +38,30 @@ If your description starts to get too long, that's a sign that you
 probably need to split up your commit to finer grained pieces.
 
 
-## Check for coding errors and style nits with pyflakes and flake8
+## Check for coding errors and style violations with flake8
 
-### Coding errors
+Run `flake8` on changed modules:
 
-Run `pyflakes` on changed modules:
-
-    pyflakes file.py
+    flake8 file.py
 
-Ideally there should be no new errors or warnings introduced.
+Note that repo generally follows [Google's Python Style Guide] rather than
+[PEP 8], with a couple of notable exceptions:
 
-### Style violations
+* Indentation is at 2 columns rather than 4
+* The maximum line length is 100 columns rather than 80
 
-Run `flake8` on changes modules:
+There should be no new errors or warnings introduced.
 
-    flake8 file.py
+Warnings that cannot be avoided without going against the Google Style Guide
+may be suppressed inline individally using a `# noqa` comment as described
+in the [flake8 documentation].
 
-Note that repo generally follows [Google's python style guide] rather than
-[PEP 8], so it's possible that the output of `flake8` will be quite noisy.
-It's not mandatory to avoid all warnings, but at least the maximum line
-length should be followed.
+If there are many occurrences of the same warning, these may be suppressed for
+the entire project in the included `.flake8` file.
 
-If there are many occurrences of the same warning that cannot be
-avoided without going against the Google style guide, these may be
-suppressed in the included `.flake8` file.
-
-[Google's python style guide]: https://google.github.io/styleguide/pyguide.html
+[Google's Python Style Guide]: https://google.github.io/styleguide/pyguide.html
 [PEP 8]: https://www.python.org/dev/peps/pep-0008/
-
+[flake8 documentation]: https://flake8.pycqa.org/en/3.1.1/user/ignoring-errors.html#in-line-ignoring-errors
 
 ## Running tests
 
@@ -154,7 +150,7 @@ Push your patches over HTTPS to the review server, possibly through
 a remembered remote to make this easier in the future:
 
     git config remote.review.url https://gerrit-review.googlesource.com/git-repo
-    git config remote.review.push HEAD:refs/for/master
+    git config remote.review.push HEAD:refs/for/main
 
     git push review
 
diff --git a/color.py b/color.py
index 5b3a282d..fdd72534 100644
--- a/color.py
+++ b/color.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -84,6 +82,7 @@ def _Color(fg=None, bg=None, attr=None):
     code = ''
   return code
 
+
 DEFAULT = None
 
 
diff --git a/command.py b/command.py
index 9e113f1a..b972a0be 100644
--- a/command.py
+++ b/command.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,25 +12,65 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import multiprocessing
 import os
 import optparse
-import platform
 import re
 import sys
 
 from event_log import EventLog
 from error import NoSuchProjectError
 from error import InvalidProjectGroupsError
+import progress
+
+
+# Are we generating man-pages?
+GENERATE_MANPAGES = os.environ.get('_REPO_GENERATE_MANPAGES_') == ' indeed! '
+
+
+# Number of projects to submit to a single worker process at a time.
+# This number represents a tradeoff between the overhead of IPC and finer
+# grained opportunity for parallelism. This particular value was chosen by
+# iterating through powers of two until the overall performance no longer
+# improved. The performance of this batch size is not a function of the
+# number of cores on the system.
+WORKER_BATCH_SIZE = 32
+
+
+# How many jobs to run in parallel by default?  This assumes the jobs are
+# largely I/O bound and do not hit the network.
+DEFAULT_LOCAL_JOBS = min(os.cpu_count(), 8)
 
 
 class Command(object):
   """Base class for any command line action in repo.
   """
 
-  common = False
+  # Singleton for all commands to track overall repo command execution and
+  # provide event summary to callers.  Only used by sync subcommand currently.
+  #
+  # NB: This is being replaced by git trace2 events.  See git_trace2_event_log.
   event_log = EventLog()
-  manifest = None
-  _optparse = None
+
+  # Whether this command is a "common" one, i.e. whether the user would commonly
+  # use it or it's a more uncommon command.  This is used by the help command to
+  # show short-vs-full summaries.
+  COMMON = False
+
+  # Whether this command supports running in parallel.  If greater than 0,
+  # it is the number of parallel jobs to default to.
+  PARALLEL_JOBS = None
+
+  def __init__(self, repodir=None, client=None, manifest=None, gitc_manifest=None,
+               git_event_log=None):
+    self.repodir = repodir
+    self.client = client
+    self.manifest = manifest
+    self.gitc_manifest = gitc_manifest
+    self.git_event_log = git_event_log
+
+    # Cache for the OptionParser property.
+    self._optparse = None
 
   def WantPager(self, _opt):
     return False
@@ -66,13 +104,39 @@ class Command(object):
         usage = self.helpUsage.strip().replace('%prog', me)
       except AttributeError:
         usage = 'repo %s' % self.NAME
-      self._optparse = optparse.OptionParser(usage=usage)
+      epilog = 'Run `repo help %s` to view the detailed manual.' % self.NAME
+      self._optparse = optparse.OptionParser(usage=usage, epilog=epilog)
+      self._CommonOptions(self._optparse)
       self._Options(self._optparse)
     return self._optparse
 
-  def _Options(self, p):
-    """Initialize the option parser.
+  def _CommonOptions(self, p, opt_v=True):
+    """Initialize the option parser with common options.
+
+    These will show up for *all* subcommands, so use sparingly.
+    NB: Keep in sync with repo:InitParser().
     """
+    g = p.add_option_group('Logging options')
+    opts = ['-v'] if opt_v else []
+    g.add_option(*opts, '--verbose',
+                 dest='output_mode', action='store_true',
+                 help='show all output')
+    g.add_option('-q', '--quiet',
+                 dest='output_mode', action='store_false',
+                 help='only show errors')
+
+    if self.PARALLEL_JOBS is not None:
+      default = 'based on number of CPU cores'
+      if not GENERATE_MANPAGES:
+        # Only include active cpu count if we aren't generating man pages.
+        default = f'%default; {default}'
+      p.add_option(
+          '-j', '--jobs',
+          type=int, default=self.PARALLEL_JOBS,
+          help=f'number of jobs to run in parallel (default: {default})')
+
+  def _Options(self, p):
+    """Initialize the option parser with subcommand-specific options."""
 
   def _RegisteredEnvironmentOptions(self):
     """Get options that can be set from environment variables.
@@ -98,6 +162,11 @@ class Command(object):
     self.OptionParser.print_usage()
     sys.exit(1)
 
+  def CommonValidateOptions(self, opt, args):
+    """Validate common options."""
+    opt.quiet = opt.output_mode is False
+    opt.verbose = opt.output_mode is True
+
   def ValidateOptions(self, opt, args):
     """Validate the user options & arguments before executing.
 
@@ -113,6 +182,44 @@ class Command(object):
     """
     raise NotImplementedError
 
+  @staticmethod
+  def ExecuteInParallel(jobs, func, inputs, callback, output=None, ordered=False):
+    """Helper for managing parallel execution boiler plate.
+
+    For subcommands that can easily split their work up.
+
+    Args:
+      jobs: How many parallel processes to use.
+      func: The function to apply to each of the |inputs|.  Usually a
+          functools.partial for wrapping additional arguments.  It will be run
+          in a separate process, so it must be pickalable, so nested functions
+          won't work.  Methods on the subcommand Command class should work.
+      inputs: The list of items to process.  Must be a list.
+      callback: The function to pass the results to for processing.  It will be
+          executed in the main thread and process the results of |func| as they
+          become available.  Thus it may be a local nested function.  Its return
+          value is passed back directly.  It takes three arguments:
+          - The processing pool (or None with one job).
+          - The |output| argument.
+          - An iterator for the results.
+      output: An output manager.  May be progress.Progess or color.Coloring.
+      ordered: Whether the jobs should be processed in order.
+
+    Returns:
+      The |callback| function's results are returned.
+    """
+    try:
+      # NB: Multiprocessing is heavy, so don't spin it up for one job.
+      if len(inputs) == 1 or jobs == 1:
+        return callback(None, output, (func(x) for x in inputs))
+      else:
+        with multiprocessing.Pool(jobs) as pool:
+          submit = pool.imap if ordered else pool.imap_unordered
+          return callback(pool, output, submit(func, inputs, chunksize=WORKER_BATCH_SIZE))
+    finally:
+      if isinstance(output, progress.Progress):
+        output.end()
+
   def _ResetPathToProjectMap(self, projects):
     self._by_path = dict((p.worktree, p) for p in projects)
 
@@ -123,9 +230,9 @@ class Command(object):
     project = None
     if os.path.exists(path):
       oldpath = None
-      while path and \
-            path != oldpath and \
-            path != manifest.topdir:
+      while (path and
+             path != oldpath and
+             path != manifest.topdir):
         try:
           project = self._by_path[path]
           break
@@ -156,9 +263,7 @@ class Command(object):
     mp = manifest.manifestProject
 
     if not groups:
-      groups = mp.config.GetString('manifest.groups')
-    if not groups:
-      groups = 'default,platform-' + platform.system().lower()
+      groups = manifest.GetGroupsStr()
     groups = [x for x in re.split(r'[,\s]+', groups) if x]
 
     if not args:
@@ -236,6 +341,7 @@ class InteractiveCommand(Command):
   """Command which requires user interaction on the tty and
      must not run within a pager, even if the user asks to.
   """
+
   def WantPager(self, _opt):
     return False
 
@@ -244,6 +350,7 @@ class PagedCommand(Command):
   """Command which defaults to output in a pager, as its
      display tends to be larger than one screen full.
   """
+
   def WantPager(self, _opt):
     return True
 
diff --git a/completion.bash b/completion.bash
new file mode 100644
index 00000000..09291d5c
--- /dev/null
+++ b/completion.bash
@@ -0,0 +1,156 @@
+# Copyright 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Programmable bash completion.  https://github.com/scop/bash-completion
+
+# TODO: Handle interspersed options.  We handle `repo h<tab>`, but not
+# `repo --time h<tab>`.
+
+# Complete the list of repo subcommands.
+__complete_repo_list_commands() {
+  local repo=${COMP_WORDS[0]}
+  (
+  # Handle completions if running outside of a checkout.
+  if ! "${repo}" help --all 2>/dev/null; then
+    repo help 2>/dev/null
+  fi
+  ) | sed -n '/^  /{s/  \([^ ]\+\) .\+/\1/;p}'
+}
+
+# Complete list of all branches available in all projects in the repo client
+# checkout.
+__complete_repo_list_branches() {
+  local repo=${COMP_WORDS[0]}
+  "${repo}" branches 2>/dev/null | \
+    sed -n '/|/{s/[ *][Pp ] *\([^ ]\+\) .*/\1/;p}'
+}
+
+# Complete list of all projects available in the repo client checkout.
+__complete_repo_list_projects() {
+  local repo=${COMP_WORDS[0]}
+  "${repo}" list -n 2>/dev/null
+  "${repo}" list -p --relative-to=. 2>/dev/null
+}
+
+# Complete the repo <command> argument.
+__complete_repo_command() {
+  if [[ ${COMP_CWORD} -ne 1 ]]; then
+    return 1
+  fi
+
+  local command=${COMP_WORDS[1]}
+  COMPREPLY=($(compgen -W "$(__complete_repo_list_commands)" -- "${command}"))
+  return 0
+}
+
+# Complete repo subcommands that take <branch> <projects>.
+__complete_repo_command_branch_projects() {
+  local current=$1
+  if [[ ${COMP_CWORD} -eq 2 ]]; then
+    COMPREPLY=($(compgen -W "$(__complete_repo_list_branches)" -- "${current}"))
+  else
+    COMPREPLY=($(compgen -W "$(__complete_repo_list_projects)" -- "${current}"))
+  fi
+}
+
+# Complete repo subcommands that take only <projects>.
+__complete_repo_command_projects() {
+  local current=$1
+  COMPREPLY=($(compgen -W "$(__complete_repo_list_projects)" -- "${current}"))
+}
+
+# Complete `repo help`.
+__complete_repo_command_help() {
+  local current=$1
+  # CWORD=1 is "start".
+  # CWORD=2 is the <subcommand> which we complete here.
+  if [[ ${COMP_CWORD} -eq 2 ]]; then
+    COMPREPLY=(
+      $(compgen -W "$(__complete_repo_list_commands)" -- "${current}")
+    )
+  fi
+}
+
+# Complete `repo forall`.
+__complete_repo_command_forall() {
+  local current=$1
+  # CWORD=1 is "forall".
+  # CWORD=2+ are <projects> *until* we hit the -c option.
+  local i
+  for (( i = 0; i < COMP_CWORD; ++i )); do
+    if [[ "${COMP_WORDS[i]}" == "-c" ]]; then
+      return 0
+    fi
+  done
+
+  COMPREPLY=(
+    $(compgen -W "$(__complete_repo_list_projects)" -- "${current}")
+  )
+}
+
+# Complete `repo start`.
+__complete_repo_command_start() {
+  local current=$1
+  # CWORD=1 is "start".
+  # CWORD=2 is the <branch> which we don't complete.
+  # CWORD=3+ are <projects> which we complete here.
+  if [[ ${COMP_CWORD} -gt 2 ]]; then
+    COMPREPLY=(
+      $(compgen -W "$(__complete_repo_list_projects)" -- "${current}")
+    )
+  fi
+}
+
+# Complete the repo subcommand arguments.
+__complete_repo_arg() {
+  if [[ ${COMP_CWORD} -le 1 ]]; then
+    return 1
+  fi
+
+  local command=${COMP_WORDS[1]}
+  local current=${COMP_WORDS[COMP_CWORD]}
+  case ${command} in
+  abandon|checkout)
+    __complete_repo_command_branch_projects "${current}"
+    return 0
+    ;;
+
+  branch|branches|diff|info|list|overview|prune|rebase|smartsync|stage|status|\
+  sync|upload)
+    __complete_repo_command_projects "${current}"
+    return 0
+    ;;
+
+  help|start|forall)
+    __complete_repo_command_${command} "${current}"
+    return 0
+    ;;
+
+  *)
+    return 1
+    ;;
+  esac
+}
+
+# Complete the repo arguments.
+__complete_repo() {
+  COMPREPLY=()
+  __complete_repo_command && return 0
+  __complete_repo_arg && return 0
+  return 0
+}
+
+# Fallback to the default complete methods if we aren't able to provide anything
+# useful.  This will allow e.g. local paths to be used when it makes sense.
+complete -F __complete_repo -o bashdefault -o default repo
diff --git a/docs/internal-fs-layout.md b/docs/internal-fs-layout.md
new file mode 100644
index 00000000..af6a4523
--- /dev/null
+++ b/docs/internal-fs-layout.md
@@ -0,0 +1,263 @@
+# Repo internal filesystem layout
+
+A reference to the `.repo/` tree in repo client checkouts.
+Hopefully it's complete & up-to-date, but who knows!
+
+*** note
+**Warning**:
+This is meant for developers of the repo project itself as a quick reference.
+**Nothing** in here must be construed as ABI, or that repo itself will never
+change its internals in backwards incompatible ways.
+***
+
+[TOC]
+
+## .repo/ layout
+
+All content under `.repo/` is managed by `repo` itself with few exceptions.
+
+In general, you should not make manual changes in here.
+If a setting was initialized using an option to `repo init`, you should use that
+command to change the setting later on.
+It is always safe to re-run `repo init` in existing repo client checkouts.
+For example, if you want to change the manifest branch, you can simply run
+`repo init --manifest-branch=<new name>` and repo will take care of the rest.
+
+*   `config`: Per-repo client checkout settings using [git-config] file format.
+*   `.repo_config.json`: JSON cache of the `config` file for repo to
+    read/process quickly.
+
+### repo/ state
+
+*   `repo/`: A git checkout of the repo project.  This is how `repo` re-execs
+    itself to get the latest released version.
+
+    It tracks the git repository at `REPO_URL` using the `REPO_REV` branch.
+    Those are specified at `repo init` time using the `--repo-url=<REPO_URL>`
+    and `--repo-rev=<REPO_REV>` options.
+
+    Any changes made to this directory will usually be automatically discarded
+    by repo itself when it checks for updates.  If you want to update to the
+    latest version of repo, use `repo selfupdate` instead.  If you want to
+    change the git URL/branch that this tracks, re-run `repo init` with the new
+    settings.
+
+*   `.repo_fetchtimes.json`: Used by `repo sync` to record stats when syncing
+    the various projects.
+
+### Manifests
+
+For more documentation on the manifest format, including the local_manifests
+support, see the [manifest-format.md] file.
+
+*   `manifests/`: A git checkout of the manifest project.  Its `.git/` state
+    points to the `manifest.git` bare checkout (see below).  It tracks the git
+    branch specified at `repo init` time via `--manifest-branch`.
+
+    The local branch name is always `default` regardless of the remote tracking
+    branch.  Do not get confused if the remote branch is not `default`, or if
+    there is a remote `default` that is completely different!
+
+    No manual changes should be made in here as it will just confuse repo and
+    it won't automatically recover causing no new changes to be picked up.
+
+*   `manifests.git/`: A bare checkout of the manifest project.  It tracks the
+    git repository specified at `repo init` time via `--manifest-url`.
+
+    No manual changes should be made in here as it will just confuse repo.
+    If you want to switch the tracking settings, re-run `repo init` with the
+    new settings.
+
+*   `manifest.xml`: The manifest that repo uses.  It is generated at `repo init`
+    and uses the `--manifest-name` to determine what manifest file to load next
+    out of `manifests/`.
+
+    Do not try to modify this to load other manifests as it will confuse repo.
+    If you want to switch manifest files, re-run `repo init` with the new
+    setting.
+
+    Older versions of repo managed this with symlinks.
+
+*   `manifest.xml -> manifests/<manifest-name>.xml`: A symlink to the manifest
+    that the user wishes to sync.  It is specified at `repo init` time via
+    `--manifest-name`.
+
+
+*   `manifests.git/.repo_config.json`: JSON cache of the `manifests.git/config`
+    file for repo to read/process quickly.
+
+*   `local_manifest.xml` (*Deprecated*): User-authored tweaks to the manifest
+    used to sync.  See [local manifests] for more details.
+*   `local_manifests/`: Directory of user-authored manifest fragments to tweak
+    the manifest used to sync.  See [local manifests] for more details.
+
+### Project objects
+
+*** note
+**Warning**: Please do not use repo's approach to projects/ & project-objects/
+layouts as a model for other tools to implement similar approaches.
+It has a number of known downsides like:
+*   [Symlinks do not work well under Windows](./windows.md).
+*   Git sometimes replaces symlinks under .git/ with real files (under unknown
+    circumstances), and then the internal state gets out of sync, and data loss
+    may ensue.
+*   When sharing project-objects between multiple project checkouts, Git might
+    automatically run `gc` or `prune` which may lead to data loss or corruption
+    (since those operate on leaf projects and miss refs in other leaves).  See
+    https://gerrit-review.googlesource.com/c/git-repo/+/254392 for more details.
+
+Instead, you should use standard Git workflows like [git worktree] or
+[gitsubmodules] with [superprojects].
+***
+
+*   `copy-link-files.json`: Tracking file used by `repo sync` to determine when
+    copyfile or linkfile are added or removed and need corresponding updates.
+*   `project.list`: Tracking file used by `repo sync` to determine when projects
+    are added or removed and need corresponding updates in the checkout.
+*   `projects/`: Bare checkouts of every project synced by the manifest.  The
+    filesystem layout matches the `<project path=...` setting in the manifest
+    (i.e. where it's checked out in the repo client source tree).  Those
+    checkouts will symlink their `.git/` state to paths under here.
+
+    Some git state is further split out under `project-objects/`.
+*   `project-objects/`: Git objects that are safe to share across multiple
+    git checkouts.  The filesystem layout matches the `<project name=...`
+    setting in the manifest (i.e. the path on the remote server) with a `.git`
+    suffix.  This allows for multiple checkouts of the same remote git repo to
+    share their objects.  For example, you could have different branches of
+    `foo/bar.git` checked out to `foo/bar-main`, `foo/bar-release`, etc...
+    There will be multiple trees under `projects/` for each one, but only one
+    under `project-objects/`.
+
+    This layout is designed to allow people to sync against different remotes
+    (e.g. a local mirror & a public review server) while avoiding duplicating
+    the content.  However, this can run into problems if different remotes use
+    the same path on their respective servers.  Best to avoid that.
+*   `subprojects/`: Like `projects/`, but for git submodules.
+*   `subproject-objects/`: Like `project-objects/`, but for git submodules.
+*   `worktrees/`: Bare checkouts of every project synced by the manifest.  The
+    filesystem layout matches the `<project name=...` setting in the manifest
+    (i.e. the path on the remote server) with a `.git` suffix.  This has the
+    same advantages as the `project-objects/` layout above.
+
+    This is used when [git worktree]'s are enabled.
+
+### Global settings
+
+The `.repo/manifests.git/config` file is used to track settings for the entire
+repo client checkout.
+
+Most settings use the `[repo]` section to avoid conflicts with git.
+
+Everything under `[repo.syncstate.*]` is used to keep track of sync details for logging
+purposes.
+
+User controlled settings are initialized when running `repo init`.
+
+| Setting                  | `repo init` Option        | Use/Meaning |
+|-------------------       |---------------------------|-------------|
+| manifest.groups          | `--groups` & `--platform` | The manifest groups to sync |
+| manifest.standalone      | `--standalone-manifest`   | Download manifest as static file instead of creating checkout |
+| repo.archive             | `--archive`               | Use `git archive` for checkouts |
+| repo.clonebundle         | `--clone-bundle`          | Whether the initial sync used clone.bundle explicitly |
+| repo.clonefilter         | `--clone-filter`          | Filter setting when using [partial git clones] |
+| repo.depth               | `--depth`                 | Create shallow checkouts when cloning |
+| repo.dissociate          | `--dissociate`            | Dissociate from any reference/mirrors after initial clone |
+| repo.mirror              | `--mirror`                | Checkout is a repo mirror |
+| repo.partialclone        | `--partial-clone`         | Create [partial git clones] |
+| repo.partialcloneexclude | `--partial-clone-exclude` | Comma-delimited list of project names (not paths) to exclude while using [partial git clones] |
+| repo.reference           | `--reference`             | Reference repo client checkout |
+| repo.submodules          | `--submodules`            | Sync git submodules |
+| repo.superproject        | `--use-superproject`      | Sync [superproject] |
+| repo.worktree            | `--worktree`              | Use [git worktree] for checkouts |
+| user.email               | `--config-name`           | User's e-mail address; Copied into `.git/config` when checking out a new project |
+| user.name                | `--config-name`           | User's name; Copied into `.git/config` when checking out a new project |
+
+[partial git clones]: https://git-scm.com/docs/gitrepository-layout#_code_partialclone_code
+[superproject]: https://en.wikibooks.org/wiki/Git/Submodules_and_Superprojects
+
+### Repo hooks settings
+
+For more details on this feature, see the [repo-hooks docs](./repo-hooks.md).
+We'll just discuss the internal configuration settings.
+These are stored in the registered `<repo-hooks>` project itself, so if the
+manifest switches to a different project, the settings will not be copied.
+
+| Setting                              | Use/Meaning |
+|--------------------------------------|-------------|
+| repo.hooks.\<hook\>.approvedmanifest | User approval for secure manifest sources (e.g. https://) |
+| repo.hooks.\<hook\>.approvedhash     | User approval for insecure manifest sources (e.g. http://) |
+
+
+For example, if our manifest had the following entries, we would store settings
+under `.repo/projects/src/repohooks.git/config` (which would be reachable via
+`git --git-dir=src/repohooks/.git config`).
+```xml
+  <project path="src/repohooks" name="chromiumos/repohooks" ... />
+  <repo-hooks in-project="chromiumos/repohooks" ... />
+```
+
+If `<hook>` is `pre-upload`, the `.git/config` setting might be:
+```ini
+[repo "hooks.pre-upload"]
+        approvedmanifest = https://chromium.googlesource.com/chromiumos/manifest
+```
+
+## Per-project settings
+
+These settings are somewhat meant to be tweaked by the user on a per-project
+basis (e.g. `git config` in a checked out source repo).
+
+Where possible, we re-use standard git settings to avoid confusion, and we
+refrain from documenting those, so see [git-config] documentation instead.
+
+See `repo help upload` for documentation on `[review]` settings.
+
+The `[remote]` settings are automatically populated/updated from the manifest.
+
+The `[branch]` settings are updated by `repo start` and `git branch`.
+
+| Setting                       | Subcommands   | Use/Meaning |
+|-------------------------------|---------------|-------------|
+| review.\<url\>.autocopy       | upload        | Automatically add to `--cc=<value>` |
+| review.\<url\>.autoreviewer   | upload        | Automatically add to `--reviewers=<value>` |
+| review.\<url\>.autoupload     | upload        | Automatically answer "yes" or "no" to all prompts |
+| review.\<url\>.uploadhashtags | upload        | Automatically add to `--hashtag=<value>` |
+| review.\<url\>.uploadlabels   | upload        | Automatically add to `--label=<value>` |
+| review.\<url\>.uploadnotify   | upload        | [Notify setting][upload-notify] to use |
+| review.\<url\>.uploadtopic    | upload        | Default [topic] to use |
+| review.\<url\>.username       | upload        | Override username with `ssh://` review URIs |
+| remote.\<remote\>.fetch       | sync          | Set of refs to fetch |
+| remote.\<remote\>.projectname | \<network\>   | The name of the project as it exists in Gerrit review |
+| remote.\<remote\>.pushurl     | upload        | The base URI for pushing CLs |
+| remote.\<remote\>.review      | upload        | The URI of the Gerrit review server |
+| remote.\<remote\>.url         | sync & upload | The URI of the git project to fetch |
+| branch.\<branch\>.merge       | sync & upload | The branch to merge & upload & track |
+| branch.\<branch\>.remote      | sync & upload | The remote to track |
+
+## ~/ dotconfig layout
+
+Repo will create & maintain a few files in the user's home directory.
+
+*   `.repoconfig/`: Repo's per-user directory for all random config files/state.
+*   `.repoconfig/config`: Per-user settings using [git-config] file format.
+*   `.repoconfig/keyring-version`: Cache file for checking if the gnupg subdir
+    has all the same keys as the repo launcher.  Used to avoid running gpg
+    constantly as that can be quite slow.
+*   `.repoconfig/gnupg/`: GnuPG's internal state directory used when repo needs
+    to run `gpg`.  This provides isolation from the user's normal `~/.gnupg/`.
+
+*   `.repoconfig/.repo_config.json`: JSON cache of the `.repoconfig/config`
+    file for repo to read/process quickly.
+*   `.repo_.gitconfig.json`: JSON cache of the `.gitconfig` file for repo to
+    read/process quickly.
+
+
+[git-config]: https://git-scm.com/docs/git-config
+[git worktree]: https://git-scm.com/docs/git-worktree
+[gitsubmodules]: https://git-scm.com/docs/gitsubmodules
+[manifest-format.md]: ./manifest-format.md
+[local manifests]: ./manifest-format.md#Local-Manifests
+[superprojects]: https://en.wikibooks.org/wiki/Git/Submodules_and_Superprojects
+[topic]: https://gerrit-review.googlesource.com/Documentation/intro-user.html#topics
+[upload-notify]: https://gerrit-review.googlesource.com/Documentation/user-upload.html#notify
diff --git a/docs/manifest-format.md b/docs/manifest-format.md
index 93d9b960..8e0049b3 100644
--- a/docs/manifest-format.md
+++ b/docs/manifest-format.md
@@ -21,6 +21,7 @@ following DTD:
 
 ```xml
 <!DOCTYPE manifest [
+
   <!ELEMENT manifest (notice?,
                       remote*,
                       default?,
@@ -29,11 +30,13 @@ following DTD:
                       project*,
                       extend-project*,
                       repo-hooks?,
+                      superproject?,
+                      contactinfo?,
                       include*)>
 
   <!ELEMENT notice (#PCDATA)>
 
-  <!ELEMENT remote EMPTY>
+  <!ELEMENT remote (annotation*)>
   <!ATTLIST remote name         ID    #REQUIRED>
   <!ATTLIST remote alias        CDATA #IMPLIED>
   <!ATTLIST remote fetch        CDATA #REQUIRED>
@@ -87,21 +90,39 @@ following DTD:
   <!ELEMENT extend-project EMPTY>
   <!ATTLIST extend-project name CDATA #REQUIRED>
   <!ATTLIST extend-project path CDATA #IMPLIED>
+  <!ATTLIST extend-project dest-path CDATA #IMPLIED>
   <!ATTLIST extend-project groups CDATA #IMPLIED>
   <!ATTLIST extend-project revision CDATA #IMPLIED>
+  <!ATTLIST extend-project remote CDATA #IMPLIED>
 
   <!ELEMENT remove-project EMPTY>
   <!ATTLIST remove-project name  CDATA #REQUIRED>
+  <!ATTLIST remove-project optional  CDATA #IMPLIED>
 
   <!ELEMENT repo-hooks EMPTY>
   <!ATTLIST repo-hooks in-project CDATA #REQUIRED>
   <!ATTLIST repo-hooks enabled-list CDATA #REQUIRED>
 
+  <!ELEMENT superproject EMPTY>
+  <!ATTLIST superproject name     CDATA #REQUIRED>
+  <!ATTLIST superproject remote   IDREF #IMPLIED>
+  <!ATTLIST superproject revision CDATA #IMPLIED>
+
+  <!ELEMENT contactinfo EMPTY>
+  <!ATTLIST contactinfo bugurl  CDATA #REQUIRED>
+
   <!ELEMENT include EMPTY>
-  <!ATTLIST include name CDATA #REQUIRED>
+  <!ATTLIST include name   CDATA #REQUIRED>
+  <!ATTLIST include groups CDATA #IMPLIED>
 ]>
 ```
 
+For compatibility purposes across repo releases, all unknown elements are
+silently ignored.  However, repo reserves all possible names for itself for
+future use.  If you want to use custom elements, the `x-*` namespace is
+reserved for that purpose, and repo guarantees to never allocate any
+corresponding names.
+
 A description of the elements and their attributes follows.
 
 
@@ -109,6 +130,10 @@ A description of the elements and their attributes follows.
 
 The root element of the file.
 
+### Element notice
+
+Arbitrary text that is displayed to users whenever `repo sync` finishes.
+The content is simply passed through as it exists in the manifest.
 
 ### Element remote
 
@@ -141,8 +166,8 @@ Attribute `review`: Hostname of the Gerrit server where reviews
 are uploaded to by `repo upload`.  This attribute is optional;
 if not specified then `repo upload` will not function.
 
-Attribute `revision`: Name of a Git branch (e.g. `master` or
-`refs/heads/master`). Remotes with their own revision will override
+Attribute `revision`: Name of a Git branch (e.g. `main` or
+`refs/heads/main`). Remotes with their own revision will override
 the default revision.
 
 ### Element default
@@ -155,11 +180,11 @@ Attribute `remote`: Name of a previously defined remote element.
 Project elements lacking a remote attribute of their own will use
 this remote.
 
-Attribute `revision`: Name of a Git branch (e.g. `master` or
-`refs/heads/master`).  Project elements lacking their own
+Attribute `revision`: Name of a Git branch (e.g. `main` or
+`refs/heads/main`).  Project elements lacking their own
 revision attribute will use this revision.
 
-Attribute `dest-branch`: Name of a Git branch (e.g. `master`).
+Attribute `dest-branch`: Name of a Git branch (e.g. `main`).
 Project elements not setting their own `dest-branch` will inherit
 this value. If this value is not set, projects will use `revision`
 by default instead.
@@ -235,24 +260,37 @@ name will be prefixed by the parent's.
 The project name must match the name Gerrit knows, if Gerrit is
 being used for code reviews.
 
+"name" must not be empty, and may not be an absolute path or use "." or ".."
+path components.  It is always interpreted relative to the remote's fetch
+settings, so if a different base path is needed, declare a different remote
+with the new settings needed.
+These restrictions are not enforced for [Local Manifests].
+
 Attribute `path`: An optional path relative to the top directory
 of the repo client where the Git working directory for this project
-should be placed.  If not supplied the project name is used.
+should be placed.  If not supplied the project "name" is used.
 If the project has a parent element, its path will be prefixed
 by the parent's.
 
+"path" may not be an absolute path or use "." or ".." path components.
+These restrictions are not enforced for [Local Manifests].
+
+If you want to place files into the root of the checkout (e.g. a README or
+Makefile or another build script), use the [copyfile] or [linkfile] elements
+instead.
+
 Attribute `remote`: Name of a previously defined remote element.
 If not supplied the remote given by the default element is used.
 
 Attribute `revision`: Name of the Git branch the manifest wants
 to track for this project.  Names can be relative to refs/heads
-(e.g. just "master") or absolute (e.g. "refs/heads/master").
+(e.g. just "main") or absolute (e.g. "refs/heads/main").
 Tags and/or explicit SHA-1s should work in theory, but have not
 been extensively tested.  If not supplied the revision given by
 the remote element is used if applicable, else the default
 element is used.
 
-Attribute `dest-branch`: Name of a Git branch (e.g. `master`).
+Attribute `dest-branch`: Name of a Git branch (e.g. `main`).
 When using `repo upload`, changes will be submitted for code
 review on this branch. If unspecified both here and in the
 default element, `revision` is used instead.
@@ -261,7 +299,7 @@ Attribute `groups`: List of groups to which this project belongs,
 whitespace or comma separated.  All projects belong to the group
 "all", and each project automatically belongs to a group of
 its name:`name` and path:`path`.  E.g. for
-<project name="monkeys" path="barrel-of"/>, that project
+`<project name="monkeys" path="barrel-of"/>`, that project
 definition is implicitly in the following manifest groups:
 default, name:monkeys, and path:barrel-of.  If you place a project in the
 group "notdefault", it will not be automatically downloaded by repo.
@@ -300,21 +338,29 @@ against changes to the original manifest.
 Attribute `path`: If specified, limit the change to projects checked out
 at the specified path, rather than all projects with the given name.
 
+Attribute `dest-path`: If specified, a path relative to the top directory
+of the repo client where the Git working directory for this project
+should be placed.  This is used to move a project in the checkout by
+overriding the existing `path` setting.
+
 Attribute `groups`: List of additional groups to which this project
 belongs.  Same syntax as the corresponding element of `project`.
 
 Attribute `revision`: If specified, overrides the revision of the original
 project.  Same syntax as the corresponding element of `project`.
 
+Attribute `remote`: If specified, overrides the remote of the original
+project.  Same syntax as the corresponding element of `project`.
+
 ### Element annotation
 
 Zero or more annotation elements may be specified as children of a
-project element. Each element describes a name-value pair that will be
-exported into each project's environment during a 'forall' command,
-prefixed with REPO__.  In addition, there is an optional attribute
-"keep" which accepts the case insensitive values "true" (default) or
-"false".  This attribute determines whether or not the annotation will
-be kept when exported with the manifest subcommand.
+project or remote element. Each element describes a name-value pair.
+For projects, this name-value pair will be exported into each project's
+environment during a 'forall' command, prefixed with `REPO__`.  In addition,
+there is an optional attribute "keep" which accepts the case insensitive values
+"true" (default) or "false".  This attribute determines whether or not the
+annotation will be kept when exported with the manifest subcommand.
 
 ### Element copyfile
 
@@ -338,7 +384,7 @@ It's just like copyfile and runs at the same time as copyfile but
 instead of copying it creates a symlink.
 
 The symlink is created at "dest" (relative to the top of the tree) and
-points to the path specified by "src".
+points to the path specified by "src" which is a path in the project.
 
 Parent directories of "dest" will be automatically created if missing.
 
@@ -355,6 +401,62 @@ This element is mostly useful in a local manifest file, where
 the user can remove a project, and possibly replace it with their
 own definition.
 
+Attribute `optional`: Set to true to ignore remove-project elements with no
+matching `project` element.
+
+### Element repo-hooks
+
+NB: See the [practical documentation](./repo-hooks.md) for using repo hooks.
+
+Only one repo-hooks element may be specified at a time.
+Attempting to redefine it will fail to parse.
+
+Attribute `in-project`: The project where the hooks are defined.  The value
+must match the `name` attribute (**not** the `path` attribute) of a previously
+defined `project` element.
+
+Attribute `enabled-list`: List of hooks to use, whitespace or comma separated.
+
+### Element superproject
+
+***
+*Note*: This is currently a WIP.
+***
+
+NB: See the [git superprojects documentation](
+https://en.wikibooks.org/wiki/Git/Submodules_and_Superprojects) for background
+information.
+
+This element is used to specify the URL of the superproject. It has "name" and
+"remote" as atrributes. Only "name" is required while the others have
+reasonable defaults. At most one superproject may be specified.
+Attempting to redefine it will fail to parse.
+
+Attribute `name`: A unique name for the superproject. This attribute has the
+same meaning as project's name attribute. See the
+[element project](#element-project) for more information.
+
+Attribute `remote`: Name of a previously defined remote element.
+If not supplied the remote given by the default element is used.
+
+Attribute `revision`: Name of the Git branch the manifest wants
+to track for this superproject. If not supplied the revision given
+by the remote element is used if applicable, else the default
+element is used.
+
+### Element contactinfo
+
+***
+*Note*: This is currently a WIP.
+***
+
+This element is used to let manifest authors self-register contact info.
+It has "bugurl" as a required atrribute. This element can be repeated,
+and any later entries will clobber earlier ones. This would allow manifest
+authors who extend manifests to specify their own contact info.
+
+Attribute `bugurl`: The URL to file a bug against the manifest owner.
+
 ### Element include
 
 This element provides the capability of including another manifest
@@ -364,8 +466,15 @@ target manifest to include - it must be a usable manifest on its own.
 Attribute `name`: the manifest to include, specified relative to
 the manifest repository's root.
 
+"name" may not be an absolute path or use "." or ".." path components.
+These restrictions are not enforced for [Local Manifests].
+
+Attribute `groups`: List of additional groups to which all projects
+in the included manifest belong. This appends and recurses, meaning
+all projects in sub-manifests carry all parent include groups.
+Same syntax as the corresponding element of `project`.
 
-## Local Manifests
+## Local Manifests {#local-manifests}
 
 Additional remotes and projects may be added through local manifest
 files stored in `$TOP_DIR/.repo/local_manifests/*.xml`.
@@ -392,10 +501,12 @@ these extra projects.
 Manifest files stored in `$TOP_DIR/.repo/local_manifests/*.xml` will
 be loaded in alphabetical order.
 
-Additional remotes and projects may also be added through a local
-manifest, stored in `$TOP_DIR/.repo/local_manifest.xml`. This method
-is deprecated in favor of using multiple manifest files as mentioned
-above.
+Projects from local manifest files are added into
+local::<local manifest filename> group.
+
+The legacy `$TOP_DIR/.repo/local_manifest.xml` path is no longer supported.
+
 
-If `$TOP_DIR/.repo/local_manifest.xml` exists, it will be loaded before
-any manifest files stored in `$TOP_DIR/.repo/local_manifests/*.xml`.
+[copyfile]: #Element-copyfile
+[linkfile]: #Element-linkfile
+[Local Manifests]: #local-manifests
diff --git a/docs/python-support.md b/docs/python-support.md
index a5c490a8..3eaaba33 100644
--- a/docs/python-support.md
+++ b/docs/python-support.md
@@ -18,13 +18,13 @@ Bugfixes may be added on a best-effort basis or from the community, but largely
 no new features will be added, nor is support guaranteed.
 
 Users can select this during `repo init` time via the [repo launcher].
-Otherwise the default branches (e.g. stable & master) will be used which will
+Otherwise the default branches (e.g. stable & main) will be used which will
 require Python 3.
 
 This means the [repo launcher] needs to support both Python 2 & Python 3, but
 since it doesn't import any other repo code, this shouldn't be too problematic.
 
-The master branch will require Python 3.6 at a minimum.
+The main branch will require Python 3.6 at a minimum.
 If the system has an older version of Python 3, then users will have to select
 the legacy Python 2 branch instead.
 
diff --git a/docs/release-process.md b/docs/release-process.md
index 22c2fd19..f71a4110 100644
--- a/docs/release-process.md
+++ b/docs/release-process.md
@@ -5,6 +5,37 @@ related topics and flows.
 
 [TOC]
 
+## Schedule
+
+There is no specific schedule for when releases are made.
+Usually it's more along the lines of "enough minor changes have been merged",
+or "there's a known issue the maintainers know should get fixed".
+If you find a fix has been merged for an issue important to you, but hasn't been
+released after a week or so, feel free to [contact] us to request a new release.
+
+### Release Freezes {#freeze}
+
+We try to observe a regular schedule for when **not** to release.
+If something goes wrong, staff need to be active in order to respond quickly &
+effectively.
+We also don't want to disrupt non-Google organizations if possible.
+
+We generally follow the rules:
+
+* Release during Mon - Thu, 9:00 - 14:00 [US PT]
+* Avoid holidays
+  * All regular [US holidays]
+  * Large international ones if possible
+  * All the various [New Years]
+    * Jan 1 in Gregorian calendar is the most obvious
+    * Check for large Lunar New Years too
+* Follow the normal [Google production freeze schedule]
+
+[US holidays]: https://en.wikipedia.org/wiki/Federal_holidays_in_the_United_States
+[US PT]: https://en.wikipedia.org/wiki/Pacific_Time_Zone
+[New Years]: https://en.wikipedia.org/wiki/New_Year
+[Google production freeze schedule]: http://goto.google.com/prod-freeze
+
 ## Launcher script
 
 The main repo script serves as a standalone program and is often referred to as
@@ -49,11 +80,12 @@ control how repo finds updates:
 
 *   `--repo-url`: This tells repo where to clone the full repo project itself.
     It defaults to the official project (`REPO_URL` in the launcher script).
-*   `--repo-branch`: This tells repo which branch to use for the full project.
+*   `--repo-rev`: This tells repo which branch to use for the full project.
     It defaults to the `stable` branch (`REPO_REV` in the launcher script).
 
-Whenever `repo sync` is run, repo will check to see if an update is available.
-It fetches the latest repo-branch from the repo-url.
+Whenever `repo sync` is run, repo will, once every 24 hours, see if an update
+is available.
+It fetches the latest repo-rev from the repo-url.
 Then it verifies that the latest commit in the branch has a valid signed tag
 using `git tag -v` (which uses gpg).
 If the tag is valid, then repo will update its internal checkout to it.
@@ -64,9 +96,14 @@ If that tag is valid, then repo will warn and use that commit instead.
 
 If that tag cannot be verified, it gives up and forces the user to resolve.
 
+### Force an update
+
+The `repo selfupdate` command can be used to force an immediate update.
+It is not subject to the 24 hour limitation.
+
 ## Branch management
 
-All development happens on the `master` branch and should generally be stable.
+All development happens on the `main` branch and should generally be stable.
 
 Since the repo launcher defaults to tracking the `stable` branch, it is not
 normally updated until a new release is available.
@@ -81,7 +118,7 @@ For example, when `stable` moves from `v1.10.x` to `v1.11.x`, then the `maint`
 branch will be updated from `v1.9.x` to `v1.10.x`.
 
 We don't have parallel release branches/series.
-Typically all tags are made against the `master` branch and then pushed to the
+Typically all tags are made against the `main` branch and then pushed to the
 `stable` branch to make it available to the rest of the world.
 Since repo doesn't typically see a lot of changes, this tends to be OK.
 
@@ -89,10 +126,10 @@ Since repo doesn't typically see a lot of changes, this tends to be OK.
 
 When you want to create a new release, you'll need to select a good version and
 create a signed tag using a key registered in repo itself.
-Typically we just tag the latest version of the `master` branch.
+Typically we just tag the latest version of the `main` branch.
 The tag could be pushed now, but it won't be used by clients normally (since the
-default `repo-branch` setting is `stable`).
-This would allow some early testing on systems who explicitly select `master`.
+default `repo-rev` setting is `stable`).
+This would allow some early testing on systems who explicitly select `main`.
 
 ### Creating a signed tag
 
@@ -113,7 +150,7 @@ $ export GNUPGHOME=~/.gnupg/repo/
 $ gpg -K
 
 # Pick whatever branch or commit you want to tag.
-$ r=master
+$ r=main
 
 # Pick the new version.
 $ t=1.12.10
@@ -161,7 +198,144 @@ You can create a short changelog using the command:
 $ git log --format="%h (%aN) %s" --no-merges origin/stable..$r
 ```
 
-
+## Project References
+
+Here's a table showing the relationship of major tools, their EOL dates, and
+their status in Ubuntu & Debian.
+Those distros tend to be good indicators of how long we need to support things.
+
+Things in bold indicate stuff to take note of, but does not guarantee that we
+still support them.
+Things in italics are things we used to care about but probably don't anymore.
+
+|   Date   |     EOL      | [Git][rel-g] | [Python][rel-p] | [SSH][rel-o] | [Ubuntu][rel-u] / [Debian][rel-d] | Git | Python | SSH |
+|:--------:|:------------:|:------------:|:---------------:|:------------:|-----------------------------------|-----|--------|-----|
+| Apr 2008 |              |              |                 | 5.0          |
+| Jun 2008 |              |              |                 | 5.1          |
+| Oct 2008 | *Oct 2013*   |              | 2.6.0           |              | *10.04 Lucid* - 10.10 Maverick / *Squeeze* |
+| Dec 2008 | *Feb 2009*   |              | 3.0.0           |
+| Feb 2009 |              |              |                 | 5.2          |
+| Feb 2009 | *Mar 2012*   |              |                 |              | Debian 5 Lenny       | 1.5.6.5 | 2.5.2 |
+| Jun 2009 | *Jun 2016*   |              | 3.1.0           |              | *10.04 Lucid* - 10.10 Maverick / *Squeeze* |
+| Sep 2009 |              |              |                 | 5.3          | *10.04 Lucid* |
+| Feb 2010 | *Oct 2012*   | 1.7.0        |                 |              | *10.04 Lucid* - *12.04 Precise* - 12.10 Quantal |
+| Mar 2010 |              |              |                 | 5.4          |
+| Apr 2010 |              |              |                 | 5.5          | 10.10 Maverick |
+| Apr 2010 | *Apr 2015*   |              |                 |              | *10.04 Lucid*        | 1.7.0.4  | 2.6.5 3.1.2  | 5.3 |
+| Jul 2010 | *Dec 2019*   |              | *2.7.0*         |              | 11.04 Natty - *<current>* |
+| Aug 2010 |              |              |                 | 5.6          |
+| Oct 2010 |              |              |                 |              | 10.10 Maverick       | 1.7.1    | 2.6.6 3.1.3  | 5.5 |
+| Jan 2011 |              |              |                 | 5.7          |
+| Feb 2011 |              |              |                 | 5.8          | 11.04 Natty |
+| Feb 2011 | *Feb 2016*   |              |                 |              | Debian 6 Squeeze     | 1.7.2.5  | 2.6.6 3.1.3  |
+| Apr 2011 |              |              |                 |              | 11.04 Natty          | 1.7.4    | 2.7.1 3.2.0  | 5.8 |
+| Sep 2011 |              |              |                 | 5.9          | *12.04 Precise* |
+| Oct 2011 | *Feb 2016*   |              | 3.2.0           |              | 11.04 Natty - 12.10 Quantal |
+| Oct 2011 |              |              |                 |              | 11.10 Ocelot         | 1.7.5.4  | 2.7.2 3.2.2  | 5.8 |
+| Apr 2012 |              |              |                 | 6.0          | 12.10 Quantal |
+| Apr 2012 | *Apr 2019*   |              |                 |              | *12.04 Precise*      | 1.7.9.5  | 2.7.3 3.2.3  | 5.9 |
+| Aug 2012 |              |              |                 | 6.1          | 13.04 Raring |
+| Sep 2012 | *Sep 2017*   |              | 3.3.0           |              | 13.04 Raring - 13.10 Saucy |
+| Oct 2012 | *Dec 2014*   | 1.8.0        |                 |              | 13.04 Raring - 13.10 Saucy |
+| Oct 2012 |              |              |                 |              | 12.10 Quantal        | 1.7.10.4 | 2.7.3 3.2.3  | 6.0 |
+| Mar 2013 |              |              |                 | 6.2          | 13.10 Saucy |
+| Apr 2013 |              |              |                 |              | 13.04 Raring         | 1.8.1.2  | 2.7.4 3.3.1  | 6.1 |
+| May 2013 | *May 2018*   |              |                 |              | Debian 7 Wheezy      | 1.7.10.4 | 2.7.3 3.2.3  |
+| Sep 2013 |              |              |                 | 6.3          |
+| Oct 2013 |              |              |                 |              | 13.10 Saucy          | 1.8.3.2  | 2.7.5 3.3.2  | 6.2 |
+| Nov 2013 |              |              |                 | 6.4          |
+| Jan 2014 |              |              |                 | 6.5          |
+| Feb 2014 | *Dec 2014*   | **1.9.0**    |                 |              | *14.04 Trusty* |
+| Mar 2014 | *Mar 2019*   |              | *3.4.0*         |              | *14.04 Trusty* - 15.10 Wily / *Jessie* |
+| Mar 2014 |              |              |                 | 6.6          | *14.04 Trusty* - 14.10 Utopic |
+| Apr 2014 | *Apr 2022*   |              |                 |              | *14.04 Trusty*       | 1.9.1    | 2.7.5 3.4.0  | 6.6 |
+| May 2014 | *Dec 2014*   | 2.0.0        |
+| Aug 2014 | *Dec 2014*   | *2.1.0*      |                 |              | 14.10 Utopic - 15.04 Vivid / *Jessie* |
+| Oct 2014 |              |              |                 | 6.7          | 15.04 Vivid |
+| Oct 2014 |              |              |                 |              | 14.10 Utopic         | 2.1.0    | 2.7.8 3.4.2  | 6.6 |
+| Nov 2014 | *Sep 2015*   | 2.2.0        |
+| Feb 2015 | *Sep 2015*   | 2.3.0        |
+| Mar 2015 |              |              |                 | 6.8          |
+| Apr 2015 | *May 2017*   | 2.4.0        |
+| Apr 2015 | *Jun 2020*   |              |                 |              | *Debian 8 Jessie*    | 2.1.4    | 2.7.9 3.4.2  |
+| Apr 2015 |              |              |                 |              | 15.04 Vivid          | 2.1.4    | 2.7.9 3.4.3  | 6.7 |
+| Jul 2015 | *May 2017*   | 2.5.0        |                 |              | 15.10 Wily |
+| Jul 2015 |              |              |                 | 6.9          | 15.10 Wily |
+| Aug 2015 |              |              |                 | 7.0          |
+| Aug 2015 |              |              |                 | 7.1          |
+| Sep 2015 | *May 2017*   | 2.6.0        |
+| Sep 2015 | *Sep 2020*   |              | *3.5.0*         |              | *16.04 Xenial* - 17.04 Zesty / *Stretch* |
+| Oct 2015 |              |              |                 |              | 15.10 Wily           | 2.5.0    | 2.7.9 3.4.3  | 6.9 |
+| Jan 2016 | *Jul 2017*   | *2.7.0*      |                 |              | *16.04 Xenial* |
+| Feb 2016 |              |              |                 | 7.2          | *16.04 Xenial* |
+| Mar 2016 | *Jul 2017*   | 2.8.0        |
+| Apr 2016 | *Apr 2024*   |              |                 |              | *16.04 Xenial*       | 2.7.4    | 2.7.11 3.5.1 | 7.2 |
+| Jun 2016 | *Jul 2017*   | 2.9.0        |                 |              | 16.10 Yakkety |
+| Jul 2016 |              |              |                 | 7.3          | 16.10 Yakkety |
+| Sep 2016 | *Sep 2017*   | 2.10.0       |
+| Oct 2016 |              |              |                 |              | 16.10 Yakkety        | 2.9.3    | 2.7.11 3.5.1 | 7.3 |
+| Nov 2016 | *Sep 2017*   | *2.11.0*     |                 |              | 17.04 Zesty / *Stretch* |
+| Dec 2016 | **Dec 2021** |              | **3.6.0**       |              | 17.10 Artful - **18.04 Bionic** - 18.10 Cosmic |
+| Dec 2016 |              |              |                 | 7.4          | 17.04 Zesty / *Debian 9 Stretch* |
+| Feb 2017 | *Sep 2017*   | 2.12.0       |
+| Mar 2017 |              |              |                 | 7.5          | 17.10 Artful |
+| Apr 2017 |              |              |                 |              | 17.04 Zesty          | 2.11.0   | 2.7.13 3.5.3 | 7.4 |
+| May 2017 | *May 2018*   | 2.13.0       |
+| Jun 2017 | *Jun 2022*   |              |                 |              | *Debian 9 Stretch*   | 2.11.0   | 2.7.13 3.5.3 | 7.4 |
+| Aug 2017 | *Dec 2019*   | 2.14.0       |                 |              | 17.10 Artful |
+| Oct 2017 | *Dec 2019*   | 2.15.0       |
+| Oct 2017 |              |              |                 | 7.6          | **18.04 Bionic** |
+| Oct 2017 |              |              |                 |              | 17.10 Artful         | 2.14.1   | 2.7.14 3.6.3 | 7.5 |
+| Jan 2018 | *Dec 2019*   | 2.16.0       |
+| Apr 2018 | *Mar 2021*   | **2.17.0**   |                 |              | **18.04 Bionic**     |
+| Apr 2018 |              |              |                 | 7.7          | 18.10 Cosmic |
+| Apr 2018 | **Apr 2028** |              |                 |              | **18.04 Bionic**     | 2.17.0   | 2.7.15 3.6.5 | 7.6 |
+| Jun 2018 | *Mar 2021*   | 2.18.0       |
+| Jun 2018 | **Jun 2023** |              | 3.7.0           |              | 19.04 Disco - **20.04 Focal** / **Buster** |
+| Aug 2018 |              |              |                 | 7.8          |
+| Sep 2018 | *Mar 2021*   | 2.19.0       |                 |              | 18.10 Cosmic |
+| Oct 2018 |              |              |                 | 7.9          | 19.04 Disco / **Buster** |
+| Oct 2018 |              |              |                 |              | 18.10 Cosmic         | 2.19.1   | 2.7.15 3.6.6 | 7.7 |
+| Dec 2018 | *Mar 2021*   | **2.20.0**   |                 |              | 19.04 Disco - 19.10 Eoan / **Buster** |
+| Feb 2019 | *Mar 2021*   | 2.21.0       |
+| Apr 2019 |              |              |                 | 8.0          | 19.10 Eoan |
+| Apr 2019 |              |              |                 |              | 19.04 Disco          | 2.20.1   | 2.7.16 3.7.3 | 7.9 |
+| Jun 2019 |              | 2.22.0       |
+| Jul 2019 | **Jul 2024** |              |                 |              | **Debian 10 Buster** | 2.20.1   | 2.7.16 3.7.3 | 7.9 |
+| Aug 2019 | *Mar 2021*   | 2.23.0       |
+| Oct 2019 | **Oct 2024** |              | 3.8.0           |              | **20.04 Focal** - 20.10 Groovy |
+| Oct 2019 |              |              |                 | 8.1          |
+| Oct 2019 |              |              |                 |              | 19.10 Eoan           | 2.20.1   | 2.7.17 3.7.5 | 8.0 |
+| Nov 2019 | *Mar 2021*   | 2.24.0       |
+| Jan 2020 | *Mar 2021*   | 2.25.0       |                 |              | **20.04 Focal** |
+| Feb 2020 |              |              |                 | 8.2          | **20.04 Focal** |
+| Mar 2020 | *Mar 2021*   | 2.26.0       |
+| Apr 2020 | **Apr 2030** |              |                 |              | **20.04 Focal**      | 2.25.1   | 2.7.17 3.8.2 | 8.2 |
+| May 2020 | *Mar 2021*   | 2.27.0       |                 |              | 20.10 Groovy |
+| May 2020 |              |              |                 | 8.3          |
+| Jul 2020 | *Mar 2021*   | 2.28.0       |
+| Sep 2020 |              |              |                 | 8.4          | 21.04 Hirsute / **Bullseye** |
+| Oct 2020 | *Mar 2021*   | 2.29.0       |
+| Oct 2020 |              |              |                 |              | 20.10 Groovy         | 2.27.0   | 2.7.18 3.8.6 | 8.3 |
+| Oct 2020 | **Oct 2025** |              | 3.9.0           |              | 21.04 Hirsute / **Bullseye** |
+| Dec 2020 | *Mar 2021*   | 2.30.0       |                 |              | 21.04 Hirsute / **Bullseye** |
+| Mar 2021 |              | 2.31.0       |
+| Mar 2021 |              |              |                 | 8.5          |
+| Apr 2021 |              |              |                 | 8.6          |
+| Apr 2021 | *Jan 2022*   |              |                 |              | 21.04 Hirsute        | 2.30.2   | 2.7.18 3.9.4 | 8.4 |
+| Jun 2021 |              | 2.32.0       |
+| Aug 2021 |              | 2.33.0       |
+| Aug 2021 |              |              |                 | 8.7          |
+| Aug 2021 | **Aug 2026** |              |                 |              | **Debian 11 Bullseye** | 2.30.2 | 2.7.18 3.9.2 | 8.4 |
+| **Date** |   **EOL**    | **[Git][rel-g]** | **[Python][rel-p]** | **[SSH][rel-o]** | **[Ubuntu][rel-u] / [Debian][rel-d]** | **Git** | **Python** | **SSH** |
+
+
+[contact]: ../README.md#contact
+[rel-d]: https://en.wikipedia.org/wiki/Debian_version_history
+[rel-g]: https://en.wikipedia.org/wiki/Git#Releases
+[rel-o]: https://www.openssh.com/releasenotes.html
+[rel-p]: https://en.wikipedia.org/wiki/History_of_Python#Table_of_versions
+[rel-u]: https://en.wikipedia.org/wiki/Ubuntu_version_history#Table_of_versions
 [example announcement]: https://groups.google.com/d/topic/repo-discuss/UGBNismWo1M/discussion
 [repo-discuss@googlegroups.com]: https://groups.google.com/forum/#!forum/repo-discuss
 [go/repo-release]: https://goto.google.com/repo-release
diff --git a/docs/repo-hooks.md b/docs/repo-hooks.md
index 7c37c30e..cbb1aac7 100644
--- a/docs/repo-hooks.md
+++ b/docs/repo-hooks.md
@@ -27,7 +27,7 @@ repohooks project is updated and a hook is triggered.
 For the full syntax, see the [repo manifest format](./manifest-format.md).
 
 Here's a short example from
-[Android](https://android.googlesource.com/platform/manifest/+/master/default.xml).
+[Android](https://android.googlesource.com/platform/manifest/+/HEAD/default.xml).
 The `<project>` line checks out the repohooks git repo to the local
 `tools/repohooks/` path.  The `<repo-hooks>` line says to look in the project
 with the name `platform/tools/repohooks` for hooks to run during the
diff --git a/docs/windows.md b/docs/windows.md
index 80912964..4282bebf 100644
--- a/docs/windows.md
+++ b/docs/windows.md
@@ -19,7 +19,33 @@ also due to most developers not using Windows.
 We will never add code specific to older versions of Windows.
 It might work, but it most likely won't, so please don't bother asking.
 
-## Symlinks
+## Git worktrees
+
+*** note
+**Warning**: Repo's support for Git worktrees is new & experimental.
+Please report any bugs and be sure to maintain backups!
+***
+
+The Repo 2.4 release introduced support for [Git worktrees][git-worktree].
+You don't have to worry about or understand this particular feature, so don't
+worry if this section of the Git manual is particularly impenetrable.
+
+The salient point is that Git worktrees allow Repo to create repo client
+checkouts that do not require symlinks at all under Windows.
+This means users no longer need Administrator access to sync code.
+
+Simply use `--worktree` when running `repo init` to opt in.
+
+This does not effect specific Git repositories that use symlinks themselves.
+
+[git-worktree]: https://git-scm.com/docs/git-worktree
+
+## Symlinks by default
+
+*** note
+**NB**: This section applies to the default Repo behavior which does not use
+Git worktrees (see the previous section for more info).
+***
 
 Repo will use symlinks heavily internally.
 On *NIX platforms, this isn't an issue, but Windows makes it a bit difficult.
@@ -62,9 +88,8 @@ This also helps `tar` unpack symlinks, so that's nice.
 
 ## Python
 
-You should make sure to be running Python 3.6 or newer under Windows.
-Python 2 might work, but due to already limited platform testing, you should
-only run newer Python versions.
+Python 3.6 or newer is required.
+Python 2 is known to be broken when running under Windows.
 See our [Python Support](./python-support.md) document for more details.
 
 You can grab the latest Windows installer here:<br>
diff --git a/editor.py b/editor.py
index fcf16386..b84a42d4 100644
--- a/editor.py
+++ b/editor.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import os
 import re
 import sys
@@ -24,6 +21,7 @@ import tempfile
 from error import EditorError
 import platform_utils
 
+
 class Editor(object):
   """Manages the user's preferred text editor."""
 
@@ -57,7 +55,7 @@ class Editor(object):
 
     if os.getenv('TERM') == 'dumb':
       print(
-"""No editor specified in GIT_EDITOR, core.editor, VISUAL or EDITOR.
+          """No editor specified in GIT_EDITOR, core.editor, VISUAL or EDITOR.
 Tried to fall back to vi but terminal is dumb.  Please configure at
 least one of these before using this command.""", file=sys.stderr)
       sys.exit(1)
@@ -104,10 +102,10 @@ least one of these before using this command.""", file=sys.stderr)
         rc = subprocess.Popen(args, shell=shell).wait()
       except OSError as e:
         raise EditorError('editor failed, %s: %s %s'
-          % (str(e), editor, path))
+                          % (str(e), editor, path))
       if rc != 0:
         raise EditorError('editor failed with exit status %d: %s %s'
-          % (rc, editor, path))
+                          % (rc, editor, path))
 
       with open(path, mode='rb') as fd2:
         return fd2.read().decode('utf-8')
diff --git a/error.py b/error.py
index 5bfe3a66..cbefcb7e 100644
--- a/error.py
+++ b/error.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,70 +12,89 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+
 class ManifestParseError(Exception):
   """Failed to parse the manifest file.
   """
 
-class ManifestInvalidRevisionError(Exception):
+
+class ManifestInvalidRevisionError(ManifestParseError):
   """The revision value in a project is incorrect.
   """
 
+
+class ManifestInvalidPathError(ManifestParseError):
+  """A path used in <copyfile> or <linkfile> is incorrect.
+  """
+
+
 class NoManifestException(Exception):
   """The required manifest does not exist.
   """
+
   def __init__(self, path, reason):
-    super(NoManifestException, self).__init__()
+    super().__init__(path, reason)
     self.path = path
     self.reason = reason
 
   def __str__(self):
     return self.reason
 
+
 class EditorError(Exception):
   """Unspecified error from the user's text editor.
   """
+
   def __init__(self, reason):
-    super(EditorError, self).__init__()
+    super().__init__(reason)
     self.reason = reason
 
   def __str__(self):
     return self.reason
 
+
 class GitError(Exception):
   """Unspecified internal error from git.
   """
+
   def __init__(self, command):
-    super(GitError, self).__init__()
+    super().__init__(command)
     self.command = command
 
   def __str__(self):
     return self.command
 
+
 class UploadError(Exception):
   """A bundle upload to Gerrit did not succeed.
   """
+
   def __init__(self, reason):
-    super(UploadError, self).__init__()
+    super().__init__(reason)
     self.reason = reason
 
   def __str__(self):
     return self.reason
 
+
 class DownloadError(Exception):
   """Cannot download a repository.
   """
+
   def __init__(self, reason):
-    super(DownloadError, self).__init__()
+    super().__init__(reason)
     self.reason = reason
 
   def __str__(self):
     return self.reason
 
+
 class NoSuchProjectError(Exception):
   """A specified project does not exist in the work tree.
   """
+
   def __init__(self, name=None):
-    super(NoSuchProjectError, self).__init__()
+    super().__init__(name)
     self.name = name
 
   def __str__(self):
@@ -89,8 +106,9 @@ class NoSuchProjectError(Exception):
 class InvalidProjectGroupsError(Exception):
   """A specified project is not suitable for the specified groups
   """
+
   def __init__(self, name=None):
-    super(InvalidProjectGroupsError, self).__init__()
+    super().__init__(name)
     self.name = name
 
   def __str__(self):
@@ -98,15 +116,18 @@ class InvalidProjectGroupsError(Exception):
       return 'in current directory'
     return self.name
 
+
 class RepoChangedException(Exception):
   """Thrown if 'repo sync' results in repo updating its internal
      repo or manifest repositories.  In this special case we must
      use exec to re-execute repo with the new code and manifest.
   """
+
   def __init__(self, extra_args=None):
-    super(RepoChangedException, self).__init__()
+    super().__init__(extra_args)
     self.extra_args = extra_args or []
 
+
 class HookError(Exception):
   """Thrown if a 'repo-hook' could not be run.
 
diff --git a/event_log.py b/event_log.py
index 315d752d..c77c5648 100644
--- a/event_log.py
+++ b/event_log.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2017 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,8 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import json
 import multiprocessing
 
@@ -23,6 +19,7 @@ TASK_COMMAND = 'command'
 TASK_SYNC_NETWORK = 'sync-network'
 TASK_SYNC_LOCAL = 'sync-local'
 
+
 class EventLog(object):
   """Event log that records events that occurred during a repo invocation.
 
@@ -138,7 +135,7 @@ class EventLog(object):
     Returns:
       A dictionary of the event added to the log.
     """
-    event['status'] =  self.GetStatusString(success)
+    event['status'] = self.GetStatusString(success)
     event['finish_time'] = finish
     return event
 
@@ -165,6 +162,7 @@ class EventLog(object):
 # An integer id that is unique across this invocation of the program.
 _EVENT_ID = multiprocessing.Value('i', 1)
 
+
 def _NextEventId():
   """Helper function for grabbing the next unique id.
 
diff --git a/fetch.py b/fetch.py
new file mode 100644
index 00000000..91d40cda
--- /dev/null
+++ b/fetch.py
@@ -0,0 +1,41 @@
+# Copyright (C) 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""This module contains functions used to fetch files from various sources."""
+
+import subprocess
+import sys
+from urllib.parse import urlparse
+
+def fetch_file(url):
+  """Fetch a file from the specified source using the appropriate protocol.
+
+  Returns:
+    The contents of the file as bytes.
+  """
+  scheme = urlparse(url).scheme
+  if scheme == 'gs':
+    cmd = ['gsutil', 'cat', url]
+    try:
+      result = subprocess.run(
+          cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
+      return result.stdout
+    except subprocess.CalledProcessError as e:
+      print('fatal: error running "gsutil": %s' % e.output,
+            file=sys.stderr)
+    sys.exit(1)
+  if scheme == 'file':
+    with open(url[len('file://'):], 'rb') as f:
+      return f.read()
+  raise ValueError('unsupported url %s' % url)
diff --git a/git_command.py b/git_command.py
index dc542c36..95db91f2 100644
--- a/git_command.py
+++ b/git_command.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,12 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
+import functools
 import os
 import sys
 import subprocess
-import tempfile
-from signal import SIGTERM
 
 from error import GitError
 from git_refs import HEAD
@@ -28,75 +24,42 @@ from repo_trace import REPO_TRACE, IsTrace, Trace
 from wrapper import Wrapper
 
 GIT = 'git'
-MIN_GIT_VERSION = (1, 5, 4)
+# NB: These do not need to be kept in sync with the repo launcher script.
+# These may be much newer as it allows the repo launcher to roll between
+# different repo releases while source versions might require a newer git.
+#
+# The soft version is when we start warning users that the version is old and
+# we'll be dropping support for it.  We'll refuse to work with versions older
+# than the hard version.
+#
+# git-1.7 is in (EOL) Ubuntu Precise.  git-1.9 is in Ubuntu Trusty.
+MIN_GIT_VERSION_SOFT = (1, 9, 1)
+MIN_GIT_VERSION_HARD = (1, 7, 2)
 GIT_DIR = 'GIT_DIR'
 
 LAST_GITDIR = None
 LAST_CWD = None
 
-_ssh_proxy_path = None
-_ssh_sock_path = None
-_ssh_clients = []
-
-def ssh_sock(create=True):
-  global _ssh_sock_path
-  if _ssh_sock_path is None:
-    if not create:
-      return None
-    tmp_dir = '/tmp'
-    if not os.path.exists(tmp_dir):
-      tmp_dir = tempfile.gettempdir()
-    _ssh_sock_path = os.path.join(
-      tempfile.mkdtemp('', 'ssh-', tmp_dir),
-      'master-%r@%h:%p')
-  return _ssh_sock_path
-
-def _ssh_proxy():
-  global _ssh_proxy_path
-  if _ssh_proxy_path is None:
-    _ssh_proxy_path = os.path.join(
-      os.path.dirname(__file__),
-      'git_ssh')
-  return _ssh_proxy_path
-
-def _add_ssh_client(p):
-  _ssh_clients.append(p)
-
-def _remove_ssh_client(p):
-  try:
-    _ssh_clients.remove(p)
-  except ValueError:
-    pass
-
-def terminate_ssh_clients():
-  global _ssh_clients
-  for p in _ssh_clients:
-    try:
-      os.kill(p.pid, SIGTERM)
-      p.wait()
-    except OSError:
-      pass
-  _ssh_clients = []
-
-_git_version = None
 
 class _GitCall(object):
+  @functools.lru_cache(maxsize=None)
   def version_tuple(self):
-    global _git_version
-    if _git_version is None:
-      _git_version = Wrapper().ParseGitVersion()
-      if _git_version is None:
-        print('fatal: unable to detect git version', file=sys.stderr)
-        sys.exit(1)
-    return _git_version
+    ret = Wrapper().ParseGitVersion()
+    if ret is None:
+      print('fatal: unable to detect git version', file=sys.stderr)
+      sys.exit(1)
+    return ret
 
   def __getattr__(self, name):
-    name = name.replace('_','-')
+    name = name.replace('_', '-')
+
     def fun(*cmdv):
       command = [name]
       command.extend(cmdv)
       return GitCommand(None, command).Wait() == 0
     return fun
+
+
 git = _GitCall()
 
 
@@ -111,11 +74,11 @@ def RepoSourceVersion():
 
     proj = os.path.dirname(os.path.abspath(__file__))
     env[GIT_DIR] = os.path.join(proj, '.git')
-
-    p = subprocess.Popen([GIT, 'describe', HEAD], stdout=subprocess.PIPE,
-                         env=env)
-    if p.wait() == 0:
-      ver = p.stdout.read().strip().decode('utf-8')
+    result = subprocess.run([GIT, 'describe', HEAD], stdout=subprocess.PIPE,
+                            stderr=subprocess.DEVNULL, encoding='utf-8',
+                            env=env, check=False)
+    if result.returncode == 0:
+      ver = result.stdout.strip()
       if ver.startswith('v'):
         ver = ver[1:]
     else:
@@ -177,8 +140,10 @@ class UserAgent(object):
 
     return self._git_ua
 
+
 user_agent = UserAgent()
 
+
 def git_require(min_version, fail=False, msg=''):
   git_version = git.version_tuple()
   if min_version <= git_version:
@@ -191,42 +156,38 @@ def git_require(min_version, fail=False, msg=''):
     sys.exit(1)
   return False
 
-def _setenv(env, name, value):
-  env[name] = value.encode()
 
 class GitCommand(object):
   def __init__(self,
                project,
                cmdv,
-               bare = False,
-               provide_stdin = False,
-               capture_stdout = False,
-               capture_stderr = False,
-               disable_editor = False,
-               ssh_proxy = False,
-               cwd = None,
-               gitdir = None):
+               bare=False,
+               input=None,
+               capture_stdout=False,
+               capture_stderr=False,
+               merge_output=False,
+               disable_editor=False,
+               ssh_proxy=None,
+               cwd=None,
+               gitdir=None):
     env = self._GetBasicEnv()
 
-    # If we are not capturing std* then need to print it.
-    self.tee = {'stdout': not capture_stdout, 'stderr': not capture_stderr}
-
     if disable_editor:
-      _setenv(env, 'GIT_EDITOR', ':')
+      env['GIT_EDITOR'] = ':'
     if ssh_proxy:
-      _setenv(env, 'REPO_SSH_SOCK', ssh_sock())
-      _setenv(env, 'GIT_SSH', _ssh_proxy())
-      _setenv(env, 'GIT_SSH_VARIANT', 'ssh')
+      env['REPO_SSH_SOCK'] = ssh_proxy.sock()
+      env['GIT_SSH'] = ssh_proxy.proxy
+      env['GIT_SSH_VARIANT'] = 'ssh'
     if 'http_proxy' in env and 'darwin' == sys.platform:
       s = "'http.proxy=%s'" % (env['http_proxy'],)
       p = env.get('GIT_CONFIG_PARAMETERS')
       if p is not None:
         s = p + ' ' + s
-      _setenv(env, 'GIT_CONFIG_PARAMETERS', s)
+      env['GIT_CONFIG_PARAMETERS'] = s
     if 'GIT_ALLOW_PROTOCOL' not in env:
-      _setenv(env, 'GIT_ALLOW_PROTOCOL',
-              'file:git:http:https:ssh:persistent-http:persistent-https:sso:rpc')
-    _setenv(env, 'GIT_HTTP_USER_AGENT', user_agent.git)
+      env['GIT_ALLOW_PROTOCOL'] = (
+          'file:git:http:https:ssh:persistent-http:persistent-https:sso:rpc')
+    env['GIT_HTTP_USER_AGENT'] = user_agent.git
 
     if project:
       if not cwd:
@@ -237,7 +198,10 @@ class GitCommand(object):
     command = [GIT]
     if bare:
       if gitdir:
-        _setenv(env, GIT_DIR, gitdir)
+        # Git on Windows wants its paths only using / for reliability.
+        if platform_utils.isWindows():
+          gitdir = gitdir.replace('\\', '/')
+        env[GIT_DIR] = gitdir
       cwd = None
     command.append(cmdv[0])
     # Need to use the --progress flag for fetch/clone so output will be
@@ -247,13 +211,10 @@ class GitCommand(object):
         command.append('--progress')
     command.extend(cmdv[1:])
 
-    if provide_stdin:
-      stdin = subprocess.PIPE
-    else:
-      stdin = None
-
-    stdout = subprocess.PIPE
-    stderr = subprocess.PIPE
+    stdin = subprocess.PIPE if input else None
+    stdout = subprocess.PIPE if capture_stdout else None
+    stderr = (subprocess.STDOUT if merge_output else
+              (subprocess.PIPE if capture_stderr else None))
 
     if IsTrace():
       global LAST_CWD
@@ -281,23 +242,38 @@ class GitCommand(object):
         dbg += ' 1>|'
       if stderr == subprocess.PIPE:
         dbg += ' 2>|'
+      elif stderr == subprocess.STDOUT:
+        dbg += ' 2>&1'
       Trace('%s', dbg)
 
     try:
       p = subprocess.Popen(command,
-                           cwd = cwd,
-                           env = env,
-                           stdin = stdin,
-                           stdout = stdout,
-                           stderr = stderr)
+                           cwd=cwd,
+                           env=env,
+                           encoding='utf-8',
+                           errors='backslashreplace',
+                           stdin=stdin,
+                           stdout=stdout,
+                           stderr=stderr)
     except Exception as e:
       raise GitError('%s: %s' % (command[1], e))
 
     if ssh_proxy:
-      _add_ssh_client(p)
+      ssh_proxy.add_client(p)
 
     self.process = p
-    self.stdin = p.stdin
+    if input:
+      if isinstance(input, str):
+        input = input.encode('utf-8')
+      p.stdin.write(input)
+      p.stdin.close()
+
+    try:
+      self.stdout, self.stderr = p.communicate()
+    finally:
+      if ssh_proxy:
+        ssh_proxy.remove_client(p)
+    self.rc = p.wait()
 
   @staticmethod
   def _GetBasicEnv():
@@ -317,35 +293,4 @@ class GitCommand(object):
     return env
 
   def Wait(self):
-    try:
-      p = self.process
-      rc = self._CaptureOutput()
-    finally:
-      _remove_ssh_client(p)
-    return rc
-
-  def _CaptureOutput(self):
-    p = self.process
-    s_in = platform_utils.FileDescriptorStreams.create()
-    s_in.add(p.stdout, sys.stdout, 'stdout')
-    s_in.add(p.stderr, sys.stderr, 'stderr')
-    self.stdout = ''
-    self.stderr = ''
-
-    while not s_in.is_done:
-      in_ready = s_in.select()
-      for s in in_ready:
-        buf = s.read()
-        if not buf:
-          s_in.remove(s)
-          continue
-        if not hasattr(buf, 'encode'):
-          buf = buf.decode()
-        if s.std_name == 'stdout':
-          self.stdout += buf
-        else:
-          self.stderr += buf
-        if self.tee[s.std_name]:
-          s.dest.write(buf)
-          s.dest.flush()
-    return p.wait()
+    return self.rc
diff --git a/git_config.py b/git_config.py
index 8de3200c..3cd09391 100644
--- a/git_config.py
+++ b/git_config.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,84 +12,83 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
 import contextlib
+import datetime
 import errno
+from http.client import HTTPException
 import json
 import os
 import re
 import ssl
 import subprocess
 import sys
-try:
-  import threading as _threading
-except ImportError:
-  import dummy_threading as _threading
-import time
-
-from pyversion import is_python3
-if is_python3():
-  import urllib.request
-  import urllib.error
-else:
-  import urllib2
-  import imp
-  urllib = imp.new_module('urllib')
-  urllib.request = urllib2
-  urllib.error = urllib2
-
-from signal import SIGTERM
+import urllib.error
+import urllib.request
+
 from error import GitError, UploadError
 import platform_utils
 from repo_trace import Trace
-if is_python3():
-  from http.client import HTTPException
-else:
-  from httplib import HTTPException
-
 from git_command import GitCommand
-from git_command import ssh_sock
-from git_command import terminate_ssh_clients
 from git_refs import R_CHANGES, R_HEADS, R_TAGS
 
+# Prefix that is prepended to all the keys of SyncAnalysisState's data
+# that is saved in the config.
+SYNC_STATE_PREFIX = 'repo.syncstate.'
+
 ID_RE = re.compile(r'^[0-9a-f]{40}$')
 
 REVIEW_CACHE = dict()
 
+
 def IsChange(rev):
   return rev.startswith(R_CHANGES)
 
+
 def IsId(rev):
   return ID_RE.match(rev)
 
+
 def IsTag(rev):
   return rev.startswith(R_TAGS)
 
+
 def IsImmutable(rev):
     return IsChange(rev) or IsId(rev) or IsTag(rev)
 
+
 def _key(name):
   parts = name.split('.')
   if len(parts) < 2:
     return name.lower()
-  parts[ 0] = parts[ 0].lower()
+  parts[0] = parts[0].lower()
   parts[-1] = parts[-1].lower()
   return '.'.join(parts)
 
+
 class GitConfig(object):
   _ForUser = None
 
+  _USER_CONFIG = '~/.gitconfig'
+
+  _ForSystem = None
+  _SYSTEM_CONFIG = '/etc/gitconfig'
+
+  @classmethod
+  def ForSystem(cls):
+    if cls._ForSystem is None:
+      cls._ForSystem = cls(configfile=cls._SYSTEM_CONFIG)
+    return cls._ForSystem
+
   @classmethod
   def ForUser(cls):
     if cls._ForUser is None:
-      cls._ForUser = cls(configfile = os.path.expanduser('~/.gitconfig'))
+      cls._ForUser = cls(configfile=os.path.expanduser(cls._USER_CONFIG))
     return cls._ForUser
 
   @classmethod
   def ForRepository(cls, gitdir, defaults=None):
-    return cls(configfile = os.path.join(gitdir, 'config'),
-               defaults = defaults)
+    return cls(configfile=os.path.join(gitdir, 'config'),
+               defaults=defaults)
 
   def __init__(self, configfile, defaults=None, jsonFile=None):
     self.file = configfile
@@ -104,18 +101,74 @@ class GitConfig(object):
     self._json = jsonFile
     if self._json is None:
       self._json = os.path.join(
-        os.path.dirname(self.file),
-        '.repo_' + os.path.basename(self.file) + '.json')
+          os.path.dirname(self.file),
+          '.repo_' + os.path.basename(self.file) + '.json')
+
+  def ClearCache(self):
+    """Clear the in-memory cache of config."""
+    self._cache_dict = None
 
-  def Has(self, name, include_defaults = True):
+  def Has(self, name, include_defaults=True):
     """Return true if this configuration file has the key.
     """
     if _key(name) in self._cache:
       return True
     if include_defaults and self.defaults:
-      return self.defaults.Has(name, include_defaults = True)
+      return self.defaults.Has(name, include_defaults=True)
     return False
 
+  def GetInt(self, name):
+    """Returns an integer from the configuration file.
+
+    This follows the git config syntax.
+
+    Args:
+      name: The key to lookup.
+
+    Returns:
+      None if the value was not defined, or is not a boolean.
+      Otherwise, the number itself.
+    """
+    v = self.GetString(name)
+    if v is None:
+      return None
+    v = v.strip()
+
+    mult = 1
+    if v.endswith('k'):
+      v = v[:-1]
+      mult = 1024
+    elif v.endswith('m'):
+      v = v[:-1]
+      mult = 1024 * 1024
+    elif v.endswith('g'):
+      v = v[:-1]
+      mult = 1024 * 1024 * 1024
+
+    base = 10
+    if v.startswith('0x'):
+      base = 16
+
+    try:
+      return int(v, base=base) * mult
+    except ValueError:
+      return None
+
+  def DumpConfigDict(self):
+    """Returns the current configuration dict.
+
+    Configuration data is information only (e.g. logging) and
+    should not be considered a stable data-source.
+
+    Returns:
+      dict of {<key>, <value>} for git configuration cache.
+      <value> are strings converted by GetString.
+    """
+    config_dict = {}
+    for key in self._cache:
+      config_dict[key] = self.GetString(key)
+    return config_dict
+
   def GetBoolean(self, name):
     """Returns a boolean from the configuration file.
        None : The value was not defined, or is not a boolean.
@@ -132,6 +185,12 @@ class GitConfig(object):
       return False
     return None
 
+  def SetBoolean(self, name, value):
+    """Set the truthy value for a key."""
+    if value is not None:
+      value = 'true' if value else 'false'
+    self.SetString(name, value)
+
   def GetString(self, name, all_keys=False):
     """Get the first value for a key, or None if it is not defined.
 
@@ -142,7 +201,7 @@ class GitConfig(object):
       v = self._cache[_key(name)]
     except KeyError:
       if self.defaults:
-        return self.defaults.GetString(name, all_keys = all_keys)
+        return self.defaults.GetString(name, all_keys=all_keys)
       v = []
 
     if not all_keys:
@@ -153,7 +212,7 @@ class GitConfig(object):
     r = []
     r.extend(v)
     if self.defaults:
-      r.extend(self.defaults.GetString(name, all_keys = True))
+      r.extend(self.defaults.GetString(name, all_keys=True))
     return r
 
   def SetString(self, name, value):
@@ -212,12 +271,28 @@ class GitConfig(object):
       self._branches[b.name] = b
     return b
 
+  def GetSyncAnalysisStateData(self):
+    """Returns data to be logged for the analysis of sync performance."""
+    return {k: v for k, v in self.DumpConfigDict().items() if k.startswith(SYNC_STATE_PREFIX)}
+
+  def UpdateSyncAnalysisState(self, options, superproject_logging_data):
+    """Update Config's SYNC_STATE_PREFIX* data with the latest sync data.
+
+    Args:
+      options: Options passed to sync returned from optparse. See _Options().
+      superproject_logging_data: A dictionary of superproject data that is to be logged.
+
+    Returns:
+      SyncAnalysisState object.
+    """
+    return SyncAnalysisState(self, options, superproject_logging_data)
+
   def GetSubSections(self, section):
     """List all subsection names matching $section.*.*
     """
     return self._sections.get(section, set())
 
-  def HasSection(self, section, subsection = ''):
+  def HasSection(self, section, subsection=''):
     """Does at least one key in section.subsection exist?
     """
     try:
@@ -268,8 +343,7 @@ class GitConfig(object):
 
   def _ReadJson(self):
     try:
-      if os.path.getmtime(self._json) \
-      <= os.path.getmtime(self.file):
+      if os.path.getmtime(self._json) <= os.path.getmtime(self.file):
         platform_utils.remove(self._json)
         return None
     except OSError:
@@ -278,8 +352,8 @@ class GitConfig(object):
       Trace(': parsing %s', self.file)
       with open(self._json) as fd:
         return json.load(fd)
-    except (IOError, ValueError):
-      platform_utils.remove(self._json)
+    except (IOError, ValueErrorl):
+      platform_utils.remove(self._json, missing_ok=True)
       return None
 
   def _SaveJson(self, cache):
@@ -287,8 +361,7 @@ class GitConfig(object):
       with open(self._json, 'w') as fd:
         json.dump(cache, fd, indent=2)
     except (IOError, TypeError):
-      if os.path.exists(self._json):
-        platform_utils.remove(self._json)
+      platform_utils.remove(self._json, missing_ok=True)
 
   def _ReadGit(self):
     """
@@ -298,11 +371,10 @@ class GitConfig(object):
 
     """
     c = {}
-    d = self._do('--null', '--list')
-    if d is None:
+    if not os.path.exists(self.file):
       return c
-    if not is_python3():
-      d = d.decode('utf-8')
+
+    d = self._do('--null', '--list')
     for line in d.rstrip('\0').split('\0'):
       if '\n' in line:
         key, val = line.split('\n', 1)
@@ -318,17 +390,26 @@ class GitConfig(object):
     return c
 
   def _do(self, *args):
-    command = ['config', '--file', self.file]
+    if self.file == self._SYSTEM_CONFIG:
+      command = ['config', '--system', '--includes']
+    else:
+      command = ['config', '--file', self.file, '--includes']
     command.extend(args)
 
     p = GitCommand(None,
                    command,
-                   capture_stdout = True,
-                   capture_stderr = True)
+                   capture_stdout=True,
+                   capture_stderr=True)
     if p.Wait() == 0:
       return p.stdout
     else:
-      GitError('git config %s: %s' % (str(args), p.stderr))
+      raise GitError('git config %s: %s' % (str(args), p.stderr))
+
+
+class RepoConfig(GitConfig):
+  """User settings for repo itself."""
+
+  _USER_CONFIG = '~/.repoconfig/config'
 
 
 class RefSpec(object):
@@ -387,133 +468,16 @@ class RefSpec(object):
     return s
 
 
-_master_processes = []
-_master_keys = set()
-_ssh_master = True
-_master_keys_lock = None
-
-def init_ssh():
-  """Should be called once at the start of repo to init ssh master handling.
-
-  At the moment, all we do is to create our lock.
-  """
-  global _master_keys_lock
-  assert _master_keys_lock is None, "Should only call init_ssh once"
-  _master_keys_lock = _threading.Lock()
-
-def _open_ssh(host, port=None):
-  global _ssh_master
-
-  # Acquire the lock.  This is needed to prevent opening multiple masters for
-  # the same host when we're running "repo sync -jN" (for N > 1) _and_ the
-  # manifest <remote fetch="ssh://xyz"> specifies a different host from the
-  # one that was passed to repo init.
-  _master_keys_lock.acquire()
-  try:
-
-    # Check to see whether we already think that the master is running; if we
-    # think it's already running, return right away.
-    if port is not None:
-      key = '%s:%s' % (host, port)
-    else:
-      key = host
-
-    if key in _master_keys:
-      return True
-
-    if not _ssh_master \
-    or 'GIT_SSH' in os.environ \
-    or sys.platform in ('win32', 'cygwin'):
-      # failed earlier, or cygwin ssh can't do this
-      #
-      return False
-
-    # We will make two calls to ssh; this is the common part of both calls.
-    command_base = ['ssh',
-                     '-o','ControlPath %s' % ssh_sock(),
-                     host]
-    if port is not None:
-      command_base[1:1] = ['-p', str(port)]
-
-    # Since the key wasn't in _master_keys, we think that master isn't running.
-    # ...but before actually starting a master, we'll double-check.  This can
-    # be important because we can't tell that that 'git@myhost.com' is the same
-    # as 'myhost.com' where "User git" is setup in the user's ~/.ssh/config file.
-    check_command = command_base + ['-O','check']
-    try:
-      Trace(': %s', ' '.join(check_command))
-      check_process = subprocess.Popen(check_command,
-                                       stdout=subprocess.PIPE,
-                                       stderr=subprocess.PIPE)
-      check_process.communicate() # read output, but ignore it...
-      isnt_running = check_process.wait()
-
-      if not isnt_running:
-        # Our double-check found that the master _was_ infact running.  Add to
-        # the list of keys.
-        _master_keys.add(key)
-        return True
-    except Exception:
-      # Ignore excpetions.  We we will fall back to the normal command and print
-      # to the log there.
-      pass
-
-    command = command_base[:1] + \
-              ['-M', '-N'] + \
-              command_base[1:]
-    try:
-      Trace(': %s', ' '.join(command))
-      p = subprocess.Popen(command)
-    except Exception as e:
-      _ssh_master = False
-      print('\nwarn: cannot enable ssh control master for %s:%s\n%s'
-             % (host,port, str(e)), file=sys.stderr)
-      return False
-
-    time.sleep(1)
-    ssh_died = (p.poll() is not None)
-    if ssh_died:
-      return False
-
-    _master_processes.append(p)
-    _master_keys.add(key)
-    return True
-  finally:
-    _master_keys_lock.release()
-
-def close_ssh():
-  global _master_keys_lock
-
-  terminate_ssh_clients()
-
-  for p in _master_processes:
-    try:
-      os.kill(p.pid, SIGTERM)
-      p.wait()
-    except OSError:
-      pass
-  del _master_processes[:]
-  _master_keys.clear()
-
-  d = ssh_sock(create=False)
-  if d:
-    try:
-      platform_utils.rmdir(os.path.dirname(d))
-    except OSError:
-      pass
-
-  # We're done with the lock, so we can delete it.
-  _master_keys_lock = None
-
-URI_SCP = re.compile(r'^([^@:]*@?[^:/]{1,}):')
 URI_ALL = re.compile(r'^([a-z][a-z+-]*)://([^@/]*@?[^/]*)/')
 
+
 def GetSchemeFromUrl(url):
   m = URI_ALL.match(url)
   if m:
     return m.group(1)
   return None
 
+
 @contextlib.contextmanager
 def GetUrlCookieFile(url, quiet):
   if url.startswith('persistent-'):
@@ -554,29 +518,11 @@ def GetUrlCookieFile(url, quiet):
     cookiefile = os.path.expanduser(cookiefile)
   yield cookiefile, None
 
-def _preconnect(url):
-  m = URI_ALL.match(url)
-  if m:
-    scheme = m.group(1)
-    host = m.group(2)
-    if ':' in host:
-      host, port = host.split(':')
-    else:
-      port = None
-    if scheme in ('ssh', 'git+ssh', 'ssh+git'):
-      return _open_ssh(host, port)
-    return False
-
-  m = URI_SCP.match(url)
-  if m:
-    host = m.group(1)
-    return _open_ssh(host)
-
-  return False
 
 class Remote(object):
   """Configuration options related to a remote.
   """
+
   def __init__(self, config, name):
     self._config = config
     self.name = name
@@ -585,7 +531,7 @@ class Remote(object):
     self.review = self._Get('review')
     self.projectname = self._Get('projectname')
     self.fetch = list(map(RefSpec.FromString,
-                      self._Get('fetch', all_keys=True)))
+                          self._Get('fetch', all_keys=True)))
     self._review_url = None
 
   def _InsteadOf(self):
@@ -599,8 +545,8 @@ class Remote(object):
       insteadOfList = globCfg.GetString(key, all_keys=True)
 
       for insteadOf in insteadOfList:
-        if self.url.startswith(insteadOf) \
-        and len(insteadOf) > len(longest):
+        if (self.url.startswith(insteadOf)
+                and len(insteadOf) > len(longest)):
           longest = insteadOf
           longestUrl = url
 
@@ -609,9 +555,23 @@ class Remote(object):
 
     return self.url.replace(longest, longestUrl, 1)
 
-  def PreConnectFetch(self):
+  def PreConnectFetch(self, ssh_proxy):
+    """Run any setup for this remote before we connect to it.
+
+    In practice, if the remote is using SSH, we'll attempt to create a new
+    SSH master session to it for reuse across projects.
+
+    Args:
+      ssh_proxy: The SSH settings for managing master sessions.
+
+    Returns:
+      Whether the preconnect phase for this remote was successful.
+    """
+    if not ssh_proxy:
+      return True
+
     connectionUrl = self._InsteadOf()
-    return _preconnect(connectionUrl)
+    return ssh_proxy.preconnect(connectionUrl)
 
   def ReviewUrl(self, userEmail, validate_certs):
     if self._review_url is None:
@@ -731,12 +691,13 @@ class Remote(object):
 
   def _Get(self, key, all_keys=False):
     key = 'remote.%s.%s' % (self.name, key)
-    return self._config.GetString(key, all_keys = all_keys)
+    return self._config.GetString(key, all_keys=all_keys)
 
 
 class Branch(object):
   """Configuration options related to a single branch.
   """
+
   def __init__(self, config, name):
     self._config = config
     self.name = name
@@ -780,4 +741,71 @@ class Branch(object):
 
   def _Get(self, key, all_keys=False):
     key = 'branch.%s.%s' % (self.name, key)
-    return self._config.GetString(key, all_keys = all_keys)
+    return self._config.GetString(key, all_keys=all_keys)
+
+
+class SyncAnalysisState:
+  """Configuration options related to logging of sync state for analysis.
+
+  This object is versioned.
+  """
+  def __init__(self, config, options, superproject_logging_data):
+    """Initializes SyncAnalysisState.
+
+    Saves the following data into the |config| object.
+    - sys.argv, options, superproject's logging data.
+    - repo.*, branch.* and remote.* parameters from config object.
+    - Current time as synctime.
+    - Version number of the object.
+
+    All the keys saved by this object are prepended with SYNC_STATE_PREFIX.
+
+    Args:
+      config: GitConfig object to store all options.
+      options: Options passed to sync returned from optparse. See _Options().
+      superproject_logging_data: A dictionary of superproject data that is to be logged.
+    """
+    self._config = config
+    now = datetime.datetime.utcnow()
+    self._Set('main.synctime', now.isoformat() + 'Z')
+    self._Set('main.version', '1')
+    self._Set('sys.argv', sys.argv)
+    for key, value in superproject_logging_data.items():
+      self._Set(f'superproject.{key}', value)
+    for key, value in options.__dict__.items():
+      self._Set(f'options.{key}', value)
+    config_items = config.DumpConfigDict().items()
+    EXTRACT_NAMESPACES = {'repo', 'branch', 'remote'}
+    self._SetDictionary({k: v for k, v in config_items
+                         if not k.startswith(SYNC_STATE_PREFIX) and
+                         k.split('.', 1)[0] in EXTRACT_NAMESPACES})
+
+  def _SetDictionary(self, data):
+    """Save all key/value pairs of |data| dictionary.
+
+    Args:
+      data: A dictionary whose key/value are to be saved.
+    """
+    for key, value in data.items():
+      self._Set(key, value)
+
+  def _Set(self, key, value):
+    """Set the |value| for a |key| in the |_config| member.
+
+    |key| is prepended with the value of SYNC_STATE_PREFIX constant.
+
+    Args:
+      key: Name of the key.
+      value: |value| could be of any type. If it is 'bool', it will be saved
+             as a Boolean and for all other types, it will be saved as a String.
+    """
+    if value is None:
+      return
+    sync_key = f'{SYNC_STATE_PREFIX}{key}'
+    sync_key = sync_key.replace('_', '')
+    if isinstance(value, str):
+      self._config.SetString(sync_key, value)
+    elif isinstance(value, bool):
+      self._config.SetBoolean(sync_key, value)
+    else:
+      self._config.SetString(sync_key, str(value))
diff --git a/git_refs.py b/git_refs.py
index debd4cbf..2d4a8090 100644
--- a/git_refs.py
+++ b/git_refs.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2009 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -18,12 +16,14 @@ import os
 from repo_trace import Trace
 import platform_utils
 
-HEAD      = 'HEAD'
+HEAD = 'HEAD'
 R_CHANGES = 'refs/changes/'
-R_HEADS   = 'refs/heads/'
-R_TAGS    = 'refs/tags/'
-R_PUB     = 'refs/published/'
-R_M       = 'refs/remotes/m/'
+R_HEADS = 'refs/heads/'
+R_TAGS = 'refs/tags/'
+R_PUB = 'refs/published/'
+R_WORKTREE = 'refs/worktree/'
+R_WORKTREE_M = R_WORKTREE + 'm/'
+R_M = 'refs/remotes/m/'
 
 
 class GitRefs(object):
@@ -131,11 +131,14 @@ class GitRefs(object):
     base = os.path.join(self._gitdir, prefix)
     for name in platform_utils.listdir(base):
       p = os.path.join(base, name)
-      if platform_utils.isdir(p):
+      # We don't implement the full ref validation algorithm, just the simple
+      # rules that would show up in local filesystems.
+      # https://git-scm.com/docs/git-check-ref-format
+      if name.startswith('.') or name.endswith('.lock'):
+        pass
+      elif platform_utils.isdir(p):
         self._mtime[prefix] = os.path.getmtime(base)
         self._ReadLoose(prefix + name + '/')
-      elif name.endswith('.lock'):
-        pass
       else:
         self._ReadLoose1(p, prefix + name)
 
@@ -144,7 +147,7 @@ class GitRefs(object):
       with open(path) as fd:
         mtime = os.path.getmtime(path)
         ref_id = fd.readline()
-    except (IOError, OSError):
+    except (OSError, UnicodeError):
       return
 
     try:
diff --git a/git_superproject.py b/git_superproject.py
new file mode 100644
index 00000000..4ca84a58
--- /dev/null
+++ b/git_superproject.py
@@ -0,0 +1,415 @@
+# Copyright (C) 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Provide functionality to get all projects and their commit ids from Superproject.
+
+For more information on superproject, check out:
+https://en.wikibooks.org/wiki/Git/Submodules_and_Superprojects
+
+Examples:
+  superproject = Superproject()
+  UpdateProjectsResult = superproject.UpdateProjectsRevisionId(projects)
+"""
+
+import hashlib
+import functools
+import os
+import sys
+import time
+from typing import NamedTuple
+
+from git_command import git_require, GitCommand
+from git_config import RepoConfig
+from git_refs import R_HEADS
+from manifest_xml import LOCAL_MANIFEST_GROUP_PREFIX
+
+_SUPERPROJECT_GIT_NAME = 'superproject.git'
+_SUPERPROJECT_MANIFEST_NAME = 'superproject_override.xml'
+
+
+class SyncResult(NamedTuple):
+  """Return the status of sync and whether caller should exit."""
+
+  # Whether the superproject sync was successful.
+  success: bool
+  # Whether the caller should exit.
+  fatal: bool
+
+
+class CommitIdsResult(NamedTuple):
+  """Return the commit ids and whether caller should exit."""
+
+  # A dictionary with the projects/commit ids on success, otherwise None.
+  commit_ids: dict
+  # Whether the caller should exit.
+  fatal: bool
+
+
+class UpdateProjectsResult(NamedTuple):
+  """Return the overriding manifest file and whether caller should exit."""
+
+  # Path name of the overriding manifest file if successful, otherwise None.
+  manifest_path: str
+  # Whether the caller should exit.
+  fatal: bool
+
+
+class Superproject(object):
+  """Get commit ids from superproject.
+
+  Initializes a local copy of a superproject for the manifest. This allows
+  lookup of commit ids for all projects. It contains _project_commit_ids which
+  is a dictionary with project/commit id entries.
+  """
+  def __init__(self, manifest, repodir, git_event_log,
+               superproject_dir='exp-superproject', quiet=False, print_messages=False):
+    """Initializes superproject.
+
+    Args:
+      manifest: A Manifest object that is to be written to a file.
+      repodir: Path to the .repo/ dir for holding all internal checkout state.
+          It must be in the top directory of the repo client checkout.
+      git_event_log: A git trace2 event log to log events.
+      superproject_dir: Relative path under |repodir| to checkout superproject.
+      quiet:  If True then only print the progress messages.
+      print_messages: if True then print error/warning messages.
+    """
+    self._project_commit_ids = None
+    self._manifest = manifest
+    self._git_event_log = git_event_log
+    self._quiet = quiet
+    self._print_messages = print_messages
+    self._branch = manifest.branch
+    self._repodir = os.path.abspath(repodir)
+    self._superproject_dir = superproject_dir
+    self._superproject_path = os.path.join(self._repodir, superproject_dir)
+    self._manifest_path = os.path.join(self._superproject_path,
+                                       _SUPERPROJECT_MANIFEST_NAME)
+    git_name = ''
+    if self._manifest.superproject:
+      remote = self._manifest.superproject['remote']
+      git_name = hashlib.md5(remote.name.encode('utf8')).hexdigest() + '-'
+      self._branch = self._manifest.superproject['revision']
+      self._remote_url = remote.url
+    else:
+      self._remote_url = None
+    self._work_git_name = git_name + _SUPERPROJECT_GIT_NAME
+    self._work_git = os.path.join(self._superproject_path, self._work_git_name)
+
+  @property
+  def project_commit_ids(self):
+    """Returns a dictionary of projects and their commit ids."""
+    return self._project_commit_ids
+
+  @property
+  def manifest_path(self):
+    """Returns the manifest path if the path exists or None."""
+    return self._manifest_path if os.path.exists(self._manifest_path) else None
+
+  def _LogMessage(self, message):
+    """Logs message to stderr and _git_event_log."""
+    if self._print_messages:
+      print(message, file=sys.stderr)
+    self._git_event_log.ErrorEvent(message, f'{message}')
+
+  def _LogMessagePrefix(self):
+    """Returns the prefix string to be logged in each log message"""
+    return f'repo superproject branch: {self._branch} url: {self._remote_url}'
+
+  def _LogError(self, message):
+    """Logs error message to stderr and _git_event_log."""
+    self._LogMessage(f'{self._LogMessagePrefix()} error: {message}')
+
+  def _LogWarning(self, message):
+    """Logs warning message to stderr and _git_event_log."""
+    self._LogMessage(f'{self._LogMessagePrefix()} warning: {message}')
+
+  def _Init(self):
+    """Sets up a local Git repository to get a copy of a superproject.
+
+    Returns:
+      True if initialization is successful, or False.
+    """
+    if not os.path.exists(self._superproject_path):
+      os.mkdir(self._superproject_path)
+    if not self._quiet and not os.path.exists(self._work_git):
+      print('%s: Performing initial setup for superproject; this might take '
+            'several minutes.' % self._work_git)
+    cmd = ['init', '--bare', self._work_git_name]
+    p = GitCommand(None,
+                   cmd,
+                   cwd=self._superproject_path,
+                   capture_stdout=True,
+                   capture_stderr=True)
+    retval = p.Wait()
+    if retval:
+      self._LogWarning(f'git init call failed, command: git {cmd}, '
+                       f'return code: {retval}, stderr: {p.stderr}')
+      return False
+    return True
+
+  def _Fetch(self):
+    """Fetches a local copy of a superproject for the manifest based on |_remote_url|.
+
+    Returns:
+      True if fetch is successful, or False.
+    """
+    if not os.path.exists(self._work_git):
+      self._LogWarning(f'git fetch missing directory: {self._work_git}')
+      return False
+    if not git_require((2, 28, 0)):
+      self._LogWarning('superproject requires a git version 2.28 or later')
+      return False
+    cmd = ['fetch', self._remote_url, '--depth', '1', '--force', '--no-tags',
+           '--filter', 'blob:none']
+    if self._branch:
+      cmd += [self._branch + ':' + self._branch]
+    p = GitCommand(None,
+                   cmd,
+                   cwd=self._work_git,
+                   capture_stdout=True,
+                   capture_stderr=True)
+    retval = p.Wait()
+    if retval:
+      self._LogWarning(f'git fetch call failed, command: git {cmd}, '
+                       f'return code: {retval}, stderr: {p.stderr}')
+      return False
+    return True
+
+  def _LsTree(self):
+    """Gets the commit ids for all projects.
+
+    Works only in git repositories.
+
+    Returns:
+      data: data returned from 'git ls-tree ...' instead of None.
+    """
+    if not os.path.exists(self._work_git):
+      self._LogWarning(f'git ls-tree missing directory: {self._work_git}')
+      return None
+    data = None
+    branch = 'HEAD' if not self._branch else self._branch
+    cmd = ['ls-tree', '-z', '-r', branch]
+
+    p = GitCommand(None,
+                   cmd,
+                   cwd=self._work_git,
+                   capture_stdout=True,
+                   capture_stderr=True)
+    retval = p.Wait()
+    if retval == 0:
+      data = p.stdout
+    else:
+      self._LogWarning(f'git ls-tree call failed, command: git {cmd}, '
+                       f'return code: {retval}, stderr: {p.stderr}')
+    return data
+
+  def Sync(self):
+    """Gets a local copy of a superproject for the manifest.
+
+    Returns:
+      SyncResult
+    """
+    if not self._manifest.superproject:
+      self._LogWarning(f'superproject tag is not defined in manifest: '
+                       f'{self._manifest.manifestFile}')
+      return SyncResult(False, False)
+
+    print('NOTICE: --use-superproject is in beta; report any issues to the '
+          'address described in `repo version`', file=sys.stderr)
+    should_exit = True
+    if not self._remote_url:
+      self._LogWarning(f'superproject URL is not defined in manifest: '
+                       f'{self._manifest.manifestFile}')
+      return SyncResult(False, should_exit)
+
+    if not self._Init():
+      return SyncResult(False, should_exit)
+    if not self._Fetch():
+      return SyncResult(False, should_exit)
+    if not self._quiet:
+      print('%s: Initial setup for superproject completed.' % self._work_git)
+    return SyncResult(True, False)
+
+  def _GetAllProjectsCommitIds(self):
+    """Get commit ids for all projects from superproject and save them in _project_commit_ids.
+
+    Returns:
+      CommitIdsResult
+    """
+    sync_result = self.Sync()
+    if not sync_result.success:
+      return CommitIdsResult(None, sync_result.fatal)
+
+    data = self._LsTree()
+    if not data:
+      self._LogWarning(f'git ls-tree failed to return data for manifest: '
+                       f'{self._manifest.manifestFile}')
+      return CommitIdsResult(None, True)
+
+    # Parse lines like the following to select lines starting with '160000' and
+    # build a dictionary with project path (last element) and its commit id (3rd element).
+    #
+    # 160000 commit 2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea\tart\x00
+    # 120000 blob acc2cbdf438f9d2141f0ae424cec1d8fc4b5d97f\tbootstrap.bash\x00
+    commit_ids = {}
+    for line in data.split('\x00'):
+      ls_data = line.split(None, 3)
+      if not ls_data:
+        break
+      if ls_data[0] == '160000':
+        commit_ids[ls_data[3]] = ls_data[2]
+
+    self._project_commit_ids = commit_ids
+    return CommitIdsResult(commit_ids, False)
+
+  def _WriteManifestFile(self):
+    """Writes manifest to a file.
+
+    Returns:
+      manifest_path: Path name of the file into which manifest is written instead of None.
+    """
+    if not os.path.exists(self._superproject_path):
+      self._LogWarning(f'missing superproject directory: {self._superproject_path}')
+      return None
+    manifest_str = self._manifest.ToXml(groups=self._manifest.GetGroupsStr()).toxml()
+    manifest_path = self._manifest_path
+    try:
+      with open(manifest_path, 'w', encoding='utf-8') as fp:
+        fp.write(manifest_str)
+    except IOError as e:
+      self._LogError(f'cannot write manifest to : {manifest_path} {e}')
+      return None
+    return manifest_path
+
+  def _SkipUpdatingProjectRevisionId(self, project):
+    """Checks if a project's revision id needs to be updated or not.
+
+    Revision id for projects from local manifest will not be updated.
+
+    Args:
+      project: project whose revision id is being updated.
+
+    Returns:
+      True if a project's revision id should not be updated, or False,
+    """
+    path = project.relpath
+    if not path:
+      return True
+    # Skip the project with revisionId.
+    if project.revisionId:
+      return True
+    # Skip the project if it comes from the local manifest.
+    return any(s.startswith(LOCAL_MANIFEST_GROUP_PREFIX) for s in project.groups)
+
+  def UpdateProjectsRevisionId(self, projects):
+    """Update revisionId of every project in projects with the commit id.
+
+    Args:
+      projects: List of projects whose revisionId needs to be updated.
+
+    Returns:
+      UpdateProjectsResult
+    """
+    commit_ids_result = self._GetAllProjectsCommitIds()
+    commit_ids = commit_ids_result.commit_ids
+    if not commit_ids:
+      return UpdateProjectsResult(None, commit_ids_result.fatal)
+
+    projects_missing_commit_ids = []
+    for project in projects:
+      if self._SkipUpdatingProjectRevisionId(project):
+        continue
+      path = project.relpath
+      commit_id = commit_ids.get(path)
+      if not commit_id:
+        projects_missing_commit_ids.append(path)
+
+    # If superproject doesn't have a commit id for a project, then report an
+    # error event and continue as if do not use superproject is specified.
+    if projects_missing_commit_ids:
+      self._LogWarning(f'please file a bug using {self._manifest.contactinfo.bugurl} '
+                       f'to report missing commit_ids for: {projects_missing_commit_ids}')
+      return UpdateProjectsResult(None, False)
+
+    for project in projects:
+      if not self._SkipUpdatingProjectRevisionId(project):
+        project.SetRevisionId(commit_ids.get(project.relpath))
+
+    manifest_path = self._WriteManifestFile()
+    return UpdateProjectsResult(manifest_path, False)
+
+
+@functools.lru_cache(maxsize=None)
+def _UseSuperprojectFromConfiguration():
+  """Returns the user choice of whether to use superproject."""
+  user_cfg = RepoConfig.ForUser()
+  time_now = int(time.time())
+
+  user_value = user_cfg.GetBoolean('repo.superprojectChoice')
+  if user_value is not None:
+    user_expiration = user_cfg.GetInt('repo.superprojectChoiceExpire')
+    if user_expiration is None or user_expiration <= 0 or user_expiration >= time_now:
+      # TODO(b/190688390) - Remove prompt when we are comfortable with the new
+      # default value.
+      if user_value:
+        print(('You are currently enrolled in Git submodules experiment '
+               '(go/android-submodules-quickstart).  Use --no-use-superproject '
+               'to override.\n'), file=sys.stderr)
+      else:
+        print(('You are not currently enrolled in Git submodules experiment '
+               '(go/android-submodules-quickstart).  Use --use-superproject '
+               'to override.\n'), file=sys.stderr)
+      return user_value
+
+  # We don't have an unexpired choice, ask for one.
+  system_cfg = RepoConfig.ForSystem()
+  system_value = system_cfg.GetBoolean('repo.superprojectChoice')
+  if system_value:
+    # The system configuration is proposing that we should enable the
+    # use of superproject. Treat the user as enrolled for two weeks.
+    #
+    # TODO(b/190688390) - Remove prompt when we are comfortable with the new
+    # default value.
+    userchoice = True
+    time_choiceexpire = time_now + (86400 * 14)
+    user_cfg.SetString('repo.superprojectChoiceExpire', str(time_choiceexpire))
+    user_cfg.SetBoolean('repo.superprojectChoice', userchoice)
+    print('You are automatically enrolled in Git submodules experiment '
+          '(go/android-submodules-quickstart) for another two weeks.\n',
+          file=sys.stderr)
+    return True
+
+  # For all other cases, we would not use superproject by default.
+  return False
+
+
+def PrintMessages(opt, manifest):
+  """Returns a boolean if error/warning messages are to be printed."""
+  return opt.use_superproject is not None or manifest.superproject
+
+
+def UseSuperproject(opt, manifest):
+  """Returns a boolean if use-superproject option is enabled."""
+
+  if opt.use_superproject is not None:
+    return opt.use_superproject
+  else:
+    client_value = manifest.manifestProject.config.GetBoolean('repo.superproject')
+    if client_value is not None:
+      return client_value
+    else:
+      if not manifest.superproject:
+        return False
+      return _UseSuperprojectFromConfiguration()
diff --git a/git_trace2_event_log.py b/git_trace2_event_log.py
new file mode 100644
index 00000000..0e5e9089
--- /dev/null
+++ b/git_trace2_event_log.py
@@ -0,0 +1,273 @@
+# Copyright (C) 2020 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Provide event logging in the git trace2 EVENT format.
+
+The git trace2 EVENT format is defined at:
+https://www.kernel.org/pub/software/scm/git/docs/technical/api-trace2.html#_event_format
+https://git-scm.com/docs/api-trace2#_the_event_format_target
+
+  Usage:
+
+  git_trace_log = EventLog()
+  git_trace_log.StartEvent()
+  ...
+  git_trace_log.ExitEvent()
+  git_trace_log.Write()
+"""
+
+
+import datetime
+import json
+import os
+import sys
+import tempfile
+import threading
+
+from git_command import GitCommand, RepoSourceVersion
+
+
+class EventLog(object):
+  """Event log that records events that occurred during a repo invocation.
+
+  Events are written to the log as a consecutive JSON entries, one per line.
+  Entries follow the git trace2 EVENT format.
+
+  Each entry contains the following common keys:
+  - event: The event name
+  - sid: session-id - Unique string to allow process instance to be identified.
+  - thread: The thread name.
+  - time: is the UTC time of the event.
+
+  Valid 'event' names and event specific fields are documented here:
+  https://git-scm.com/docs/api-trace2#_event_format
+  """
+
+  def __init__(self, env=None):
+    """Initializes the event log."""
+    self._log = []
+    # Try to get session-id (sid) from environment (setup in repo launcher).
+    KEY = 'GIT_TRACE2_PARENT_SID'
+    if env is None:
+      env = os.environ
+
+    now = datetime.datetime.utcnow()
+
+    # Save both our sid component and the complete sid.
+    # We use our sid component (self._sid) as the unique filename prefix and
+    # the full sid (self._full_sid) in the log itself.
+    self._sid = 'repo-%s-P%08x' % (now.strftime('%Y%m%dT%H%M%SZ'), os.getpid())
+    parent_sid = env.get(KEY)
+    # Append our sid component to the parent sid (if it exists).
+    if parent_sid is not None:
+      self._full_sid = parent_sid + '/' + self._sid
+    else:
+      self._full_sid = self._sid
+
+    # Set/update the environment variable.
+    # Environment handling across systems is messy.
+    try:
+      env[KEY] = self._full_sid
+    except UnicodeEncodeError:
+      env[KEY] = self._full_sid.encode()
+
+    # Add a version event to front of the log.
+    self._AddVersionEvent()
+
+  @property
+  def full_sid(self):
+    return self._full_sid
+
+  def _AddVersionEvent(self):
+    """Adds a 'version' event at the beginning of current log."""
+    version_event = self._CreateEventDict('version')
+    version_event['evt'] = "2"
+    version_event['exe'] = RepoSourceVersion()
+    self._log.insert(0, version_event)
+
+  def _CreateEventDict(self, event_name):
+    """Returns a dictionary with the common keys/values for git trace2 events.
+
+    Args:
+      event_name: The event name.
+
+    Returns:
+      Dictionary with the common event fields populated.
+    """
+    return {
+        'event': event_name,
+        'sid': self._full_sid,
+        'thread': threading.currentThread().getName(),
+        'time': datetime.datetime.utcnow().isoformat() + 'Z',
+    }
+
+  def StartEvent(self):
+    """Append a 'start' event to the current log."""
+    start_event = self._CreateEventDict('start')
+    start_event['argv'] = sys.argv
+    self._log.append(start_event)
+
+  def ExitEvent(self, result):
+    """Append an 'exit' event to the current log.
+
+    Args:
+      result: Exit code of the event
+    """
+    exit_event = self._CreateEventDict('exit')
+
+    # Consider 'None' success (consistent with event_log result handling).
+    if result is None:
+      result = 0
+    exit_event['code'] = result
+    self._log.append(exit_event)
+
+  def CommandEvent(self, name, subcommands):
+    """Append a 'command' event to the current log.
+
+    Args:
+      name: Name of the primary command (ex: repo, git)
+      subcommands: List of the sub-commands (ex: version, init, sync)
+    """
+    command_event = self._CreateEventDict('command')
+    command_event['name'] = name
+    command_event['subcommands'] = subcommands
+    self._log.append(command_event)
+
+  def LogConfigEvents(self, config, event_dict_name):
+    """Append a |event_dict_name| event for each config key in |config|.
+
+    Args:
+      config: Configuration dictionary.
+      event_dict_name: Name of the event dictionary for items to be logged under.
+    """
+    for param, value in config.items():
+      event = self._CreateEventDict(event_dict_name)
+      event['param'] = param
+      event['value'] = value
+      self._log.append(event)
+
+  def DefParamRepoEvents(self, config):
+    """Append a 'def_param' event for each repo.* config key to the current log.
+
+    Args:
+      config: Repo configuration dictionary
+    """
+    # Only output the repo.* config parameters.
+    repo_config = {k: v for k, v in config.items() if k.startswith('repo.')}
+    self.LogConfigEvents(repo_config, 'def_param')
+
+  def GetDataEventName(self, value):
+    """Returns 'data-json' if the value is an array else returns 'data'."""
+    return 'data-json' if value[0] == '[' and value[-1] == ']' else 'data'
+
+  def LogDataConfigEvents(self, config, prefix):
+    """Append a 'data' event for each config key/value in |config| to the current log.
+
+    For each keyX and valueX of the config, "key" field of the event is '|prefix|/keyX'
+    and the "value" of the "key" field is valueX.
+
+    Args:
+      config: Configuration dictionary.
+      prefix: Prefix for each key that is logged.
+    """
+    for key, value in config.items():
+      event = self._CreateEventDict(self.GetDataEventName(value))
+      event['key'] = f'{prefix}/{key}'
+      event['value'] = value
+      self._log.append(event)
+
+  def ErrorEvent(self, msg, fmt):
+    """Append a 'error' event to the current log."""
+    error_event = self._CreateEventDict('error')
+    error_event['msg'] = msg
+    error_event['fmt'] = fmt
+    self._log.append(error_event)
+
+  def _GetEventTargetPath(self):
+    """Get the 'trace2.eventtarget' path from git configuration.
+
+    Returns:
+      path: git config's 'trace2.eventtarget' path if it exists, or None
+    """
+    path = None
+    cmd = ['config', '--get', 'trace2.eventtarget']
+    # TODO(https://crbug.com/gerrit/13706): Use GitConfig when it supports
+    # system git config variables.
+    p = GitCommand(None, cmd, capture_stdout=True, capture_stderr=True,
+                   bare=True)
+    retval = p.Wait()
+    if retval == 0:
+      # Strip trailing carriage-return in path.
+      path = p.stdout.rstrip('\n')
+    elif retval != 1:
+      # `git config --get` is documented to produce an exit status of `1` if
+      # the requested variable is not present in the configuration. Report any
+      # other return value as an error.
+      print("repo: error: 'git config --get' call failed with return code: %r, stderr: %r" % (
+          retval, p.stderr), file=sys.stderr)
+    return path
+
+  def Write(self, path=None):
+    """Writes the log out to a file.
+
+    Log is only written if 'path' or 'git config --get trace2.eventtarget'
+    provide a valid path to write logs to.
+
+    Logging filename format follows the git trace2 style of being a unique
+    (exclusive writable) file.
+
+    Args:
+      path: Path to where logs should be written.
+
+    Returns:
+      log_path: Path to the log file if log is written, otherwise None
+    """
+    log_path = None
+    # If no logging path is specified, get the path from 'trace2.eventtarget'.
+    if path is None:
+      path = self._GetEventTargetPath()
+
+    # If no logging path is specified, exit.
+    if path is None:
+      return None
+
+    if isinstance(path, str):
+      # Get absolute path.
+      path = os.path.abspath(os.path.expanduser(path))
+    else:
+      raise TypeError('path: str required but got %s.' % type(path))
+
+    # Git trace2 requires a directory to write log to.
+
+    # TODO(https://crbug.com/gerrit/13706): Support file (append) mode also.
+    if not os.path.isdir(path):
+      return None
+    # Use NamedTemporaryFile to generate a unique filename as required by git trace2.
+    try:
+      with tempfile.NamedTemporaryFile(mode='x', prefix=self._sid, dir=path,
+                                       delete=False) as f:
+        # TODO(https://crbug.com/gerrit/13706): Support writing events as they
+        # occur.
+        for e in self._log:
+          # Dump in compact encoding mode.
+          # See 'Compact encoding' in Python docs:
+          # https://docs.python.org/3/library/json.html#module-json
+          json.dump(e, f, indent=None, separators=(',', ':'))
+          f.write('\n')
+        log_path = f.name
+    except FileExistsError as err:
+      print('repo: warning: git trace2 logging failed: %r' % err,
+            file=sys.stderr)
+      return None
+    return log_path
diff --git a/gitc_utils.py b/gitc_utils.py
index b47e181c..486bbeb0 100644
--- a/gitc_utils.py
+++ b/gitc_utils.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2015 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,8 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import os
+import multiprocessing
 import platform
 import re
 import sys
@@ -29,12 +27,24 @@ from error import ManifestParseError
 
 NUM_BATCH_RETRIEVE_REVISIONID = 32
 
+
 def get_gitc_manifest_dir():
   return wrapper.Wrapper().get_gitc_manifest_dir()
 
+
 def parse_clientdir(gitc_fs_path):
   return wrapper.Wrapper().gitc_parse_clientdir(gitc_fs_path)
 
+
+def _get_project_revision(args):
+  """Worker for _set_project_revisions to lookup one project remote."""
+  (i, url, expr) = args
+  gitcmd = git_command.GitCommand(
+      None, ['ls-remote', url, expr], capture_stdout=True, cwd='/tmp')
+  rc = gitcmd.Wait()
+  return (i, rc, gitcmd.stdout.split('\t', 1)[0])
+
+
 def _set_project_revisions(projects):
   """Sets the revisionExpr for a list of projects.
 
@@ -42,47 +52,38 @@ def _set_project_revisions(projects):
   should not be overly large. Recommend calling this function multiple times
   with each call not exceeding NUM_BATCH_RETRIEVE_REVISIONID projects.
 
-  @param projects: List of project objects to set the revionExpr for.
+  Args:
+    projects: List of project objects to set the revionExpr for.
   """
   # Retrieve the commit id for each project based off of it's current
   # revisionExpr and it is not already a commit id.
-  project_gitcmds = [(
-      project, git_command.GitCommand(None,
-                                      ['ls-remote',
-                                       project.remote.url,
-                                       project.revisionExpr],
-                                      capture_stdout=True, cwd='/tmp'))
-      for project in projects if not git_config.IsId(project.revisionExpr)]
-  for proj, gitcmd in project_gitcmds:
-    if gitcmd.Wait():
-      print('FATAL: Failed to retrieve revisionExpr for %s' % proj)
-      sys.exit(1)
-    revisionExpr = gitcmd.stdout.split('\t')[0]
-    if not revisionExpr:
-      raise ManifestParseError('Invalid SHA-1 revision project %s (%s)' %
-                               (proj.remote.url, proj.revisionExpr))
-    proj.revisionExpr = revisionExpr
-
-def _manifest_groups(manifest):
-  """Returns the manifest group string that should be synced
-
-  This is the same logic used by Command.GetProjects(), which is used during
-  repo sync
-
-  @param manifest: The XmlManifest object
-  """
-  mp = manifest.manifestProject
-  groups = mp.config.GetString('manifest.groups')
-  if not groups:
-    groups = 'default,platform-' + platform.system().lower()
-  return groups
+  with multiprocessing.Pool(NUM_BATCH_RETRIEVE_REVISIONID) as pool:
+    results_iter = pool.imap_unordered(
+        _get_project_revision,
+        ((i, project.remote.url, project.revisionExpr)
+         for i, project in enumerate(projects)
+         if not git_config.IsId(project.revisionExpr)),
+        chunksize=8)
+    for (i, rc, revisionExpr) in results_iter:
+      project = projects[i]
+      if rc:
+        print('FATAL: Failed to retrieve revisionExpr for %s' % project.name)
+        pool.terminate()
+        sys.exit(1)
+      if not revisionExpr:
+        pool.terminate()
+        raise ManifestParseError('Invalid SHA-1 revision project %s (%s)' %
+                                 (project.remote.url, project.revisionExpr))
+      project.revisionExpr = revisionExpr
+
 
 def generate_gitc_manifest(gitc_manifest, manifest, paths=None):
   """Generate a manifest for shafsd to use for this GITC client.
 
-  @param gitc_manifest: Current gitc manifest, or None if there isn't one yet.
-  @param manifest: A GitcManifest object loaded with the current repo manifest.
-  @param paths: List of project paths we want to update.
+  Args:
+    gitc_manifest: Current gitc manifest, or None if there isn't one yet.
+    manifest: A GitcManifest object loaded with the current repo manifest.
+    paths: List of project paths we want to update.
   """
 
   print('Generating GITC Manifest by fetching revision SHAs for each '
@@ -90,7 +91,7 @@ def generate_gitc_manifest(gitc_manifest, manifest, paths=None):
   if paths is None:
     paths = list(manifest.paths.keys())
 
-  groups = [x for x in re.split(r'[,\s]+', _manifest_groups(manifest)) if x]
+  groups = [x for x in re.split(r'[,\s]+', manifest.GetGroupsStr()) if x]
 
   # Convert the paths to projects, and filter them to the matched groups.
   projects = [manifest.paths[p] for p in paths]
@@ -104,11 +105,11 @@ def generate_gitc_manifest(gitc_manifest, manifest, paths=None):
       if not proj.upstream and not git_config.IsId(proj.revisionExpr):
         proj.upstream = proj.revisionExpr
 
-      if not path in gitc_manifest.paths:
+      if path not in gitc_manifest.paths:
         # Any new projects need their first revision, even if we weren't asked
         # for them.
         projects.append(proj)
-      elif not path in paths:
+      elif path not in paths:
         # And copy revisions from the previous manifest if we're not updating
         # them now.
         gitc_proj = gitc_manifest.paths[path]
@@ -118,11 +119,7 @@ def generate_gitc_manifest(gitc_manifest, manifest, paths=None):
         else:
           proj.revisionExpr = gitc_proj.revisionExpr
 
-  index = 0
-  while index < len(projects):
-    _set_project_revisions(
-        projects[index:(index+NUM_BATCH_RETRIEVE_REVISIONID)])
-    index += NUM_BATCH_RETRIEVE_REVISIONID
+  _set_project_revisions(projects)
 
   if gitc_manifest is not None:
     for path, proj in gitc_manifest.paths.items():
@@ -140,16 +137,20 @@ def generate_gitc_manifest(gitc_manifest, manifest, paths=None):
   # Save the manifest.
   save_manifest(manifest)
 
+
 def save_manifest(manifest, client_dir=None):
   """Save the manifest file in the client_dir.
 
-  @param client_dir: Client directory to save the manifest in.
-  @param manifest: Manifest object to save.
+  Args:
+    manifest: Manifest object to save.
+    client_dir: Client directory to save the manifest in.
   """
   if not client_dir:
-    client_dir = manifest.gitc_client_dir
-  with open(os.path.join(client_dir, '.manifest'), 'w') as f:
-    manifest.Save(f, groups=_manifest_groups(manifest))
+    manifest_file = manifest.manifestFile
+  else:
+    manifest_file = os.path.join(client_dir, '.manifest')
+  with open(manifest_file, 'w') as f:
+    manifest.Save(f, groups=manifest.GetGroupsStr())
   # TODO(sbasi/jorg): Come up with a solution to remove the sleep below.
   # Give the GITC filesystem time to register the manifest changes.
   time.sleep(3)
diff --git a/hooks.py b/hooks.py
new file mode 100644
index 00000000..67c21a25
--- /dev/null
+++ b/hooks.py
@@ -0,0 +1,509 @@
+# Copyright (C) 2008 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import errno
+import json
+import os
+import re
+import subprocess
+import sys
+import traceback
+import urllib.parse
+
+from error import HookError
+from git_refs import HEAD
+
+
+class RepoHook(object):
+  """A RepoHook contains information about a script to run as a hook.
+
+  Hooks are used to run a python script before running an upload (for instance,
+  to run presubmit checks).  Eventually, we may have hooks for other actions.
+
+  This shouldn't be confused with files in the 'repo/hooks' directory.  Those
+  files are copied into each '.git/hooks' folder for each project.  Repo-level
+  hooks are associated instead with repo actions.
+
+  Hooks are always python.  When a hook is run, we will load the hook into the
+  interpreter and execute its main() function.
+
+  Combinations of hook option flags:
+  - no-verify=False, verify=False (DEFAULT):
+    If stdout is a tty, can prompt about running hooks if needed.
+    If user denies running hooks, the action is cancelled. If stdout is
+    not a tty and we would need to prompt about hooks, action is
+    cancelled.
+  - no-verify=False, verify=True:
+    Always run hooks with no prompt.
+  - no-verify=True, verify=False:
+    Never run hooks, but run action anyway (AKA bypass hooks).
+  - no-verify=True, verify=True:
+    Invalid
+  """
+
+  def __init__(self,
+               hook_type,
+               hooks_project,
+               repo_topdir,
+               manifest_url,
+               bypass_hooks=False,
+               allow_all_hooks=False,
+               ignore_hooks=False,
+               abort_if_user_denies=False):
+    """RepoHook constructor.
+
+    Params:
+      hook_type: A string representing the type of hook.  This is also used
+          to figure out the name of the file containing the hook.  For
+          example: 'pre-upload'.
+      hooks_project: The project containing the repo hooks.
+          If you have a manifest, this is manifest.repo_hooks_project.
+          OK if this is None, which will make the hook a no-op.
+      repo_topdir: The top directory of the repo client checkout.
+          This is the one containing the .repo directory. Scripts will
+          run with CWD as this directory.
+          If you have a manifest, this is manifest.topdir.
+      manifest_url: The URL to the manifest git repo.
+      bypass_hooks: If True, then 'Do not run the hook'.
+      allow_all_hooks: If True, then 'Run the hook without prompting'.
+      ignore_hooks: If True, then 'Do not abort action if hooks fail'.
+      abort_if_user_denies: If True, we'll abort running the hook if the user
+          doesn't allow us to run the hook.
+    """
+    self._hook_type = hook_type
+    self._hooks_project = hooks_project
+    self._repo_topdir = repo_topdir
+    self._manifest_url = manifest_url
+    self._bypass_hooks = bypass_hooks
+    self._allow_all_hooks = allow_all_hooks
+    self._ignore_hooks = ignore_hooks
+    self._abort_if_user_denies = abort_if_user_denies
+
+    # Store the full path to the script for convenience.
+    if self._hooks_project:
+      self._script_fullpath = os.path.join(self._hooks_project.worktree,
+                                           self._hook_type + '.py')
+    else:
+      self._script_fullpath = None
+
+  def _GetHash(self):
+    """Return a hash of the contents of the hooks directory.
+
+    We'll just use git to do this.  This hash has the property that if anything
+    changes in the directory we will return a different has.
+
+    SECURITY CONSIDERATION:
+      This hash only represents the contents of files in the hook directory, not
+      any other files imported or called by hooks.  Changes to imported files
+      can change the script behavior without affecting the hash.
+
+    Returns:
+      A string representing the hash.  This will always be ASCII so that it can
+      be printed to the user easily.
+    """
+    assert self._hooks_project, "Must have hooks to calculate their hash."
+
+    # We will use the work_git object rather than just calling GetRevisionId().
+    # That gives us a hash of the latest checked in version of the files that
+    # the user will actually be executing.  Specifically, GetRevisionId()
+    # doesn't appear to change even if a user checks out a different version
+    # of the hooks repo (via git checkout) nor if a user commits their own revs.
+    #
+    # NOTE: Local (non-committed) changes will not be factored into this hash.
+    # I think this is OK, since we're really only worried about warning the user
+    # about upstream changes.
+    return self._hooks_project.work_git.rev_parse(HEAD)
+
+  def _GetMustVerb(self):
+    """Return 'must' if the hook is required; 'should' if not."""
+    if self._abort_if_user_denies:
+      return 'must'
+    else:
+      return 'should'
+
+  def _CheckForHookApproval(self):
+    """Check to see whether this hook has been approved.
+
+    We'll accept approval of manifest URLs if they're using secure transports.
+    This way the user can say they trust the manifest hoster.  For insecure
+    hosts, we fall back to checking the hash of the hooks repo.
+
+    Note that we ask permission for each individual hook even though we use
+    the hash of all hooks when detecting changes.  We'd like the user to be
+    able to approve / deny each hook individually.  We only use the hash of all
+    hooks because there is no other easy way to detect changes to local imports.
+
+    Returns:
+      True if this hook is approved to run; False otherwise.
+
+    Raises:
+      HookError: Raised if the user doesn't approve and abort_if_user_denies
+          was passed to the consturctor.
+    """
+    if self._ManifestUrlHasSecureScheme():
+      return self._CheckForHookApprovalManifest()
+    else:
+      return self._CheckForHookApprovalHash()
+
+  def _CheckForHookApprovalHelper(self, subkey, new_val, main_prompt,
+                                  changed_prompt):
+    """Check for approval for a particular attribute and hook.
+
+    Args:
+      subkey: The git config key under [repo.hooks.<hook_type>] to store the
+          last approved string.
+      new_val: The new value to compare against the last approved one.
+      main_prompt: Message to display to the user to ask for approval.
+      changed_prompt: Message explaining why we're re-asking for approval.
+
+    Returns:
+      True if this hook is approved to run; False otherwise.
+
+    Raises:
+      HookError: Raised if the user doesn't approve and abort_if_user_denies
+          was passed to the consturctor.
+    """
+    hooks_config = self._hooks_project.config
+    git_approval_key = 'repo.hooks.%s.%s' % (self._hook_type, subkey)
+
+    # Get the last value that the user approved for this hook; may be None.
+    old_val = hooks_config.GetString(git_approval_key)
+
+    if old_val is not None:
+      # User previously approved hook and asked not to be prompted again.
+      if new_val == old_val:
+        # Approval matched.  We're done.
+        return True
+      else:
+        # Give the user a reason why we're prompting, since they last told
+        # us to "never ask again".
+        prompt = 'WARNING: %s\n\n' % (changed_prompt,)
+    else:
+      prompt = ''
+
+    # Prompt the user if we're not on a tty; on a tty we'll assume "no".
+    if sys.stdout.isatty():
+      prompt += main_prompt + ' (yes/always/NO)? '
+      response = input(prompt).lower()
+      print()
+
+      # User is doing a one-time approval.
+      if response in ('y', 'yes'):
+        return True
+      elif response == 'always':
+        hooks_config.SetString(git_approval_key, new_val)
+        return True
+
+    # For anything else, we'll assume no approval.
+    if self._abort_if_user_denies:
+      raise HookError('You must allow the %s hook or use --no-verify.' %
+                      self._hook_type)
+
+    return False
+
+  def _ManifestUrlHasSecureScheme(self):
+    """Check if the URI for the manifest is a secure transport."""
+    secure_schemes = ('file', 'https', 'ssh', 'persistent-https', 'sso', 'rpc')
+    parse_results = urllib.parse.urlparse(self._manifest_url)
+    return parse_results.scheme in secure_schemes
+
+  def _CheckForHookApprovalManifest(self):
+    """Check whether the user has approved this manifest host.
+
+    Returns:
+      True if this hook is approved to run; False otherwise.
+    """
+    return self._CheckForHookApprovalHelper(
+        'approvedmanifest',
+        self._manifest_url,
+        'Run hook scripts from %s' % (self._manifest_url,),
+        'Manifest URL has changed since %s was allowed.' % (self._hook_type,))
+
+  def _CheckForHookApprovalHash(self):
+    """Check whether the user has approved the hooks repo.
+
+    Returns:
+      True if this hook is approved to run; False otherwise.
+    """
+    prompt = ('Repo %s run the script:\n'
+              '  %s\n'
+              '\n'
+              'Do you want to allow this script to run')
+    return self._CheckForHookApprovalHelper(
+        'approvedhash',
+        self._GetHash(),
+        prompt % (self._GetMustVerb(), self._script_fullpath),
+        'Scripts have changed since %s was allowed.' % (self._hook_type,))
+
+  @staticmethod
+  def _ExtractInterpFromShebang(data):
+    """Extract the interpreter used in the shebang.
+
+    Try to locate the interpreter the script is using (ignoring `env`).
+
+    Args:
+      data: The file content of the script.
+
+    Returns:
+      The basename of the main script interpreter, or None if a shebang is not
+      used or could not be parsed out.
+    """
+    firstline = data.splitlines()[:1]
+    if not firstline:
+      return None
+
+    # The format here can be tricky.
+    shebang = firstline[0].strip()
+    m = re.match(r'^#!\s*([^\s]+)(?:\s+([^\s]+))?', shebang)
+    if not m:
+      return None
+
+    # If the using `env`, find the target program.
+    interp = m.group(1)
+    if os.path.basename(interp) == 'env':
+      interp = m.group(2)
+
+    return interp
+
+  def _ExecuteHookViaReexec(self, interp, context, **kwargs):
+    """Execute the hook script through |interp|.
+
+    Note: Support for this feature should be dropped ~Jun 2021.
+
+    Args:
+      interp: The Python program to run.
+      context: Basic Python context to execute the hook inside.
+      kwargs: Arbitrary arguments to pass to the hook script.
+
+    Raises:
+      HookError: When the hooks failed for any reason.
+    """
+    # This logic needs to be kept in sync with _ExecuteHookViaImport below.
+    script = """
+import json, os, sys
+path = '''%(path)s'''
+kwargs = json.loads('''%(kwargs)s''')
+context = json.loads('''%(context)s''')
+sys.path.insert(0, os.path.dirname(path))
+data = open(path).read()
+exec(compile(data, path, 'exec'), context)
+context['main'](**kwargs)
+""" % {
+        'path': self._script_fullpath,
+        'kwargs': json.dumps(kwargs),
+        'context': json.dumps(context),
+    }
+
+    # We pass the script via stdin to avoid OS argv limits.  It also makes
+    # unhandled exception tracebacks less verbose/confusing for users.
+    cmd = [interp, '-c', 'import sys; exec(sys.stdin.read())']
+    proc = subprocess.Popen(cmd, stdin=subprocess.PIPE)
+    proc.communicate(input=script.encode('utf-8'))
+    if proc.returncode:
+      raise HookError('Failed to run %s hook.' % (self._hook_type,))
+
+  def _ExecuteHookViaImport(self, data, context, **kwargs):
+    """Execute the hook code in |data| directly.
+
+    Args:
+      data: The code of the hook to execute.
+      context: Basic Python context to execute the hook inside.
+      kwargs: Arbitrary arguments to pass to the hook script.
+
+    Raises:
+      HookError: When the hooks failed for any reason.
+    """
+    # Exec, storing global context in the context dict.  We catch exceptions
+    # and convert to a HookError w/ just the failing traceback.
+    try:
+      exec(compile(data, self._script_fullpath, 'exec'), context)
+    except Exception:
+      raise HookError('%s\nFailed to import %s hook; see traceback above.' %
+                      (traceback.format_exc(), self._hook_type))
+
+    # Running the script should have defined a main() function.
+    if 'main' not in context:
+      raise HookError('Missing main() in: "%s"' % self._script_fullpath)
+
+    # Call the main function in the hook.  If the hook should cause the
+    # build to fail, it will raise an Exception.  We'll catch that convert
+    # to a HookError w/ just the failing traceback.
+    try:
+      context['main'](**kwargs)
+    except Exception:
+      raise HookError('%s\nFailed to run main() for %s hook; see traceback '
+                      'above.' % (traceback.format_exc(), self._hook_type))
+
+  def _ExecuteHook(self, **kwargs):
+    """Actually execute the given hook.
+
+    This will run the hook's 'main' function in our python interpreter.
+
+    Args:
+      kwargs: Keyword arguments to pass to the hook.  These are often specific
+          to the hook type.  For instance, pre-upload hooks will contain
+          a project_list.
+    """
+    # Keep sys.path and CWD stashed away so that we can always restore them
+    # upon function exit.
+    orig_path = os.getcwd()
+    orig_syspath = sys.path
+
+    try:
+      # Always run hooks with CWD as topdir.
+      os.chdir(self._repo_topdir)
+
+      # Put the hook dir as the first item of sys.path so hooks can do
+      # relative imports.  We want to replace the repo dir as [0] so
+      # hooks can't import repo files.
+      sys.path = [os.path.dirname(self._script_fullpath)] + sys.path[1:]
+
+      # Initial global context for the hook to run within.
+      context = {'__file__': self._script_fullpath}
+
+      # Add 'hook_should_take_kwargs' to the arguments to be passed to main.
+      # We don't actually want hooks to define their main with this argument--
+      # it's there to remind them that their hook should always take **kwargs.
+      # For instance, a pre-upload hook should be defined like:
+      #   def main(project_list, **kwargs):
+      #
+      # This allows us to later expand the API without breaking old hooks.
+      kwargs = kwargs.copy()
+      kwargs['hook_should_take_kwargs'] = True
+
+      # See what version of python the hook has been written against.
+      data = open(self._script_fullpath).read()
+      interp = self._ExtractInterpFromShebang(data)
+      reexec = False
+      if interp:
+        prog = os.path.basename(interp)
+        if prog.startswith('python2') and sys.version_info.major != 2:
+          reexec = True
+        elif prog.startswith('python3') and sys.version_info.major == 2:
+          reexec = True
+
+      # Attempt to execute the hooks through the requested version of Python.
+      if reexec:
+        try:
+          self._ExecuteHookViaReexec(interp, context, **kwargs)
+        except OSError as e:
+          if e.errno == errno.ENOENT:
+            # We couldn't find the interpreter, so fallback to importing.
+            reexec = False
+          else:
+            raise
+
+      # Run the hook by importing directly.
+      if not reexec:
+        self._ExecuteHookViaImport(data, context, **kwargs)
+    finally:
+      # Restore sys.path and CWD.
+      sys.path = orig_syspath
+      os.chdir(orig_path)
+
+  def _CheckHook(self):
+    # Bail with a nice error if we can't find the hook.
+    if not os.path.isfile(self._script_fullpath):
+      raise HookError('Couldn\'t find repo hook: %s' % self._script_fullpath)
+
+  def Run(self, **kwargs):
+    """Run the hook.
+
+    If the hook doesn't exist (because there is no hooks project or because
+    this particular hook is not enabled), this is a no-op.
+
+    Args:
+      user_allows_all_hooks: If True, we will never prompt about running the
+          hook--we'll just assume it's OK to run it.
+      kwargs: Keyword arguments to pass to the hook.  These are often specific
+          to the hook type.  For instance, pre-upload hooks will contain
+          a project_list.
+
+    Returns:
+      True: On success or ignore hooks by user-request
+      False: The hook failed. The caller should respond with aborting the action.
+        Some examples in which False is returned:
+        * Finding the hook failed while it was enabled, or
+        * the user declined to run a required hook (from _CheckForHookApproval)
+        In all these cases the user did not pass the proper arguments to
+        ignore the result through the option combinations as listed in
+        AddHookOptionGroup().
+    """
+    # Do not do anything in case bypass_hooks is set, or
+    # no-op if there is no hooks project or if hook is disabled.
+    if (self._bypass_hooks or
+        not self._hooks_project or
+        self._hook_type not in self._hooks_project.enabled_repo_hooks):
+      return True
+
+    passed = True
+    try:
+      self._CheckHook()
+
+      # Make sure the user is OK with running the hook.
+      if self._allow_all_hooks or self._CheckForHookApproval():
+        # Run the hook with the same version of python we're using.
+        self._ExecuteHook(**kwargs)
+    except SystemExit as e:
+      passed = False
+      print('ERROR: %s hooks exited with exit code: %s' % (self._hook_type, str(e)),
+            file=sys.stderr)
+    except HookError as e:
+      passed = False
+      print('ERROR: %s' % str(e), file=sys.stderr)
+
+    if not passed and self._ignore_hooks:
+      print('\nWARNING: %s hooks failed, but continuing anyways.' % self._hook_type,
+            file=sys.stderr)
+      passed = True
+
+    return passed
+
+  @classmethod
+  def FromSubcmd(cls, manifest, opt, *args, **kwargs):
+    """Method to construct the repo hook class
+
+    Args:
+      manifest: The current active manifest for this command from which we
+          extract a couple of fields.
+      opt: Contains the commandline options for the action of this hook.
+          It should contain the options added by AddHookOptionGroup() in which
+          we are interested in RepoHook execution.
+    """
+    for key in ('bypass_hooks', 'allow_all_hooks', 'ignore_hooks'):
+      kwargs.setdefault(key, getattr(opt, key))
+    kwargs.update({
+        'hooks_project': manifest.repo_hooks_project,
+        'repo_topdir': manifest.topdir,
+        'manifest_url': manifest.manifestProject.GetRemote('origin').url,
+    })
+    return cls(*args, **kwargs)
+
+  @staticmethod
+  def AddOptionGroup(parser, name):
+    """Help options relating to the various hooks."""
+
+    # Note that verify and no-verify are NOT opposites of each other, which
+    # is why they store to different locations. We are using them to match
+    # 'git commit' syntax.
+    group = parser.add_option_group(name + ' hooks')
+    group.add_option('--no-verify',
+                     dest='bypass_hooks', action='store_true',
+                     help='Do not run the %s hook.' % name)
+    group.add_option('--verify',
+                     dest='allow_all_hooks', action='store_true',
+                     help='Run the %s hook without prompting.' % name)
+    group.add_option('--ignore-hooks',
+                     action='store_true',
+                     help='Do not abort if %s hooks fail.' % name)
diff --git a/hooks/commit-msg b/hooks/commit-msg
index d9bb188b..70d67eaf 100755
--- a/hooks/commit-msg
+++ b/hooks/commit-msg
@@ -1,5 +1,5 @@
 #!/bin/sh
-# From Gerrit Code Review 2.14.6
+# From Gerrit Code Review 3.1.3
 #
 # Part of Gerrit Code Review (https://www.gerritcodereview.com/)
 #
@@ -16,176 +16,48 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
-#
-
-unset GREP_OPTIONS
-
-CHANGE_ID_AFTER="Bug|Depends-On|Issue|Test|Feature|Fixes|Fixed"
-MSG="$1"
-
-# Check for, and add if missing, a unique Change-Id
-#
-add_ChangeId() {
-        clean_message=`sed -e '
-                /^diff --git .*/{
-                        s///
-                        q
-                }
-                /^Signed-off-by:/d
-                /^#/d
-        ' "$MSG" | git stripspace`
-        if test -z "$clean_message"
-        then
-                return
-        fi
-
-        # Do not add Change-Id to temp commits
-        if echo "$clean_message" | head -1 | grep -q '^\(fixup\|squash\)!'
-        then
-                return
-        fi
-
-        if test "false" = "`git config --bool --get gerrit.createChangeId`"
-        then
-                return
-        fi
-
-        # Does Change-Id: already exist? if so, exit (no change).
-        if grep -i '^Change-Id:' "$MSG" >/dev/null
-        then
-                return
-        fi
-
-        id=`_gen_ChangeId`
-        T="$MSG.tmp.$$"
-        AWK=awk
-        if [ -x /usr/xpg4/bin/awk ]; then
-                # Solaris AWK is just too broken
-                AWK=/usr/xpg4/bin/awk
-        fi
-
-        # Get core.commentChar from git config or use default symbol
-        commentChar=`git config --get core.commentChar`
-        commentChar=${commentChar:-#}
-
-        # How this works:
-        # - parse the commit message as (textLine+ blankLine*)*
-        # - assume textLine+ to be a footer until proven otherwise
-        # - exception: the first block is not footer (as it is the title)
-        # - read textLine+ into a variable
-        # - then count blankLines
-        # - once the next textLine appears, print textLine+ blankLine* as these
-        #   aren't footer
-        # - in END, the last textLine+ block is available for footer parsing
-        $AWK '
-        BEGIN {
-                # while we start with the assumption that textLine+
-                # is a footer, the first block is not.
-                isFooter = 0
-                footerComment = 0
-                blankLines = 0
-        }
-
-        # Skip lines starting with commentChar without any spaces before it.
-        /^'"$commentChar"'/ { next }
-
-        # Skip the line starting with the diff command and everything after it,
-        # up to the end of the file, assuming it is only patch data.
-        # If more than one line before the diff was empty, strip all but one.
-        /^diff --git / {
-                blankLines = 0
-                while (getline) { }
-                next
-        }
-
-        # Count blank lines outside footer comments
-        /^$/ && (footerComment == 0) {
-                blankLines++
-                next
-        }
-
-        # Catch footer comment
-        /^\[[a-zA-Z0-9-]+:/ && (isFooter == 1) {
-                footerComment = 1
-        }
-
-        /]$/ && (footerComment == 1) {
-                footerComment = 2
-        }
-
-        # We have a non-blank line after blank lines. Handle this.
-        (blankLines > 0) {
-                print lines
-                for (i = 0; i < blankLines; i++) {
-                        print ""
-                }
-
-                lines = ""
-                blankLines = 0
-                isFooter = 1
-                footerComment = 0
-        }
-
-        # Detect that the current block is not the footer
-        (footerComment == 0) && (!/^\[?[a-zA-Z0-9-]+:/ || /^[a-zA-Z0-9-]+:\/\//) {
-                isFooter = 0
-        }
-
-        {
-                # We need this information about the current last comment line
-                if (footerComment == 2) {
-                        footerComment = 0
-                }
-                if (lines != "") {
-                        lines = lines "\n";
-                }
-                lines = lines $0
-        }
-
-        # Footer handling:
-        # If the last block is considered a footer, splice in the Change-Id at the
-        # right place.
-        # Look for the right place to inject Change-Id by considering
-        # CHANGE_ID_AFTER. Keys listed in it (case insensitive) come first,
-        # then Change-Id, then everything else (eg. Signed-off-by:).
-        #
-        # Otherwise just print the last block, a new line and the Change-Id as a
-        # block of its own.
-        END {
-                unprinted = 1
-                if (isFooter == 0) {
-                        print lines "\n"
-                        lines = ""
-                }
-                changeIdAfter = "^(" tolower("'"$CHANGE_ID_AFTER"'") "):"
-                numlines = split(lines, footer, "\n")
-                for (line = 1; line <= numlines; line++) {
-                        if (unprinted && match(tolower(footer[line]), changeIdAfter) != 1) {
-                                unprinted = 0
-                                print "Change-Id: I'"$id"'"
-                        }
-                        print footer[line]
-                }
-                if (unprinted) {
-                        print "Change-Id: I'"$id"'"
-                }
-        }' "$MSG" > "$T" && mv "$T" "$MSG" || rm -f "$T"
-}
-_gen_ChangeIdInput() {
-        echo "tree `git write-tree`"
-        if parent=`git rev-parse "HEAD^0" 2>/dev/null`
-        then
-                echo "parent $parent"
-        fi
-        echo "author `git var GIT_AUTHOR_IDENT`"
-        echo "committer `git var GIT_COMMITTER_IDENT`"
-        echo
-        printf '%s' "$clean_message"
-}
-_gen_ChangeId() {
-        _gen_ChangeIdInput |
-        git hash-object -t commit --stdin
-}
-
 
-add_ChangeId
+# avoid [[ which is not POSIX sh.
+if test "$#" != 1 ; then
+  echo "$0 requires an argument."
+  exit 1
+fi
+
+if test ! -f "$1" ; then
+  echo "file does not exist: $1"
+  exit 1
+fi
+
+# Do not create a change id if requested
+if test "false" = "`git config --bool --get gerrit.createChangeId`" ; then
+  exit 0
+fi
+
+# $RANDOM will be undefined if not using bash, so don't use set -u
+random=$( (whoami ; hostname ; date; cat $1 ; echo $RANDOM) | git hash-object --stdin)
+dest="$1.tmp.${random}"
+
+trap 'rm -f "${dest}"' EXIT
+
+if ! git stripspace --strip-comments < "$1" > "${dest}" ; then
+   echo "cannot strip comments from $1"
+   exit 1
+fi
+
+if test ! -s "${dest}" ; then
+  echo "file is empty: $1"
+  exit 1
+fi
+
+# Avoid the --in-place option which only appeared in Git 2.8
+# Avoid the --if-exists option which only appeared in Git 2.15
+if ! git -c trailer.ifexists=doNothing interpret-trailers \
+      --trailer "Change-Id: I${random}" < "$1" > "${dest}" ; then
+  echo "cannot insert change-id line in $1"
+  exit 1
+fi
+
+if ! mv "${dest}" "$1" ; then
+  echo "cannot mv ${dest} to $1"
+  exit 1
+fi
diff --git a/main.py b/main.py
index 16db144f..2050cabb 100755
--- a/main.py
+++ b/main.py
@@ -1,5 +1,4 @@
-#!/usr/bin/env python
-# -*- coding:utf-8 -*-
+#!/usr/bin/env python3
 #
 # Copyright (C) 2008 The Android Open Source Project
 #
@@ -21,23 +20,15 @@ People shouldn't run this directly; instead, they should use the `repo` wrapper
 which takes care of execing this entry point.
 """
 
-from __future__ import print_function
 import getpass
 import netrc
 import optparse
 import os
+import shlex
 import sys
 import textwrap
 import time
-
-from pyversion import is_python3
-if is_python3():
-  import urllib.request
-else:
-  import imp
-  import urllib2
-  urllib = imp.new_module('urllib')
-  urllib.request = urllib2
+import urllib.request
 
 try:
   import kerberos
@@ -47,8 +38,9 @@ except ImportError:
 from color import SetDefaultColoring
 import event_log
 from repo_trace import SetTrace
-from git_command import git, GitCommand, user_agent
-from git_config import init_ssh, close_ssh
+from git_command import user_agent
+from git_config import RepoConfig
+from git_trace2_event_log import EventLog
 from command import InteractiveCommand
 from command import MirrorSafeCommand
 from command import GitcAvailableCommand, GitcClientCommand
@@ -62,25 +54,54 @@ from error import NoManifestException
 from error import NoSuchProjectError
 from error import RepoChangedException
 import gitc_utils
-from manifest_xml import GitcManifest, XmlManifest
+from manifest_xml import GitcClient, RepoClient
 from pager import RunPager, TerminatePager
 from wrapper import WrapperPath, Wrapper
 
 from subcmds import all_commands
 
-if not is_python3():
-  input = raw_input
+
+# NB: These do not need to be kept in sync with the repo launcher script.
+# These may be much newer as it allows the repo launcher to roll between
+# different repo releases while source versions might require a newer python.
+#
+# The soft version is when we start warning users that the version is old and
+# we'll be dropping support for it.  We'll refuse to work with versions older
+# than the hard version.
+#
+# python-3.6 is in Ubuntu Bionic.
+MIN_PYTHON_VERSION_SOFT = (3, 6)
+MIN_PYTHON_VERSION_HARD = (3, 6)
+
+if sys.version_info.major < 3:
+  print('repo: error: Python 2 is no longer supported; '
+        'Please upgrade to Python {}.{}+.'.format(*MIN_PYTHON_VERSION_SOFT),
+        file=sys.stderr)
+  sys.exit(1)
+else:
+  if sys.version_info < MIN_PYTHON_VERSION_HARD:
+    print('repo: error: Python 3 version is too old; '
+          'Please upgrade to Python {}.{}+.'.format(*MIN_PYTHON_VERSION_SOFT),
+          file=sys.stderr)
+    sys.exit(1)
+  elif sys.version_info < MIN_PYTHON_VERSION_SOFT:
+    print('repo: warning: your Python 3 version is no longer supported; '
+          'Please upgrade to Python {}.{}+.'.format(*MIN_PYTHON_VERSION_SOFT),
+          file=sys.stderr)
+
 
 global_options = optparse.OptionParser(
     usage='repo [-p|--paginate|--no-pager] COMMAND [ARGS]',
     add_help_option=False)
 global_options.add_option('-h', '--help', action='store_true',
                           help='show this help message and exit')
+global_options.add_option('--help-all', action='store_true',
+                          help='show this help message with all subcommands and exit')
 global_options.add_option('-p', '--paginate',
                           dest='pager', action='store_true',
                           help='display command output in the pager')
 global_options.add_option('--no-pager',
-                          dest='no_pager', action='store_true',
+                          dest='pager', action='store_false',
                           help='disable the pager')
 global_options.add_option('--color',
                           choices=('auto', 'always', 'never'), default=None,
@@ -97,76 +118,125 @@ global_options.add_option('--time',
 global_options.add_option('--version',
                           dest='show_version', action='store_true',
                           help='display this version of repo')
+global_options.add_option('--show-toplevel',
+                          action='store_true',
+                          help='display the path of the top-level directory of '
+                               'the repo client checkout')
 global_options.add_option('--event-log',
                           dest='event_log', action='store',
                           help='filename of event log to append timeline to')
+global_options.add_option('--git-trace2-event-log', action='store',
+                          help='directory to write git trace2 event log to')
+
 
 class _Repo(object):
   def __init__(self, repodir):
     self.repodir = repodir
     self.commands = all_commands
-    # add 'branch' as an alias for 'branches'
-    all_commands['branch'] = all_commands['branches']
+
+  def _PrintHelp(self, short: bool = False, all_commands: bool = False):
+    """Show --help screen."""
+    global_options.print_help()
+    print()
+    if short:
+      commands = ' '.join(sorted(self.commands))
+      wrapped_commands = textwrap.wrap(commands, width=77)
+      print('Available commands:\n  %s' % ('\n  '.join(wrapped_commands),))
+      print('\nRun `repo help <command>` for command-specific details.')
+      print('Bug reports:', Wrapper().BUG_URL)
+    else:
+      cmd = self.commands['help']()
+      if all_commands:
+        cmd.PrintAllCommandsBody()
+      else:
+        cmd.PrintCommonCommandsBody()
 
   def _ParseArgs(self, argv):
     """Parse the main `repo` command line options."""
-    name = None
-    glob = []
-
-    for i in range(len(argv)):
-      if not argv[i].startswith('-'):
-        name = argv[i]
-        if i > 0:
-          glob = argv[:i]
+    for i, arg in enumerate(argv):
+      if not arg.startswith('-'):
+        name = arg
+        glob = argv[:i]
         argv = argv[i + 1:]
         break
-    if not name:
+    else:
+      name = None
       glob = argv
-      name = 'help'
       argv = []
     gopts, _gargs = global_options.parse_args(glob)
 
-    if gopts.help:
-      global_options.print_help()
-      commands = ' '.join(sorted(self.commands))
-      wrapped_commands = textwrap.wrap(commands, width=77)
-      print('\nAvailable commands:\n  %s' % ('\n  '.join(wrapped_commands),))
-      print('\nRun `repo help <command>` for command-specific details.')
-      global_options.exit()
+    if name:
+      name, alias_args = self._ExpandAlias(name)
+      argv = alias_args + argv
 
     return (name, gopts, argv)
 
+  def _ExpandAlias(self, name):
+    """Look up user registered aliases."""
+    # We don't resolve aliases for existing subcommands.  This matches git.
+    if name in self.commands:
+      return name, []
+
+    key = 'alias.%s' % (name,)
+    alias = RepoConfig.ForRepository(self.repodir).GetString(key)
+    if alias is None:
+      alias = RepoConfig.ForUser().GetString(key)
+    if alias is None:
+      return name, []
+
+    args = alias.strip().split(' ', 1)
+    name = args[0]
+    if len(args) == 2:
+      args = shlex.split(args[1])
+    else:
+      args = []
+    return name, args
+
   def _Run(self, name, gopts, argv):
     """Execute the requested subcommand."""
     result = 0
 
     if gopts.trace:
       SetTrace()
-    if gopts.show_version:
-      if name == 'help':
-        name = 'version'
-      else:
-        print('fatal: invalid usage of --version', file=sys.stderr)
-        return 1
+
+    # Handle options that terminate quickly first.
+    if gopts.help or gopts.help_all:
+      self._PrintHelp(short=False, all_commands=gopts.help_all)
+      return 0
+    elif gopts.show_version:
+      # Always allow global --version regardless of subcommand validity.
+      name = 'version'
+    elif gopts.show_toplevel:
+      print(os.path.dirname(self.repodir))
+      return 0
+    elif not name:
+      # No subcommand specified, so show the help/subcommand.
+      self._PrintHelp(short=True)
+      return 1
 
     SetDefaultColoring(gopts.color)
 
+    git_trace2_event_log = EventLog()
+    repo_client = RepoClient(self.repodir)
+    gitc_manifest = None
+    gitc_client_name = gitc_utils.parse_clientdir(os.getcwd())
+    if gitc_client_name:
+      gitc_manifest = GitcClient(self.repodir, gitc_client_name)
+      repo_client.isGitcClient = True
+
     try:
-      cmd = self.commands[name]
+      cmd = self.commands[name](
+          repodir=self.repodir,
+          client=repo_client,
+          manifest=repo_client.manifest,
+          gitc_manifest=gitc_manifest,
+          git_event_log=git_trace2_event_log)
     except KeyError:
       print("repo: '%s' is not a repo command.  See 'repo help'." % name,
             file=sys.stderr)
       return 1
 
-    cmd.repodir = self.repodir
-    cmd.manifest = XmlManifest(cmd.repodir)
-    cmd.gitc_manifest = None
-    gitc_client_name = gitc_utils.parse_clientdir(os.getcwd())
-    if gitc_client_name:
-      cmd.gitc_manifest = GitcManifest(cmd.repodir, gitc_client_name)
-      cmd.manifest.isGitcClient = True
-
-    Editor.globalConfig = cmd.manifest.globalConfig
+    Editor.globalConfig = cmd.client.globalConfig
 
     if not isinstance(cmd, MirrorSafeCommand) and cmd.manifest.IsMirror:
       print("fatal: '%s' requires a working directory" % name,
@@ -188,13 +258,13 @@ class _Repo(object):
       copts = cmd.ReadEnvironmentOptions(copts)
     except NoManifestException as e:
       print('error: in `%s`: %s' % (' '.join([name] + argv), str(e)),
-        file=sys.stderr)
+            file=sys.stderr)
       print('error: manifest missing or unreadable -- please run init',
             file=sys.stderr)
       return 1
 
-    if not gopts.no_pager and not isinstance(cmd, InteractiveCommand):
-      config = cmd.manifest.globalConfig
+    if gopts.pager is not False and not isinstance(cmd, InteractiveCommand):
+      config = cmd.client.globalConfig
       if gopts.pager:
         use_pager = True
       else:
@@ -207,13 +277,17 @@ class _Repo(object):
     start = time.time()
     cmd_event = cmd.event_log.Add(name, event_log.TASK_COMMAND, start)
     cmd.event_log.SetParent(cmd_event)
+    git_trace2_event_log.StartEvent()
+    git_trace2_event_log.CommandEvent(name='repo', subcommands=[name])
+
     try:
+      cmd.CommonValidateOptions(copts, cargs)
       cmd.ValidateOptions(copts, cargs)
       result = cmd.Execute(copts, cargs)
     except (DownloadError, ManifestInvalidRevisionError,
-        NoManifestException) as e:
+            NoManifestException) as e:
       print('error: in `%s`: %s' % (' '.join([name] + argv), str(e)),
-        file=sys.stderr)
+            file=sys.stderr)
       if isinstance(e, NoManifestException):
         print('error: manifest missing or unreadable -- please run init',
               file=sys.stderr)
@@ -228,7 +302,8 @@ class _Repo(object):
       if e.name:
         print('error: project group must be enabled for project %s' % e.name, file=sys.stderr)
       else:
-        print('error: project group must be enabled for the project in the current directory', file=sys.stderr)
+        print('error: project group must be enabled for the project in the current directory',
+              file=sys.stderr)
       result = 1
     except SystemExit as e:
       if e.code:
@@ -248,49 +323,78 @@ class _Repo(object):
 
       cmd.event_log.FinishEvent(cmd_event, finish,
                                 result is None or result == 0)
+      git_trace2_event_log.DefParamRepoEvents(
+          cmd.manifest.manifestProject.config.DumpConfigDict())
+      git_trace2_event_log.ExitEvent(result)
+
       if gopts.event_log:
         cmd.event_log.Write(os.path.abspath(
                             os.path.expanduser(gopts.event_log)))
 
+      git_trace2_event_log.Write(gopts.git_trace2_event_log)
     return result
 
 
-def _CheckWrapperVersion(ver, repo_path):
+def _CheckWrapperVersion(ver_str, repo_path):
+  """Verify the repo launcher is new enough for this checkout.
+
+  Args:
+    ver_str: The version string passed from the repo launcher when it ran us.
+    repo_path: The path to the repo launcher that loaded us.
+  """
+  # Refuse to work with really old wrapper versions.  We don't test these,
+  # so might as well require a somewhat recent sane version.
+  # v1.15 of the repo launcher was released in ~Mar 2012.
+  MIN_REPO_VERSION = (1, 15)
+  min_str = '.'.join(str(x) for x in MIN_REPO_VERSION)
+
   if not repo_path:
     repo_path = '~/bin/repo'
 
-  if not ver:
+  if not ver_str:
     print('no --wrapper-version argument', file=sys.stderr)
     sys.exit(1)
 
+  # Pull out the version of the repo launcher we know about to compare.
   exp = Wrapper().VERSION
-  ver = tuple(map(int, ver.split('.')))
-  if len(ver) == 1:
-    ver = (0, ver[0])
+  ver = tuple(map(int, ver_str.split('.')))
 
   exp_str = '.'.join(map(str, exp))
-  if exp[0] > ver[0] or ver < (0, 4):
+  if ver < MIN_REPO_VERSION:
     print("""
-!!! A new repo command (%5s) is available.    !!!
-!!! You must upgrade before you can continue:   !!!
+repo: error:
+!!! Your version of repo %s is too old.
+!!! We need at least version %s.
+!!! A new version of repo (%s) is available.
+!!! You must upgrade before you can continue:
 
     cp %s %s
-""" % (exp_str, WrapperPath(), repo_path), file=sys.stderr)
+""" % (ver_str, min_str, exp_str, WrapperPath(), repo_path), file=sys.stderr)
     sys.exit(1)
 
   if exp > ver:
-    print("""
-... A new repo command (%5s) is available.
+    print('\n... A new version of repo (%s) is available.' % (exp_str,),
+          file=sys.stderr)
+    if os.access(repo_path, os.W_OK):
+      print("""\
 ... You should upgrade soon:
-
     cp %s %s
-""" % (exp_str, WrapperPath(), repo_path), file=sys.stderr)
+""" % (WrapperPath(), repo_path), file=sys.stderr)
+    else:
+      print("""\
+... New version is available at: %s
+... The launcher is run from: %s
+!!! The launcher is not writable.  Please talk to your sysadmin or distro
+!!! to get an update installed.
+""" % (WrapperPath(), repo_path), file=sys.stderr)
+
 
 def _CheckRepoDir(repo_dir):
   if not repo_dir:
     print('no --repo-dir argument', file=sys.stderr)
     sys.exit(1)
 
+
 def _PruneOptions(argv, opt):
   i = 0
   while i < len(argv):
@@ -306,6 +410,7 @@ def _PruneOptions(argv, opt):
       continue
     i += 1
 
+
 class _UserAgentHandler(urllib.request.BaseHandler):
   def http_request(self, req):
     req.add_header('User-Agent', user_agent.repo)
@@ -315,6 +420,7 @@ class _UserAgentHandler(urllib.request.BaseHandler):
     req.add_header('User-Agent', user_agent.repo)
     return req
 
+
 def _AddPasswordFromUserInput(handler, msg, req):
   # If repo could not find auth info from netrc, try to get it from user input
   url = req.get_full_url()
@@ -328,22 +434,24 @@ def _AddPasswordFromUserInput(handler, msg, req):
       return
     handler.passwd.add_password(None, url, user, password)
 
+
 class _BasicAuthHandler(urllib.request.HTTPBasicAuthHandler):
   def http_error_401(self, req, fp, code, msg, headers):
     _AddPasswordFromUserInput(self, msg, req)
     return urllib.request.HTTPBasicAuthHandler.http_error_401(
-      self, req, fp, code, msg, headers)
+        self, req, fp, code, msg, headers)
 
   def http_error_auth_reqed(self, authreq, host, req, headers):
     try:
       old_add_header = req.add_header
+
       def _add_header(name, val):
         val = val.replace('\n', '')
         old_add_header(name, val)
       req.add_header = _add_header
       return urllib.request.AbstractBasicAuthHandler.http_error_auth_reqed(
-        self, authreq, host, req, headers)
-    except:
+          self, authreq, host, req, headers)
+    except Exception:
       reset = getattr(self, 'reset_retry_count', None)
       if reset is not None:
         reset()
@@ -351,22 +459,24 @@ class _BasicAuthHandler(urllib.request.HTTPBasicAuthHandler):
         self.retried = 0
       raise
 
+
 class _DigestAuthHandler(urllib.request.HTTPDigestAuthHandler):
   def http_error_401(self, req, fp, code, msg, headers):
     _AddPasswordFromUserInput(self, msg, req)
     return urllib.request.HTTPDigestAuthHandler.http_error_401(
-      self, req, fp, code, msg, headers)
+        self, req, fp, code, msg, headers)
 
   def http_error_auth_reqed(self, auth_header, host, req, headers):
     try:
       old_add_header = req.add_header
+
       def _add_header(name, val):
         val = val.replace('\n', '')
         old_add_header(name, val)
       req.add_header = _add_header
       return urllib.request.AbstractDigestAuthHandler.http_error_auth_reqed(
-        self, auth_header, host, req, headers)
-    except:
+          self, auth_header, host, req, headers)
+    except Exception:
       reset = getattr(self, 'reset_retry_count', None)
       if reset is not None:
         reset()
@@ -374,6 +484,7 @@ class _DigestAuthHandler(urllib.request.HTTPDigestAuthHandler):
         self.retried = 0
       raise
 
+
 class _KerberosAuthHandler(urllib.request.BaseHandler):
   def __init__(self):
     self.retried = 0
@@ -392,7 +503,7 @@ class _KerberosAuthHandler(urllib.request.BaseHandler):
 
       if self.retried > 3:
         raise urllib.request.HTTPError(req.get_full_url(), 401,
-          "Negotiate auth failed", headers, None)
+                                       "Negotiate auth failed", headers, None)
       else:
         self.retried += 1
 
@@ -408,7 +519,7 @@ class _KerberosAuthHandler(urllib.request.BaseHandler):
         return response
     except kerberos.GSSError:
       return None
-    except:
+    except Exception:
       self.reset_retry_count()
       raise
     finally:
@@ -454,6 +565,7 @@ class _KerberosAuthHandler(urllib.request.BaseHandler):
       kerberos.authGSSClientClean(self.context)
       self.context = None
 
+
 def init_http():
   handlers = [_UserAgentHandler()]
 
@@ -462,7 +574,7 @@ def init_http():
     n = netrc.netrc()
     for host in n.hosts:
       p = n.hosts[host]
-      mgr.add_password(p[1], 'http://%s/'  % host, p[0], p[2])
+      mgr.add_password(p[1], 'http://%s/' % host, p[0], p[2])
       mgr.add_password(p[1], 'https://%s/' % host, p[0], p[2])
   except netrc.NetrcParseError:
     pass
@@ -481,6 +593,7 @@ def init_http():
     handlers.append(urllib.request.HTTPSHandler(debuglevel=1))
   urllib.request.install_opener(urllib.request.build_opener(*handlers))
 
+
 def _Main(argv):
   result = 0
 
@@ -502,20 +615,16 @@ def _Main(argv):
 
   repo = _Repo(opt.repodir)
   try:
-    try:
-      init_ssh()
-      init_http()
-      name, gopts, argv = repo._ParseArgs(argv)
-      run = lambda: repo._Run(name, gopts, argv) or 0
-      if gopts.trace_python:
-        import trace
-        tracer = trace.Trace(count=False, trace=True, timing=True,
-                             ignoredirs=set(sys.path[1:]))
-        result = tracer.runfunc(run)
-      else:
-        result = run()
-    finally:
-      close_ssh()
+    init_http()
+    name, gopts, argv = repo._ParseArgs(argv)
+    run = lambda: repo._Run(name, gopts, argv) or 0
+    if gopts.trace_python:
+      import trace
+      tracer = trace.Trace(count=False, trace=True, timing=True,
+                           ignoredirs=set(sys.path[1:]))
+      result = tracer.runfunc(run)
+    else:
+      result = run()
   except KeyboardInterrupt:
     print('aborted by user', file=sys.stderr)
     result = 1
@@ -528,7 +637,7 @@ def _Main(argv):
     argv = list(sys.argv)
     argv.extend(rce.extra_args)
     try:
-      os.execv(__file__, argv)
+      os.execv(sys.executable, [__file__] + argv)
     except OSError as e:
       print('fatal: cannot restart repo after upgrade', file=sys.stderr)
       print('fatal: %s' % e, file=sys.stderr)
@@ -537,5 +646,6 @@ def _Main(argv):
   TerminatePager()
   sys.exit(result)
 
+
 if __name__ == '__main__':
   _Main(sys.argv[1:])
diff --git a/man/repo-abandon.1 b/man/repo-abandon.1
new file mode 100644
index 00000000..b3c0422f
--- /dev/null
+++ b/man/repo-abandon.1
@@ -0,0 +1,36 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo abandon" "Repo Manual"
+.SH NAME
+repo \- repo abandon - manual page for repo abandon
+.SH SYNOPSIS
+.B repo
+\fI\,abandon \/\fR[\fI\,--all | <branchname>\/\fR] [\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Permanently abandon a development branch
+.PP
+This subcommand permanently abandons a development branch by
+deleting it (and all its history) from your local repository.
+.PP
+It is equivalent to "git branch \fB\-D\fR <branchname>".
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.TP
+\fB\-\-all\fR
+delete all branches in all projects
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help abandon` to view the detailed manual.
diff --git a/man/repo-branch.1 b/man/repo-branch.1
new file mode 100644
index 00000000..854ee98b
--- /dev/null
+++ b/man/repo-branch.1
@@ -0,0 +1 @@
+.so man1/repo-branches.1
\ No newline at end of file
diff --git a/man/repo-branches.1 b/man/repo-branches.1
new file mode 100644
index 00000000..7fe0b02d
--- /dev/null
+++ b/man/repo-branches.1
@@ -0,0 +1,59 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo branches" "Repo Manual"
+.SH NAME
+repo \- repo branches - manual page for repo branches
+.SH SYNOPSIS
+.B repo
+\fI\,branches \/\fR[\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+View current topic branches
+.PP
+Summarizes the currently available topic branches.
+.PP
+# Branch Display
+.PP
+The branch display output by this command is organized into four
+columns of information; for example:
+.TP
+*P nocolor
+| in repo
+.TP
+repo2
+|
+.PP
+The first column contains a * if the branch is the currently
+checked out branch in any of the specified projects, or a blank
+if no project has the branch checked out.
+.PP
+The second column contains either blank, p or P, depending upon
+the upload status of the branch.
+.IP
+(blank): branch not yet published by repo upload
+.IP
+P: all commits were published by repo upload
+p: only some commits were published by repo upload
+.PP
+The third column contains the branch name.
+.PP
+The fourth column (after the | separator) lists the projects that
+the branch appears in, or does not appear in.  If no project list
+is shown, then the branch appears in all projects.
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help branches` to view the detailed manual.
diff --git a/man/repo-checkout.1 b/man/repo-checkout.1
new file mode 100644
index 00000000..6dd3e6ca
--- /dev/null
+++ b/man/repo-checkout.1
@@ -0,0 +1,36 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo checkout" "Repo Manual"
+.SH NAME
+repo \- repo checkout - manual page for repo checkout
+.SH SYNOPSIS
+.B repo
+\fI\,checkout <branchname> \/\fR[\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Checkout a branch for development
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help checkout` to view the detailed manual.
+.SH DETAILS
+.PP
+The 'repo checkout' command checks out an existing branch that was previously
+created by 'repo start'.
+.PP
+The command is equivalent to:
+.IP
+repo forall [<project>...] \fB\-c\fR git checkout <branchname>
diff --git a/man/repo-cherry-pick.1 b/man/repo-cherry-pick.1
new file mode 100644
index 00000000..e7716c55
--- /dev/null
+++ b/man/repo-cherry-pick.1
@@ -0,0 +1,28 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo cherry-pick" "Repo Manual"
+.SH NAME
+repo \- repo cherry-pick - manual page for repo cherry-pick
+.SH SYNOPSIS
+.B repo
+\fI\,cherry-pick <sha1>\/\fR
+.SH DESCRIPTION
+Summary
+.PP
+Cherry\-pick a change.
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help cherry\-pick` to view the detailed manual.
+.SH DETAILS
+.PP
+\&'repo cherry\-pick' cherry\-picks a change from one branch to another. The change
+id will be updated, and a reference to the old change id will be added.
diff --git a/man/repo-diff.1 b/man/repo-diff.1
new file mode 100644
index 00000000..890f8d22
--- /dev/null
+++ b/man/repo-diff.1
@@ -0,0 +1,35 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo diff" "Repo Manual"
+.SH NAME
+repo \- repo diff - manual page for repo diff
+.SH SYNOPSIS
+.B repo
+\fI\,diff \/\fR[\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Show changes between commit and working tree
+.PP
+The \fB\-u\fR option causes 'repo diff' to generate diff output with file paths
+relative to the repository root, so the output can be applied
+to the Unix 'patch' command.
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.TP
+\fB\-u\fR, \fB\-\-absolute\fR
+paths are relative to the repository root
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help diff` to view the detailed manual.
diff --git a/man/repo-diffmanifests.1 b/man/repo-diffmanifests.1
new file mode 100644
index 00000000..add50f17
--- /dev/null
+++ b/man/repo-diffmanifests.1
@@ -0,0 +1,61 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo diffmanifests" "Repo Manual"
+.SH NAME
+repo \- repo diffmanifests - manual page for repo diffmanifests
+.SH SYNOPSIS
+.B repo
+\fI\,diffmanifests manifest1.xml \/\fR[\fI\,manifest2.xml\/\fR] [\fI\,options\/\fR]
+.SH DESCRIPTION
+Summary
+.PP
+Manifest diff utility
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-\-raw\fR
+display raw diff
+.TP
+\fB\-\-no\-color\fR
+does not display the diff in color
+.TP
+\fB\-\-pretty\-format=\fR<FORMAT>
+print the log using a custom git pretty format string
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help diffmanifests` to view the detailed manual.
+.SH DETAILS
+.PP
+The repo diffmanifests command shows differences between project revisions of
+manifest1 and manifest2. if manifest2 is not specified, current manifest.xml
+will be used instead. Both absolute and relative paths may be used for
+manifests. Relative paths start from project's ".repo/manifests" folder.
+.PP
+The \fB\-\-raw\fR option Displays the diff in a way that facilitates parsing, the
+project pattern will be <status> <path> <revision from> [<revision to>] and the
+commit pattern will be <status> <onelined log> with status values respectively :
+.IP
+A = Added project
+R = Removed project
+C = Changed project
+U = Project with unreachable revision(s) (revision(s) not found)
+.PP
+for project, and
+.IP
+A = Added commit
+R = Removed commit
+.PP
+for a commit.
+.PP
+Only changed projects may contain commits, and commit status always starts with
+a space, and are part of last printed project. Unreachable revisions may occur
+if project is not up to date or if repo has not been initialized with all the
+groups, in which case some projects won't be synced and their revisions won't be
+found.
diff --git a/man/repo-download.1 b/man/repo-download.1
new file mode 100644
index 00000000..cf7f767d
--- /dev/null
+++ b/man/repo-download.1
@@ -0,0 +1,44 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo download" "Repo Manual"
+.SH NAME
+repo \- repo download - manual page for repo download
+.SH SYNOPSIS
+.B repo
+\fI\,download {\/\fR[\fI\,project\/\fR] \fI\,change\/\fR[\fI\,/patchset\/\fR]\fI\,}\/\fR...
+.SH DESCRIPTION
+Summary
+.PP
+Download and checkout a change
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-b\fR BRANCH, \fB\-\-branch\fR=\fI\,BRANCH\/\fR
+create a new branch first
+.TP
+\fB\-c\fR, \fB\-\-cherry\-pick\fR
+cherry\-pick instead of checkout
+.TP
+\fB\-x\fR, \fB\-\-record\-origin\fR
+pass \fB\-x\fR when cherry\-picking
+.TP
+\fB\-r\fR, \fB\-\-revert\fR
+revert instead of checkout
+.TP
+\fB\-f\fR, \fB\-\-ff\-only\fR
+force fast\-forward merge
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help download` to view the detailed manual.
+.SH DETAILS
+.PP
+The 'repo download' command downloads a change from the review system and makes
+it available in your project's local working directory. If no project is
+specified try to use current directory as a project.
diff --git a/man/repo-forall.1 b/man/repo-forall.1
new file mode 100644
index 00000000..eb2ad57b
--- /dev/null
+++ b/man/repo-forall.1
@@ -0,0 +1,128 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo forall" "Repo Manual"
+.SH NAME
+repo \- repo forall - manual page for repo forall
+.SH SYNOPSIS
+.B repo
+\fI\,forall \/\fR[\fI\,<project>\/\fR...] \fI\,-c <command> \/\fR[\fI\,<arg>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Run a shell command in each project
+.PP
+repo forall \fB\-r\fR str1 [str2] ... \fB\-c\fR <command> [<arg>...]
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.TP
+\fB\-r\fR, \fB\-\-regex\fR
+execute the command only on projects matching regex or
+wildcard expression
+.TP
+\fB\-i\fR, \fB\-\-inverse\-regex\fR
+execute the command only on projects not matching
+regex or wildcard expression
+.TP
+\fB\-g\fR GROUPS, \fB\-\-groups\fR=\fI\,GROUPS\/\fR
+execute the command only on projects matching the
+specified groups
+.TP
+\fB\-c\fR, \fB\-\-command\fR
+command (and arguments) to execute
+.TP
+\fB\-e\fR, \fB\-\-abort\-on\-errors\fR
+abort if a command exits unsuccessfully
+.TP
+\fB\-\-ignore\-missing\fR
+silently skip & do not exit non\-zero due missing
+checkouts
+.TP
+\fB\-\-interactive\fR
+force interactive usage
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.TP
+\fB\-p\fR
+show project headers before output
+.PP
+Run `repo help forall` to view the detailed manual.
+.SH DETAILS
+.PP
+Executes the same shell command in each project.
+.PP
+The \fB\-r\fR option allows running the command only on projects matching regex or
+wildcard expression.
+.PP
+By default, projects are processed non\-interactively in parallel. If you want to
+run interactive commands, make sure to pass \fB\-\-interactive\fR to force \fB\-\-jobs\fR 1.
+While the processing order of projects is not guaranteed, the order of project
+output is stable.
+.PP
+Output Formatting
+.PP
+The \fB\-p\fR option causes 'repo forall' to bind pipes to the command's stdin, stdout
+and stderr streams, and pipe all output into a continuous stream that is
+displayed in a single pager session. Project headings are inserted before the
+output of each command is displayed. If the command produces no output in a
+project, no heading is displayed.
+.PP
+The formatting convention used by \fB\-p\fR is very suitable for some types of
+searching, e.g. `repo forall \fB\-p\fR \fB\-c\fR git log \fB\-SFoo\fR` will print all commits that
+add or remove references to Foo.
+.PP
+The \fB\-v\fR option causes 'repo forall' to display stderr messages if a command
+produces output only on stderr. Normally the \fB\-p\fR option causes command output to
+be suppressed until the command produces at least one byte of output on stdout.
+.PP
+Environment
+.PP
+pwd is the project's working directory. If the current client is a mirror
+client, then pwd is the Git repository.
+.PP
+REPO_PROJECT is set to the unique name of the project.
+.PP
+REPO_PATH is the path relative the the root of the client.
+.PP
+REPO_REMOTE is the name of the remote system from the manifest.
+.PP
+REPO_LREV is the name of the revision from the manifest, translated to a local
+tracking branch. If you need to pass the manifest revision to a locally executed
+git command, use REPO_LREV.
+.PP
+REPO_RREV is the name of the revision from the manifest, exactly as written in
+the manifest.
+.PP
+REPO_COUNT is the total number of projects being iterated.
+.PP
+REPO_I is the current (1\-based) iteration count. Can be used in conjunction with
+REPO_COUNT to add a simple progress indicator to your command.
+.PP
+REPO__* are any extra environment variables, specified by the "annotation"
+element under any project element. This can be useful for differentiating trees
+based on user\-specific criteria, or simply annotating tree details.
+.PP
+shell positional arguments ($1, $2, .., $#) are set to any arguments following
+<command>.
+.PP
+Example: to list projects:
+.IP
+repo forall \fB\-c\fR 'echo $REPO_PROJECT'
+.PP
+Notice that $REPO_PROJECT is quoted to ensure it is expanded in the context of
+running <command> instead of in the calling shell.
+.PP
+Unless \fB\-p\fR is used, stdin, stdout, stderr are inherited from the terminal and are
+not redirected.
+.PP
+If \fB\-e\fR is used, when a command exits unsuccessfully, 'repo forall' will abort
+without iterating through the remaining projects.
diff --git a/man/repo-gitc-delete.1 b/man/repo-gitc-delete.1
new file mode 100644
index 00000000..c84c6e45
--- /dev/null
+++ b/man/repo-gitc-delete.1
@@ -0,0 +1,31 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo gitc-delete" "Repo Manual"
+.SH NAME
+repo \- repo gitc-delete - manual page for repo gitc-delete
+.SH SYNOPSIS
+.B repo
+\fI\,gitc-delete\/\fR
+.SH DESCRIPTION
+Summary
+.PP
+Delete a GITC Client.
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-f\fR, \fB\-\-force\fR
+force the deletion (no prompt)
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help gitc\-delete` to view the detailed manual.
+.SH DETAILS
+.PP
+This subcommand deletes the current GITC client, deleting the GITC manifest and
+all locally downloaded sources.
diff --git a/man/repo-gitc-init.1 b/man/repo-gitc-init.1
new file mode 100644
index 00000000..9b61866e
--- /dev/null
+++ b/man/repo-gitc-init.1
@@ -0,0 +1,150 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "September 2021" "repo gitc-init" "Repo Manual"
+.SH NAME
+repo \- repo gitc-init - manual page for repo gitc-init
+.SH SYNOPSIS
+.B repo
+\fI\,gitc-init \/\fR[\fI\,options\/\fR] [\fI\,client name\/\fR]
+.SH DESCRIPTION
+Summary
+.PP
+Initialize a GITC Client.
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.SS Manifest options:
+.TP
+\fB\-u\fR URL, \fB\-\-manifest\-url\fR=\fI\,URL\/\fR
+manifest repository location
+.TP
+\fB\-b\fR REVISION, \fB\-\-manifest\-branch\fR=\fI\,REVISION\/\fR
+manifest branch or revision (use HEAD for default)
+.TP
+\fB\-m\fR NAME.xml, \fB\-\-manifest\-name\fR=\fI\,NAME\/\fR.xml
+initial manifest file
+.TP
+\fB\-\-standalone\-manifest\fR
+download the manifest as a static file rather then
+create a git checkout of the manifest repo
+.TP
+\fB\-g\fR GROUP, \fB\-\-groups\fR=\fI\,GROUP\/\fR
+restrict manifest projects to ones with specified
+group(s) [default|all|G1,G2,G3|G4,\-G5,\-G6]
+.TP
+\fB\-p\fR PLATFORM, \fB\-\-platform\fR=\fI\,PLATFORM\/\fR
+restrict manifest projects to ones with a specified
+platform group [auto|all|none|linux|darwin|...]
+.TP
+\fB\-\-submodules\fR
+sync any submodules associated with the manifest repo
+.SS Manifest (only) checkout options:
+.TP
+\fB\-\-current\-branch\fR
+fetch only current manifest branch from server
+.TP
+\fB\-\-no\-current\-branch\fR
+fetch all manifest branches from server
+.TP
+\fB\-\-tags\fR
+fetch tags in the manifest
+.TP
+\fB\-\-no\-tags\fR
+don't fetch tags in the manifest
+.SS Checkout modes:
+.TP
+\fB\-\-mirror\fR
+create a replica of the remote repositories rather
+than a client working directory
+.TP
+\fB\-\-archive\fR
+checkout an archive instead of a git repository for
+each project. See git archive.
+.TP
+\fB\-\-worktree\fR
+use git\-worktree to manage projects
+.SS Project checkout optimizations:
+.TP
+\fB\-\-reference\fR=\fI\,DIR\/\fR
+location of mirror directory
+.TP
+\fB\-\-dissociate\fR
+dissociate from reference mirrors after clone
+.TP
+\fB\-\-depth\fR=\fI\,DEPTH\/\fR
+create a shallow clone with given depth; see git clone
+.TP
+\fB\-\-partial\-clone\fR
+perform partial clone (https://gitscm.com/docs/gitrepositorylayout#_code_partialclone_code)
+.TP
+\fB\-\-no\-partial\-clone\fR
+disable use of partial clone (https://gitscm.com/docs/gitrepositorylayout#_code_partialclone_code)
+.TP
+\fB\-\-partial\-clone\-exclude\fR=\fI\,PARTIAL_CLONE_EXCLUDE\/\fR
+exclude the specified projects (a comma\-delimited
+project names) from partial clone (https://gitscm.com/docs/gitrepositorylayout#_code_partialclone_code)
+.TP
+\fB\-\-clone\-filter\fR=\fI\,CLONE_FILTER\/\fR
+filter for use with \fB\-\-partial\-clone\fR [default:
+blob:none]
+.TP
+\fB\-\-use\-superproject\fR
+use the manifest superproject to sync projects
+.TP
+\fB\-\-no\-use\-superproject\fR
+disable use of manifest superprojects
+.TP
+\fB\-\-clone\-bundle\fR
+enable use of \fI\,/clone.bundle\/\fP on HTTP/HTTPS (default if
+not \fB\-\-partial\-clone\fR)
+.TP
+\fB\-\-no\-clone\-bundle\fR
+disable use of \fI\,/clone.bundle\/\fP on HTTP/HTTPS (default if
+\fB\-\-partial\-clone\fR)
+.SS repo Version options:
+.TP
+\fB\-\-repo\-url\fR=\fI\,URL\/\fR
+repo repository location ($REPO_URL)
+.TP
+\fB\-\-repo\-rev\fR=\fI\,REV\/\fR
+repo branch or revision ($REPO_REV)
+.TP
+\fB\-\-no\-repo\-verify\fR
+do not verify repo source code
+.SS Other options:
+.TP
+\fB\-\-config\-name\fR
+Always prompt for name/e\-mail
+.SS GITC options:
+.TP
+\fB\-f\fR MANIFEST_FILE, \fB\-\-manifest\-file\fR=\fI\,MANIFEST_FILE\/\fR
+Optional manifest file to use for this GITC client.
+.TP
+\fB\-c\fR GITC_CLIENT, \fB\-\-gitc\-client\fR=\fI\,GITC_CLIENT\/\fR
+Name of the gitc_client instance to create or modify.
+.PP
+Run `repo help gitc\-init` to view the detailed manual.
+.SH DETAILS
+.PP
+The 'repo gitc\-init' command is ran to initialize a new GITC client for use with
+the GITC file system.
+.PP
+This command will setup the client directory, initialize repo, just like repo
+init does, and then downloads the manifest collection and installs it in the
+\&.repo/directory of the GITC client.
+.PP
+Once this is done, a GITC manifest is generated by pulling the HEAD SHA for each
+project and generates the properly formatted XML file and installs it as
+\&.manifest in the GITC client directory.
+.PP
+The \fB\-c\fR argument is required to specify the GITC client name.
+.PP
+The optional \fB\-f\fR argument can be used to specify the manifest file to use for
+this GITC client.
diff --git a/man/repo-grep.1 b/man/repo-grep.1
new file mode 100644
index 00000000..be410588
--- /dev/null
+++ b/man/repo-grep.1
@@ -0,0 +1,119 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo grep" "Repo Manual"
+.SH NAME
+repo \- repo grep - manual page for repo grep
+.SH SYNOPSIS
+.B repo
+\fI\,grep {pattern | -e pattern} \/\fR[\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Print lines matching a pattern
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.SS Logging options:
+.TP
+\fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.SS Sources:
+.TP
+\fB\-\-cached\fR
+Search the index, instead of the work tree
+.TP
+\fB\-r\fR TREEish, \fB\-\-revision\fR=\fI\,TREEish\/\fR
+Search TREEish, instead of the work tree
+.SS Pattern:
+.TP
+\fB\-e\fR PATTERN
+Pattern to search for
+.TP
+\fB\-i\fR, \fB\-\-ignore\-case\fR
+Ignore case differences
+.TP
+\fB\-a\fR, \fB\-\-text\fR
+Process binary files as if they were text
+.TP
+\fB\-I\fR
+Don't match the pattern in binary files
+.TP
+\fB\-w\fR, \fB\-\-word\-regexp\fR
+Match the pattern only at word boundaries
+.TP
+\fB\-v\fR, \fB\-\-invert\-match\fR
+Select non\-matching lines
+.TP
+\fB\-G\fR, \fB\-\-basic\-regexp\fR
+Use POSIX basic regexp for patterns (default)
+.TP
+\fB\-E\fR, \fB\-\-extended\-regexp\fR
+Use POSIX extended regexp for patterns
+.TP
+\fB\-F\fR, \fB\-\-fixed\-strings\fR
+Use fixed strings (not regexp) for pattern
+.SS Pattern Grouping:
+.TP
+\fB\-\-all\-match\fR
+Limit match to lines that have all patterns
+.TP
+\fB\-\-and\fR, \fB\-\-or\fR, \fB\-\-not\fR
+Boolean operators to combine patterns
+.TP
+\-(, \-)
+Boolean operator grouping
+.SS Output:
+.TP
+\fB\-n\fR
+Prefix the line number to matching lines
+.TP
+\fB\-C\fR CONTEXT
+Show CONTEXT lines around match
+.TP
+\fB\-B\fR CONTEXT
+Show CONTEXT lines before match
+.TP
+\fB\-A\fR CONTEXT
+Show CONTEXT lines after match
+.TP
+\fB\-l\fR, \fB\-\-name\-only\fR, \fB\-\-files\-with\-matches\fR
+Show only file names containing matching lines
+.TP
+\fB\-L\fR, \fB\-\-files\-without\-match\fR
+Show only file names not containing matching lines
+.PP
+Run `repo help grep` to view the detailed manual.
+.SH DETAILS
+.PP
+Search for the specified patterns in all project files.
+.PP
+Boolean Options
+.PP
+The following options can appear as often as necessary to express the pattern to
+locate:
+.HP
+\fB\-e\fR PATTERN
+.HP
+\fB\-\-and\fR, \fB\-\-or\fR, \fB\-\-not\fR, \-(, \-)
+.PP
+Further, the \fB\-r\fR/\-\-revision option may be specified multiple times in order to
+scan multiple trees. If the same file matches in more than one tree, only the
+first result is reported, prefixed by the revision name it was found under.
+.PP
+Examples
+.PP
+Look for a line that has '#define' and either 'MAX_PATH or 'PATH_MAX':
+.IP
+repo grep \fB\-e\fR '#define' \fB\-\-and\fR \-\e( \fB\-e\fR MAX_PATH \fB\-e\fR PATH_MAX \e)
+.PP
+Look for a line that has 'NODE' or 'Unexpected' in files that contain a line
+that matches both expressions:
+.IP
+repo grep \fB\-\-all\-match\fR \fB\-e\fR NODE \fB\-e\fR Unexpected
diff --git a/man/repo-help.1 b/man/repo-help.1
new file mode 100644
index 00000000..d6da3c51
--- /dev/null
+++ b/man/repo-help.1
@@ -0,0 +1,33 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo help" "Repo Manual"
+.SH NAME
+repo \- repo help - manual page for repo help
+.SH SYNOPSIS
+.B repo
+\fI\,help \/\fR[\fI\,--all|command\/\fR]
+.SH DESCRIPTION
+Summary
+.PP
+Display detailed help on a command
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-a\fR, \fB\-\-all\fR
+show the complete list of commands
+.TP
+\fB\-\-help\-all\fR
+show the \fB\-\-help\fR of all commands
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help help` to view the detailed manual.
+.SH DETAILS
+.PP
+Displays detailed usage information about a command.
diff --git a/man/repo-info.1 b/man/repo-info.1
new file mode 100644
index 00000000..cf7c17b8
--- /dev/null
+++ b/man/repo-info.1
@@ -0,0 +1,40 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo info" "Repo Manual"
+.SH NAME
+repo \- repo info - manual page for repo info
+.SH SYNOPSIS
+.B repo
+\fI\,info \/\fR[\fI\,-dl\/\fR] [\fI\,-o \/\fR[\fI\,-c\/\fR]] [\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Get info on the manifest branch, current branch or unmerged branches
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-d\fR, \fB\-\-diff\fR
+show full info and commit diff including remote
+branches
+.TP
+\fB\-o\fR, \fB\-\-overview\fR
+show overview of all local commits
+.TP
+\fB\-c\fR, \fB\-\-current\-branch\fR
+consider only checked out branches
+.TP
+\fB\-\-no\-current\-branch\fR
+consider all local branches
+.TP
+\fB\-l\fR, \fB\-\-local\-only\fR
+disable all remote operations
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help info` to view the detailed manual.
diff --git a/man/repo-init.1 b/man/repo-init.1
new file mode 100644
index 00000000..9957b64d
--- /dev/null
+++ b/man/repo-init.1
@@ -0,0 +1,170 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "September 2021" "repo init" "Repo Manual"
+.SH NAME
+repo \- repo init - manual page for repo init
+.SH SYNOPSIS
+.B repo
+\fI\,init \/\fR[\fI\,options\/\fR] [\fI\,manifest url\/\fR]
+.SH DESCRIPTION
+Summary
+.PP
+Initialize a repo client checkout in the current directory
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.SS Manifest options:
+.TP
+\fB\-u\fR URL, \fB\-\-manifest\-url\fR=\fI\,URL\/\fR
+manifest repository location
+.TP
+\fB\-b\fR REVISION, \fB\-\-manifest\-branch\fR=\fI\,REVISION\/\fR
+manifest branch or revision (use HEAD for default)
+.TP
+\fB\-m\fR NAME.xml, \fB\-\-manifest\-name\fR=\fI\,NAME\/\fR.xml
+initial manifest file
+.TP
+\fB\-\-standalone\-manifest\fR
+download the manifest as a static file rather then
+create a git checkout of the manifest repo
+.TP
+\fB\-g\fR GROUP, \fB\-\-groups\fR=\fI\,GROUP\/\fR
+restrict manifest projects to ones with specified
+group(s) [default|all|G1,G2,G3|G4,\-G5,\-G6]
+.TP
+\fB\-p\fR PLATFORM, \fB\-\-platform\fR=\fI\,PLATFORM\/\fR
+restrict manifest projects to ones with a specified
+platform group [auto|all|none|linux|darwin|...]
+.TP
+\fB\-\-submodules\fR
+sync any submodules associated with the manifest repo
+.SS Manifest (only) checkout options:
+.TP
+\fB\-c\fR, \fB\-\-current\-branch\fR
+fetch only current manifest branch from server
+.TP
+\fB\-\-no\-current\-branch\fR
+fetch all manifest branches from server
+.TP
+\fB\-\-tags\fR
+fetch tags in the manifest
+.TP
+\fB\-\-no\-tags\fR
+don't fetch tags in the manifest
+.SS Checkout modes:
+.TP
+\fB\-\-mirror\fR
+create a replica of the remote repositories rather
+than a client working directory
+.TP
+\fB\-\-archive\fR
+checkout an archive instead of a git repository for
+each project. See git archive.
+.TP
+\fB\-\-worktree\fR
+use git\-worktree to manage projects
+.SS Project checkout optimizations:
+.TP
+\fB\-\-reference\fR=\fI\,DIR\/\fR
+location of mirror directory
+.TP
+\fB\-\-dissociate\fR
+dissociate from reference mirrors after clone
+.TP
+\fB\-\-depth\fR=\fI\,DEPTH\/\fR
+create a shallow clone with given depth; see git clone
+.TP
+\fB\-\-partial\-clone\fR
+perform partial clone (https://gitscm.com/docs/gitrepositorylayout#_code_partialclone_code)
+.TP
+\fB\-\-no\-partial\-clone\fR
+disable use of partial clone (https://gitscm.com/docs/gitrepositorylayout#_code_partialclone_code)
+.TP
+\fB\-\-partial\-clone\-exclude\fR=\fI\,PARTIAL_CLONE_EXCLUDE\/\fR
+exclude the specified projects (a comma\-delimited
+project names) from partial clone (https://gitscm.com/docs/gitrepositorylayout#_code_partialclone_code)
+.TP
+\fB\-\-clone\-filter\fR=\fI\,CLONE_FILTER\/\fR
+filter for use with \fB\-\-partial\-clone\fR [default:
+blob:none]
+.TP
+\fB\-\-use\-superproject\fR
+use the manifest superproject to sync projects
+.TP
+\fB\-\-no\-use\-superproject\fR
+disable use of manifest superprojects
+.TP
+\fB\-\-clone\-bundle\fR
+enable use of \fI\,/clone.bundle\/\fP on HTTP/HTTPS (default if
+not \fB\-\-partial\-clone\fR)
+.TP
+\fB\-\-no\-clone\-bundle\fR
+disable use of \fI\,/clone.bundle\/\fP on HTTP/HTTPS (default if
+\fB\-\-partial\-clone\fR)
+.SS repo Version options:
+.TP
+\fB\-\-repo\-url\fR=\fI\,URL\/\fR
+repo repository location ($REPO_URL)
+.TP
+\fB\-\-repo\-rev\fR=\fI\,REV\/\fR
+repo branch or revision ($REPO_REV)
+.TP
+\fB\-\-no\-repo\-verify\fR
+do not verify repo source code
+.SS Other options:
+.TP
+\fB\-\-config\-name\fR
+Always prompt for name/e\-mail
+.PP
+Run `repo help init` to view the detailed manual.
+.SH DETAILS
+.PP
+The 'repo init' command is run once to install and initialize repo. The latest
+repo source code and manifest collection is downloaded from the server and is
+installed in the .repo/ directory in the current working directory.
+.PP
+When creating a new checkout, the manifest URL is the only required setting. It
+may be specified using the \fB\-\-manifest\-url\fR option, or as the first optional
+argument.
+.PP
+The optional \fB\-b\fR argument can be used to select the manifest branch to checkout
+and use. If no branch is specified, the remote's default branch is used. This is
+equivalent to using \fB\-b\fR HEAD.
+.PP
+The optional \fB\-m\fR argument can be used to specify an alternate manifest to be
+used. If no manifest is specified, the manifest default.xml will be used.
+.PP
+If the \fB\-\-standalone\-manifest\fR argument is set, the manifest will be downloaded
+directly from the specified \fB\-\-manifest\-url\fR as a static file (rather than setting
+up a manifest git checkout). With \fB\-\-standalone\-manifest\fR, the manifest will be
+fully static and will not be re\-downloaded during subsesquent `repo init` and
+`repo sync` calls.
+.PP
+The \fB\-\-reference\fR option can be used to point to a directory that has the content
+of a \fB\-\-mirror\fR sync. This will make the working directory use as much data as
+possible from the local reference directory when fetching from the server. This
+will make the sync go a lot faster by reducing data traffic on the network.
+.PP
+The \fB\-\-dissociate\fR option can be used to borrow the objects from the directory
+specified with the \fB\-\-reference\fR option only to reduce network transfer, and stop
+borrowing from them after a first clone is made by making necessary local copies
+of borrowed objects.
+.PP
+The \fB\-\-no\-clone\-bundle\fR option disables any attempt to use \fI\,$URL/clone.bundle\/\fP to
+bootstrap a new Git repository from a resumeable bundle file on a content
+delivery network. This may be necessary if there are problems with the local
+Python HTTP client or proxy configuration, but the Git binary works.
+.PP
+Switching Manifest Branches
+.PP
+To switch to another manifest branch, `repo init \fB\-b\fR otherbranch` may be used in
+an existing client. However, as this only updates the manifest, a subsequent
+`repo sync` (or `repo sync \fB\-d\fR`) is necessary to update the working directory
+files.
diff --git a/man/repo-list.1 b/man/repo-list.1
new file mode 100644
index 00000000..7f85e612
--- /dev/null
+++ b/man/repo-list.1
@@ -0,0 +1,61 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo list" "Repo Manual"
+.SH NAME
+repo \- repo list - manual page for repo list
+.SH SYNOPSIS
+.B repo
+\fI\,list \/\fR[\fI\,-f\/\fR] [\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+List projects and their associated directories
+.PP
+repo list [\-f] \fB\-r\fR str1 [str2]...
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-r\fR, \fB\-\-regex\fR
+filter the project list based on regex or wildcard
+matching of strings
+.TP
+\fB\-g\fR GROUPS, \fB\-\-groups\fR=\fI\,GROUPS\/\fR
+filter the project list based on the groups the
+project is in
+.TP
+\fB\-a\fR, \fB\-\-all\fR
+show projects regardless of checkout state
+.TP
+\fB\-n\fR, \fB\-\-name\-only\fR
+display only the name of the repository
+.TP
+\fB\-p\fR, \fB\-\-path\-only\fR
+display only the path of the repository
+.TP
+\fB\-f\fR, \fB\-\-fullpath\fR
+display the full work tree path instead of the
+relative path
+.TP
+\fB\-\-relative\-to\fR=\fI\,PATH\/\fR
+display paths relative to this one (default: top of
+repo client checkout)
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help list` to view the detailed manual.
+.SH DETAILS
+.PP
+List all projects; pass '.' to list the project for the cwd.
+.PP
+By default, only projects that currently exist in the checkout are shown. If you
+want to list all projects (using the specified filter settings), use the \fB\-\-all\fR
+option. If you want to show all projects regardless of the manifest groups, then
+also pass \fB\-\-groups\fR all.
+.PP
+This is similar to running: repo forall \fB\-c\fR 'echo "$REPO_PATH : $REPO_PROJECT"'.
diff --git a/man/repo-manifest.1 b/man/repo-manifest.1
new file mode 100644
index 00000000..be467607
--- /dev/null
+++ b/man/repo-manifest.1
@@ -0,0 +1,548 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo manifest" "Repo Manual"
+.SH NAME
+repo \- repo manifest - manual page for repo manifest
+.SH SYNOPSIS
+.B repo
+\fI\,manifest \/\fR[\fI\,-o {-|NAME.xml}\/\fR] [\fI\,-m MANIFEST.xml\/\fR] [\fI\,-r\/\fR]
+.SH DESCRIPTION
+Summary
+.PP
+Manifest inspection utility
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-r\fR, \fB\-\-revision\-as\-HEAD\fR
+save revisions as current HEAD
+.TP
+\fB\-m\fR NAME.xml, \fB\-\-manifest\-name\fR=\fI\,NAME\/\fR.xml
+temporary manifest to use for this sync
+.TP
+\fB\-\-suppress\-upstream\-revision\fR
+if in \fB\-r\fR mode, do not write the upstream field (only
+of use if the branch names for a sha1 manifest are
+sensitive)
+.TP
+\fB\-\-suppress\-dest\-branch\fR
+if in \fB\-r\fR mode, do not write the dest\-branch field
+(only of use if the branch names for a sha1 manifest
+are sensitive)
+.TP
+\fB\-\-json\fR
+output manifest in JSON format (experimental)
+.TP
+\fB\-\-pretty\fR
+format output for humans to read
+.TP
+\fB\-\-no\-local\-manifests\fR
+ignore local manifests
+.TP
+\fB\-o\fR \-|NAME.xml, \fB\-\-output\-file\fR=\fI\,\-\/\fR|NAME.xml
+file to save the manifest to
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help manifest` to view the detailed manual.
+.SH DETAILS
+.PP
+With the \fB\-o\fR option, exports the current manifest for inspection. The manifest
+and (if present) local_manifests/ are combined together to produce a single
+manifest file. This file can be stored in a Git repository for use during future
+\&'repo init' invocations.
+.PP
+The \fB\-r\fR option can be used to generate a manifest file with project revisions set
+to the current commit hash. These are known as "revision locked manifests", as
+they don't follow a particular branch. In this case, the 'upstream' attribute is
+set to the ref we were on when the manifest was generated. The 'dest\-branch'
+attribute is set to indicate the remote ref to push changes to via 'repo
+upload'.
+.PP
+repo Manifest Format
+.PP
+A repo manifest describes the structure of a repo client; that is the
+directories that are visible and where they should be obtained from with git.
+.PP
+The basic structure of a manifest is a bare Git repository holding a single
+`default.xml` XML file in the top level directory.
+.PP
+Manifests are inherently version controlled, since they are kept within a Git
+repository. Updates to manifests are automatically obtained by clients during
+`repo sync`.
+.PP
+[TOC]
+.PP
+XML File Format
+.PP
+A manifest XML file (e.g. `default.xml`) roughly conforms to the following DTD:
+.PP
+```xml <!DOCTYPE manifest [
+.TP
+<!ELEMENT manifest (notice?,
+remote*,
+default?,
+manifest\-server?,
+remove\-project*,
+project*,
+extend\-project*,
+repo\-hooks?,
+superproject?,
+contactinfo?,
+include*)>
+.IP
+<!ELEMENT notice (#PCDATA)>
+.IP
+<!ELEMENT remote (annotation*)>
+<!ATTLIST remote name         ID    #REQUIRED>
+<!ATTLIST remote alias        CDATA #IMPLIED>
+<!ATTLIST remote fetch        CDATA #REQUIRED>
+<!ATTLIST remote pushurl      CDATA #IMPLIED>
+<!ATTLIST remote review       CDATA #IMPLIED>
+<!ATTLIST remote revision     CDATA #IMPLIED>
+.IP
+<!ELEMENT default EMPTY>
+<!ATTLIST default remote      IDREF #IMPLIED>
+<!ATTLIST default revision    CDATA #IMPLIED>
+<!ATTLIST default dest\-branch CDATA #IMPLIED>
+<!ATTLIST default upstream    CDATA #IMPLIED>
+<!ATTLIST default sync\-j      CDATA #IMPLIED>
+<!ATTLIST default sync\-c      CDATA #IMPLIED>
+<!ATTLIST default sync\-s      CDATA #IMPLIED>
+<!ATTLIST default sync\-tags   CDATA #IMPLIED>
+.IP
+<!ELEMENT manifest\-server EMPTY>
+<!ATTLIST manifest\-server url CDATA #REQUIRED>
+.TP
+<!ELEMENT project (annotation*,
+project*,
+copyfile*,
+linkfile*)>
+.TP
+<!ATTLIST project name
+CDATA #REQUIRED>
+.TP
+<!ATTLIST project path
+CDATA #IMPLIED>
+.TP
+<!ATTLIST project remote
+IDREF #IMPLIED>
+.TP
+<!ATTLIST project revision
+CDATA #IMPLIED>
+.IP
+<!ATTLIST project dest\-branch CDATA #IMPLIED>
+<!ATTLIST project groups      CDATA #IMPLIED>
+<!ATTLIST project sync\-c      CDATA #IMPLIED>
+<!ATTLIST project sync\-s      CDATA #IMPLIED>
+<!ATTLIST project sync\-tags   CDATA #IMPLIED>
+<!ATTLIST project upstream CDATA #IMPLIED>
+<!ATTLIST project clone\-depth CDATA #IMPLIED>
+<!ATTLIST project force\-path CDATA #IMPLIED>
+.IP
+<!ELEMENT annotation EMPTY>
+<!ATTLIST annotation name  CDATA #REQUIRED>
+<!ATTLIST annotation value CDATA #REQUIRED>
+<!ATTLIST annotation keep  CDATA "true">
+.IP
+<!ELEMENT copyfile EMPTY>
+<!ATTLIST copyfile src  CDATA #REQUIRED>
+<!ATTLIST copyfile dest CDATA #REQUIRED>
+.IP
+<!ELEMENT linkfile EMPTY>
+<!ATTLIST linkfile src CDATA #REQUIRED>
+<!ATTLIST linkfile dest CDATA #REQUIRED>
+.IP
+<!ELEMENT extend\-project EMPTY>
+<!ATTLIST extend\-project name CDATA #REQUIRED>
+<!ATTLIST extend\-project path CDATA #IMPLIED>
+<!ATTLIST extend\-project groups CDATA #IMPLIED>
+<!ATTLIST extend\-project revision CDATA #IMPLIED>
+<!ATTLIST extend\-project remote CDATA #IMPLIED>
+.IP
+<!ELEMENT remove\-project EMPTY>
+<!ATTLIST remove\-project name  CDATA #REQUIRED>
+<!ATTLIST remove\-project optional  CDATA #IMPLIED>
+.IP
+<!ELEMENT repo\-hooks EMPTY>
+<!ATTLIST repo\-hooks in\-project CDATA #REQUIRED>
+<!ATTLIST repo\-hooks enabled\-list CDATA #REQUIRED>
+.IP
+<!ELEMENT superproject EMPTY>
+<!ATTLIST superproject name    CDATA #REQUIRED>
+<!ATTLIST superproject remote  IDREF #IMPLIED>
+.IP
+<!ELEMENT contactinfo EMPTY>
+<!ATTLIST contactinfo bugurl  CDATA #REQUIRED>
+.IP
+<!ELEMENT include EMPTY>
+<!ATTLIST include name   CDATA #REQUIRED>
+<!ATTLIST include groups CDATA #IMPLIED>
+.PP
+]>
+```
+.PP
+For compatibility purposes across repo releases, all unknown elements are
+silently ignored. However, repo reserves all possible names for itself for
+future use. If you want to use custom elements, the `x\-*` namespace is reserved
+for that purpose, and repo guarantees to never allocate any corresponding names.
+.PP
+A description of the elements and their attributes follows.
+.PP
+Element manifest
+.PP
+The root element of the file.
+.PP
+Element notice
+.PP
+Arbitrary text that is displayed to users whenever `repo sync` finishes. The
+content is simply passed through as it exists in the manifest.
+.PP
+Element remote
+.PP
+One or more remote elements may be specified. Each remote element specifies a
+Git URL shared by one or more projects and (optionally) the Gerrit review server
+those projects upload changes through.
+.PP
+Attribute `name`: A short name unique to this manifest file. The name specified
+here is used as the remote name in each project's .git/config, and is therefore
+automatically available to commands like `git fetch`, `git remote`, `git pull`
+and `git push`.
+.PP
+Attribute `alias`: The alias, if specified, is used to override `name` to be set
+as the remote name in each project's .git/config. Its value can be duplicated
+while attribute `name` has to be unique in the manifest file. This helps each
+project to be able to have same remote name which actually points to different
+remote url.
+.PP
+Attribute `fetch`: The Git URL prefix for all projects which use this remote.
+Each project's name is appended to this prefix to form the actual URL used to
+clone the project.
+.PP
+Attribute `pushurl`: The Git "push" URL prefix for all projects which use this
+remote. Each project's name is appended to this prefix to form the actual URL
+used to "git push" the project. This attribute is optional; if not specified
+then "git push" will use the same URL as the `fetch` attribute.
+.PP
+Attribute `review`: Hostname of the Gerrit server where reviews are uploaded to
+by `repo upload`. This attribute is optional; if not specified then `repo
+upload` will not function.
+.PP
+Attribute `revision`: Name of a Git branch (e.g. `main` or `refs/heads/main`).
+Remotes with their own revision will override the default revision.
+.PP
+Element default
+.PP
+At most one default element may be specified. Its remote and revision attributes
+are used when a project element does not specify its own remote or revision
+attribute.
+.PP
+Attribute `remote`: Name of a previously defined remote element. Project
+elements lacking a remote attribute of their own will use this remote.
+.PP
+Attribute `revision`: Name of a Git branch (e.g. `main` or `refs/heads/main`).
+Project elements lacking their own revision attribute will use this revision.
+.PP
+Attribute `dest\-branch`: Name of a Git branch (e.g. `main`). Project elements
+not setting their own `dest\-branch` will inherit this value. If this value is
+not set, projects will use `revision` by default instead.
+.PP
+Attribute `upstream`: Name of the Git ref in which a sha1 can be found. Used
+when syncing a revision locked manifest in \fB\-c\fR mode to avoid having to sync the
+entire ref space. Project elements not setting their own `upstream` will inherit
+this value.
+.PP
+Attribute `sync\-j`: Number of parallel jobs to use when synching.
+.PP
+Attribute `sync\-c`: Set to true to only sync the given Git branch (specified in
+the `revision` attribute) rather than the whole ref space. Project elements
+lacking a sync\-c element of their own will use this value.
+.PP
+Attribute `sync\-s`: Set to true to also sync sub\-projects.
+.PP
+Attribute `sync\-tags`: Set to false to only sync the given Git branch (specified
+in the `revision` attribute) rather than the other ref tags.
+.PP
+Element manifest\-server
+.PP
+At most one manifest\-server may be specified. The url attribute is used to
+specify the URL of a manifest server, which is an XML RPC service.
+.PP
+The manifest server should implement the following RPC methods:
+.IP
+GetApprovedManifest(branch, target)
+.PP
+Return a manifest in which each project is pegged to a known good revision for
+the current branch and target. This is used by repo sync when the \fB\-\-smart\-sync\fR
+option is given.
+.PP
+The target to use is defined by environment variables TARGET_PRODUCT and
+TARGET_BUILD_VARIANT. These variables are used to create a string of the form
+$TARGET_PRODUCT\-$TARGET_BUILD_VARIANT, e.g. passion\-userdebug. If one of those
+variables or both are not present, the program will call GetApprovedManifest
+without the target parameter and the manifest server should choose a reasonable
+default target.
+.IP
+GetManifest(tag)
+.PP
+Return a manifest in which each project is pegged to the revision at the
+specified tag. This is used by repo sync when the \fB\-\-smart\-tag\fR option is given.
+.PP
+Element project
+.PP
+One or more project elements may be specified. Each element describes a single
+Git repository to be cloned into the repo client workspace. You may specify
+Git\-submodules by creating a nested project. Git\-submodules will be
+automatically recognized and inherit their parent's attributes, but those may be
+overridden by an explicitly specified project element.
+.PP
+Attribute `name`: A unique name for this project. The project's name is appended
+onto its remote's fetch URL to generate the actual URL to configure the Git
+remote with. The URL gets formed as:
+.IP
+${remote_fetch}/${project_name}.git
+.PP
+where ${remote_fetch} is the remote's fetch attribute and ${project_name} is the
+project's name attribute. The suffix ".git" is always appended as repo assumes
+the upstream is a forest of bare Git repositories. If the project has a parent
+element, its name will be prefixed by the parent's.
+.PP
+The project name must match the name Gerrit knows, if Gerrit is being used for
+code reviews.
+.PP
+"name" must not be empty, and may not be an absolute path or use "." or ".."
+path components. It is always interpreted relative to the remote's fetch
+settings, so if a different base path is needed, declare a different remote with
+the new settings needed. These restrictions are not enforced for [Local
+Manifests].
+.PP
+Attribute `path`: An optional path relative to the top directory of the repo
+client where the Git working directory for this project should be placed. If not
+supplied the project "name" is used. If the project has a parent element, its
+path will be prefixed by the parent's.
+.PP
+"path" may not be an absolute path or use "." or ".." path components. These
+restrictions are not enforced for [Local Manifests].
+.PP
+If you want to place files into the root of the checkout (e.g. a README or
+Makefile or another build script), use the [copyfile] or [linkfile] elements
+instead.
+.PP
+Attribute `remote`: Name of a previously defined remote element. If not supplied
+the remote given by the default element is used.
+.PP
+Attribute `revision`: Name of the Git branch the manifest wants to track for
+this project. Names can be relative to refs/heads (e.g. just "main") or absolute
+(e.g. "refs/heads/main"). Tags and/or explicit SHA\-1s should work in theory, but
+have not been extensively tested. If not supplied the revision given by the
+remote element is used if applicable, else the default element is used.
+.PP
+Attribute `dest\-branch`: Name of a Git branch (e.g. `main`). When using `repo
+upload`, changes will be submitted for code review on this branch. If
+unspecified both here and in the default element, `revision` is used instead.
+.PP
+Attribute `groups`: List of groups to which this project belongs, whitespace or
+comma separated. All projects belong to the group "all", and each project
+automatically belongs to a group of its name:`name` and path:`path`. E.g. for
+`<project name="monkeys" path="barrel\-of"/>`, that project definition is
+implicitly in the following manifest groups: default, name:monkeys, and
+path:barrel\-of. If you place a project in the group "notdefault", it will not be
+automatically downloaded by repo. If the project has a parent element, the
+`name` and `path` here are the prefixed ones.
+.PP
+Attribute `sync\-c`: Set to true to only sync the given Git branch (specified in
+the `revision` attribute) rather than the whole ref space.
+.PP
+Attribute `sync\-s`: Set to true to also sync sub\-projects.
+.PP
+Attribute `upstream`: Name of the Git ref in which a sha1 can be found. Used
+when syncing a revision locked manifest in \fB\-c\fR mode to avoid having to sync the
+entire ref space.
+.PP
+Attribute `clone\-depth`: Set the depth to use when fetching this project. If
+specified, this value will override any value given to repo init with the
+\fB\-\-depth\fR option on the command line.
+.PP
+Attribute `force\-path`: Set to true to force this project to create the local
+mirror repository according to its `path` attribute (if supplied) rather than
+the `name` attribute. This attribute only applies to the local mirrors syncing,
+it will be ignored when syncing the projects in a client working directory.
+.PP
+Element extend\-project
+.PP
+Modify the attributes of the named project.
+.PP
+This element is mostly useful in a local manifest file, to modify the attributes
+of an existing project without completely replacing the existing project
+definition. This makes the local manifest more robust against changes to the
+original manifest.
+.PP
+Attribute `path`: If specified, limit the change to projects checked out at the
+specified path, rather than all projects with the given name.
+.PP
+Attribute `groups`: List of additional groups to which this project belongs.
+Same syntax as the corresponding element of `project`.
+.PP
+Attribute `revision`: If specified, overrides the revision of the original
+project. Same syntax as the corresponding element of `project`.
+.PP
+Attribute `remote`: If specified, overrides the remote of the original project.
+Same syntax as the corresponding element of `project`.
+.PP
+Element annotation
+.PP
+Zero or more annotation elements may be specified as children of a project or
+remote element. Each element describes a name\-value pair. For projects, this
+name\-value pair will be exported into each project's environment during a
+\&'forall' command, prefixed with `REPO__`. In addition, there is an optional
+attribute "keep" which accepts the case insensitive values "true" (default) or
+"false". This attribute determines whether or not the annotation will be kept
+when exported with the manifest subcommand.
+.PP
+Element copyfile
+.PP
+Zero or more copyfile elements may be specified as children of a project
+element. Each element describes a src\-dest pair of files; the "src" file will be
+copied to the "dest" place during `repo sync` command.
+.PP
+"src" is project relative, "dest" is relative to the top of the tree. Copying
+from paths outside of the project or to paths outside of the repo client is not
+allowed.
+.PP
+"src" and "dest" must be files. Directories or symlinks are not allowed.
+Intermediate paths must not be symlinks either.
+.PP
+Parent directories of "dest" will be automatically created if missing.
+.PP
+Element linkfile
+.PP
+It's just like copyfile and runs at the same time as copyfile but instead of
+copying it creates a symlink.
+.PP
+The symlink is created at "dest" (relative to the top of the tree) and points to
+the path specified by "src" which is a path in the project.
+.PP
+Parent directories of "dest" will be automatically created if missing.
+.PP
+The symlink target may be a file or directory, but it may not point outside of
+the repo client.
+.PP
+Element remove\-project
+.PP
+Deletes the named project from the internal manifest table, possibly allowing a
+subsequent project element in the same manifest file to replace the project with
+a different source.
+.PP
+This element is mostly useful in a local manifest file, where the user can
+remove a project, and possibly replace it with their own definition.
+.PP
+Attribute `optional`: Set to true to ignore remove\-project elements with no
+matching `project` element.
+.PP
+Element repo\-hooks
+.PP
+NB: See the [practical documentation](./repo\-hooks.md) for using repo hooks.
+.PP
+Only one repo\-hooks element may be specified at a time. Attempting to redefine
+it will fail to parse.
+.PP
+Attribute `in\-project`: The project where the hooks are defined. The value must
+match the `name` attribute (**not** the `path` attribute) of a previously
+defined `project` element.
+.PP
+Attribute `enabled\-list`: List of hooks to use, whitespace or comma separated.
+.PP
+Element superproject
+.PP
+*** *Note*: This is currently a WIP. ***
+.PP
+NB: See the [git superprojects documentation](
+https://en.wikibooks.org/wiki/Git/Submodules_and_Superprojects) for background
+information.
+.PP
+This element is used to specify the URL of the superproject. It has "name" and
+"remote" as atrributes. Only "name" is required while the others have reasonable
+defaults. At most one superproject may be specified. Attempting to redefine it
+will fail to parse.
+.PP
+Attribute `name`: A unique name for the superproject. This attribute has the
+same meaning as project's name attribute. See the [element
+project](#element\-project) for more information.
+.PP
+Attribute `remote`: Name of a previously defined remote element. If not supplied
+the remote given by the default element is used.
+.PP
+Element contactinfo
+.PP
+*** *Note*: This is currently a WIP. ***
+.PP
+This element is used to let manifest authors self\-register contact info. It has
+"bugurl" as a required atrribute. This element can be repeated, and any later
+entries will clobber earlier ones. This would allow manifest authors who extend
+manifests to specify their own contact info.
+.PP
+Attribute `bugurl`: The URL to file a bug against the manifest owner.
+.PP
+Element include
+.PP
+This element provides the capability of including another manifest file into the
+originating manifest. Normal rules apply for the target manifest to include \- it
+must be a usable manifest on its own.
+.PP
+Attribute `name`: the manifest to include, specified relative to the manifest
+repository's root.
+.PP
+"name" may not be an absolute path or use "." or ".." path components. These
+restrictions are not enforced for [Local Manifests].
+.PP
+Attribute `groups`: List of additional groups to which all projects in the
+included manifest belong. This appends and recurses, meaning all projects in
+sub\-manifests carry all parent include groups. Same syntax as the corresponding
+element of `project`.
+.PP
+Local Manifests
+.PP
+Additional remotes and projects may be added through local manifest files stored
+in `$TOP_DIR/.repo/local_manifests/*.xml`.
+.PP
+For example:
+.IP
+\f(CW$ ls .repo/local_manifests\fR
+.IP
+local_manifest.xml
+another_local_manifest.xml
+.IP
+\f(CW$ cat .repo/local_manifests/local_manifest.xml\fR
+.IP
+<?xml version="1.0" encoding="UTF\-8"?>
+<manifest>
+.IP
+<project path="manifest"
+.IP
+name="tools/manifest" />
+.IP
+<project path="platform\-manifest"
+.IP
+name="platform/manifest" />
+.IP
+</manifest>
+.PP
+Users may add projects to the local manifest(s) prior to a `repo sync`
+invocation, instructing repo to automatically download and manage these extra
+projects.
+.PP
+Manifest files stored in `$TOP_DIR/.repo/local_manifests/*.xml` will be loaded
+in alphabetical order.
+.PP
+Projects from local manifest files are added into local::<local manifest
+filename> group.
+.PP
+The legacy `$TOP_DIR/.repo/local_manifest.xml` path is no longer supported.
+.SS [copyfile]: #Element\-copyfile [linkfile]: #Element\-linkfile [Local Manifests]:
+.PP
+#local\-manifests
diff --git a/man/repo-overview.1 b/man/repo-overview.1
new file mode 100644
index 00000000..a12c7640
--- /dev/null
+++ b/man/repo-overview.1
@@ -0,0 +1,39 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo overview" "Repo Manual"
+.SH NAME
+repo \- repo overview - manual page for repo overview
+.SH SYNOPSIS
+.B repo
+\fI\,overview \/\fR[\fI\,--current-branch\/\fR] [\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Display overview of unmerged project branches
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-c\fR, \fB\-\-current\-branch\fR
+consider only checked out branches
+.TP
+\fB\-\-no\-current\-branch\fR
+consider all local branches
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help overview` to view the detailed manual.
+.SH DETAILS
+.PP
+The 'repo overview' command is used to display an overview of the projects
+branches, and list any local commits that have not yet been merged into the
+project.
+.PP
+The \fB\-c\fR/\-\-current\-branch option can be used to restrict the output to only
+branches currently checked out in each project. By default, all branches are
+displayed.
diff --git a/man/repo-prune.1 b/man/repo-prune.1
new file mode 100644
index 00000000..bd68a373
--- /dev/null
+++ b/man/repo-prune.1
@@ -0,0 +1,28 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo prune" "Repo Manual"
+.SH NAME
+repo \- repo prune - manual page for repo prune
+.SH SYNOPSIS
+.B repo
+\fI\,prune \/\fR[\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Prune (delete) already merged topics
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help prune` to view the detailed manual.
diff --git a/man/repo-rebase.1 b/man/repo-rebase.1
new file mode 100644
index 00000000..aa261036
--- /dev/null
+++ b/man/repo-rebase.1
@@ -0,0 +1,55 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo rebase" "Repo Manual"
+.SH NAME
+repo \- repo rebase - manual page for repo rebase
+.SH SYNOPSIS
+.B repo
+\fI\,rebase {\/\fR[\fI\,<project>\/\fR...] \fI\,| -i <project>\/\fR...\fI\,}\/\fR
+.SH DESCRIPTION
+Summary
+.PP
+Rebase local branches on upstream branch
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-\-fail\-fast\fR
+stop rebasing after first error is hit
+.TP
+\fB\-f\fR, \fB\-\-force\-rebase\fR
+pass \fB\-\-force\-rebase\fR to git rebase
+.TP
+\fB\-\-no\-ff\fR
+pass \fB\-\-no\-ff\fR to git rebase
+.TP
+\fB\-\-autosquash\fR
+pass \fB\-\-autosquash\fR to git rebase
+.TP
+\fB\-\-whitespace\fR=\fI\,WS\/\fR
+pass \fB\-\-whitespace\fR to git rebase
+.TP
+\fB\-\-auto\-stash\fR
+stash local modifications before starting
+.TP
+\fB\-m\fR, \fB\-\-onto\-manifest\fR
+rebase onto the manifest version instead of upstream
+HEAD (this helps to make sure the local tree stays
+consistent if you previously synced to a manifest)
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.TP
+\fB\-i\fR, \fB\-\-interactive\fR
+interactive rebase (single project only)
+.PP
+Run `repo help rebase` to view the detailed manual.
+.SH DETAILS
+.PP
+\&'repo rebase' uses git rebase to move local changes in the current topic branch
+to the HEAD of the upstream history, useful when you have made commits in a
+topic branch but need to incorporate new upstream changes "underneath" them.
diff --git a/man/repo-selfupdate.1 b/man/repo-selfupdate.1
new file mode 100644
index 00000000..70c855ab
--- /dev/null
+++ b/man/repo-selfupdate.1
@@ -0,0 +1,35 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo selfupdate" "Repo Manual"
+.SH NAME
+repo \- repo selfupdate - manual page for repo selfupdate
+.SH SYNOPSIS
+.B repo
+\fI\,selfupdate\/\fR
+.SH DESCRIPTION
+Summary
+.PP
+Update repo to the latest version
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.SS repo Version options:
+.TP
+\fB\-\-no\-repo\-verify\fR
+do not verify repo source code
+.PP
+Run `repo help selfupdate` to view the detailed manual.
+.SH DETAILS
+.PP
+The 'repo selfupdate' command upgrades repo to the latest version, if a newer
+version is available.
+.PP
+Normally this is done automatically by 'repo sync' and does not need to be
+performed by an end\-user.
diff --git a/man/repo-smartsync.1 b/man/repo-smartsync.1
new file mode 100644
index 00000000..5d939117
--- /dev/null
+++ b/man/repo-smartsync.1
@@ -0,0 +1,118 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo smartsync" "Repo Manual"
+.SH NAME
+repo \- repo smartsync - manual page for repo smartsync
+.SH SYNOPSIS
+.B repo
+\fI\,smartsync \/\fR[\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Update working tree to the latest known good revision
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.TP
+\fB\-\-jobs\-network\fR=\fI\,JOBS\/\fR
+number of network jobs to run in parallel (defaults to
+\fB\-\-jobs\fR)
+.TP
+\fB\-\-jobs\-checkout\fR=\fI\,JOBS\/\fR
+number of local checkout jobs to run in parallel
+(defaults to \fB\-\-jobs\fR)
+.TP
+\fB\-f\fR, \fB\-\-force\-broken\fR
+obsolete option (to be deleted in the future)
+.TP
+\fB\-\-fail\-fast\fR
+stop syncing after first error is hit
+.TP
+\fB\-\-force\-sync\fR
+overwrite an existing git directory if it needs to
+point to a different object directory. WARNING: this
+may cause loss of data
+.TP
+\fB\-\-force\-remove\-dirty\fR
+force remove projects with uncommitted modifications
+if projects no longer exist in the manifest. WARNING:
+this may cause loss of data
+.TP
+\fB\-l\fR, \fB\-\-local\-only\fR
+only update working tree, don't fetch
+.TP
+\fB\-\-no\-manifest\-update\fR, \fB\-\-nmu\fR
+use the existing manifest checkout as\-is. (do not
+update to the latest revision)
+.TP
+\fB\-n\fR, \fB\-\-network\-only\fR
+fetch only, don't update working tree
+.TP
+\fB\-d\fR, \fB\-\-detach\fR
+detach projects back to manifest revision
+.TP
+\fB\-c\fR, \fB\-\-current\-branch\fR
+fetch only current branch from server
+.TP
+\fB\-\-no\-current\-branch\fR
+fetch all branches from server
+.TP
+\fB\-m\fR NAME.xml, \fB\-\-manifest\-name\fR=\fI\,NAME\/\fR.xml
+temporary manifest to use for this sync
+.TP
+\fB\-\-clone\-bundle\fR
+enable use of \fI\,/clone.bundle\/\fP on HTTP/HTTPS
+.TP
+\fB\-\-no\-clone\-bundle\fR
+disable use of \fI\,/clone.bundle\/\fP on HTTP/HTTPS
+.TP
+\fB\-u\fR MANIFEST_SERVER_USERNAME, \fB\-\-manifest\-server\-username\fR=\fI\,MANIFEST_SERVER_USERNAME\/\fR
+username to authenticate with the manifest server
+.TP
+\fB\-p\fR MANIFEST_SERVER_PASSWORD, \fB\-\-manifest\-server\-password\fR=\fI\,MANIFEST_SERVER_PASSWORD\/\fR
+password to authenticate with the manifest server
+.TP
+\fB\-\-fetch\-submodules\fR
+fetch submodules from server
+.TP
+\fB\-\-use\-superproject\fR
+use the manifest superproject to sync projects
+.TP
+\fB\-\-no\-use\-superproject\fR
+disable use of manifest superprojects
+.TP
+\fB\-\-tags\fR
+fetch tags
+.TP
+\fB\-\-no\-tags\fR
+don't fetch tags
+.TP
+\fB\-\-optimized\-fetch\fR
+only fetch projects fixed to sha1 if revision does not
+exist locally
+.TP
+\fB\-\-retry\-fetches\fR=\fI\,RETRY_FETCHES\/\fR
+number of times to retry fetches on transient errors
+.TP
+\fB\-\-prune\fR
+delete refs that no longer exist on the remote
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.SS repo Version options:
+.TP
+\fB\-\-no\-repo\-verify\fR
+do not verify repo source code
+.PP
+Run `repo help smartsync` to view the detailed manual.
+.SH DETAILS
+.PP
+The 'repo smartsync' command is a shortcut for sync \fB\-s\fR.
diff --git a/man/repo-stage.1 b/man/repo-stage.1
new file mode 100644
index 00000000..07e1cac6
--- /dev/null
+++ b/man/repo-stage.1
@@ -0,0 +1,30 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo stage" "Repo Manual"
+.SH NAME
+repo \- repo stage - manual page for repo stage
+.SH SYNOPSIS
+.B repo
+\fI\,stage -i \/\fR[\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Stage file(s) for commit
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.TP
+\fB\-i\fR, \fB\-\-interactive\fR
+use interactive staging
+.PP
+Run `repo help stage` to view the detailed manual.
+.SH DETAILS
+.PP
+The 'repo stage' command stages files to prepare the next commit.
diff --git a/man/repo-start.1 b/man/repo-start.1
new file mode 100644
index 00000000..b00a31f4
--- /dev/null
+++ b/man/repo-start.1
@@ -0,0 +1,41 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo start" "Repo Manual"
+.SH NAME
+repo \- repo start - manual page for repo start
+.SH SYNOPSIS
+.B repo
+\fI\,start <newbranchname> \/\fR[\fI\,--all | <project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Start a new branch for development
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.TP
+\fB\-\-all\fR
+begin branch in all projects
+.TP
+\fB\-r\fR REVISION, \fB\-\-rev\fR=\fI\,REVISION\/\fR, \fB\-\-revision\fR=\fI\,REVISION\/\fR
+point branch at this revision instead of upstream
+.TP
+\fB\-\-head\fR, \fB\-\-HEAD\fR
+abbreviation for \fB\-\-rev\fR HEAD
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help start` to view the detailed manual.
+.SH DETAILS
+.PP
+\&'repo start' begins a new branch of development, starting from the revision
+specified in the manifest.
diff --git a/man/repo-status.1 b/man/repo-status.1
new file mode 100644
index 00000000..fbae2c5d
--- /dev/null
+++ b/man/repo-status.1
@@ -0,0 +1,98 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo status" "Repo Manual"
+.SH NAME
+repo \- repo status - manual page for repo status
+.SH SYNOPSIS
+.B repo
+\fI\,status \/\fR[\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Show the working tree status
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.TP
+\fB\-o\fR, \fB\-\-orphans\fR
+include objects in working directory outside of repo
+projects
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help status` to view the detailed manual.
+.SH DETAILS
+.PP
+\&'repo status' compares the working tree to the staging area (aka index), and the
+most recent commit on this branch (HEAD), in each project specified. A summary
+is displayed, one line per file where there is a difference between these three
+states.
+.PP
+The \fB\-j\fR/\-\-jobs option can be used to run multiple status queries in parallel.
+.PP
+The \fB\-o\fR/\-\-orphans option can be used to show objects that are in the working
+directory, but not associated with a repo project. This includes unmanaged
+top\-level files and directories, but also includes deeper items. For example, if
+dir/subdir/proj1 and dir/subdir/proj2 are repo projects, dir/subdir/proj3 will
+be shown if it is not known to repo.
+.PP
+Status Display
+.PP
+The status display is organized into three columns of information, for example
+if the file 'subcmds/status.py' is modified in the project 'repo' on branch
+\&'devwork':
+.TP
+project repo/
+branch devwork
+.TP
+\fB\-m\fR
+subcmds/status.py
+.PP
+The first column explains how the staging area (index) differs from the last
+commit (HEAD). Its values are always displayed in upper case and have the
+following meanings:
+.TP
+\-:
+no difference
+.TP
+A:
+added         (not in HEAD,     in index                     )
+.TP
+M:
+modified      (    in HEAD,     in index, different content  )
+.TP
+D:
+deleted       (    in HEAD, not in index                     )
+.TP
+R:
+renamed       (not in HEAD,     in index, path changed       )
+.TP
+C:
+copied        (not in HEAD,     in index, copied from another)
+.TP
+T:
+mode changed  (    in HEAD,     in index, same content       )
+.TP
+U:
+unmerged; conflict resolution required
+.PP
+The second column explains how the working directory differs from the index. Its
+values are always displayed in lower case and have the following meanings:
+.TP
+\-:
+new / unknown (not in index,     in work tree                )
+.TP
+m:
+modified      (    in index,     in work tree, modified      )
+.TP
+d:
+deleted       (    in index, not in work tree                )
diff --git a/man/repo-sync.1 b/man/repo-sync.1
new file mode 100644
index 00000000..c87c9701
--- /dev/null
+++ b/man/repo-sync.1
@@ -0,0 +1,209 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo sync" "Repo Manual"
+.SH NAME
+repo \- repo sync - manual page for repo sync
+.SH SYNOPSIS
+.B repo
+\fI\,sync \/\fR[\fI\,<project>\/\fR...]
+.SH DESCRIPTION
+Summary
+.PP
+Update working tree to the latest revision
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.TP
+\fB\-\-jobs\-network\fR=\fI\,JOBS\/\fR
+number of network jobs to run in parallel (defaults to
+\fB\-\-jobs\fR)
+.TP
+\fB\-\-jobs\-checkout\fR=\fI\,JOBS\/\fR
+number of local checkout jobs to run in parallel
+(defaults to \fB\-\-jobs\fR)
+.TP
+\fB\-f\fR, \fB\-\-force\-broken\fR
+obsolete option (to be deleted in the future)
+.TP
+\fB\-\-fail\-fast\fR
+stop syncing after first error is hit
+.TP
+\fB\-\-force\-sync\fR
+overwrite an existing git directory if it needs to
+point to a different object directory. WARNING: this
+may cause loss of data
+.TP
+\fB\-\-force\-remove\-dirty\fR
+force remove projects with uncommitted modifications
+if projects no longer exist in the manifest. WARNING:
+this may cause loss of data
+.TP
+\fB\-l\fR, \fB\-\-local\-only\fR
+only update working tree, don't fetch
+.TP
+\fB\-\-no\-manifest\-update\fR, \fB\-\-nmu\fR
+use the existing manifest checkout as\-is. (do not
+update to the latest revision)
+.TP
+\fB\-n\fR, \fB\-\-network\-only\fR
+fetch only, don't update working tree
+.TP
+\fB\-d\fR, \fB\-\-detach\fR
+detach projects back to manifest revision
+.TP
+\fB\-c\fR, \fB\-\-current\-branch\fR
+fetch only current branch from server
+.TP
+\fB\-\-no\-current\-branch\fR
+fetch all branches from server
+.TP
+\fB\-m\fR NAME.xml, \fB\-\-manifest\-name\fR=\fI\,NAME\/\fR.xml
+temporary manifest to use for this sync
+.TP
+\fB\-\-clone\-bundle\fR
+enable use of \fI\,/clone.bundle\/\fP on HTTP/HTTPS
+.TP
+\fB\-\-no\-clone\-bundle\fR
+disable use of \fI\,/clone.bundle\/\fP on HTTP/HTTPS
+.TP
+\fB\-u\fR MANIFEST_SERVER_USERNAME, \fB\-\-manifest\-server\-username\fR=\fI\,MANIFEST_SERVER_USERNAME\/\fR
+username to authenticate with the manifest server
+.TP
+\fB\-p\fR MANIFEST_SERVER_PASSWORD, \fB\-\-manifest\-server\-password\fR=\fI\,MANIFEST_SERVER_PASSWORD\/\fR
+password to authenticate with the manifest server
+.TP
+\fB\-\-fetch\-submodules\fR
+fetch submodules from server
+.TP
+\fB\-\-use\-superproject\fR
+use the manifest superproject to sync projects
+.TP
+\fB\-\-no\-use\-superproject\fR
+disable use of manifest superprojects
+.TP
+\fB\-\-tags\fR
+fetch tags
+.TP
+\fB\-\-no\-tags\fR
+don't fetch tags
+.TP
+\fB\-\-optimized\-fetch\fR
+only fetch projects fixed to sha1 if revision does not
+exist locally
+.TP
+\fB\-\-retry\-fetches\fR=\fI\,RETRY_FETCHES\/\fR
+number of times to retry fetches on transient errors
+.TP
+\fB\-\-prune\fR
+delete refs that no longer exist on the remote
+.TP
+\fB\-s\fR, \fB\-\-smart\-sync\fR
+smart sync using manifest from the latest known good
+build
+.TP
+\fB\-t\fR SMART_TAG, \fB\-\-smart\-tag\fR=\fI\,SMART_TAG\/\fR
+smart sync using manifest from a known tag
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.SS repo Version options:
+.TP
+\fB\-\-no\-repo\-verify\fR
+do not verify repo source code
+.PP
+Run `repo help sync` to view the detailed manual.
+.SH DETAILS
+.PP
+The 'repo sync' command synchronizes local project directories with the remote
+repositories specified in the manifest. If a local project does not yet exist,
+it will clone a new local directory from the remote repository and set up
+tracking branches as specified in the manifest. If the local project already
+exists, 'repo sync' will update the remote branches and rebase any new local
+changes on top of the new remote changes.
+.PP
+\&'repo sync' will synchronize all projects listed at the command line. Projects
+can be specified either by name, or by a relative or absolute path to the
+project's local directory. If no projects are specified, 'repo sync' will
+synchronize all projects listed in the manifest.
+.PP
+The \fB\-d\fR/\-\-detach option can be used to switch specified projects back to the
+manifest revision. This option is especially helpful if the project is currently
+on a topic branch, but the manifest revision is temporarily needed.
+.PP
+The \fB\-s\fR/\-\-smart\-sync option can be used to sync to a known good build as
+specified by the manifest\-server element in the current manifest. The
+\fB\-t\fR/\-\-smart\-tag option is similar and allows you to specify a custom tag/label.
+.PP
+The \fB\-u\fR/\-\-manifest\-server\-username and \fB\-p\fR/\-\-manifest\-server\-password options can
+be used to specify a username and password to authenticate with the manifest
+server when using the \fB\-s\fR or \fB\-t\fR option.
+.PP
+If \fB\-u\fR and \fB\-p\fR are not specified when using the \fB\-s\fR or \fB\-t\fR option, 'repo sync' will
+attempt to read authentication credentials for the manifest server from the
+user's .netrc file.
+.PP
+\&'repo sync' will not use authentication credentials from \fB\-u\fR/\-p or .netrc if the
+manifest server specified in the manifest file already includes credentials.
+.PP
+By default, all projects will be synced. The \fB\-\-fail\-fast\fR option can be used to
+halt syncing as soon as possible when the first project fails to sync.
+.PP
+The \fB\-\-force\-sync\fR option can be used to overwrite existing git directories if
+they have previously been linked to a different object directory. WARNING: This
+may cause data to be lost since refs may be removed when overwriting.
+.PP
+The \fB\-\-force\-remove\-dirty\fR option can be used to remove previously used projects
+with uncommitted changes. WARNING: This may cause data to be lost since
+uncommitted changes may be removed with projects that no longer exist in the
+manifest.
+.PP
+The \fB\-\-no\-clone\-bundle\fR option disables any attempt to use \fI\,$URL/clone.bundle\/\fP to
+bootstrap a new Git repository from a resumeable bundle file on a content
+delivery network. This may be necessary if there are problems with the local
+Python HTTP client or proxy configuration, but the Git binary works.
+.PP
+The \fB\-\-fetch\-submodules\fR option enables fetching Git submodules of a project from
+server.
+.PP
+The \fB\-c\fR/\-\-current\-branch option can be used to only fetch objects that are on the
+branch specified by a project's revision.
+.PP
+The \fB\-\-optimized\-fetch\fR option can be used to only fetch projects that are fixed
+to a sha1 revision if the sha1 revision does not already exist locally.
+.PP
+The \fB\-\-prune\fR option can be used to remove any refs that no longer exist on the
+remote.
+.PP
+SSH Connections
+.PP
+If at least one project remote URL uses an SSH connection (ssh://, git+ssh://,
+or user@host:path syntax) repo will automatically enable the SSH ControlMaster
+option when connecting to that host. This feature permits other projects in the
+same 'repo sync' session to reuse the same SSH tunnel, saving connection setup
+overheads.
+.PP
+To disable this behavior on UNIX platforms, set the GIT_SSH environment variable
+to 'ssh'. For example:
+.IP
+export GIT_SSH=ssh
+repo sync
+.PP
+Compatibility
+.PP
+This feature is automatically disabled on Windows, due to the lack of UNIX
+domain socket support.
+.PP
+This feature is not compatible with url.insteadof rewrites in the user's
+~/.gitconfig. 'repo sync' is currently not able to perform the rewrite early
+enough to establish the ControlMaster tunnel.
+.PP
+If the remote SSH daemon is Gerrit Code Review, version 2.0.10 or later is
+required to fix a server side protocol bug.
diff --git a/man/repo-upload.1 b/man/repo-upload.1
new file mode 100644
index 00000000..36a0daca
--- /dev/null
+++ b/man/repo-upload.1
@@ -0,0 +1,175 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo upload" "Repo Manual"
+.SH NAME
+repo \- repo upload - manual page for repo upload
+.SH SYNOPSIS
+.B repo
+\fI\,upload \/\fR[\fI\,--re --cc\/\fR] [\fI\,<project>\/\fR]...
+.SH DESCRIPTION
+Summary
+.PP
+Upload changes for code review
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-j\fR JOBS, \fB\-\-jobs\fR=\fI\,JOBS\/\fR
+number of jobs to run in parallel (default: based on
+number of CPU cores)
+.TP
+\fB\-t\fR
+send local branch name to Gerrit Code Review
+.TP
+\fB\-\-hashtag\fR=\fI\,HASHTAGS\/\fR, \fB\-\-ht\fR=\fI\,HASHTAGS\/\fR
+add hashtags (comma delimited) to the review
+.TP
+\fB\-\-hashtag\-branch\fR, \fB\-\-htb\fR
+add local branch name as a hashtag
+.TP
+\fB\-l\fR LABELS, \fB\-\-label\fR=\fI\,LABELS\/\fR
+add a label when uploading
+.TP
+\fB\-\-re\fR=\fI\,REVIEWERS\/\fR, \fB\-\-reviewers\fR=\fI\,REVIEWERS\/\fR
+request reviews from these people
+.TP
+\fB\-\-cc\fR=\fI\,CC\/\fR
+also send email to these email addresses
+.TP
+\fB\-\-br\fR=\fI\,BRANCH\/\fR, \fB\-\-branch\fR=\fI\,BRANCH\/\fR
+(local) branch to upload
+.TP
+\fB\-c\fR, \fB\-\-current\-branch\fR
+upload current git branch
+.TP
+\fB\-\-no\-current\-branch\fR
+upload all git branches
+.TP
+\fB\-\-ne\fR, \fB\-\-no\-emails\fR
+do not send e\-mails on upload
+.TP
+\fB\-p\fR, \fB\-\-private\fR
+upload as a private change (deprecated; use \fB\-\-wip\fR)
+.TP
+\fB\-w\fR, \fB\-\-wip\fR
+upload as a work\-in\-progress change
+.TP
+\fB\-o\fR PUSH_OPTIONS, \fB\-\-push\-option\fR=\fI\,PUSH_OPTIONS\/\fR
+additional push options to transmit
+.TP
+\fB\-D\fR BRANCH, \fB\-\-destination\fR=\fI\,BRANCH\/\fR, \fB\-\-dest\fR=\fI\,BRANCH\/\fR
+submit for review on this target branch
+.TP
+\fB\-n\fR, \fB\-\-dry\-run\fR
+do everything except actually upload the CL
+.TP
+\fB\-y\fR, \fB\-\-yes\fR
+answer yes to all safe prompts
+.TP
+\fB\-\-no\-cert\-checks\fR
+disable verifying ssl certs (unsafe)
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.SS pre\-upload hooks:
+.TP
+\fB\-\-no\-verify\fR
+Do not run the pre\-upload hook.
+.TP
+\fB\-\-verify\fR
+Run the pre\-upload hook without prompting.
+.TP
+\fB\-\-ignore\-hooks\fR
+Do not abort if pre\-upload hooks fail.
+.PP
+Run `repo help upload` to view the detailed manual.
+.SH DETAILS
+.PP
+The 'repo upload' command is used to send changes to the Gerrit Code Review
+system. It searches for topic branches in local projects that have not yet been
+published for review. If multiple topic branches are found, 'repo upload' opens
+an editor to allow the user to select which branches to upload.
+.PP
+\&'repo upload' searches for uploadable changes in all projects listed at the
+command line. Projects can be specified either by name, or by a relative or
+absolute path to the project's local directory. If no projects are specified,
+\&'repo upload' will search for uploadable changes in all projects listed in the
+manifest.
+.PP
+If the \fB\-\-reviewers\fR or \fB\-\-cc\fR options are passed, those emails are added to the
+respective list of users, and emails are sent to any new users. Users passed as
+\fB\-\-reviewers\fR must already be registered with the code review system, or the
+upload will fail.
+.PP
+Configuration
+.PP
+review.URL.autoupload:
+.PP
+To disable the "Upload ... (y/N)?" prompt, you can set a per\-project or global
+Git configuration option. If review.URL.autoupload is set to "true" then repo
+will assume you always answer "y" at the prompt, and will not prompt you
+further. If it is set to "false" then repo will assume you always answer "n",
+and will abort.
+.PP
+review.URL.autoreviewer:
+.PP
+To automatically append a user or mailing list to reviews, you can set a
+per\-project or global Git option to do so.
+.PP
+review.URL.autocopy:
+.PP
+To automatically copy a user or mailing list to all uploaded reviews, you can
+set a per\-project or global Git option to do so. Specifically,
+review.URL.autocopy can be set to a comma separated list of reviewers who you
+always want copied on all uploads with a non\-empty \fB\-\-re\fR argument.
+.PP
+review.URL.username:
+.PP
+Override the username used to connect to Gerrit Code Review. By default the
+local part of the email address is used.
+.PP
+The URL must match the review URL listed in the manifest XML file, or in the
+\&.git/config within the project. For example:
+.IP
+[remote "origin"]
+.IP
+url = git://git.example.com/project.git
+review = http://review.example.com/
+.IP
+[review "http://review.example.com/"]
+.IP
+autoupload = true
+autocopy = johndoe@company.com,my\-team\-alias@company.com
+.PP
+review.URL.uploadtopic:
+.PP
+To add a topic branch whenever uploading a commit, you can set a per\-project or
+global Git option to do so. If review.URL.uploadtopic is set to "true" then repo
+will assume you always want the equivalent of the \fB\-t\fR option to the repo command.
+If unset or set to "false" then repo will make use of only the command line
+option.
+.PP
+review.URL.uploadhashtags:
+.PP
+To add hashtags whenever uploading a commit, you can set a per\-project or global
+Git option to do so. The value of review.URL.uploadhashtags will be used as
+comma delimited hashtags like the \fB\-\-hashtag\fR option.
+.PP
+review.URL.uploadlabels:
+.PP
+To add labels whenever uploading a commit, you can set a per\-project or global
+Git option to do so. The value of review.URL.uploadlabels will be used as comma
+delimited labels like the \fB\-\-label\fR option.
+.PP
+review.URL.uploadnotify:
+.PP
+Control e\-mail notifications when uploading.
+https://gerrit\-review.googlesource.com/Documentation/user\-upload.html#notify
+.PP
+References
+.PP
+Gerrit Code Review: https://www.gerritcodereview.com/
diff --git a/man/repo-version.1 b/man/repo-version.1
new file mode 100644
index 00000000..cc703f61
--- /dev/null
+++ b/man/repo-version.1
@@ -0,0 +1,24 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo version" "Repo Manual"
+.SH NAME
+repo \- repo version - manual page for repo version
+.SH SYNOPSIS
+.B repo
+\fI\,version\/\fR
+.SH DESCRIPTION
+Summary
+.PP
+Display the version of repo
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.SS Logging options:
+.TP
+\fB\-v\fR, \fB\-\-verbose\fR
+show all output
+.TP
+\fB\-q\fR, \fB\-\-quiet\fR
+only show errors
+.PP
+Run `repo help version` to view the detailed manual.
diff --git a/man/repo.1 b/man/repo.1
new file mode 100644
index 00000000..4aa76380
--- /dev/null
+++ b/man/repo.1
@@ -0,0 +1,133 @@
+.\" DO NOT MODIFY THIS FILE!  It was generated by help2man.
+.TH REPO "1" "July 2021" "repo" "Repo Manual"
+.SH NAME
+repo \- repository management tool built on top of git
+.SH SYNOPSIS
+.B repo
+[\fI\,-p|--paginate|--no-pager\/\fR] \fI\,COMMAND \/\fR[\fI\,ARGS\/\fR]
+.SH OPTIONS
+.TP
+\fB\-h\fR, \fB\-\-help\fR
+show this help message and exit
+.TP
+\fB\-\-help\-all\fR
+show this help message with all subcommands and exit
+.TP
+\fB\-p\fR, \fB\-\-paginate\fR
+display command output in the pager
+.TP
+\fB\-\-no\-pager\fR
+disable the pager
+.TP
+\fB\-\-color\fR=\fI\,COLOR\/\fR
+control color usage: auto, always, never
+.TP
+\fB\-\-trace\fR
+trace git command execution (REPO_TRACE=1)
+.TP
+\fB\-\-trace\-python\fR
+trace python command execution
+.TP
+\fB\-\-time\fR
+time repo command execution
+.TP
+\fB\-\-version\fR
+display this version of repo
+.TP
+\fB\-\-show\-toplevel\fR
+display the path of the top\-level directory of the
+repo client checkout
+.TP
+\fB\-\-event\-log\fR=\fI\,EVENT_LOG\/\fR
+filename of event log to append timeline to
+.TP
+\fB\-\-git\-trace2\-event\-log\fR=\fI\,GIT_TRACE2_EVENT_LOG\/\fR
+directory to write git trace2 event log to
+.SS "The complete list of recognized repo commands are:"
+.TP
+abandon
+Permanently abandon a development branch
+.TP
+branch
+View current topic branches
+.TP
+branches
+View current topic branches
+.TP
+checkout
+Checkout a branch for development
+.TP
+cherry\-pick
+Cherry\-pick a change.
+.TP
+diff
+Show changes between commit and working tree
+.TP
+diffmanifests
+Manifest diff utility
+.TP
+download
+Download and checkout a change
+.TP
+forall
+Run a shell command in each project
+.TP
+gitc\-delete
+Delete a GITC Client.
+.TP
+gitc\-init
+Initialize a GITC Client.
+.TP
+grep
+Print lines matching a pattern
+.TP
+help
+Display detailed help on a command
+.TP
+info
+Get info on the manifest branch, current branch or unmerged branches
+.TP
+init
+Initialize a repo client checkout in the current directory
+.TP
+list
+List projects and their associated directories
+.TP
+manifest
+Manifest inspection utility
+.TP
+overview
+Display overview of unmerged project branches
+.TP
+prune
+Prune (delete) already merged topics
+.TP
+rebase
+Rebase local branches on upstream branch
+.TP
+selfupdate
+Update repo to the latest version
+.TP
+smartsync
+Update working tree to the latest known good revision
+.TP
+stage
+Stage file(s) for commit
+.TP
+start
+Start a new branch for development
+.TP
+status
+Show the working tree status
+.TP
+sync
+Update working tree to the latest revision
+.TP
+upload
+Upload changes for code review
+.TP
+version
+Display the version of repo
+.PP
+See 'repo help <command>' for more information on a specific command.
+Bug reports: https://bugs.chromium.org/p/gerrit/issues/entry?template=Repo+tool+issue
diff --git a/manifest_xml.py b/manifest_xml.py
index 3814a25a..68ead53c 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,33 +12,34 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
+import collections
 import itertools
 import os
+import platform
 import re
 import sys
 import xml.dom.minidom
-
-from pyversion import is_python3
-if is_python3():
-  import urllib.parse
-else:
-  import imp
-  import urlparse
-  urllib = imp.new_module('urllib')
-  urllib.parse = urlparse
+import urllib.parse
 
 import gitc_utils
-from git_config import GitConfig
+from git_config import GitConfig, IsId
 from git_refs import R_HEADS, HEAD
 import platform_utils
-from project import RemoteSpec, Project, MetaProject
-from error import ManifestParseError, ManifestInvalidRevisionError
+from project import Annotation, RemoteSpec, Project, MetaProject
+from error import (ManifestParseError, ManifestInvalidPathError,
+                   ManifestInvalidRevisionError)
+from wrapper import Wrapper
 
 MANIFEST_FILE_NAME = 'manifest.xml'
 LOCAL_MANIFEST_NAME = 'local_manifest.xml'
 LOCAL_MANIFESTS_DIR_NAME = 'local_manifests'
 
+# Add all projects from local manifest into a group.
+LOCAL_MANIFEST_GROUP_PREFIX = 'local:'
+
+# ContactInfo has the self-registered bug url, supplied by the manifest authors.
+ContactInfo = collections.namedtuple('ContactInfo', 'bugurl')
+
 # urljoin gets confused if the scheme is not known.
 urllib.parse.uses_relative.extend([
     'ssh',
@@ -55,6 +54,61 @@ urllib.parse.uses_netloc.extend([
     'sso',
     'rpc'])
 
+
+def XmlBool(node, attr, default=None):
+  """Determine boolean value of |node|'s |attr|.
+
+  Invalid values will issue a non-fatal warning.
+
+  Args:
+    node: XML node whose attributes we access.
+    attr: The attribute to access.
+    default: If the attribute is not set (value is empty), then use this.
+
+  Returns:
+    True if the attribute is a valid string representing true.
+    False if the attribute is a valid string representing false.
+    |default| otherwise.
+  """
+  value = node.getAttribute(attr)
+  s = value.lower()
+  if s == '':
+    return default
+  elif s in {'yes', 'true', '1'}:
+    return True
+  elif s in {'no', 'false', '0'}:
+    return False
+  else:
+    print('warning: manifest: %s="%s": ignoring invalid XML boolean' %
+          (attr, value), file=sys.stderr)
+    return default
+
+
+def XmlInt(node, attr, default=None):
+  """Determine integer value of |node|'s |attr|.
+
+  Args:
+    node: XML node whose attributes we access.
+    attr: The attribute to access.
+    default: If the attribute is not set (value is empty), then use this.
+
+  Returns:
+    The number if the attribute is a valid number.
+
+  Raises:
+    ManifestParseError: The number is invalid.
+  """
+  value = node.getAttribute(attr)
+  if not value:
+    return default
+
+  try:
+    return int(value)
+  except ValueError:
+    raise ManifestParseError('manifest: invalid %s="%s" integer' %
+                             (attr, value))
+
+
 class _Default(object):
   """Project defaults within the manifest."""
 
@@ -68,11 +122,16 @@ class _Default(object):
   sync_tags = True
 
   def __eq__(self, other):
+    if not isinstance(other, _Default):
+      return False
     return self.__dict__ == other.__dict__
 
   def __ne__(self, other):
+    if not isinstance(other, _Default):
+      return True
     return self.__dict__ != other.__dict__
 
+
 class _XmlRemote(object):
   def __init__(self,
                name,
@@ -90,14 +149,22 @@ class _XmlRemote(object):
     self.reviewUrl = review
     self.revision = revision
     self.resolvedFetchUrl = self._resolveFetchUrl()
+    self.annotations = []
 
   def __eq__(self, other):
-    return self.__dict__ == other.__dict__
+    if not isinstance(other, _XmlRemote):
+      return False
+    return (sorted(self.annotations) == sorted(other.annotations) and
+      self.name == other.name and self.fetchUrl == other.fetchUrl and
+      self.pushUrl == other.pushUrl and self.remoteAlias == other.remoteAlias
+      and self.reviewUrl == other.reviewUrl and self.revision == other.revision)
 
   def __ne__(self, other):
-    return self.__dict__ != other.__dict__
+    return not self.__eq__(other)
 
   def _resolveFetchUrl(self):
+    if self.fetchUrl is None:
+      return ''
     url = self.fetchUrl.rstrip('/')
     manifestUrl = self.manifestUrl.rstrip('/')
     # urljoin will gets confused over quite a few things.  The ones we care
@@ -126,25 +193,48 @@ class _XmlRemote(object):
                       orig_name=self.name,
                       fetchUrl=self.fetchUrl)
 
+  def AddAnnotation(self, name, value, keep):
+    self.annotations.append(Annotation(name, value, keep))
+
+
 class XmlManifest(object):
   """manages the repo configuration file"""
 
-  def __init__(self, repodir):
+  def __init__(self, repodir, manifest_file, local_manifests=None):
+    """Initialize.
+
+    Args:
+      repodir: Path to the .repo/ dir for holding all internal checkout state.
+          It must be in the top directory of the repo client checkout.
+      manifest_file: Full path to the manifest file to parse.  This will usually
+          be |repodir|/|MANIFEST_FILE_NAME|.
+      local_manifests: Full path to the directory of local override manifests.
+          This will usually be |repodir|/|LOCAL_MANIFESTS_DIR_NAME|.
+    """
+    # TODO(vapier): Move this out of this class.
+    self.globalConfig = GitConfig.ForUser()
+
     self.repodir = os.path.abspath(repodir)
     self.topdir = os.path.dirname(self.repodir)
-    self.manifestFile = os.path.join(self.repodir, MANIFEST_FILE_NAME)
-    self.globalConfig = GitConfig.ForUser()
-    self.localManifestWarning = False
-    self.isGitcClient = False
+    self.manifestFile = manifest_file
+    self.local_manifests = local_manifests
     self._load_local_manifests = True
 
     self.repoProject = MetaProject(self, 'repo',
-      gitdir   = os.path.join(repodir, 'repo/.git'),
-      worktree = os.path.join(repodir, 'repo'))
+                                   gitdir=os.path.join(repodir, 'repo/.git'),
+                                   worktree=os.path.join(repodir, 'repo'))
 
-    self.manifestProject = MetaProject(self, 'manifests',
-      gitdir   = os.path.join(repodir, 'manifests.git'),
-      worktree = os.path.join(repodir, 'manifests'))
+    mp = MetaProject(self, 'manifests',
+                     gitdir=os.path.join(repodir, 'manifests.git'),
+                     worktree=os.path.join(repodir, 'manifests'))
+    self.manifestProject = mp
+
+    # This is a bit hacky, but we're in a chicken & egg situation: all the
+    # normal repo settings live in the manifestProject which we just setup
+    # above, so we couldn't easily query before that.  We assume Project()
+    # init doesn't care if this changes afterwards.
+    if os.path.exists(mp.gitdir) and mp.config.GetBoolean('repo.worktree'):
+      mp.use_git_worktrees = True
 
     self._Unload()
 
@@ -179,12 +269,26 @@ class XmlManifest(object):
     """
     self.Override(name)
 
-    try:
-      if os.path.lexists(self.manifestFile):
-        platform_utils.remove(self.manifestFile)
-      platform_utils.symlink(os.path.join('manifests', name), self.manifestFile)
-    except OSError as e:
-      raise ManifestParseError('cannot link manifest %s: %s' % (name, str(e)))
+    # Old versions of repo would generate symlinks we need to clean up.
+    platform_utils.remove(self.manifestFile, missing_ok=True)
+    # This file is interpreted as if it existed inside the manifest repo.
+    # That allows us to use <include> with the relative file name.
+    with open(self.manifestFile, 'w') as fp:
+      fp.write("""<?xml version="1.0" encoding="UTF-8"?>
+<!--
+DO NOT EDIT THIS FILE!  It is generated by repo and changes will be discarded.
+If you want to use a different manifest, use `repo init -m <file>` instead.
+
+If you want to customize your checkout by overriding manifest settings, use
+the local_manifests/ directory instead.
+
+For more information on repo manifests, check out:
+https://gerrit.googlesource.com/git-repo/+/HEAD/docs/manifest-format.md
+-->
+<manifest>
+  <include name="%s" />
+</manifest>
+""" % (name,))
 
   def _RemoteToXml(self, r, doc, root):
     e = doc.createElement('remote')
@@ -200,18 +304,28 @@ class XmlManifest(object):
     if r.revision is not None:
       e.setAttribute('revision', r.revision)
 
-  def _ParseGroups(self, groups):
-    return [x for x in re.split(r'[,\s]+', groups) if x]
+    for a in r.annotations:
+      if a.keep == 'true':
+        ae = doc.createElement('annotation')
+        ae.setAttribute('name', a.name)
+        ae.setAttribute('value', a.value)
+        e.appendChild(ae)
+
+  def _ParseList(self, field):
+    """Parse fields that contain flattened lists.
 
-  def Save(self, fd, peg_rev=False, peg_rev_upstream=True, groups=None):
-    """Write the current manifest out to the given file descriptor.
+    These are whitespace & comma separated.  Empty elements will be discarded.
     """
+    return [x for x in re.split(r'[,\s]+', field) if x]
+
+  def ToXml(self, peg_rev=False, peg_rev_upstream=True, peg_rev_dest_branch=True, groups=None):
+    """Return the current manifest XML."""
     mp = self.manifestProject
 
     if groups is None:
       groups = mp.config.GetString('manifest.groups')
     if groups:
-      groups = self._ParseGroups(groups)
+      groups = self._ParseList(groups)
 
     doc = xml.dom.minidom.Document()
     root = doc.createElement('manifest')
@@ -223,7 +337,7 @@ class XmlManifest(object):
     if self.notice:
       notice_element = root.appendChild(doc.createElement('notice'))
       notice_lines = self.notice.splitlines()
-      indented_notice = ('\n'.join(" "*4 + line for line in notice_lines))[4:]
+      indented_notice = ('\n'.join(" " * 4 + line for line in notice_lines))[4:]
       notice_element.appendChild(doc.createTextNode(indented_notice))
 
     d = self.default
@@ -308,10 +422,19 @@ class XmlManifest(object):
             # Only save the origin if the origin is not a sha1, and the default
             # isn't our value
             e.setAttribute('upstream', p.revisionExpr)
+
+        if peg_rev_dest_branch:
+          if p.dest_branch:
+            e.setAttribute('dest-branch', p.dest_branch)
+          elif value != p.revisionExpr:
+            e.setAttribute('dest-branch', p.revisionExpr)
+
       else:
         revision = self.remotes[p.remote.orig_name].revision or d.revisionExpr
         if not revision or revision != p.revisionExpr:
           e.setAttribute('revision', p.revisionExpr)
+        elif p.revisionId:
+          e.setAttribute('revision', p.revisionId)
         if (p.upstream and (p.upstream != p.revisionExpr or
                             p.upstream != d.upstreamExpr)):
           e.setAttribute('upstream', p.upstream)
@@ -372,11 +495,84 @@ class XmlManifest(object):
                      ' '.join(self._repo_hooks_project.enabled_repo_hooks))
       root.appendChild(e)
 
+    if self._superproject:
+      root.appendChild(doc.createTextNode(''))
+      e = doc.createElement('superproject')
+      e.setAttribute('name', self._superproject['name'])
+      remoteName = None
+      if d.remote:
+        remoteName = d.remote.name
+      remote = self._superproject.get('remote')
+      if not d.remote or remote.orig_name != remoteName:
+        remoteName = remote.orig_name
+        e.setAttribute('remote', remoteName)
+      revision = remote.revision or d.revisionExpr
+      if not revision or revision != self._superproject['revision']:
+        e.setAttribute('revision', self._superproject['revision'])
+      root.appendChild(e)
+
+    if self._contactinfo.bugurl != Wrapper().BUG_URL:
+      root.appendChild(doc.createTextNode(''))
+      e = doc.createElement('contactinfo')
+      e.setAttribute('bugurl', self._contactinfo.bugurl)
+      root.appendChild(e)
+
+    return doc
+
+  def ToDict(self, **kwargs):
+    """Return the current manifest as a dictionary."""
+    # Elements that may only appear once.
+    SINGLE_ELEMENTS = {
+        'notice',
+        'default',
+        'manifest-server',
+        'repo-hooks',
+        'superproject',
+        'contactinfo',
+    }
+    # Elements that may be repeated.
+    MULTI_ELEMENTS = {
+        'remote',
+        'remove-project',
+        'project',
+        'extend-project',
+        'include',
+        # These are children of 'project' nodes.
+        'annotation',
+        'project',
+        'copyfile',
+        'linkfile',
+    }
+
+    doc = self.ToXml(**kwargs)
+    ret = {}
+
+    def append_children(ret, node):
+      for child in node.childNodes:
+        if child.nodeType == xml.dom.Node.ELEMENT_NODE:
+          attrs = child.attributes
+          element = dict((attrs.item(i).localName, attrs.item(i).value)
+                         for i in range(attrs.length))
+          if child.nodeName in SINGLE_ELEMENTS:
+            ret[child.nodeName] = element
+          elif child.nodeName in MULTI_ELEMENTS:
+            ret.setdefault(child.nodeName, []).append(element)
+          else:
+            raise ManifestParseError('Unhandled element "%s"' % (child.nodeName,))
+
+          append_children(element, child)
+
+    append_children(ret, doc.firstChild)
+
+    return ret
+
+  def Save(self, fd, **kwargs):
+    """Write the current manifest out to the given file descriptor."""
+    doc = self.ToXml(**kwargs)
     doc.writexml(fd, '', '  ', '\n', 'UTF-8')
 
   def _output_manifest_project_extras(self, p, e):
     """Manifests can modify e if they support extra project attributes."""
-    pass
 
   @property
   def paths(self):
@@ -404,6 +600,16 @@ class XmlManifest(object):
     return self._repo_hooks_project
 
   @property
+  def superproject(self):
+    self._Load()
+    return self._superproject
+
+  @property
+  def contactinfo(self):
+    self._Load()
+    return self._contactinfo
+
+  @property
   def notice(self):
     self._Load()
     return self._notice
@@ -414,16 +620,45 @@ class XmlManifest(object):
     return self._manifest_server
 
   @property
+  def CloneBundle(self):
+    clone_bundle = self.manifestProject.config.GetBoolean('repo.clonebundle')
+    if clone_bundle is None:
+      return False if self.manifestProject.config.GetBoolean('repo.partialclone') else True
+    else:
+      return clone_bundle
+
+  @property
   def CloneFilter(self):
     if self.manifestProject.config.GetBoolean('repo.partialclone'):
       return self.manifestProject.config.GetString('repo.clonefilter')
     return None
 
   @property
+  def PartialCloneExclude(self):
+    exclude = self.manifest.manifestProject.config.GetString(
+        'repo.partialcloneexclude') or ''
+    return set(x.strip() for x in exclude.split(','))
+
+  @property
+  def UseLocalManifests(self):
+    return self._load_local_manifests
+
+  def SetUseLocalManifests(self, value):
+    self._load_local_manifests = value
+
+  @property
+  def HasLocalManifests(self):
+    return self._load_local_manifests and self.local_manifests
+
+  @property
   def IsMirror(self):
     return self.manifestProject.config.GetBoolean('repo.mirror')
 
   @property
+  def UseGitWorktrees(self):
+    return self.manifestProject.config.GetBoolean('repo.worktree')
+
+  @property
   def IsArchive(self):
     return self.manifestProject.config.GetBoolean('repo.archive')
 
@@ -431,6 +666,17 @@ class XmlManifest(object):
   def HasSubmodules(self):
     return self.manifestProject.config.GetBoolean('repo.submodules')
 
+  def GetDefaultGroupsStr(self):
+    """Returns the default group string for the platform."""
+    return 'default,platform-' + platform.system().lower()
+
+  def GetGroupsStr(self):
+    """Returns the manifest group string that should be synced."""
+    groups = self.manifestProject.config.GetString('manifest.groups')
+    if not groups:
+      groups = self.GetDefaultGroupsStr()
+    return groups
+
   def _Unload(self):
     self._loaded = False
     self._projects = {}
@@ -438,6 +684,8 @@ class XmlManifest(object):
     self._remotes = {}
     self._default = None
     self._repo_hooks_project = None
+    self._superproject = {}
+    self._contactinfo = ContactInfo(Wrapper().BUG_URL)
     self._notice = None
     self.branch = None
     self._manifest_server = None
@@ -450,28 +698,24 @@ class XmlManifest(object):
         b = b[len(R_HEADS):]
       self.branch = b
 
+      # The manifestFile was specified by the user which is why we allow include
+      # paths to point anywhere.
       nodes = []
-      nodes.append(self._ParseManifestXml(self.manifestFile,
-                                          self.manifestProject.worktree))
-
-      if self._load_local_manifests:
-        local = os.path.join(self.repodir, LOCAL_MANIFEST_NAME)
-        if os.path.exists(local):
-          if not self.localManifestWarning:
-            self.localManifestWarning = True
-            print('warning: %s is deprecated; put local manifests '
-                  'in `%s` instead' % (LOCAL_MANIFEST_NAME,
-                  os.path.join(self.repodir, LOCAL_MANIFESTS_DIR_NAME)),
-                  file=sys.stderr)
-          nodes.append(self._ParseManifestXml(local, self.repodir))
-
-        local_dir = os.path.abspath(os.path.join(self.repodir,
-                                    LOCAL_MANIFESTS_DIR_NAME))
+      nodes.append(self._ParseManifestXml(
+          self.manifestFile, self.manifestProject.worktree,
+          restrict_includes=False))
+
+      if self._load_local_manifests and self.local_manifests:
         try:
-          for local_file in sorted(platform_utils.listdir(local_dir)):
+          for local_file in sorted(platform_utils.listdir(self.local_manifests)):
             if local_file.endswith('.xml'):
-              local = os.path.join(local_dir, local_file)
-              nodes.append(self._ParseManifestXml(local, self.repodir))
+              local = os.path.join(self.local_manifests, local_file)
+              # Since local manifests are entirely managed by the user, allow
+              # them to point anywhere the user wants.
+              nodes.append(self._ParseManifestXml(
+                  local, self.repodir,
+                  parent_groups=f'{LOCAL_MANIFEST_GROUP_PREFIX}:{local_file[:-4]}',
+                  restrict_includes=False))
         except OSError:
           pass
 
@@ -489,7 +733,19 @@ class XmlManifest(object):
 
       self._loaded = True
 
-  def _ParseManifestXml(self, path, include_root):
+  def _ParseManifestXml(self, path, include_root, parent_groups='',
+                        restrict_includes=True):
+    """Parse a manifest XML and return the computed nodes.
+
+    Args:
+      path: The XML file to read & parse.
+      include_root: The path to interpret include "name"s relative to.
+      parent_groups: The groups to apply to this projects.
+      restrict_includes: Whether to constrain the "name" attribute of includes.
+
+    Returns:
+      List of XML nodes.
+    """
     try:
       root = xml.dom.minidom.parse(path)
     except (OSError, xml.parsers.expat.ExpatError) as e:
@@ -508,20 +764,35 @@ class XmlManifest(object):
     for node in manifest.childNodes:
       if node.nodeName == 'include':
         name = self._reqatt(node, 'name')
+        if restrict_includes:
+          msg = self._CheckLocalPath(name)
+          if msg:
+            raise ManifestInvalidPathError(
+                '<include> invalid "name": %s: %s' % (name, msg))
+        include_groups = ''
+        if parent_groups:
+          include_groups = parent_groups
+        if node.hasAttribute('groups'):
+          include_groups = node.getAttribute('groups') + ',' + include_groups
         fp = os.path.join(include_root, name)
         if not os.path.isfile(fp):
-          raise ManifestParseError("include %s doesn't exist or isn't a file"
-              % (name,))
+          raise ManifestParseError("include [%s/]%s doesn't exist or isn't a file"
+                                   % (include_root, name))
         try:
-          nodes.extend(self._ParseManifestXml(fp, include_root))
+          nodes.extend(self._ParseManifestXml(fp, include_root, include_groups))
         # should isolate this to the exact exception, but that's
         # tricky.  actual parsing implementation may vary.
-        except (KeyboardInterrupt, RuntimeError, SystemExit):
+        except (KeyboardInterrupt, RuntimeError, SystemExit, ManifestParseError):
           raise
         except Exception as e:
           raise ManifestParseError(
               "failed parsing included manifest %s: %s" % (name, e))
       else:
+        if parent_groups and node.nodeName == 'project':
+          nodeGroups = parent_groups
+          if node.hasAttribute('groups'):
+            nodeGroups = node.getAttribute('groups') + ',' + nodeGroups
+          node.setAttribute('groups', nodeGroups)
         nodes.append(node)
     return nodes
 
@@ -541,9 +812,10 @@ class XmlManifest(object):
     for node in itertools.chain(*node_list):
       if node.nodeName == 'default':
         new_default = self._ParseDefault(node)
+        emptyDefault = not node.hasAttributes() and not node.hasChildNodes()
         if self._default is None:
           self._default = new_default
-        elif new_default != self._default:
+        elif not emptyDefault and new_default != self._default:
           raise ManifestParseError('duplicate default in %s' %
                                    (self.manifestFile))
 
@@ -582,6 +854,8 @@ class XmlManifest(object):
       for subproject in project.subprojects:
         recursively_add_projects(subproject)
 
+    repo_hooks_project = None
+    enabled_repo_hooks = None
     for node in itertools.chain(*node_list):
       if node.nodeName == 'project':
         project = self._ParseProject(node)
@@ -594,61 +868,108 @@ class XmlManifest(object):
                                    'project: %s' % name)
 
         path = node.getAttribute('path')
+        dest_path = node.getAttribute('dest-path')
         groups = node.getAttribute('groups')
         if groups:
-          groups = self._ParseGroups(groups)
+          groups = self._ParseList(groups)
         revision = node.getAttribute('revision')
+        remote = node.getAttribute('remote')
+        if remote:
+          remote = self._get_remote(node)
 
+        named_projects = self._projects[name]
+        if dest_path and not path and len(named_projects) > 1:
+          raise ManifestParseError('extend-project cannot use dest-path when '
+                                   'matching multiple projects: %s' % name)
         for p in self._projects[name]:
           if path and p.relpath != path:
             continue
           if groups:
             p.groups.extend(groups)
           if revision:
-            p.revisionExpr = revision
-      if node.nodeName == 'repo-hooks':
-        # Get the name of the project and the (space-separated) list of enabled.
-        repo_hooks_project = self._reqatt(node, 'in-project')
-        enabled_repo_hooks = self._reqatt(node, 'enabled-list').split()
+            p.SetRevision(revision)
+
+          if remote:
+            p.remote = remote.ToRemoteSpec(name)
+
+          if dest_path:
+            del self._paths[p.relpath]
+            relpath, worktree, gitdir, objdir, _ = self.GetProjectPaths(name, dest_path)
+            p.UpdatePaths(relpath, worktree, gitdir, objdir)
+            self._paths[p.relpath] = p
 
+      if node.nodeName == 'repo-hooks':
         # Only one project can be the hooks project
-        if self._repo_hooks_project is not None:
+        if repo_hooks_project is not None:
           raise ManifestParseError(
               'duplicate repo-hooks in %s' %
               (self.manifestFile))
 
-        # Store a reference to the Project.
-        try:
-          repo_hooks_projects = self._projects[repo_hooks_project]
-        except KeyError:
-          raise ManifestParseError(
-              'project %s not found for repo-hooks' %
-              (repo_hooks_project))
-
-        if len(repo_hooks_projects) != 1:
+        # Get the name of the project and the (space-separated) list of enabled.
+        repo_hooks_project = self._reqatt(node, 'in-project')
+        enabled_repo_hooks = self._ParseList(self._reqatt(node, 'enabled-list'))
+      if node.nodeName == 'superproject':
+        name = self._reqatt(node, 'name')
+        # There can only be one superproject.
+        if self._superproject.get('name'):
           raise ManifestParseError(
-              'internal error parsing repo-hooks in %s' %
+              'duplicate superproject in %s' %
               (self.manifestFile))
-        self._repo_hooks_project = repo_hooks_projects[0]
+        self._superproject['name'] = name
+        remote_name = node.getAttribute('remote')
+        if not remote_name:
+          remote = self._default.remote
+        else:
+          remote = self._get_remote(node)
+        if remote is None:
+          raise ManifestParseError("no remote for superproject %s within %s" %
+                                   (name, self.manifestFile))
+        self._superproject['remote'] = remote.ToRemoteSpec(name)
+        revision = node.getAttribute('revision') or remote.revision
+        if not revision:
+          revision = self._default.revisionExpr
+        if not revision:
+          raise ManifestParseError('no revision for superproject %s within %s' %
+                                   (name, self.manifestFile))
+        self._superproject['revision'] = revision
+      if node.nodeName == 'contactinfo':
+        bugurl = self._reqatt(node, 'bugurl')
+        # This element can be repeated, later entries will clobber earlier ones.
+        self._contactinfo = ContactInfo(bugurl)
 
-        # Store the enabled hooks in the Project object.
-        self._repo_hooks_project.enabled_repo_hooks = enabled_repo_hooks
       if node.nodeName == 'remove-project':
         name = self._reqatt(node, 'name')
 
-        if name not in self._projects:
+        if name in self._projects:
+          for p in self._projects[name]:
+            del self._paths[p.relpath]
+          del self._projects[name]
+
+          # If the manifest removes the hooks project, treat it as if it deleted
+          # the repo-hooks element too.
+          if repo_hooks_project == name:
+            repo_hooks_project = None
+        elif not XmlBool(node, 'optional', False):
           raise ManifestParseError('remove-project element specifies non-existent '
                                    'project: %s' % name)
 
-        for p in self._projects[name]:
-          del self._paths[p.relpath]
-        del self._projects[name]
-
-        # If the manifest removes the hooks project, treat it as if it deleted
-        # the repo-hooks element too.
-        if self._repo_hooks_project and (self._repo_hooks_project.name == name):
-          self._repo_hooks_project = None
+    # Store repo hooks project information.
+    if repo_hooks_project:
+      # Store a reference to the Project.
+      try:
+        repo_hooks_projects = self._projects[repo_hooks_project]
+      except KeyError:
+        raise ManifestParseError(
+            'project %s not found for repo-hooks' %
+            (repo_hooks_project))
 
+      if len(repo_hooks_projects) != 1:
+        raise ManifestParseError(
+            'internal error parsing repo-hooks in %s' %
+            (self.manifestFile))
+      self._repo_hooks_project = repo_hooks_projects[0]
+      # Store the enabled hooks in the Project object.
+      self._repo_hooks_project.enabled_repo_hooks = enabled_repo_hooks
 
   def _AddMetaProjectMirror(self, m):
     name = None
@@ -676,15 +997,15 @@ class XmlManifest(object):
     if name not in self._projects:
       m.PreSync()
       gitdir = os.path.join(self.topdir, '%s.git' % name)
-      project = Project(manifest = self,
-                        name = name,
-                        remote = remote.ToRemoteSpec(name),
-                        gitdir = gitdir,
-                        objdir = gitdir,
-                        worktree = None,
-                        relpath = name or None,
-                        revisionExpr = m.revisionExpr,
-                        revisionId = None)
+      project = Project(manifest=self,
+                        name=name,
+                        remote=remote.ToRemoteSpec(name),
+                        gitdir=gitdir,
+                        objdir=gitdir,
+                        worktree=None,
+                        relpath=name or None,
+                        revisionExpr=m.revisionExpr,
+                        revisionId=None)
       self._projects[project.name] = [project]
       self._paths[project.relpath] = project
 
@@ -707,7 +1028,14 @@ class XmlManifest(object):
     if revision == '':
       revision = None
     manifestUrl = self.manifestProject.config.GetString('remote.origin.url')
-    return _XmlRemote(name, alias, fetch, pushUrl, manifestUrl, review, revision)
+
+    remote = _XmlRemote(name, alias, fetch, pushUrl, manifestUrl, review, revision)
+
+    for n in node.childNodes:
+      if n.nodeName == 'annotation':
+        self._ParseAnnotation(remote, n)
+
+    return remote
 
   def _ParseDefault(self, node):
     """
@@ -722,29 +1050,14 @@ class XmlManifest(object):
     d.destBranchExpr = node.getAttribute('dest-branch') or None
     d.upstreamExpr = node.getAttribute('upstream') or None
 
-    sync_j = node.getAttribute('sync-j')
-    if sync_j == '' or sync_j is None:
-      d.sync_j = 1
-    else:
-      d.sync_j = int(sync_j)
-
-    sync_c = node.getAttribute('sync-c')
-    if not sync_c:
-      d.sync_c = False
-    else:
-      d.sync_c = sync_c.lower() in ("yes", "true", "1")
+    d.sync_j = XmlInt(node, 'sync-j', 1)
+    if d.sync_j <= 0:
+      raise ManifestParseError('%s: sync-j must be greater than 0, not "%s"' %
+                               (self.manifestFile, d.sync_j))
 
-    sync_s = node.getAttribute('sync-s')
-    if not sync_s:
-      d.sync_s = False
-    else:
-      d.sync_s = sync_s.lower() in ("yes", "true", "1")
-
-    sync_tags = node.getAttribute('sync-tags')
-    if not sync_tags:
-      d.sync_tags = True
-    else:
-      d.sync_tags = sync_tags.lower() in ("yes", "true", "1")
+    d.sync_c = XmlBool(node, 'sync-c', False)
+    d.sync_s = XmlBool(node, 'sync-s', False)
+    d.sync_tags = XmlBool(node, 'sync-tags', True)
     return d
 
   def _ParseNotice(self, node):
@@ -792,11 +1105,15 @@ class XmlManifest(object):
   def _UnjoinName(self, parent_name, name):
     return os.path.relpath(name, parent_name)
 
-  def _ParseProject(self, node, parent = None, **extra_proj_attrs):
+  def _ParseProject(self, node, parent=None, **extra_proj_attrs):
     """
     reads a <project> element from the manifest file
     """
     name = self._reqatt(node, 'name')
+    msg = self._CheckLocalPath(name, dir_ok=True)
+    if msg:
+      raise ManifestInvalidPathError(
+          '<project> invalid "name": %s: %s' % (name, msg))
     if parent:
       name = self._JoinName(parent.name, name)
 
@@ -805,55 +1122,34 @@ class XmlManifest(object):
       remote = self._default.remote
     if remote is None:
       raise ManifestParseError("no remote for project %s within %s" %
-            (name, self.manifestFile))
+                               (name, self.manifestFile))
 
     revisionExpr = node.getAttribute('revision') or remote.revision
     if not revisionExpr:
       revisionExpr = self._default.revisionExpr
     if not revisionExpr:
       raise ManifestParseError("no revision for project %s within %s" %
-            (name, self.manifestFile))
+                               (name, self.manifestFile))
 
     path = node.getAttribute('path')
     if not path:
       path = name
-    if path.startswith('/'):
-      raise ManifestParseError("project %s path cannot be absolute in %s" %
-            (name, self.manifestFile))
-
-    rebase = node.getAttribute('rebase')
-    if not rebase:
-      rebase = True
     else:
-      rebase = rebase.lower() in ("yes", "true", "1")
-
-    sync_c = node.getAttribute('sync-c')
-    if not sync_c:
-      sync_c = False
-    else:
-      sync_c = sync_c.lower() in ("yes", "true", "1")
-
-    sync_s = node.getAttribute('sync-s')
-    if not sync_s:
-      sync_s = self._default.sync_s
-    else:
-      sync_s = sync_s.lower() in ("yes", "true", "1")
-
-    sync_tags = node.getAttribute('sync-tags')
-    if not sync_tags:
-      sync_tags = self._default.sync_tags
-    else:
-      sync_tags = sync_tags.lower() in ("yes", "true", "1")
-
-    clone_depth = node.getAttribute('clone-depth')
-    if clone_depth:
-      try:
-        clone_depth = int(clone_depth)
-        if  clone_depth <= 0:
-          raise ValueError()
-      except ValueError:
-        raise ManifestParseError('invalid clone-depth %s in %s' %
-                                 (clone_depth, self.manifestFile))
+      # NB: The "." project is handled specially in Project.Sync_LocalHalf.
+      msg = self._CheckLocalPath(path, dir_ok=True, cwd_dot_ok=True)
+      if msg:
+        raise ManifestInvalidPathError(
+            '<project> invalid "path": %s: %s' % (path, msg))
+
+    rebase = XmlBool(node, 'rebase', True)
+    sync_c = XmlBool(node, 'sync-c', False)
+    sync_s = XmlBool(node, 'sync-s', self._default.sync_s)
+    sync_tags = XmlBool(node, 'sync-tags', self._default.sync_tags)
+
+    clone_depth = XmlInt(node, 'clone-depth')
+    if clone_depth is not None and clone_depth <= 0:
+      raise ManifestParseError('%s: clone-depth must be greater than 0, not "%s"' %
+                               (self.manifestFile, clone_depth))
 
     dest_branch = node.getAttribute('dest-branch') or self._default.destBranchExpr
 
@@ -862,11 +1158,13 @@ class XmlManifest(object):
     groups = ''
     if node.hasAttribute('groups'):
       groups = node.getAttribute('groups')
-    groups = self._ParseGroups(groups)
+    groups = self._ParseList(groups)
 
     if parent is None:
-      relpath, worktree, gitdir, objdir = self.GetProjectPaths(name, path)
+      relpath, worktree, gitdir, objdir, use_git_worktrees = \
+          self.GetProjectPaths(name, path)
     else:
+      use_git_worktrees = False
       relpath, worktree, gitdir, objdir = \
           self.GetSubprojectPaths(parent, name, path)
 
@@ -874,27 +1172,28 @@ class XmlManifest(object):
     groups.extend(set(default_groups).difference(groups))
 
     if self.IsMirror and node.hasAttribute('force-path'):
-      if node.getAttribute('force-path').lower() in ("yes", "true", "1"):
+      if XmlBool(node, 'force-path', False):
         gitdir = os.path.join(self.topdir, '%s.git' % path)
 
-    project = Project(manifest = self,
-                      name = name,
-                      remote = remote.ToRemoteSpec(name),
-                      gitdir = gitdir,
-                      objdir = objdir,
-                      worktree = worktree,
-                      relpath = relpath,
-                      revisionExpr = revisionExpr,
-                      revisionId = None,
-                      rebase = rebase,
-                      groups = groups,
-                      sync_c = sync_c,
-                      sync_s = sync_s,
-                      sync_tags = sync_tags,
-                      clone_depth = clone_depth,
-                      upstream = upstream,
-                      parent = parent,
-                      dest_branch = dest_branch,
+    project = Project(manifest=self,
+                      name=name,
+                      remote=remote.ToRemoteSpec(name),
+                      gitdir=gitdir,
+                      objdir=objdir,
+                      worktree=worktree,
+                      relpath=relpath,
+                      revisionExpr=revisionExpr,
+                      revisionId=None,
+                      rebase=rebase,
+                      groups=groups,
+                      sync_c=sync_c,
+                      sync_s=sync_s,
+                      sync_tags=sync_tags,
+                      clone_depth=clone_depth,
+                      upstream=upstream,
+                      parent=parent,
+                      dest_branch=dest_branch,
+                      use_git_worktrees=use_git_worktrees,
                       **extra_proj_attrs)
 
     for n in node.childNodes:
@@ -905,11 +1204,16 @@ class XmlManifest(object):
       if n.nodeName == 'annotation':
         self._ParseAnnotation(project, n)
       if n.nodeName == 'project':
-        project.subprojects.append(self._ParseProject(n, parent = project))
+        project.subprojects.append(self._ParseProject(n, parent=project))
 
     return project
 
   def GetProjectPaths(self, name, path):
+    # The manifest entries might have trailing slashes.  Normalize them to avoid
+    # unexpected filesystem behavior since we do string concatenation below.
+    path = path.rstrip('/')
+    name = name.rstrip('/')
+    use_git_worktrees = False
     relpath = path
     if self.IsMirror:
       worktree = None
@@ -918,8 +1222,15 @@ class XmlManifest(object):
     else:
       worktree = os.path.join(self.topdir, path).replace('\\', '/')
       gitdir = os.path.join(self.repodir, 'projects', '%s.git' % path)
-      objdir = os.path.join(self.repodir, 'project-objects', '%s.git' % name)
-    return relpath, worktree, gitdir, objdir
+      # We allow people to mix git worktrees & non-git worktrees for now.
+      # This allows for in situ migration of repo clients.
+      if os.path.exists(gitdir) or not self.UseGitWorktrees:
+        objdir = os.path.join(self.repodir, 'project-objects', '%s.git' % name)
+      else:
+        use_git_worktrees = True
+        gitdir = os.path.join(self.repodir, 'worktrees', '%s.git' % name)
+        objdir = gitdir
+    return relpath, worktree, gitdir, objdir, use_git_worktrees
 
   def GetProjectsWithName(self, name):
     return self._projects.get(name, [])
@@ -934,6 +1245,10 @@ class XmlManifest(object):
     return os.path.relpath(relpath, parent_relpath)
 
   def GetSubprojectPaths(self, parent, name, path):
+    # The manifest entries might have trailing slashes.  Normalize them to avoid
+    # unexpected filesystem behavior since we do string concatenation below.
+    path = path.rstrip('/')
+    name = name.rstrip('/')
     relpath = self._JoinRelpath(parent.relpath, path)
     gitdir = os.path.join(parent.gitdir, 'subprojects', '%s.git' % path)
     objdir = os.path.join(parent.gitdir, 'subproject-objects', '%s.git' % name)
@@ -943,23 +1258,151 @@ class XmlManifest(object):
       worktree = os.path.join(parent.worktree, path).replace('\\', '/')
     return relpath, worktree, gitdir, objdir
 
+  @staticmethod
+  def _CheckLocalPath(path, dir_ok=False, cwd_dot_ok=False):
+    """Verify |path| is reasonable for use in filesystem paths.
+
+    Used with <copyfile> & <linkfile> & <project> elements.
+
+    This only validates the |path| in isolation: it does not check against the
+    current filesystem state.  Thus it is suitable as a first-past in a parser.
+
+    It enforces a number of constraints:
+    * No empty paths.
+    * No "~" in paths.
+    * No Unicode codepoints that filesystems might elide when normalizing.
+    * No relative path components like "." or "..".
+    * No absolute paths.
+    * No ".git" or ".repo*" path components.
+
+    Args:
+      path: The path name to validate.
+      dir_ok: Whether |path| may force a directory (e.g. end in a /).
+      cwd_dot_ok: Whether |path| may be just ".".
+
+    Returns:
+      None if |path| is OK, a failure message otherwise.
+    """
+    if not path:
+      return 'empty paths not allowed'
+
+    if '~' in path:
+      return '~ not allowed (due to 8.3 filenames on Windows filesystems)'
+
+    path_codepoints = set(path)
+
+    # Some filesystems (like Apple's HFS+) try to normalize Unicode codepoints
+    # which means there are alternative names for ".git".  Reject paths with
+    # these in it as there shouldn't be any reasonable need for them here.
+    # The set of codepoints here was cribbed from jgit's implementation:
+    # https://eclipse.googlesource.com/jgit/jgit/+/9110037e3e9461ff4dac22fee84ef3694ed57648/org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectChecker.java#884
+    BAD_CODEPOINTS = {
+        u'\u200C',  # ZERO WIDTH NON-JOINER
+        u'\u200D',  # ZERO WIDTH JOINER
+        u'\u200E',  # LEFT-TO-RIGHT MARK
+        u'\u200F',  # RIGHT-TO-LEFT MARK
+        u'\u202A',  # LEFT-TO-RIGHT EMBEDDING
+        u'\u202B',  # RIGHT-TO-LEFT EMBEDDING
+        u'\u202C',  # POP DIRECTIONAL FORMATTING
+        u'\u202D',  # LEFT-TO-RIGHT OVERRIDE
+        u'\u202E',  # RIGHT-TO-LEFT OVERRIDE
+        u'\u206A',  # INHIBIT SYMMETRIC SWAPPING
+        u'\u206B',  # ACTIVATE SYMMETRIC SWAPPING
+        u'\u206C',  # INHIBIT ARABIC FORM SHAPING
+        u'\u206D',  # ACTIVATE ARABIC FORM SHAPING
+        u'\u206E',  # NATIONAL DIGIT SHAPES
+        u'\u206F',  # NOMINAL DIGIT SHAPES
+        u'\uFEFF',  # ZERO WIDTH NO-BREAK SPACE
+    }
+    if BAD_CODEPOINTS & path_codepoints:
+      # This message is more expansive than reality, but should be fine.
+      return 'Unicode combining characters not allowed'
+
+    # Reject newlines as there shouldn't be any legitmate use for them, they'll
+    # be confusing to users, and they can easily break tools that expect to be
+    # able to iterate over newline delimited lists.  This even applies to our
+    # own code like .repo/project.list.
+    if {'\r', '\n'} & path_codepoints:
+      return 'Newlines not allowed'
+
+    # Assume paths might be used on case-insensitive filesystems.
+    path = path.lower()
+
+    # Split up the path by its components.  We can't use os.path.sep exclusively
+    # as some platforms (like Windows) will convert / to \ and that bypasses all
+    # our constructed logic here.  Especially since manifest authors only use
+    # / in their paths.
+    resep = re.compile(r'[/%s]' % re.escape(os.path.sep))
+    # Strip off trailing slashes as those only produce '' elements, and we use
+    # parts to look for individual bad components.
+    parts = resep.split(path.rstrip('/'))
+
+    # Some people use src="." to create stable links to projects.  Lets allow
+    # that but reject all other uses of "." to keep things simple.
+    if not cwd_dot_ok or parts != ['.']:
+      for part in set(parts):
+        if part in {'.', '..', '.git'} or part.startswith('.repo'):
+          return 'bad component: %s' % (part,)
+
+    if not dir_ok and resep.match(path[-1]):
+      return 'dirs not allowed'
+
+    # NB: The two abspath checks here are to handle platforms with multiple
+    # filesystem path styles (e.g. Windows).
+    norm = os.path.normpath(path)
+    if (norm == '..' or
+        (len(norm) >= 3 and norm.startswith('..') and resep.match(norm[0])) or
+        os.path.isabs(norm) or
+        norm.startswith('/')):
+      return 'path cannot be outside'
+
+  @classmethod
+  def _ValidateFilePaths(cls, element, src, dest):
+    """Verify |src| & |dest| are reasonable for <copyfile> & <linkfile>.
+
+    We verify the path independent of any filesystem state as we won't have a
+    checkout available to compare to.  i.e. This is for parsing validation
+    purposes only.
+
+    We'll do full/live sanity checking before we do the actual filesystem
+    modifications in _CopyFile/_LinkFile/etc...
+    """
+    # |dest| is the file we write to or symlink we create.
+    # It is relative to the top of the repo client checkout.
+    msg = cls._CheckLocalPath(dest)
+    if msg:
+      raise ManifestInvalidPathError(
+          '<%s> invalid "dest": %s: %s' % (element, dest, msg))
+
+    # |src| is the file we read from or path we point to for symlinks.
+    # It is relative to the top of the git project checkout.
+    is_linkfile = element == 'linkfile'
+    msg = cls._CheckLocalPath(src, dir_ok=is_linkfile, cwd_dot_ok=is_linkfile)
+    if msg:
+      raise ManifestInvalidPathError(
+          '<%s> invalid "src": %s: %s' % (element, src, msg))
+
   def _ParseCopyFile(self, project, node):
     src = self._reqatt(node, 'src')
     dest = self._reqatt(node, 'dest')
     if not self.IsMirror:
       # src is project relative;
-      # dest is relative to the top of the tree
-      project.AddCopyFile(src, dest, os.path.join(self.topdir, dest))
+      # dest is relative to the top of the tree.
+      # We only validate paths if we actually plan to process them.
+      self._ValidateFilePaths('copyfile', src, dest)
+      project.AddCopyFile(src, dest, self.topdir)
 
   def _ParseLinkFile(self, project, node):
     src = self._reqatt(node, 'src')
     dest = self._reqatt(node, 'dest')
     if not self.IsMirror:
       # src is project relative;
-      # dest is relative to the top of the tree
-      project.AddLinkFile(src, dest, os.path.join(self.topdir, dest))
+      # dest is relative to the top of the tree.
+      # We only validate paths if we actually plan to process them.
+      self._ValidateFilePaths('linkfile', src, dest)
+      project.AddLinkFile(src, dest, self.topdir)
 
-  def _ParseAnnotation(self, project, node):
+  def _ParseAnnotation(self, element, node):
     name = self._reqatt(node, 'name')
     value = self._reqatt(node, 'value')
     try:
@@ -968,8 +1411,8 @@ class XmlManifest(object):
       keep = "true"
     if keep != "true" and keep != "false":
       raise ManifestParseError('optional "keep" attribute must be '
-            '"true" or "false"')
-    project.AddAnnotation(name, value, keep)
+                               '"true" or "false"')
+    element.AddAnnotation(name, value, keep)
 
   def _get_remote(self, node):
     name = node.getAttribute('remote')
@@ -979,7 +1422,7 @@ class XmlManifest(object):
     v = self._remotes.get(name)
     if not v:
       raise ManifestParseError("remote %s not defined in %s" %
-            (name, self.manifestFile))
+                               (name, self.manifestFile))
     return v
 
   def _reqatt(self, node, attname):
@@ -989,7 +1432,7 @@ class XmlManifest(object):
     v = node.getAttribute(attname)
     if not v:
       raise ManifestParseError("no %s in <%s> within %s" %
-            (attname, node.nodeName, self.manifestFile))
+                               (attname, node.nodeName, self.manifestFile))
     return v
 
   def projectsDiff(self, manifest):
@@ -1007,7 +1450,7 @@ class XmlManifest(object):
     diff = {'added': [], 'removed': [], 'changed': [], 'unreachable': []}
 
     for proj in fromKeys:
-      if not proj in toKeys:
+      if proj not in toKeys:
         diff['removed'].append(fromProjects[proj])
       else:
         fromProj = fromProjects[proj]
@@ -1029,19 +1472,11 @@ class XmlManifest(object):
 
 
 class GitcManifest(XmlManifest):
+  """Parser for GitC (git-in-the-cloud) manifests."""
 
-  def __init__(self, repodir, gitc_client_name):
-    """Initialize the GitcManifest object."""
-    super(GitcManifest, self).__init__(repodir)
-    self.isGitcClient = True
-    self.gitc_client_name = gitc_client_name
-    self.gitc_client_dir = os.path.join(gitc_utils.get_gitc_manifest_dir(),
-                                        gitc_client_name)
-    self.manifestFile = os.path.join(self.gitc_client_dir, '.manifest')
-
-  def _ParseProject(self, node, parent = None):
+  def _ParseProject(self, node, parent=None):
     """Override _ParseProject and add support for GITC specific attributes."""
-    return super(GitcManifest, self)._ParseProject(
+    return super()._ParseProject(
         node, parent=parent, old_revision=node.getAttribute('old-revision'))
 
   def _output_manifest_project_extras(self, p, e):
@@ -1049,3 +1484,36 @@ class GitcManifest(XmlManifest):
     if p.old_revision:
       e.setAttribute('old-revision', str(p.old_revision))
 
+
+class RepoClient(XmlManifest):
+  """Manages a repo client checkout."""
+
+  def __init__(self, repodir, manifest_file=None):
+    self.isGitcClient = False
+
+    if os.path.exists(os.path.join(repodir, LOCAL_MANIFEST_NAME)):
+      print('error: %s is not supported; put local manifests in `%s` instead' %
+            (LOCAL_MANIFEST_NAME, os.path.join(repodir, LOCAL_MANIFESTS_DIR_NAME)),
+            file=sys.stderr)
+      sys.exit(1)
+
+    if manifest_file is None:
+      manifest_file = os.path.join(repodir, MANIFEST_FILE_NAME)
+    local_manifests = os.path.abspath(os.path.join(repodir, LOCAL_MANIFESTS_DIR_NAME))
+    super().__init__(repodir, manifest_file, local_manifests)
+
+    # TODO: Completely separate manifest logic out of the client.
+    self.manifest = self
+
+
+class GitcClient(RepoClient, GitcManifest):
+  """Manages a GitC client checkout."""
+
+  def __init__(self, repodir, gitc_client_name):
+    """Initialize the GitcManifest object."""
+    self.gitc_client_name = gitc_client_name
+    self.gitc_client_dir = os.path.join(gitc_utils.get_gitc_manifest_dir(),
+                                        gitc_client_name)
+
+    super().__init__(repodir, os.path.join(self.gitc_client_dir, '.manifest'))
+    self.isGitcClient = True
diff --git a/pager.py b/pager.py
index 221baf3c..352923d9 100644
--- a/pager.py
+++ b/pager.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import os
 import select
 import subprocess
@@ -27,6 +24,7 @@ pager_process = None
 old_stdout = None
 old_stderr = None
 
+
 def RunPager(globalConfig):
   if not os.isatty(0) or not os.isatty(1):
     return
@@ -35,33 +33,37 @@ def RunPager(globalConfig):
     return
 
   if platform_utils.isWindows():
-    _PipePager(pager);
+    _PipePager(pager)
   else:
     _ForkPager(pager)
 
+
 def TerminatePager():
   global pager_process, old_stdout, old_stderr
   if pager_process:
     sys.stdout.flush()
     sys.stderr.flush()
     pager_process.stdin.close()
-    pager_process.wait();
+    pager_process.wait()
     pager_process = None
     # Restore initial stdout/err in case there is more output in this process
     # after shutting down the pager process
     sys.stdout = old_stdout
     sys.stderr = old_stderr
 
+
 def _PipePager(pager):
   global pager_process, old_stdout, old_stderr
   assert pager_process is None, "Only one active pager process at a time"
   # Create pager process, piping stdout/err into its stdin
-  pager_process = subprocess.Popen([pager], stdin=subprocess.PIPE, stdout=sys.stdout, stderr=sys.stderr)
+  pager_process = subprocess.Popen([pager], stdin=subprocess.PIPE, stdout=sys.stdout,
+                                   stderr=sys.stderr)
   old_stdout = sys.stdout
   old_stderr = sys.stderr
   sys.stdout = pager_process.stdin
   sys.stderr = pager_process.stdin
 
+
 def _ForkPager(pager):
   global active
   # This process turns into the pager; a child it forks will
@@ -88,6 +90,7 @@ def _ForkPager(pager):
     print("fatal: cannot start pager '%s'" % pager, file=sys.stderr)
     sys.exit(255)
 
+
 def _SelectPager(globalConfig):
   try:
     return os.environ['GIT_PAGER']
@@ -105,6 +108,7 @@ def _SelectPager(globalConfig):
 
   return 'less'
 
+
 def _BecomePager(pager):
   # Delaying execution of the pager until we have output
   # ready works around a long-standing bug in popularly
diff --git a/platform_utils.py b/platform_utils.py
index 06ef9b18..0203249a 100644
--- a/platform_utils.py
+++ b/platform_utils.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2016 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -17,18 +15,9 @@
 import errno
 import os
 import platform
-import select
 import shutil
 import stat
 
-from pyversion import is_python3
-if is_python3():
-  from queue import Queue
-else:
-  from Queue import Queue
-
-from threading import Thread
-
 
 def isWindows():
   """ Returns True when running with the native port of Python for Windows,
@@ -39,145 +28,6 @@ def isWindows():
   return platform.system() == "Windows"
 
 
-class FileDescriptorStreams(object):
-  """ Platform agnostic abstraction enabling non-blocking I/O over a
-  collection of file descriptors. This abstraction is required because
-  fctnl(os.O_NONBLOCK) is not supported on Windows.
-  """
-  @classmethod
-  def create(cls):
-    """ Factory method: instantiates the concrete class according to the
-    current platform.
-    """
-    if isWindows():
-      return _FileDescriptorStreamsThreads()
-    else:
-      return _FileDescriptorStreamsNonBlocking()
-
-  def __init__(self):
-    self.streams = []
-
-  def add(self, fd, dest, std_name):
-    """ Wraps an existing file descriptor as a stream.
-    """
-    self.streams.append(self._create_stream(fd, dest, std_name))
-
-  def remove(self, stream):
-    """ Removes a stream, when done with it.
-    """
-    self.streams.remove(stream)
-
-  @property
-  def is_done(self):
-    """ Returns True when all streams have been processed.
-    """
-    return len(self.streams) == 0
-
-  def select(self):
-    """ Returns the set of streams that have data available to read.
-    The returned streams each expose a read() and a close() method.
-    When done with a stream, call the remove(stream) method.
-    """
-    raise NotImplementedError
-
-  def _create_stream(self, fd, dest, std_name):
-    """ Creates a new stream wrapping an existing file descriptor.
-    """
-    raise NotImplementedError
-
-
-class _FileDescriptorStreamsNonBlocking(FileDescriptorStreams):
-  """ Implementation of FileDescriptorStreams for platforms that support
-  non blocking I/O.
-  """
-  class Stream(object):
-    """ Encapsulates a file descriptor """
-    def __init__(self, fd, dest, std_name):
-      self.fd = fd
-      self.dest = dest
-      self.std_name = std_name
-      self.set_non_blocking()
-
-    def set_non_blocking(self):
-      import fcntl
-      flags = fcntl.fcntl(self.fd, fcntl.F_GETFL)
-      fcntl.fcntl(self.fd, fcntl.F_SETFL, flags | os.O_NONBLOCK)
-
-    def fileno(self):
-      return self.fd.fileno()
-
-    def read(self):
-      return self.fd.read(4096)
-
-    def close(self):
-      self.fd.close()
-
-  def _create_stream(self, fd, dest, std_name):
-    return self.Stream(fd, dest, std_name)
-
-  def select(self):
-    ready_streams, _, _ = select.select(self.streams, [], [])
-    return ready_streams
-
-
-class _FileDescriptorStreamsThreads(FileDescriptorStreams):
-  """ Implementation of FileDescriptorStreams for platforms that don't support
-  non blocking I/O. This implementation requires creating threads issuing
-  blocking read operations on file descriptors.
-  """
-  def __init__(self):
-    super(_FileDescriptorStreamsThreads, self).__init__()
-    # The queue is shared accross all threads so we can simulate the
-    # behavior of the select() function
-    self.queue = Queue(10)  # Limit incoming data from streams
-
-  def _create_stream(self, fd, dest, std_name):
-    return self.Stream(fd, dest, std_name, self.queue)
-
-  def select(self):
-    # Return only one stream at a time, as it is the most straighforward
-    # thing to do and it is compatible with the select() function.
-    item = self.queue.get()
-    stream = item.stream
-    stream.data = item.data
-    return [stream]
-
-  class QueueItem(object):
-    """ Item put in the shared queue """
-    def __init__(self, stream, data):
-      self.stream = stream
-      self.data = data
-
-  class Stream(object):
-    """ Encapsulates a file descriptor """
-    def __init__(self, fd, dest, std_name, queue):
-      self.fd = fd
-      self.dest = dest
-      self.std_name = std_name
-      self.queue = queue
-      self.data = None
-      self.thread = Thread(target=self.read_to_queue)
-      self.thread.daemon = True
-      self.thread.start()
-
-    def close(self):
-      self.fd.close()
-
-    def read(self):
-      data = self.data
-      self.data = None
-      return data
-
-    def read_to_queue(self):
-      """ The thread function: reads everything from the file descriptor into
-      the shared queue and terminates when reaching EOF.
-      """
-      for line in iter(self.fd.readline, b''):
-        self.queue.put(_FileDescriptorStreamsThreads.QueueItem(self, line))
-      self.fd.close()
-      self.queue.put(_FileDescriptorStreamsThreads.QueueItem(self, None))
-
-
 def symlink(source, link_name):
   """Creates a symbolic link pointing to source named link_name.
   Note: On Windows, source must exist on disk, as the implementation needs
@@ -274,31 +124,30 @@ def rename(src, dst):
       else:
         raise
   else:
-    os.rename(src, dst)
+    shutil.move(src, dst)
 
 
-def remove(path):
+def remove(path, missing_ok=False):
   """Remove (delete) the file path. This is a replacement for os.remove that
   allows deleting read-only files on Windows, with support for long paths and
   for deleting directory symbolic links.
 
   Availability: Unix, Windows."""
-  if isWindows():
-    longpath = _makelongpath(path)
-    try:
-      os.remove(longpath)
-    except OSError as e:
-      if e.errno == errno.EACCES:
-        os.chmod(longpath, stat.S_IWRITE)
-        # Directory symbolic links must be deleted with 'rmdir'.
-        if islink(longpath) and isdir(longpath):
-          os.rmdir(longpath)
-        else:
-          os.remove(longpath)
+  longpath = _makelongpath(path) if isWindows() else path
+  try:
+    os.remove(longpath)
+  except OSError as e:
+    if e.errno == errno.EACCES:
+      os.chmod(longpath, stat.S_IWRITE)
+      # Directory symbolic links must be deleted with 'rmdir'.
+      if islink(longpath) and isdir(longpath):
+        os.rmdir(longpath)
       else:
-        raise
-  else:
-    os.remove(path)
+        os.remove(longpath)
+    elif missing_ok and e.errno == errno.ENOENT:
+      pass
+    else:
+      raise
 
 
 def walk(top, topdown=True, onerror=None, followlinks=False):
diff --git a/platform_utils_win32.py b/platform_utils_win32.py
index e20755a4..bf916d47 100644
--- a/platform_utils_win32.py
+++ b/platform_utils_win32.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2016 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,16 +14,13 @@
 
 import errno
 
-from pyversion import is_python3
 from ctypes import WinDLL, get_last_error, FormatError, WinError, addressof
-from ctypes import c_buffer
-from ctypes.wintypes import BOOL, BOOLEAN, LPCWSTR, DWORD, HANDLE, POINTER, c_ubyte
-from ctypes.wintypes import WCHAR, USHORT, LPVOID, Structure, Union, ULONG
-from ctypes.wintypes import byref
+from ctypes import c_buffer, c_ubyte, Structure, Union, byref
+from ctypes.wintypes import BOOL, BOOLEAN, LPCWSTR, DWORD, HANDLE
+from ctypes.wintypes import WCHAR, USHORT, LPVOID, ULONG, LPDWORD
 
 kernel32 = WinDLL('kernel32', use_last_error=True)
 
-LPDWORD = POINTER(DWORD)
 UCHAR = c_ubyte
 
 # Win32 error codes
@@ -147,7 +142,8 @@ def create_dirsymlink(source, link_name):
 
 
 def _create_symlink(source, link_name, dwFlags):
-  if not CreateSymbolicLinkW(link_name, source, dwFlags | SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE):
+  if not CreateSymbolicLinkW(link_name, source,
+                             dwFlags | SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE):
     # See https://github.com/golang/go/pull/24307/files#diff-b87bc12e4da2497308f9ef746086e4f0
     # "the unprivileged create flag is unsupported below Windows 10 (1703, v10.0.14972).
     # retry without it."
@@ -198,26 +194,15 @@ def readlink(path):
         'Error reading symbolic link \"%s\"'.format(path))
   rdb = REPARSE_DATA_BUFFER.from_buffer(target_buffer)
   if rdb.ReparseTag == IO_REPARSE_TAG_SYMLINK:
-    return _preserve_encoding(path, rdb.SymbolicLinkReparseBuffer.PrintName)
+    return rdb.SymbolicLinkReparseBuffer.PrintName
   elif rdb.ReparseTag == IO_REPARSE_TAG_MOUNT_POINT:
-    return _preserve_encoding(path, rdb.MountPointReparseBuffer.PrintName)
+    return rdb.MountPointReparseBuffer.PrintName
   # Unsupported reparse point type
   _raise_winerror(
       ERROR_NOT_SUPPORTED,
       'Error reading symbolic link \"%s\"'.format(path))
 
 
-def _preserve_encoding(source, target):
-  """Ensures target is the same string type (i.e. unicode or str) as source."""
-
-  if is_python3():
-    return target
-
-  if isinstance(source, unicode):
-    return unicode(target)
-  return str(target)
-
-
 def _raise_winerror(code, error_desc):
   win_error_desc = FormatError(code).strip()
   error_desc = "%s: %s".format(error_desc, win_error_desc)
diff --git a/progress.py b/progress.py
index d2ed4bae..43c7ad21 100644
--- a/progress.py
+++ b/progress.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2009 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -26,18 +24,53 @@ _NOT_TTY = not os.isatty(2)
 # column 0.
 CSI_ERASE_LINE = '\x1b[2K'
 
+
+def duration_str(total):
+  """A less noisy timedelta.__str__.
+
+  The default timedelta stringification contains a lot of leading zeros and
+  uses microsecond resolution.  This makes for noisy output.
+  """
+  hours, rem = divmod(total, 3600)
+  mins, secs = divmod(rem, 60)
+  ret = '%.3fs' % (secs,)
+  if mins:
+    ret = '%im%s' % (mins, ret)
+  if hours:
+    ret = '%ih%s' % (hours, ret)
+  return ret
+
+
 class Progress(object):
-  def __init__(self, title, total=0, units='', print_newline=False,
-               always_print_percentage=False):
+  def __init__(self, title, total=0, units='', print_newline=False, delay=True,
+               quiet=False):
     self._title = title
     self._total = total
     self._done = 0
-    self._lastp = -1
     self._start = time()
-    self._show = False
+    self._show = not delay
     self._units = units
     self._print_newline = print_newline
-    self._always_print_percentage = always_print_percentage
+    # Only show the active jobs section if we run more than one in parallel.
+    self._show_jobs = False
+    self._active = 0
+
+    # When quiet, never show any output.  It's a bit hacky, but reusing the
+    # existing logic that delays initial output keeps the rest of the class
+    # clean.  Basically we set the start time to years in the future.
+    if quiet:
+      self._show = False
+      self._start += 2**32
+
+  def start(self, name):
+    self._active += 1
+    if not self._show_jobs:
+      self._show_jobs = self._active > 1
+    self.update(inc=0, msg='started ' + name)
+
+  def finish(self, name):
+    self.update(msg='finished ' + name)
+    self._active -= 1
 
   def update(self, inc=1, msg=''):
     self._done += inc
@@ -53,41 +86,46 @@ class Progress(object):
 
     if self._total <= 0:
       sys.stderr.write('%s\r%s: %d,' % (
-        CSI_ERASE_LINE,
-        self._title,
-        self._done))
+          CSI_ERASE_LINE,
+          self._title,
+          self._done))
       sys.stderr.flush()
     else:
       p = (100 * self._done) / self._total
-
-      if self._lastp != p or self._always_print_percentage:
-        self._lastp = p
-        sys.stderr.write('%s\r%s: %3d%% (%d%s/%d%s)%s%s%s' % (
+      if self._show_jobs:
+        jobs = '[%d job%s] ' % (self._active, 's' if self._active > 1 else '')
+      else:
+        jobs = ''
+      sys.stderr.write('%s\r%s: %2d%% %s(%d%s/%d%s)%s%s%s' % (
           CSI_ERASE_LINE,
           self._title,
           p,
+          jobs,
           self._done, self._units,
           self._total, self._units,
           ' ' if msg else '', msg,
-          "\n" if self._print_newline else ""))
-        sys.stderr.flush()
+          '\n' if self._print_newline else ''))
+      sys.stderr.flush()
 
   def end(self):
     if _NOT_TTY or IsTrace() or not self._show:
       return
 
+    duration = duration_str(time() - self._start)
     if self._total <= 0:
-      sys.stderr.write('%s\r%s: %d, done.\n' % (
-        CSI_ERASE_LINE,
-        self._title,
-        self._done))
+      sys.stderr.write('%s\r%s: %d, done in %s\n' % (
+          CSI_ERASE_LINE,
+          self._title,
+          self._done,
+          duration))
       sys.stderr.flush()
     else:
       p = (100 * self._done) / self._total
-      sys.stderr.write('%s\r%s: %3d%% (%d%s/%d%s), done.\n' % (
-        CSI_ERASE_LINE,
-        self._title,
-        p,
-        self._done, self._units,
-        self._total, self._units))
+      sys.stderr.write('%s\r%s: %3d%% (%d%s/%d%s), done in %s\n' % (
+          CSI_ERASE_LINE,
+          self._title,
+          p,
+          self._done, self._units,
+          self._total, self._units,
+          duration))
       sys.stderr.flush()
diff --git a/project.py b/project.py
index 8fdacc65..5b26b64c 100644
--- a/project.py
+++ b/project.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,11 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import errno
 import filecmp
 import glob
-import json
 import os
 import random
 import re
@@ -29,36 +25,33 @@ import sys
 import tarfile
 import tempfile
 import time
-import traceback
+import urllib.parse
 
 from color import Coloring
 from git_command import GitCommand, git_require
 from git_config import GitConfig, IsId, GetSchemeFromUrl, GetUrlCookieFile, \
     ID_RE
-from error import GitError, HookError, UploadError, DownloadError
-from error import ManifestInvalidRevisionError
+from error import GitError, UploadError, DownloadError
+from error import ManifestInvalidRevisionError, ManifestInvalidPathError
 from error import NoManifestException
 import platform_utils
 import progress
 from repo_trace import IsTrace, Trace
 
-from git_refs import GitRefs, HEAD, R_HEADS, R_TAGS, R_PUB, R_M
+from git_refs import GitRefs, HEAD, R_HEADS, R_TAGS, R_PUB, R_M, R_WORKTREE_M
+
 
-from pyversion import is_python3
-if is_python3():
-  import urllib.parse
-else:
-  import imp
-  import urlparse
-  urllib = imp.new_module('urllib')
-  urllib.parse = urlparse
-  input = raw_input
+# Maximum sleep time allowed during retries.
+MAXIMUM_RETRY_SLEEP_SEC = 3600.0
+# +-10% random jitter is added to each Fetches retry sleep duration.
+RETRY_JITTER_PERCENT = 0.1
 
 
 def _lwrite(path, content):
   lock = '%s.lock' % path
 
-  with open(lock, 'w') as fd:
+  # Maintain Unix line endings on all OS's to match git behavior.
+  with open(lock, 'w', newline='\n') as fd:
     fd.write(content)
 
   try:
@@ -85,6 +78,7 @@ def not_rev(r):
 def sq(r):
   return "'" + r.replace("'", "'\''") + "'"
 
+
 _project_hook_list = None
 
 
@@ -197,18 +191,22 @@ class ReviewableBranch(object):
     return self._base_exists
 
   def UploadForReview(self, people,
+                      dryrun=False,
                       auto_topic=False,
-                      draft=False,
+                      hashtags=(),
+                      labels=(),
                       private=False,
                       notify=None,
                       wip=False,
                       dest_branch=None,
                       validate_certs=True,
                       push_options=None):
-    self.project.UploadForReview(self.name,
-                                 people,
+    self.project.UploadForReview(branch=self.name,
+                                 people=people,
+                                 dryrun=dryrun,
                                  auto_topic=auto_topic,
-                                 draft=draft,
+                                 hashtags=hashtags,
+                                 labels=labels,
                                  private=private,
                                  notify=notify,
                                  wip=wip,
@@ -234,7 +232,7 @@ class ReviewableBranch(object):
 class StatusColoring(Coloring):
 
   def __init__(self, config):
-    Coloring.__init__(self, config, 'status')
+    super().__init__(config, 'status')
     self.project = self.printer('header', attr='bold')
     self.branch = self.printer('header', attr='bold')
     self.nobranch = self.printer('nobranch', fg='red')
@@ -248,30 +246,104 @@ class StatusColoring(Coloring):
 class DiffColoring(Coloring):
 
   def __init__(self, config):
-    Coloring.__init__(self, config, 'diff')
+    super().__init__(config, 'diff')
     self.project = self.printer('header', attr='bold')
     self.fail = self.printer('fail', fg='red')
 
 
-class _Annotation(object):
+class Annotation(object):
 
   def __init__(self, name, value, keep):
     self.name = name
     self.value = value
     self.keep = keep
 
+  def __eq__(self, other):
+    if not isinstance(other, Annotation):
+      return False
+    return self.__dict__ == other.__dict__
+
+  def __lt__(self, other):
+    # This exists just so that lists of Annotation objects can be sorted, for
+    # use in comparisons.
+    if not isinstance(other, Annotation):
+      raise ValueError('comparison is not between two Annotation objects')
+    if self.name == other.name:
+      if self.value == other.value:
+        return self.keep < other.keep
+      return self.value < other.value
+    return self.name < other.name
+
+
+def _SafeExpandPath(base, subpath, skipfinal=False):
+  """Make sure |subpath| is completely safe under |base|.
+
+  We make sure no intermediate symlinks are traversed, and that the final path
+  is not a special file (e.g. not a socket or fifo).
+
+  NB: We rely on a number of paths already being filtered out while parsing the
+  manifest.  See the validation logic in manifest_xml.py for more details.
+  """
+  # Split up the path by its components.  We can't use os.path.sep exclusively
+  # as some platforms (like Windows) will convert / to \ and that bypasses all
+  # our constructed logic here.  Especially since manifest authors only use
+  # / in their paths.
+  resep = re.compile(r'[/%s]' % re.escape(os.path.sep))
+  components = resep.split(subpath)
+  if skipfinal:
+    # Whether the caller handles the final component itself.
+    finalpart = components.pop()
+
+  path = base
+  for part in components:
+    if part in {'.', '..'}:
+      raise ManifestInvalidPathError(
+          '%s: "%s" not allowed in paths' % (subpath, part))
+
+    path = os.path.join(path, part)
+    if platform_utils.islink(path):
+      raise ManifestInvalidPathError(
+          '%s: traversing symlinks not allow' % (path,))
+
+    if os.path.exists(path):
+      if not os.path.isfile(path) and not platform_utils.isdir(path):
+        raise ManifestInvalidPathError(
+            '%s: only regular files & directories allowed' % (path,))
+
+  if skipfinal:
+    path = os.path.join(path, finalpart)
+
+  return path
+
 
 class _CopyFile(object):
+  """Container for <copyfile> manifest element."""
+
+  def __init__(self, git_worktree, src, topdir, dest):
+    """Register a <copyfile> request.
 
-  def __init__(self, src, dest, abssrc, absdest):
+    Args:
+      git_worktree: Absolute path to the git project checkout.
+      src: Relative path under |git_worktree| of file to read.
+      topdir: Absolute path to the top of the repo client checkout.
+      dest: Relative path under |topdir| of file to write.
+    """
+    self.git_worktree = git_worktree
+    self.topdir = topdir
     self.src = src
     self.dest = dest
-    self.abs_src = abssrc
-    self.abs_dest = absdest
 
   def _Copy(self):
-    src = self.abs_src
-    dest = self.abs_dest
+    src = _SafeExpandPath(self.git_worktree, self.src)
+    dest = _SafeExpandPath(self.topdir, self.dest)
+
+    if platform_utils.isdir(src):
+      raise ManifestInvalidPathError(
+          '%s: copying from directory not supported' % (self.src,))
+    if platform_utils.isdir(dest):
+      raise ManifestInvalidPathError(
+          '%s: copying to directory not allowed' % (self.dest,))
+
     # copy file if it does not exist or is out of date
     if not os.path.exists(dest) or not filecmp.cmp(src, dest):
       try:
@@ -292,13 +364,21 @@ class _CopyFile(object):
 
 
 class _LinkFile(object):
+  """Container for <linkfile> manifest element."""
 
-  def __init__(self, git_worktree, src, dest, relsrc, absdest):
+  def __init__(self, git_worktree, src, topdir, dest):
+    """Register a <linkfile> request.
+
+    Args:
+      git_worktree: Absolute path to the git project checkout.
+      src: Target of symlink relative to path under |git_worktree|.
+      topdir: Absolute path to the top of the repo client checkout.
+      dest: Relative path under |topdir| of symlink to create.
+    """
     self.git_worktree = git_worktree
+    self.topdir = topdir
     self.src = src
     self.dest = dest
-    self.src_rel_to_dest = relsrc
-    self.abs_dest = absdest
 
   def __linkIt(self, relSrc, absDest):
     # link file if it does not exist or is out of date
@@ -316,35 +396,42 @@ class _LinkFile(object):
         _error('Cannot link file %s to %s', relSrc, absDest)
 
   def _Link(self):
-    """Link the self.rel_src_to_dest and self.abs_dest. Handles wild cards
-    on the src linking all of the files in the source in to the destination
-    directory.
+    """Link the self.src & self.dest paths.
+
+    Handles wild cards on the src linking all of the files in the source in to
+    the destination directory.
     """
-    # We use the absSrc to handle the situation where the current directory
-    # is not the root of the repo
-    absSrc = os.path.join(self.git_worktree, self.src)
-    if os.path.exists(absSrc):
-      # Entity exists so just a simple one to one link operation
-      self.__linkIt(self.src_rel_to_dest, self.abs_dest)
+    # Some people use src="." to create stable links to projects.  Lets allow
+    # that but reject all other uses of "." to keep things simple.
+    if self.src == '.':
+      src = self.git_worktree
+    else:
+      src = _SafeExpandPath(self.git_worktree, self.src)
+
+    if not glob.has_magic(src):
+      # Entity does not contain a wild card so just a simple one to one link operation.
+      dest = _SafeExpandPath(self.topdir, self.dest, skipfinal=True)
+      # dest & src are absolute paths at this point.  Make sure the target of
+      # the symlink is relative in the context of the repo client checkout.
+      relpath = os.path.relpath(src, os.path.dirname(dest))
+      self.__linkIt(relpath, dest)
     else:
-      # Entity doesn't exist assume there is a wild card
-      absDestDir = self.abs_dest
-      if os.path.exists(absDestDir) and not platform_utils.isdir(absDestDir):
-        _error('Link error: src with wildcard, %s must be a directory',
-               absDestDir)
+      dest = _SafeExpandPath(self.topdir, self.dest)
+      # Entity contains a wild card.
+      if os.path.exists(dest) and not platform_utils.isdir(dest):
+        _error('Link error: src with wildcard, %s must be a directory', dest)
       else:
-        absSrcFiles = glob.glob(absSrc)
-        for absSrcFile in absSrcFiles:
+        for absSrcFile in glob.glob(src):
           # Create a releative path from source dir to destination dir
           absSrcDir = os.path.dirname(absSrcFile)
-          relSrcDir = os.path.relpath(absSrcDir, absDestDir)
+          relSrcDir = os.path.relpath(absSrcDir, dest)
 
           # Get the source file name
           srcFile = os.path.basename(absSrcFile)
 
           # Now form the final full paths to srcFile. They will be
           # absolute for the desintaiton and relative for the srouce.
-          absDest = os.path.join(absDestDir, srcFile)
+          absDest = os.path.join(dest, srcFile)
           relSrc = os.path.join(relSrcDir, srcFile)
           self.__linkIt(relSrc, absDest)
 
@@ -368,405 +455,6 @@ class RemoteSpec(object):
     self.fetchUrl = fetchUrl
 
 
-class RepoHook(object):
-
-  """A RepoHook contains information about a script to run as a hook.
-
-  Hooks are used to run a python script before running an upload (for instance,
-  to run presubmit checks).  Eventually, we may have hooks for other actions.
-
-  This shouldn't be confused with files in the 'repo/hooks' directory.  Those
-  files are copied into each '.git/hooks' folder for each project.  Repo-level
-  hooks are associated instead with repo actions.
-
-  Hooks are always python.  When a hook is run, we will load the hook into the
-  interpreter and execute its main() function.
-  """
-
-  def __init__(self,
-               hook_type,
-               hooks_project,
-               topdir,
-               manifest_url,
-               abort_if_user_denies=False):
-    """RepoHook constructor.
-
-    Params:
-      hook_type: A string representing the type of hook.  This is also used
-          to figure out the name of the file containing the hook.  For
-          example: 'pre-upload'.
-      hooks_project: The project containing the repo hooks.  If you have a
-          manifest, this is manifest.repo_hooks_project.  OK if this is None,
-          which will make the hook a no-op.
-      topdir: Repo's top directory (the one containing the .repo directory).
-          Scripts will run with CWD as this directory.  If you have a manifest,
-          this is manifest.topdir
-      manifest_url: The URL to the manifest git repo.
-      abort_if_user_denies: If True, we'll throw a HookError() if the user
-          doesn't allow us to run the hook.
-    """
-    self._hook_type = hook_type
-    self._hooks_project = hooks_project
-    self._manifest_url = manifest_url
-    self._topdir = topdir
-    self._abort_if_user_denies = abort_if_user_denies
-
-    # Store the full path to the script for convenience.
-    if self._hooks_project:
-      self._script_fullpath = os.path.join(self._hooks_project.worktree,
-                                           self._hook_type + '.py')
-    else:
-      self._script_fullpath = None
-
-  def _GetHash(self):
-    """Return a hash of the contents of the hooks directory.
-
-    We'll just use git to do this.  This hash has the property that if anything
-    changes in the directory we will return a different has.
-
-    SECURITY CONSIDERATION:
-      This hash only represents the contents of files in the hook directory, not
-      any other files imported or called by hooks.  Changes to imported files
-      can change the script behavior without affecting the hash.
-
-    Returns:
-      A string representing the hash.  This will always be ASCII so that it can
-      be printed to the user easily.
-    """
-    assert self._hooks_project, "Must have hooks to calculate their hash."
-
-    # We will use the work_git object rather than just calling GetRevisionId().
-    # That gives us a hash of the latest checked in version of the files that
-    # the user will actually be executing.  Specifically, GetRevisionId()
-    # doesn't appear to change even if a user checks out a different version
-    # of the hooks repo (via git checkout) nor if a user commits their own revs.
-    #
-    # NOTE: Local (non-committed) changes will not be factored into this hash.
-    # I think this is OK, since we're really only worried about warning the user
-    # about upstream changes.
-    return self._hooks_project.work_git.rev_parse('HEAD')
-
-  def _GetMustVerb(self):
-    """Return 'must' if the hook is required; 'should' if not."""
-    if self._abort_if_user_denies:
-      return 'must'
-    else:
-      return 'should'
-
-  def _CheckForHookApproval(self):
-    """Check to see whether this hook has been approved.
-
-    We'll accept approval of manifest URLs if they're using secure transports.
-    This way the user can say they trust the manifest hoster.  For insecure
-    hosts, we fall back to checking the hash of the hooks repo.
-
-    Note that we ask permission for each individual hook even though we use
-    the hash of all hooks when detecting changes.  We'd like the user to be
-    able to approve / deny each hook individually.  We only use the hash of all
-    hooks because there is no other easy way to detect changes to local imports.
-
-    Returns:
-      True if this hook is approved to run; False otherwise.
-
-    Raises:
-      HookError: Raised if the user doesn't approve and abort_if_user_denies
-          was passed to the consturctor.
-    """
-    if self._ManifestUrlHasSecureScheme():
-      return self._CheckForHookApprovalManifest()
-    else:
-      return self._CheckForHookApprovalHash()
-
-  def _CheckForHookApprovalHelper(self, subkey, new_val, main_prompt,
-                                  changed_prompt):
-    """Check for approval for a particular attribute and hook.
-
-    Args:
-      subkey: The git config key under [repo.hooks.<hook_type>] to store the
-          last approved string.
-      new_val: The new value to compare against the last approved one.
-      main_prompt: Message to display to the user to ask for approval.
-      changed_prompt: Message explaining why we're re-asking for approval.
-
-    Returns:
-      True if this hook is approved to run; False otherwise.
-
-    Raises:
-      HookError: Raised if the user doesn't approve and abort_if_user_denies
-          was passed to the consturctor.
-    """
-    hooks_config = self._hooks_project.config
-    git_approval_key = 'repo.hooks.%s.%s' % (self._hook_type, subkey)
-
-    # Get the last value that the user approved for this hook; may be None.
-    old_val = hooks_config.GetString(git_approval_key)
-
-    if old_val is not None:
-      # User previously approved hook and asked not to be prompted again.
-      if new_val == old_val:
-        # Approval matched.  We're done.
-        return True
-      else:
-        # Give the user a reason why we're prompting, since they last told
-        # us to "never ask again".
-        prompt = 'WARNING: %s\n\n' % (changed_prompt,)
-    else:
-      prompt = ''
-
-    # Prompt the user if we're not on a tty; on a tty we'll assume "no".
-    if sys.stdout.isatty():
-      prompt += main_prompt + ' (yes/always/NO)? '
-      response = input(prompt).lower()
-      print()
-
-      # User is doing a one-time approval.
-      if response in ('y', 'yes'):
-        return True
-      elif response == 'always':
-        hooks_config.SetString(git_approval_key, new_val)
-        return True
-
-    # For anything else, we'll assume no approval.
-    if self._abort_if_user_denies:
-      raise HookError('You must allow the %s hook or use --no-verify.' %
-                      self._hook_type)
-
-    return False
-
-  def _ManifestUrlHasSecureScheme(self):
-    """Check if the URI for the manifest is a secure transport."""
-    secure_schemes = ('file', 'https', 'ssh', 'persistent-https', 'sso', 'rpc')
-    parse_results = urllib.parse.urlparse(self._manifest_url)
-    return parse_results.scheme in secure_schemes
-
-  def _CheckForHookApprovalManifest(self):
-    """Check whether the user has approved this manifest host.
-
-    Returns:
-      True if this hook is approved to run; False otherwise.
-    """
-    return self._CheckForHookApprovalHelper(
-        'approvedmanifest',
-        self._manifest_url,
-        'Run hook scripts from %s' % (self._manifest_url,),
-        'Manifest URL has changed since %s was allowed.' % (self._hook_type,))
-
-  def _CheckForHookApprovalHash(self):
-    """Check whether the user has approved the hooks repo.
-
-    Returns:
-      True if this hook is approved to run; False otherwise.
-    """
-    prompt = ('Repo %s run the script:\n'
-              '  %s\n'
-              '\n'
-              'Do you want to allow this script to run')
-    return self._CheckForHookApprovalHelper(
-        'approvedhash',
-        self._GetHash(),
-        prompt % (self._GetMustVerb(), self._script_fullpath),
-        'Scripts have changed since %s was allowed.' % (self._hook_type,))
-
-  @staticmethod
-  def _ExtractInterpFromShebang(data):
-    """Extract the interpreter used in the shebang.
-
-    Try to locate the interpreter the script is using (ignoring `env`).
-
-    Args:
-      data: The file content of the script.
-
-    Returns:
-      The basename of the main script interpreter, or None if a shebang is not
-      used or could not be parsed out.
-    """
-    firstline = data.splitlines()[:1]
-    if not firstline:
-      return None
-
-    # The format here can be tricky.
-    shebang = firstline[0].strip()
-    m = re.match(r'^#!\s*([^\s]+)(?:\s+([^\s]+))?', shebang)
-    if not m:
-      return None
-
-    # If the using `env`, find the target program.
-    interp = m.group(1)
-    if os.path.basename(interp) == 'env':
-      interp = m.group(2)
-
-    return interp
-
-  def _ExecuteHookViaReexec(self, interp, context, **kwargs):
-    """Execute the hook script through |interp|.
-
-    Note: Support for this feature should be dropped ~Jun 2021.
-
-    Args:
-      interp: The Python program to run.
-      context: Basic Python context to execute the hook inside.
-      kwargs: Arbitrary arguments to pass to the hook script.
-
-    Raises:
-      HookError: When the hooks failed for any reason.
-    """
-    # This logic needs to be kept in sync with _ExecuteHookViaImport below.
-    script = """
-import json, os, sys
-path = '''%(path)s'''
-kwargs = json.loads('''%(kwargs)s''')
-context = json.loads('''%(context)s''')
-sys.path.insert(0, os.path.dirname(path))
-data = open(path).read()
-exec(compile(data, path, 'exec'), context)
-context['main'](**kwargs)
-""" % {
-        'path': self._script_fullpath,
-        'kwargs': json.dumps(kwargs),
-        'context': json.dumps(context),
-    }
-
-    # We pass the script via stdin to avoid OS argv limits.  It also makes
-    # unhandled exception tracebacks less verbose/confusing for users.
-    cmd = [interp, '-c', 'import sys; exec(sys.stdin.read())']
-    proc = subprocess.Popen(cmd, stdin=subprocess.PIPE)
-    proc.communicate(input=script.encode('utf-8'))
-    if proc.returncode:
-      raise HookError('Failed to run %s hook.' % (self._hook_type,))
-
-  def _ExecuteHookViaImport(self, data, context, **kwargs):
-    """Execute the hook code in |data| directly.
-
-    Args:
-      data: The code of the hook to execute.
-      context: Basic Python context to execute the hook inside.
-      kwargs: Arbitrary arguments to pass to the hook script.
-
-    Raises:
-      HookError: When the hooks failed for any reason.
-    """
-    # Exec, storing global context in the context dict.  We catch exceptions
-    # and convert to a HookError w/ just the failing traceback.
-    try:
-      exec(compile(data, self._script_fullpath, 'exec'), context)
-    except Exception:
-      raise HookError('%s\nFailed to import %s hook; see traceback above.' %
-                      (traceback.format_exc(), self._hook_type))
-
-    # Running the script should have defined a main() function.
-    if 'main' not in context:
-      raise HookError('Missing main() in: "%s"' % self._script_fullpath)
-
-    # Call the main function in the hook.  If the hook should cause the
-    # build to fail, it will raise an Exception.  We'll catch that convert
-    # to a HookError w/ just the failing traceback.
-    try:
-      context['main'](**kwargs)
-    except Exception:
-      raise HookError('%s\nFailed to run main() for %s hook; see traceback '
-                      'above.' % (traceback.format_exc(), self._hook_type))
-
-  def _ExecuteHook(self, **kwargs):
-    """Actually execute the given hook.
-
-    This will run the hook's 'main' function in our python interpreter.
-
-    Args:
-      kwargs: Keyword arguments to pass to the hook.  These are often specific
-          to the hook type.  For instance, pre-upload hooks will contain
-          a project_list.
-    """
-    # Keep sys.path and CWD stashed away so that we can always restore them
-    # upon function exit.
-    orig_path = os.getcwd()
-    orig_syspath = sys.path
-
-    try:
-      # Always run hooks with CWD as topdir.
-      os.chdir(self._topdir)
-
-      # Put the hook dir as the first item of sys.path so hooks can do
-      # relative imports.  We want to replace the repo dir as [0] so
-      # hooks can't import repo files.
-      sys.path = [os.path.dirname(self._script_fullpath)] + sys.path[1:]
-
-      # Initial global context for the hook to run within.
-      context = {'__file__': self._script_fullpath}
-
-      # Add 'hook_should_take_kwargs' to the arguments to be passed to main.
-      # We don't actually want hooks to define their main with this argument--
-      # it's there to remind them that their hook should always take **kwargs.
-      # For instance, a pre-upload hook should be defined like:
-      #   def main(project_list, **kwargs):
-      #
-      # This allows us to later expand the API without breaking old hooks.
-      kwargs = kwargs.copy()
-      kwargs['hook_should_take_kwargs'] = True
-
-      # See what version of python the hook has been written against.
-      data = open(self._script_fullpath).read()
-      interp = self._ExtractInterpFromShebang(data)
-      reexec = False
-      if interp:
-        prog = os.path.basename(interp)
-        if prog.startswith('python2') and sys.version_info.major != 2:
-          reexec = True
-        elif prog.startswith('python3') and sys.version_info.major == 2:
-          reexec = True
-
-      # Attempt to execute the hooks through the requested version of Python.
-      if reexec:
-        try:
-          self._ExecuteHookViaReexec(interp, context, **kwargs)
-        except OSError as e:
-          if e.errno == errno.ENOENT:
-            # We couldn't find the interpreter, so fallback to importing.
-            reexec = False
-          else:
-            raise
-
-      # Run the hook by importing directly.
-      if not reexec:
-        self._ExecuteHookViaImport(data, context, **kwargs)
-    finally:
-      # Restore sys.path and CWD.
-      sys.path = orig_syspath
-      os.chdir(orig_path)
-
-  def Run(self, user_allows_all_hooks, **kwargs):
-    """Run the hook.
-
-    If the hook doesn't exist (because there is no hooks project or because
-    this particular hook is not enabled), this is a no-op.
-
-    Args:
-      user_allows_all_hooks: If True, we will never prompt about running the
-          hook--we'll just assume it's OK to run it.
-      kwargs: Keyword arguments to pass to the hook.  These are often specific
-          to the hook type.  For instance, pre-upload hooks will contain
-          a project_list.
-
-    Raises:
-      HookError: If there was a problem finding the hook or the user declined
-          to run a required hook (from _CheckForHookApproval).
-    """
-    # No-op if there is no hooks project or if hook is disabled.
-    if ((not self._hooks_project) or (self._hook_type not in
-                                      self._hooks_project.enabled_repo_hooks)):
-      return
-
-    # Bail with a nice error if we can't find the hook.
-    if not os.path.isfile(self._script_fullpath):
-      raise HookError('Couldn\'t find repo hook: "%s"' % self._script_fullpath)
-
-    # Make sure the user is OK with running the hook.
-    if (not user_allows_all_hooks) and (not self._CheckForHookApproval()):
-      return
-
-    # Run the hook with the same version of python we're using.
-    self._ExecuteHook(**kwargs)
-
-
 class Project(object):
   # These objects can be shared between several working trees.
   shareable_files = ['description', 'info']
@@ -793,9 +481,11 @@ class Project(object):
                clone_depth=None,
                upstream=None,
                parent=None,
+               use_git_worktrees=False,
                is_derived=False,
                dest_branch=None,
                optimized_fetch=False,
+               retry_fetches=0,
                old_revision=None):
     """Init a Project object.
 
@@ -816,31 +506,21 @@ class Project(object):
       sync_tags: The `sync-tags` attribute of manifest.xml's project element.
       upstream: The `upstream` attribute of manifest.xml's project element.
       parent: The parent Project object.
+      use_git_worktrees: Whether to use `git worktree` for this project.
       is_derived: False if the project was explicitly defined in the manifest;
                   True if the project is a discovered submodule.
       dest_branch: The branch to which to push changes for review by default.
       optimized_fetch: If True, when a project is set to a sha1 revision, only
                        fetch from the remote if the sha1 is not present locally.
+      retry_fetches: Retry remote fetches n times upon receiving transient error
+                     with exponential backoff and jitter.
       old_revision: saved git commit id for open GITC projects.
     """
-    self.manifest = manifest
+    self.client = self.manifest = manifest
     self.name = name
     self.remote = remote
-    self.gitdir = gitdir.replace('\\', '/')
-    self.objdir = objdir.replace('\\', '/')
-    if worktree:
-      self.worktree = os.path.normpath(worktree).replace('\\', '/')
-    else:
-      self.worktree = None
-    self.relpath = relpath
-    self.revisionExpr = revisionExpr
-
-    if revisionId is None \
-            and revisionExpr \
-            and IsId(revisionExpr):
-      self.revisionId = revisionExpr
-    else:
-      self.revisionId = revisionId
+    self.UpdatePaths(relpath, worktree, gitdir, objdir)
+    self.SetRevision(revisionExpr, revisionId=revisionId)
 
     self.rebase = rebase
     self.groups = groups
@@ -850,24 +530,19 @@ class Project(object):
     self.clone_depth = clone_depth
     self.upstream = upstream
     self.parent = parent
+    # NB: Do not use this setting in __init__ to change behavior so that the
+    # manifest.git checkout can inspect & change it after instantiating.  See
+    # the XmlManifest init code for more info.
+    self.use_git_worktrees = use_git_worktrees
     self.is_derived = is_derived
     self.optimized_fetch = optimized_fetch
+    self.retry_fetches = max(0, retry_fetches)
     self.subprojects = []
 
     self.snapshots = {}
     self.copyfiles = []
     self.linkfiles = []
     self.annotations = []
-    self.config = GitConfig.ForRepository(gitdir=self.gitdir,
-                                          defaults=self.manifest.globalConfig)
-
-    if self.worktree:
-      self.work_git = self._GitGetByExec(self, bare=False, gitdir=gitdir)
-    else:
-      self.work_git = None
-    self.bare_git = self._GitGetByExec(self, bare=True, gitdir=gitdir)
-    self.bare_ref = GitRefs(gitdir)
-    self.bare_objdir = self._GitGetByExec(self, bare=True, gitdir=objdir)
     self.dest_branch = dest_branch
     self.old_revision = old_revision
 
@@ -875,6 +550,35 @@ class Project(object):
     # project containing repo hooks.
     self.enabled_repo_hooks = []
 
+  def SetRevision(self, revisionExpr, revisionId=None):
+    """Set revisionId based on revision expression and id"""
+    self.revisionExpr = revisionExpr
+    if revisionId is None and revisionExpr and IsId(revisionExpr):
+      self.revisionId = self.revisionExpr
+    else:
+      self.revisionId = revisionId
+
+  def UpdatePaths(self, relpath, worktree, gitdir, objdir):
+    """Update paths used by this project"""
+    self.gitdir = gitdir.replace('\\', '/')
+    self.objdir = objdir.replace('\\', '/')
+    if worktree:
+      self.worktree = os.path.normpath(worktree).replace('\\', '/')
+    else:
+      self.worktree = None
+    self.relpath = relpath
+
+    self.config = GitConfig.ForRepository(gitdir=self.gitdir,
+                                          defaults=self.manifest.globalConfig)
+
+    if self.worktree:
+      self.work_git = self._GitGetByExec(self, bare=False, gitdir=self.gitdir)
+    else:
+      self.work_git = None
+    self.bare_git = self._GitGetByExec(self, bare=True, gitdir=self.gitdir)
+    self.bare_ref = GitRefs(self.gitdir)
+    self.bare_objdir = self._GitGetByExec(self, bare=True, gitdir=self.objdir)
+
   @property
   def Derived(self):
     return self.is_derived
@@ -902,11 +606,9 @@ class Project(object):
     return None
 
   def IsRebaseInProgress(self):
-    w = self.worktree
-    g = os.path.join(w, '.git')
-    return os.path.exists(os.path.join(g, 'rebase-apply')) \
-        or os.path.exists(os.path.join(g, 'rebase-merge')) \
-        or os.path.exists(os.path.join(w, '.dotest'))
+    return (os.path.exists(self.work_git.GetDotgitPath('rebase-apply')) or
+            os.path.exists(self.work_git.GetDotgitPath('rebase-merge')) or
+            os.path.exists(os.path.join(self.worktree, '.dotest')))
 
   def IsDirty(self, consider_untracked=True):
     """Is the working directory modified in some way?
@@ -1152,10 +854,12 @@ class Project(object):
 
     return 'DIRTY'
 
-  def PrintWorkTreeDiff(self, absolute_paths=False):
+  def PrintWorkTreeDiff(self, absolute_paths=False, output_redir=None):
     """Prints the status of the repository to stdout.
     """
     out = DiffColoring(self.config)
+    if output_redir:
+      out.redirect(output_redir)
     cmd = ['diff']
     if out.is_on:
       cmd.append('--color')
@@ -1169,6 +873,7 @@ class Project(object):
                      cmd,
                      capture_stdout=True,
                      capture_stderr=True)
+      p.Wait()
     except GitError as e:
       out.nl()
       out.project('project %s/' % self.relpath)
@@ -1176,21 +881,14 @@ class Project(object):
       out.fail('%s', str(e))
       out.nl()
       return False
-    has_diff = False
-    for line in p.process.stdout:
-      if not hasattr(line, 'encode'):
-        line = line.decode()
-      if not has_diff:
-        out.nl()
-        out.project('project %s/' % self.relpath)
-        out.nl()
-        has_diff = True
-      print(line[:-1])
+    if p.stdout:
+      out.nl()
+      out.project('project %s/' % self.relpath)
+      out.nl()
+      out.write('%s', p.stdout)
     return p.Wait() == 0
 
-
 # Publish / Upload ##
-
   def WasPublished(self, branch, all_refs=None):
     """Was the branch published (uploaded) for code review?
        If so, returns the SHA-1 hash of the last published
@@ -1263,8 +961,10 @@ class Project(object):
 
   def UploadForReview(self, branch=None,
                       people=([], []),
+                      dryrun=False,
                       auto_topic=False,
-                      draft=False,
+                      hashtags=(),
+                      labels=(),
                       private=False,
                       notify=None,
                       wip=False,
@@ -1299,6 +999,8 @@ class Project(object):
     if url is None:
       raise UploadError('review not configured')
     cmd = ['push']
+    if dryrun:
+      cmd.append('-n')
 
     if url.startswith('ssh://'):
       cmd.append('--receive-pack=gerrit receive-pack')
@@ -1312,15 +1014,12 @@ class Project(object):
     if dest_branch.startswith(R_HEADS):
       dest_branch = dest_branch[len(R_HEADS):]
 
-    upload_type = 'for'
-    if draft:
-      upload_type = 'drafts'
-
-    ref_spec = '%s:refs/%s/%s' % (R_HEADS + branch.name, upload_type,
-                                  dest_branch)
+    ref_spec = '%s:refs/for/%s' % (R_HEADS + branch.name, dest_branch)
     opts = []
     if auto_topic:
       opts += ['topic=' + branch.name]
+    opts += ['t=%s' % p for p in hashtags]
+    opts += ['l=%s' % p for p in labels]
 
     opts += ['r=%s' % p for p in people[0]]
     opts += ['cc=%s' % p for p in people[1]]
@@ -1337,14 +1036,13 @@ class Project(object):
     if GitCommand(self, cmd, bare=True).Wait() != 0:
       raise UploadError('Upload failed')
 
-    msg = "posted to %s for %s" % (branch.remote.review, dest_branch)
-    self.bare_git.UpdateRef(R_PUB + branch.name,
-                            R_HEADS + branch.name,
-                            message=msg)
-
+    if not dryrun:
+      msg = "posted to %s for %s" % (branch.remote.review, dest_branch)
+      self.bare_git.UpdateRef(R_PUB + branch.name,
+                              R_HEADS + branch.name,
+                              message=msg)
 
 # Sync ##
-
   def _ExtractArchive(self, tarpath, path=None):
     """Extract the given tar on its current location
 
@@ -1362,16 +1060,21 @@ class Project(object):
 
   def Sync_NetworkHalf(self,
                        quiet=False,
+                       verbose=False,
+                       output_redir=None,
                        is_new=None,
-                       current_branch_only=False,
+                       current_branch_only=None,
                        force_sync=False,
                        clone_bundle=True,
-                       no_tags=False,
+                       tags=None,
                        archive=False,
                        optimized_fetch=False,
+                       retry_fetches=0,
                        prune=False,
                        submodules=False,
-                       clone_filter=None):
+                       ssh_proxy=None,
+                       clone_filter=None,
+                       partial_clone_exclude=set()):
     """Perform only the network IO portion of the sync process.
        Local working directory/branch state is not affected.
     """
@@ -1402,12 +1105,22 @@ class Project(object):
         _warn("Cannot remove archive %s: %s", tarpath, str(e))
       self._CopyAndLinkFiles()
       return True
+
+    # If the shared object dir already exists, don't try to rebootstrap with a
+    # clone bundle download.  We should have the majority of objects already.
+    if clone_bundle and os.path.exists(self.objdir):
+      clone_bundle = False
+
+    if self.name in partial_clone_exclude:
+      clone_bundle = True
+      clone_filter = None
+
     if is_new is None:
       is_new = not self.Exists
     if is_new:
-      self._InitGitDir(force_sync=force_sync)
+      self._InitGitDir(force_sync=force_sync, quiet=quiet)
     else:
-      self._UpdateHooks()
+      self._UpdateHooks(quiet=quiet)
     self._InitRemote()
 
     if is_new:
@@ -1421,12 +1134,12 @@ class Project(object):
     else:
       alt_dir = None
 
-    if clone_bundle \
-            and alt_dir is None \
-            and self._ApplyCloneBundle(initial=is_new, quiet=quiet):
+    if (clone_bundle
+            and alt_dir is None
+            and self._ApplyCloneBundle(initial=is_new, quiet=quiet, verbose=verbose)):
       is_new = False
 
-    if not current_branch_only:
+    if current_branch_only is None:
       if self.sync_c:
         current_branch_only = True
       elif not self.manifest._loaded:
@@ -1435,25 +1148,27 @@ class Project(object):
       elif self.manifest.default.sync_c:
         current_branch_only = True
 
-    if not no_tags:
-      if not self.sync_tags:
-        no_tags = True
+    if tags is None:
+      tags = self.sync_tags
 
     if self.clone_depth:
       depth = self.clone_depth
     else:
       depth = self.manifest.manifestProject.config.GetString('repo.depth')
 
-    need_to_fetch = not (optimized_fetch and
-                         (ID_RE.match(self.revisionExpr) and
-                          self._CheckForImmutableRevision()))
-    if (need_to_fetch and
-        not self._RemoteFetch(initial=is_new, quiet=quiet, alt_dir=alt_dir,
-                              current_branch_only=current_branch_only,
-                              no_tags=no_tags, prune=prune, depth=depth,
-                              submodules=submodules, force_sync=force_sync,
-                              clone_filter=clone_filter)):
-      return False
+    # See if we can skip the network fetch entirely.
+    if not (optimized_fetch and
+            (ID_RE.match(self.revisionExpr) and
+             self._CheckForImmutableRevision())):
+      if not self._RemoteFetch(
+              initial=is_new,
+              quiet=quiet, verbose=verbose, output_redir=output_redir,
+              alt_dir=alt_dir, current_branch_only=current_branch_only,
+              tags=tags, prune=prune, depth=depth,
+              submodules=submodules, force_sync=force_sync,
+              ssh_proxy=ssh_proxy,
+              clone_filter=clone_filter, retry_fetches=retry_fetches):
+        return False
 
     mp = self.manifest.manifestProject
     dissociate = mp.config.GetBoolean('repo.dissociate')
@@ -1461,7 +1176,11 @@ class Project(object):
       alternates_file = os.path.join(self.gitdir, 'objects/info/alternates')
       if os.path.exists(alternates_file):
         cmd = ['repack', '-a', '-d']
-        if GitCommand(self, cmd, bare=True).Wait() != 0:
+        p = GitCommand(self, cmd, bare=True, capture_stdout=bool(output_redir),
+                       merge_output=bool(output_redir))
+        if p.stdout and output_redir:
+          output_redir.write(p.stdout)
+        if p.Wait() != 0:
           return False
         platform_utils.remove(alternates_file)
 
@@ -1469,17 +1188,15 @@ class Project(object):
       self._InitMRef()
     else:
       self._InitMirrorHead()
-      try:
-        platform_utils.remove(os.path.join(self.gitdir, 'FETCH_HEAD'))
-      except OSError:
-        pass
+      platform_utils.remove(os.path.join(self.gitdir, 'FETCH_HEAD'),
+                            missing_ok=True)
     return True
 
   def PostRepoUpgrade(self):
     self._InitHooks()
 
   def _CopyAndLinkFiles(self):
-    if self.manifest.isGitcClient:
+    if self.client.isGitcClient:
       return
     for copyfile in self.copyfiles:
       copyfile._Copy()
@@ -1518,6 +1235,12 @@ class Project(object):
       raise ManifestInvalidRevisionError('revision %s in %s not found' %
                                          (self.revisionExpr, self.name))
 
+  def SetRevisionId(self, revisionId):
+    if self.revisionExpr:
+      self.upstream = self.revisionExpr
+
+    self.revisionId = revisionId
+
   def Sync_LocalHalf(self, syncbuf, force_sync=False, submodules=False):
     """Perform only the local IO portion of the sync process.
        Network access is not required.
@@ -1534,6 +1257,18 @@ class Project(object):
     self.CleanPublishedCache(all_refs)
     revid = self.GetRevisionId(all_refs)
 
+    # Special case the root of the repo client checkout.  Make sure it doesn't
+    # contain files being checked out to dirs we don't allow.
+    if self.relpath == '.':
+      PROTECTED_PATHS = {'.repo'}
+      paths = set(self.work_git.ls_tree('-z', '--name-only', '--', revid).split('\0'))
+      bad_paths = paths & PROTECTED_PATHS
+      if bad_paths:
+        syncbuf.fail(self,
+                     'Refusing to checkout project that writes to protected '
+                     'paths: %s' % (', '.join(bad_paths),))
+        return
+
     def _doff():
       self._FastForward(revid)
       self._CopyAndLinkFiles()
@@ -1712,21 +1447,28 @@ class Project(object):
       if submodules:
         syncbuf.later1(self, _dosubmodules)
 
-  def AddCopyFile(self, src, dest, absdest):
-    # dest should already be an absolute path, but src is project relative
-    # make src an absolute path
-    abssrc = os.path.join(self.worktree, src)
-    self.copyfiles.append(_CopyFile(src, dest, abssrc, absdest))
+  def AddCopyFile(self, src, dest, topdir):
+    """Mark |src| for copying to |dest| (relative to |topdir|).
+
+    No filesystem changes occur here.  Actual copying happens later on.
+
+    Paths should have basic validation run on them before being queued.
+    Further checking will be handled when the actual copy happens.
+    """
+    self.copyfiles.append(_CopyFile(self.worktree, src, topdir, dest))
 
-  def AddLinkFile(self, src, dest, absdest):
-    # dest should already be an absolute path, but src is project relative
-    # make src relative path to dest
-    absdestdir = os.path.dirname(absdest)
-    relsrc = os.path.relpath(os.path.join(self.worktree, src), absdestdir)
-    self.linkfiles.append(_LinkFile(self.worktree, src, dest, relsrc, absdest))
+  def AddLinkFile(self, src, dest, topdir):
+    """Mark |dest| to create a symlink (relative to |topdir|) pointing to |src|.
+
+    No filesystem changes occur here.  Actual linking happens later on.
+
+    Paths should have basic validation run on them before being queued.
+    Further checking will be handled when the actual link happens.
+    """
+    self.linkfiles.append(_LinkFile(self.worktree, src, topdir, dest))
 
   def AddAnnotation(self, name, value, keep):
-    self.annotations.append(_Annotation(name, value, keep))
+    self.annotations.append(Annotation(name, value, keep))
 
   def DownloadPatchSet(self, change_id, patch_id):
     """Download a single patch set of a single change to FETCH_HEAD.
@@ -1744,9 +1486,123 @@ class Project(object):
                             patch_id,
                             self.bare_git.rev_parse('FETCH_HEAD'))
 
+  def DeleteWorktree(self, quiet=False, force=False):
+    """Delete the source checkout and any other housekeeping tasks.
 
-# Branch Management ##
+    This currently leaves behind the internal .repo/ cache state.  This helps
+    when switching branches or manifest changes get reverted as we don't have
+    to redownload all the git objects.  But we should do some GC at some point.
+
+    Args:
+      quiet: Whether to hide normal messages.
+      force: Always delete tree even if dirty.
+
+    Returns:
+      True if the worktree was completely cleaned out.
+    """
+    if self.IsDirty():
+      if force:
+        print('warning: %s: Removing dirty project: uncommitted changes lost.' %
+              (self.relpath,), file=sys.stderr)
+      else:
+        print('error: %s: Cannot remove project: uncommitted changes are '
+              'present.\n' % (self.relpath,), file=sys.stderr)
+        return False
+
+    if not quiet:
+      print('%s: Deleting obsolete checkout.' % (self.relpath,))
+
+    # Unlock and delink from the main worktree.  We don't use git's worktree
+    # remove because it will recursively delete projects -- we handle that
+    # ourselves below.  https://crbug.com/git/48
+    if self.use_git_worktrees:
+      needle = platform_utils.realpath(self.gitdir)
+      # Find the git worktree commondir under .repo/worktrees/.
+      output = self.bare_git.worktree('list', '--porcelain').splitlines()[0]
+      assert output.startswith('worktree '), output
+      commondir = output[9:]
+      # Walk each of the git worktrees to see where they point.
+      configs = os.path.join(commondir, 'worktrees')
+      for name in os.listdir(configs):
+        gitdir = os.path.join(configs, name, 'gitdir')
+        with open(gitdir) as fp:
+          relpath = fp.read().strip()
+        # Resolve the checkout path and see if it matches this project.
+        fullpath = platform_utils.realpath(os.path.join(configs, name, relpath))
+        if fullpath == needle:
+          platform_utils.rmtree(os.path.join(configs, name))
+
+    # Delete the .git directory first, so we're less likely to have a partially
+    # working git repository around. There shouldn't be any git projects here,
+    # so rmtree works.
+
+    # Try to remove plain files first in case of git worktrees.  If this fails
+    # for any reason, we'll fall back to rmtree, and that'll display errors if
+    # it can't remove things either.
+    try:
+      platform_utils.remove(self.gitdir)
+    except OSError:
+      pass
+    try:
+      platform_utils.rmtree(self.gitdir)
+    except OSError as e:
+      if e.errno != errno.ENOENT:
+        print('error: %s: %s' % (self.gitdir, e), file=sys.stderr)
+        print('error: %s: Failed to delete obsolete checkout; remove manually, '
+              'then run `repo sync -l`.' % (self.relpath,), file=sys.stderr)
+        return False
+
+    # Delete everything under the worktree, except for directories that contain
+    # another git project.
+    dirs_to_remove = []
+    failed = False
+    for root, dirs, files in platform_utils.walk(self.worktree):
+      for f in files:
+        path = os.path.join(root, f)
+        try:
+          platform_utils.remove(path)
+        except OSError as e:
+          if e.errno != errno.ENOENT:
+            print('error: %s: Failed to remove: %s' % (path, e), file=sys.stderr)
+            failed = True
+      dirs[:] = [d for d in dirs
+                 if not os.path.lexists(os.path.join(root, d, '.git'))]
+      dirs_to_remove += [os.path.join(root, d) for d in dirs
+                         if os.path.join(root, d) not in dirs_to_remove]
+    for d in reversed(dirs_to_remove):
+      if platform_utils.islink(d):
+        try:
+          platform_utils.remove(d)
+        except OSError as e:
+          if e.errno != errno.ENOENT:
+            print('error: %s: Failed to remove: %s' % (d, e), file=sys.stderr)
+            failed = True
+      elif not platform_utils.listdir(d):
+        try:
+          platform_utils.rmdir(d)
+        except OSError as e:
+          if e.errno != errno.ENOENT:
+            print('error: %s: Failed to remove: %s' % (d, e), file=sys.stderr)
+            failed = True
+    if failed:
+      print('error: %s: Failed to delete obsolete checkout.' % (self.relpath,),
+            file=sys.stderr)
+      print('       Remove manually, then run `repo sync -l`.', file=sys.stderr)
+      return False
 
+    # Try deleting parent dirs if they are empty.
+    path = self.worktree
+    while path != self.manifest.topdir:
+      try:
+        platform_utils.rmdir(path)
+      except OSError as e:
+        if e.errno != errno.ENOENT:
+          break
+      path = os.path.dirname(path)
+
+    return True
+
+# Branch Management ##
   def StartBranch(self, name, branch_merge='', revision=None):
     """Create a new branch off the manifest's revision.
     """
@@ -1780,14 +1636,9 @@ class Project(object):
       except KeyError:
         head = None
     if revid and head and revid == head:
-      ref = os.path.join(self.gitdir, R_HEADS + name)
-      try:
-        os.makedirs(os.path.dirname(ref))
-      except OSError:
-        pass
-      _lwrite(ref, '%s\n' % revid)
-      _lwrite(os.path.join(self.worktree, '.git', HEAD),
-              'ref: %s%s\n' % (R_HEADS, name))
+      ref = R_HEADS + name
+      self.work_git.update_ref(ref, revid)
+      self.work_git.symbolic_ref(HEAD, ref)
       branch.Save()
       return True
 
@@ -1834,7 +1685,7 @@ class Project(object):
       # Same revision; just update HEAD to point to the new
       # target branch, but otherwise take no other action.
       #
-      _lwrite(os.path.join(self.worktree, '.git', HEAD),
+      _lwrite(self.work_git.GetDotgitPath(subpath=HEAD),
               'ref: %s%s\n' % (R_HEADS, name))
       return True
 
@@ -1868,8 +1719,7 @@ class Project(object):
 
       revid = self.GetRevisionId(all_refs)
       if head == revid:
-        _lwrite(os.path.join(self.worktree, '.git', HEAD),
-                '%s\n' % revid)
+        _lwrite(self.work_git.GetDotgitPath(subpath=HEAD), '%s\n' % revid)
       else:
         self._Checkout(revid, quiet=True)
 
@@ -1890,6 +1740,11 @@ class Project(object):
         if cb is None or name != cb:
           kill.append(name)
 
+    # Minor optimization: If there's nothing to prune, then don't try to read
+    # any project state.
+    if not kill and not cb:
+      return []
+
     rev = self.GetRevisionId(left)
     if cb is not None \
        and not self._revlist(HEAD + '...' + rev) \
@@ -1935,9 +1790,7 @@ class Project(object):
         kept.append(ReviewableBranch(self, branch, base))
     return kept
 
-
 # Submodule Management ##
-
   def GetRegisteredSubprojects(self):
     result = []
 
@@ -2088,13 +1941,57 @@ class Project(object):
       result.extend(subproject.GetDerivedSubprojects())
     return result
 
-
 # Direct Git Commands ##
+  def EnableRepositoryExtension(self, key, value='true', version=1):
+    """Enable git repository extension |key| with |value|.
+
+    Args:
+      key: The extension to enabled.  Omit the "extensions." prefix.
+      value: The value to use for the extension.
+      version: The minimum git repository version needed.
+    """
+    # Make sure the git repo version is new enough already.
+    found_version = self.config.GetInt('core.repositoryFormatVersion')
+    if found_version is None:
+      found_version = 0
+    if found_version < version:
+      self.config.SetString('core.repositoryFormatVersion', str(version))
+
+    # Enable the extension!
+    self.config.SetString('extensions.%s' % (key,), value)
+
+  def ResolveRemoteHead(self, name=None):
+    """Find out what the default branch (HEAD) points to.
+
+    Normally this points to refs/heads/master, but projects are moving to main.
+    Support whatever the server uses rather than hardcoding "master" ourselves.
+    """
+    if name is None:
+      name = self.remote.name
+
+    # The output will look like (NB: tabs are separators):
+    # ref: refs/heads/master    HEAD
+    # 5f6803b100bb3cd0f534e96e88c91373e8ed1c44  HEAD
+    output = self.bare_git.ls_remote('-q', '--symref', '--exit-code', name, 'HEAD')
+
+    for line in output.splitlines():
+      lhs, rhs = line.split('\t', 1)
+      if rhs == 'HEAD' and lhs.startswith('ref:'):
+        return lhs[4:].strip()
+
+    return None
+
   def _CheckForImmutableRevision(self):
     try:
       # if revision (sha or tag) is not present then following function
       # throws an error.
-      self.bare_git.rev_parse('--verify', '%s^0' % self.revisionExpr)
+      self.bare_git.rev_list('-1', '--missing=allow-any',
+                             '%s^0' % self.revisionExpr, '--')
+      if self.upstream:
+        rev = self.GetRemote(self.remote.name).ToLocal(self.upstream)
+        self.bare_git.rev_list('-1', '--missing=allow-any',
+                               '%s^0' % rev, '--')
+        self.bare_git.merge_base('--is-ancestor', self.revisionExpr, rev)
       return True
     except GitError:
       # There is no such persistent revision. We have to fetch it.
@@ -2117,14 +2014,19 @@ class Project(object):
                    current_branch_only=False,
                    initial=False,
                    quiet=False,
+                   verbose=False,
+                   output_redir=None,
                    alt_dir=None,
-                   no_tags=False,
+                   tags=True,
                    prune=False,
                    depth=None,
                    submodules=False,
+                   ssh_proxy=None,
                    force_sync=False,
-                   clone_filter=None):
-
+                   clone_filter=None,
+                   retry_fetches=2,
+                   retry_sleep_initial_sec=4.0,
+                   retry_exp_factor=2.0):
     is_sha1 = False
     tag_name = None
     # The depth should not be used when fetching to a mirror because
@@ -2147,7 +2049,7 @@ class Project(object):
 
       if is_sha1 or tag_name is not None:
         if self._CheckForImmutableRevision():
-          if not quiet:
+          if verbose:
             print('Skipped fetching project %s (already have persistent ref)'
                   % self.name)
           return True
@@ -2167,16 +2069,14 @@ class Project(object):
     if not name:
       name = self.remote.name
 
-    ssh_proxy = False
     remote = self.GetRemote(name)
-    if remote.PreConnectFetch():
-      ssh_proxy = True
+    if not remote.PreConnectFetch(ssh_proxy):
+      ssh_proxy = None
 
     if initial:
       if alt_dir and 'objects' == os.path.basename(alt_dir):
         ref_dir = os.path.dirname(alt_dir)
         packed_refs = os.path.join(self.gitdir, 'packed-refs')
-        remote = self.GetRemote(name)
 
         all_refs = self.bare_ref.all
         ids = set(all_refs.values())
@@ -2217,7 +2117,7 @@ class Project(object):
     if clone_filter:
       git_require((2, 19, 0), fail=True, msg='partial clones')
       cmd.append('--filter=%s' % clone_filter)
-      self.config.SetString('extensions.partialclone', self.remote.name)
+      self.EnableRepositoryExtension('partialclone', self.remote.name)
 
     if depth:
       cmd.append('--depth=%s' % depth)
@@ -2229,8 +2129,10 @@ class Project(object):
       if os.path.exists(os.path.join(self.gitdir, 'shallow')):
         cmd.append('--depth=2147483647')
 
-    if quiet:
+    if not verbose:
       cmd.append('--quiet')
+    if not quiet and sys.stdout.isatty():
+      cmd.append('--progress')
     if not self.worktree:
       cmd.append('--update-head-ok')
     cmd.append(name)
@@ -2257,10 +2159,12 @@ class Project(object):
     else:
       branch = self.revisionExpr
     if (not self.manifest.IsMirror and is_sha1 and depth
-        and git_require((1, 8, 3))):
+            and git_require((1, 8, 3))):
       # Shallow checkout of a specific commit, fetch from that commit and not
       # the heads only as the commit might be deeper in the history.
       spec.append(branch)
+      if self.upstream:
+        spec.append(self.upstream)
     else:
       if is_sha1:
         branch = self.upstream
@@ -2276,7 +2180,7 @@ class Project(object):
 
     # If using depth then we should not get all the tags since they may
     # be outside of the depth.
-    if no_tags or depth:
+    if not tags or depth:
       cmd.append('--no-tags')
     else:
       cmd.append('--tags')
@@ -2284,22 +2188,42 @@ class Project(object):
 
     cmd.extend(spec)
 
-    ok = False
-    for _i in range(2):
-      gitcmd = GitCommand(self, cmd, bare=True, ssh_proxy=ssh_proxy)
+    # At least one retry minimum due to git remote prune.
+    retry_fetches = max(retry_fetches, 2)
+    retry_cur_sleep = retry_sleep_initial_sec
+    ok = prune_tried = False
+    for try_n in range(retry_fetches):
+      gitcmd = GitCommand(self, cmd, bare=True, ssh_proxy=ssh_proxy,
+                          merge_output=True, capture_stdout=quiet or bool(output_redir))
+      if gitcmd.stdout and not quiet and output_redir:
+        output_redir.write(gitcmd.stdout)
       ret = gitcmd.Wait()
       if ret == 0:
         ok = True
         break
-      # If needed, run the 'git remote prune' the first time through the loop
-      elif (not _i and
-            "error:" in gitcmd.stderr and
-            "git remote prune" in gitcmd.stderr):
+
+      # Retry later due to HTTP 429 Too Many Requests.
+      elif (gitcmd.stdout and
+            'error:' in gitcmd.stdout and
+            'HTTP 429' in gitcmd.stdout):
+        # Fallthru to sleep+retry logic at the bottom.
+        pass
+
+      # Try to prune remote branches once in case there are conflicts.
+      # For example, if the remote had refs/heads/upstream, but deleted that and
+      # now has refs/heads/upstream/foo.
+      elif (gitcmd.stdout and
+            'error:' in gitcmd.stdout and
+            'git remote prune' in gitcmd.stdout and
+            not prune_tried):
+        prune_tried = True
         prunecmd = GitCommand(self, ['remote', 'prune', name], bare=True,
                               ssh_proxy=ssh_proxy)
         ret = prunecmd.Wait()
         if ret:
           break
+        print('retrying fetch after pruning remote branches', file=output_redir)
+        # Continue right away so we don't sleep as we shouldn't need to.
         continue
       elif current_branch_only and is_sha1 and ret == 128:
         # Exit code 128 means "couldn't find the ref you asked for"; if we're
@@ -2309,7 +2233,18 @@ class Project(object):
       elif ret < 0:
         # Git died with a signal, exit immediately
         break
-      time.sleep(random.randint(30, 45))
+
+      # Figure out how long to sleep before the next attempt, if there is one.
+      if not verbose and gitcmd.stdout:
+        print('\n%s:\n%s' % (self.name, gitcmd.stdout), end='', file=output_redir)
+      if try_n < retry_fetches - 1:
+        print('%s: sleeping %s seconds before retrying' % (self.name, retry_cur_sleep),
+              file=output_redir)
+        time.sleep(retry_cur_sleep)
+        retry_cur_sleep = min(retry_exp_factor * retry_cur_sleep,
+                              MAXIMUM_RETRY_SLEEP_SEC)
+        retry_cur_sleep *= (1 - random.uniform(-RETRY_JITTER_PERCENT,
+                                               RETRY_JITTER_PERCENT))
 
     if initial:
       if alt_dir:
@@ -2324,21 +2259,17 @@ class Project(object):
       # got what we wanted, else trigger a second run of all
       # refs.
       if not self._CheckForImmutableRevision():
-        if current_branch_only and depth:
-          # Sync the current branch only with depth set to None
-          return self._RemoteFetch(name=name,
-                                   current_branch_only=current_branch_only,
-                                   initial=False, quiet=quiet, alt_dir=alt_dir,
-                                   depth=None, clone_filter=clone_filter)
-        else:
-          # Avoid infinite recursion: sync all branches with depth set to None
-          return self._RemoteFetch(name=name, current_branch_only=False,
-                                   initial=False, quiet=quiet, alt_dir=alt_dir,
-                                   depth=None, clone_filter=clone_filter)
+        # Sync the current branch only with depth set to None.
+        # We always pass depth=None down to avoid infinite recursion.
+        return self._RemoteFetch(
+            name=name, quiet=quiet, verbose=verbose, output_redir=output_redir,
+            current_branch_only=current_branch_only and depth,
+            initial=False, alt_dir=alt_dir,
+            depth=None, ssh_proxy=ssh_proxy, clone_filter=clone_filter)
 
     return ok
 
-  def _ApplyCloneBundle(self, initial=False, quiet=False):
+  def _ApplyCloneBundle(self, initial=False, quiet=False, verbose=False):
     if initial and \
         (self.manifest.manifestProject.config.GetString('repo.depth') or
          self.clone_depth):
@@ -2362,13 +2293,16 @@ class Project(object):
       return False
 
     if not exist_dst:
-      exist_dst = self._FetchBundle(bundle_url, bundle_tmp, bundle_dst, quiet)
+      exist_dst = self._FetchBundle(bundle_url, bundle_tmp, bundle_dst, quiet,
+                                    verbose)
     if not exist_dst:
       return False
 
     cmd = ['fetch']
-    if quiet:
+    if not verbose:
       cmd.append('--quiet')
+    if not quiet and sys.stdout.isatty():
+      cmd.append('--progress')
     if not self.worktree:
       cmd.append('--update-head-ok')
     cmd.append(bundle_dst)
@@ -2377,19 +2311,16 @@ class Project(object):
     cmd.append('+refs/tags/*:refs/tags/*')
 
     ok = GitCommand(self, cmd, bare=True).Wait() == 0
-    if os.path.exists(bundle_dst):
-      platform_utils.remove(bundle_dst)
-    if os.path.exists(bundle_tmp):
-      platform_utils.remove(bundle_tmp)
+    platform_utils.remove(bundle_dst, missing_ok=True)
+    platform_utils.remove(bundle_tmp, missing_ok=True)
     return ok
 
-  def _FetchBundle(self, srcUrl, tmpPath, dstPath, quiet):
-    if os.path.exists(dstPath):
-      platform_utils.remove(dstPath)
+  def _FetchBundle(self, srcUrl, tmpPath, dstPath, quiet, verbose):
+    platform_utils.remove(dstPath, missing_ok=True)
 
     cmd = ['curl', '--fail', '--output', tmpPath, '--netrc', '--location']
     if quiet:
-      cmd += ['--silent']
+      cmd += ['--silent', '--show-error']
     if os.path.exists(tmpPath):
       size = os.stat(tmpPath).st_size
       if size >= 1024:
@@ -2411,22 +2342,30 @@ class Project(object):
 
       if IsTrace():
         Trace('%s', ' '.join(cmd))
+      if verbose:
+        print('%s: Downloading bundle: %s' % (self.name, srcUrl))
+      stdout = None if verbose else subprocess.PIPE
+      stderr = None if verbose else subprocess.STDOUT
       try:
-        proc = subprocess.Popen(cmd)
+        proc = subprocess.Popen(cmd, stdout=stdout, stderr=stderr)
       except OSError:
         return False
 
-      curlret = proc.wait()
+      (output, _) = proc.communicate()
+      curlret = proc.returncode
 
       if curlret == 22:
         # From curl man page:
         # 22: HTTP page not retrieved. The requested url was not found or
         # returned another error with the HTTP error code being 400 or above.
         # This return code only appears if -f, --fail is used.
-        if not quiet:
-          print("Server does not provide clone.bundle; ignoring.",
-                file=sys.stderr)
+        if verbose:
+          print('%s: Unable to retrieve clone.bundle; ignoring.' % self.name)
+          if output:
+            print('Curl output:\n%s' % output)
         return False
+      elif curlret and not verbose and output:
+        print('%s' % output, file=sys.stderr)
 
     if os.path.exists(tmpPath):
       if curlret == 0 and self._IsValidBundle(tmpPath, quiet):
@@ -2460,8 +2399,12 @@ class Project(object):
       if self._allrefs:
         raise GitError('%s checkout %s ' % (self.name, rev))
 
-  def _CherryPick(self, rev):
+  def _CherryPick(self, rev, ffonly=False, record_origin=False):
     cmd = ['cherry-pick']
+    if ffonly:
+      cmd.append('--ff')
+    if record_origin:
+      cmd.append('-x')
     cmd.append(rev)
     cmd.append('--')
     if GitCommand(self, cmd).Wait() != 0:
@@ -2508,13 +2451,13 @@ class Project(object):
       raise GitError('%s rebase %s ' % (self.name, upstream))
 
   def _FastForward(self, head, ffonly=False):
-    cmd = ['merge', head]
+    cmd = ['merge', '--no-stat', head]
     if ffonly:
       cmd.append("--ff-only")
     if GitCommand(self, cmd).Wait() != 0:
       raise GitError('%s merge %s ' % (self.name, head))
 
-  def _InitGitDir(self, mirror_git=None, force_sync=False):
+  def _InitGitDir(self, mirror_git=None, force_sync=False, quiet=False):
     init_git_dir = not os.path.exists(self.gitdir)
     init_obj_dir = not os.path.exists(self.objdir)
     try:
@@ -2523,6 +2466,12 @@ class Project(object):
         os.makedirs(self.objdir)
         self.bare_objdir.init()
 
+        if self.use_git_worktrees:
+          # Enable per-worktree config file support if possible.  This is more a
+          # nice-to-have feature for users rather than a hard requirement.
+          if git_require((2, 20, 0)):
+            self.EnableRepositoryExtension('worktreeConfig')
+
       # If we have a separate directory to hold refs, initialize it as well.
       if self.objdir != self.gitdir:
         if init_git_dir:
@@ -2542,8 +2491,9 @@ class Project(object):
               if self.worktree and os.path.exists(platform_utils.realpath
                                                   (self.worktree)):
                 platform_utils.rmtree(platform_utils.realpath(self.worktree))
-              return self._InitGitDir(mirror_git=mirror_git, force_sync=False)
-            except:
+              return self._InitGitDir(mirror_git=mirror_git, force_sync=False,
+                                      quiet=quiet)
+            except Exception:
               raise e
           raise e
 
@@ -2556,13 +2506,15 @@ class Project(object):
             mirror_git = os.path.join(ref_dir, self.name + '.git')
           repo_git = os.path.join(ref_dir, '.repo', 'projects',
                                   self.relpath + '.git')
+          worktrees_git = os.path.join(ref_dir, '.repo', 'worktrees',
+                                       self.name + '.git')
 
           if os.path.exists(mirror_git):
             ref_dir = mirror_git
-
           elif os.path.exists(repo_git):
             ref_dir = repo_git
-
+          elif os.path.exists(worktrees_git):
+            ref_dir = worktrees_git
           else:
             ref_dir = None
 
@@ -2574,7 +2526,7 @@ class Project(object):
             _lwrite(os.path.join(self.gitdir, 'objects/info/alternates'),
                     os.path.join(ref_dir, 'objects') + '\n')
 
-        self._UpdateHooks()
+        self._UpdateHooks(quiet=quiet)
 
         m = self.manifest.manifestProject.config
         for key in ['user.name', 'user.email']:
@@ -2582,10 +2534,7 @@ class Project(object):
             self.config.SetString(key, m.GetString(key))
         self.config.SetString('filter.lfs.smudge', 'git-lfs smudge --skip -- %f')
         self.config.SetString('filter.lfs.process', 'git-lfs filter-process --skip')
-        if self.manifest.IsMirror:
-          self.config.SetString('core.bare', 'true')
-        else:
-          self.config.SetString('core.bare', None)
+        self.config.SetBoolean('core.bare', True if self.manifest.IsMirror else None)
     except Exception:
       if init_obj_dir and os.path.exists(self.objdir):
         platform_utils.rmtree(self.objdir)
@@ -2593,11 +2542,11 @@ class Project(object):
         platform_utils.rmtree(self.gitdir)
       raise
 
-  def _UpdateHooks(self):
+  def _UpdateHooks(self, quiet=False):
     if os.path.exists(self.gitdir):
-      self._InitHooks()
+      self._InitHooks(quiet=quiet)
 
-  def _InitHooks(self):
+  def _InitHooks(self, quiet=False):
     hooks = platform_utils.realpath(self._gitdir_path('hooks'))
     if not os.path.exists(hooks):
       os.makedirs(hooks)
@@ -2617,18 +2566,23 @@ class Project(object):
       if platform_utils.islink(dst):
         continue
       if os.path.exists(dst):
-        if filecmp.cmp(stock_hook, dst, shallow=False):
-          platform_utils.remove(dst)
-        else:
-          _warn("%s: Not replacing locally modified %s hook",
-                self.relpath, name)
-          continue
+        # If the files are the same, we'll leave it alone.  We create symlinks
+        # below by default but fallback to hardlinks if the OS blocks them.
+        # So if we're here, it's probably because we made a hardlink below.
+        if not filecmp.cmp(stock_hook, dst, shallow=False):
+          if not quiet:
+            _warn("%s: Not replacing locally modified %s hook",
+                  self.relpath, name)
+        continue
       try:
         platform_utils.symlink(
             os.path.relpath(stock_hook, os.path.dirname(dst)), dst)
       except OSError as e:
         if e.errno == errno.EPERM:
-          raise GitError(self._get_symlink_error_message())
+          try:
+            os.link(stock_hook, dst)
+          except OSError:
+            raise GitError(self._get_symlink_error_message())
         else:
           raise
 
@@ -2648,27 +2602,56 @@ class Project(object):
 
   def _InitMRef(self):
     if self.manifest.branch:
-      self._InitAnyMRef(R_M + self.manifest.branch)
+      if self.use_git_worktrees:
+        # Set up the m/ space to point to the worktree-specific ref space.
+        # We'll update the worktree-specific ref space on each checkout.
+        ref = R_M + self.manifest.branch
+        if not self.bare_ref.symref(ref):
+          self.bare_git.symbolic_ref(
+              '-m', 'redirecting to worktree scope',
+              ref, R_WORKTREE_M + self.manifest.branch)
+
+        # We can't update this ref with git worktrees until it exists.
+        # We'll wait until the initial checkout to set it.
+        if not os.path.exists(self.worktree):
+          return
+
+        base = R_WORKTREE_M
+        active_git = self.work_git
+
+        self._InitAnyMRef(HEAD, self.bare_git, detach=True)
+      else:
+        base = R_M
+        active_git = self.bare_git
+
+      self._InitAnyMRef(base + self.manifest.branch, active_git)
 
   def _InitMirrorHead(self):
-    self._InitAnyMRef(HEAD)
+    self._InitAnyMRef(HEAD, self.bare_git)
 
-  def _InitAnyMRef(self, ref):
+  def _InitAnyMRef(self, ref, active_git, detach=False):
     cur = self.bare_ref.symref(ref)
 
     if self.revisionId:
       if cur != '' or self.bare_ref.get(ref) != self.revisionId:
         msg = 'manifest set to %s' % self.revisionId
         dst = self.revisionId + '^0'
-        self.bare_git.UpdateRef(ref, dst, message=msg, detach=True)
+        active_git.UpdateRef(ref, dst, message=msg, detach=True)
     else:
       remote = self.GetRemote(self.remote.name)
       dst = remote.ToLocal(self.revisionExpr)
       if cur != dst:
         msg = 'manifest set to %s' % self.revisionExpr
-        self.bare_git.symbolic_ref('-m', msg, ref, dst)
+        if detach:
+          active_git.UpdateRef(ref, dst, message=msg, detach=True)
+        else:
+          active_git.symbolic_ref('-m', msg, ref, dst)
 
   def _CheckDirReference(self, srcdir, destdir, share_refs):
+    # Git worktrees don't use symlinks to share at all.
+    if self.use_git_worktrees:
+      return
+
     symlink_files = self.shareable_files[:]
     symlink_dirs = self.shareable_dirs[:]
     if share_refs:
@@ -2676,9 +2659,31 @@ class Project(object):
       symlink_dirs += self.working_tree_dirs
     to_symlink = symlink_files + symlink_dirs
     for name in set(to_symlink):
-      dst = platform_utils.realpath(os.path.join(destdir, name))
+      # Try to self-heal a bit in simple cases.
+      dst_path = os.path.join(destdir, name)
+      src_path = os.path.join(srcdir, name)
+
+      if name in self.working_tree_dirs:
+        # If the dir is missing under .repo/projects/, create it.
+        if not os.path.exists(src_path):
+          os.makedirs(src_path)
+
+      elif name in self.working_tree_files:
+        # If it's a file under the checkout .git/ and the .repo/projects/ has
+        # nothing, move the file under the .repo/projects/ tree.
+        if not os.path.exists(src_path) and os.path.isfile(dst_path):
+          platform_utils.rename(dst_path, src_path)
+
+      # If the path exists under the .repo/projects/ and there's no symlink
+      # under the checkout .git/, recreate the symlink.
+      if name in self.working_tree_dirs or name in self.working_tree_files:
+        if os.path.exists(src_path) and not os.path.exists(dst_path):
+          platform_utils.symlink(
+              os.path.relpath(src_path, os.path.dirname(dst_path)), dst_path)
+
+      dst = platform_utils.realpath(dst_path)
       if os.path.lexists(dst):
-        src = platform_utils.realpath(os.path.join(srcdir, name))
+        src = platform_utils.realpath(src_path)
         # Fail if the links are pointing to the wrong place
         if src != dst:
           _error('%s is different in %s vs %s', name, destdir, srcdir)
@@ -2735,10 +2740,7 @@ class Project(object):
         # If the source file doesn't exist, ensure the destination
         # file doesn't either.
         if name in symlink_files and not os.path.lexists(src):
-          try:
-            platform_utils.remove(dst)
-          except OSError:
-            pass
+          platform_utils.remove(dst, missing_ok=True)
 
       except OSError as e:
         if e.errno == errno.EPERM:
@@ -2746,11 +2748,45 @@ class Project(object):
         else:
           raise
 
+  def _InitGitWorktree(self):
+    """Init the project using git worktrees."""
+    self.bare_git.worktree('prune')
+    self.bare_git.worktree('add', '-ff', '--checkout', '--detach', '--lock',
+                           self.worktree, self.GetRevisionId())
+
+    # Rewrite the internal state files to use relative paths between the
+    # checkouts & worktrees.
+    dotgit = os.path.join(self.worktree, '.git')
+    with open(dotgit, 'r') as fp:
+      # Figure out the checkout->worktree path.
+      setting = fp.read()
+      assert setting.startswith('gitdir:')
+      git_worktree_path = setting.split(':', 1)[1].strip()
+    # Some platforms (e.g. Windows) won't let us update dotgit in situ because
+    # of file permissions.  Delete it and recreate it from scratch to avoid.
+    platform_utils.remove(dotgit)
+    # Use relative path from checkout->worktree & maintain Unix line endings
+    # on all OS's to match git behavior.
+    with open(dotgit, 'w', newline='\n') as fp:
+      print('gitdir:', os.path.relpath(git_worktree_path, self.worktree),
+            file=fp)
+    # Use relative path from worktree->checkout & maintain Unix line endings
+    # on all OS's to match git behavior.
+    with open(os.path.join(git_worktree_path, 'gitdir'), 'w', newline='\n') as fp:
+      print(os.path.relpath(dotgit, git_worktree_path), file=fp)
+
+    self._InitMRef()
+
   def _InitWorkTree(self, force_sync=False, submodules=False):
     realdotgit = os.path.join(self.worktree, '.git')
     tmpdotgit = realdotgit + '.tmp'
     init_dotgit = not os.path.exists(realdotgit)
     if init_dotgit:
+      if self.use_git_worktrees:
+        self._InitGitWorktree()
+        self._CopyAndLinkFiles()
+        return
+
       dotgit = tmpdotgit
       platform_utils.rmtree(tmpdotgit, ignore_errors=True)
       os.makedirs(tmpdotgit)
@@ -2766,7 +2802,7 @@ class Project(object):
         try:
           platform_utils.rmtree(dotgit)
           return self._InitWorkTree(force_sync=False, submodules=submodules)
-        except:
+        except Exception:
           raise e
       raise e
 
@@ -2857,6 +2893,13 @@ class Project(object):
       self._bare = bare
       self._gitdir = gitdir
 
+    # __getstate__ and __setstate__ are required for pickling because __getattr__ exists.
+    def __getstate__(self):
+      return (self._project, self._bare, self._gitdir)
+
+    def __setstate__(self, state):
+      self._project, self._bare, self._gitdir = state
+
     def LsOthers(self):
       p = GitCommand(self._project,
                      ['ls-files',
@@ -2885,54 +2928,67 @@ class Project(object):
                      bare=False,
                      capture_stdout=True,
                      capture_stderr=True)
-      try:
-        out = p.process.stdout.read()
-        if not hasattr(out, 'encode'):
-          out = out.decode()
-        r = {}
-        if out:
-          out = iter(out[:-1].split('\0'))
-          while out:
-            try:
-              info = next(out)
-              path = next(out)
-            except StopIteration:
-              break
-
-            class _Info(object):
-
-              def __init__(self, path, omode, nmode, oid, nid, state):
-                self.path = path
-                self.src_path = None
-                self.old_mode = omode
-                self.new_mode = nmode
-                self.old_id = oid
-                self.new_id = nid
-
-                if len(state) == 1:
-                  self.status = state
-                  self.level = None
-                else:
-                  self.status = state[:1]
-                  self.level = state[1:]
-                  while self.level.startswith('0'):
-                    self.level = self.level[1:]
-
-            info = info[1:].split(' ')
-            info = _Info(path, *info)
-            if info.status in ('R', 'C'):
-              info.src_path = info.path
-              info.path = next(out)
-            r[info.path] = info
-        return r
-      finally:
-        p.Wait()
-
-    def GetHead(self):
+      p.Wait()
+      r = {}
+      out = p.stdout
+      if out:
+        out = iter(out[:-1].split('\0'))
+        while out:
+          try:
+            info = next(out)
+            path = next(out)
+          except StopIteration:
+            break
+
+          class _Info(object):
+
+            def __init__(self, path, omode, nmode, oid, nid, state):
+              self.path = path
+              self.src_path = None
+              self.old_mode = omode
+              self.new_mode = nmode
+              self.old_id = oid
+              self.new_id = nid
+
+              if len(state) == 1:
+                self.status = state
+                self.level = None
+              else:
+                self.status = state[:1]
+                self.level = state[1:]
+                while self.level.startswith('0'):
+                  self.level = self.level[1:]
+
+          info = info[1:].split(' ')
+          info = _Info(path, *info)
+          if info.status in ('R', 'C'):
+            info.src_path = info.path
+            info.path = next(out)
+          r[info.path] = info
+      return r
+
+    def GetDotgitPath(self, subpath=None):
+      """Return the full path to the .git dir.
+
+      As a convenience, append |subpath| if provided.
+      """
       if self._bare:
-        path = os.path.join(self._project.gitdir, HEAD)
+        dotgit = self._gitdir
       else:
-        path = os.path.join(self._project.worktree, '.git', HEAD)
+        dotgit = os.path.join(self._project.worktree, '.git')
+        if os.path.isfile(dotgit):
+          # Git worktrees use a "gitdir:" syntax to point to the scratch space.
+          with open(dotgit) as fp:
+            setting = fp.read()
+          assert setting.startswith('gitdir:')
+          gitdir = setting.split(':', 1)[1].strip()
+          dotgit = os.path.normpath(os.path.join(self._project.worktree, gitdir))
+
+      return dotgit if subpath is None else os.path.join(dotgit, subpath)
+
+    def GetHead(self):
+      """Return the ref that HEAD points to."""
+      path = self.GetDotgitPath(subpath=HEAD)
       try:
         with open(path) as fd:
           line = fd.readline()
@@ -3027,9 +3083,6 @@ class Project(object):
           raise TypeError('%s() got an unexpected keyword argument %r'
                           % (name, k))
         if config is not None:
-          if not git_require((1, 7, 2)):
-            raise ValueError('cannot set config on command line for %s()'
-                             % name)
           for k, v in config.items():
             cmdv.append('-c')
             cmdv.append('%s=%s' % (k, v))
@@ -3109,7 +3162,7 @@ class _Later(object):
 class _SyncColoring(Coloring):
 
   def __init__(self, config):
-    Coloring.__init__(self, config, 'reposync')
+    super().__init__(config, 'reposync')
     self.project = self.printer('header', attr='bold')
     self.info = self.printer('info')
     self.fail = self.printer('fail', fg='red')
diff --git a/pyversion.py b/pyversion.py
deleted file mode 100644
index f6082408..00000000
--- a/pyversion.py
+++ /dev/null
@@ -1,20 +0,0 @@
-# -*- coding:utf-8 -*-
-#
-# Copyright (C) 2013 The Android Open Source Project
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#      http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-import sys
-
-def is_python3():
-  return sys.version_info[0] == 3
diff --git a/release/README.md b/release/README.md
new file mode 100644
index 00000000..3b81d532
--- /dev/null
+++ b/release/README.md
@@ -0,0 +1,2 @@
+These are helper tools for managing official releases.
+See the [release process](../docs/release-process.md) document for more details.
diff --git a/release/sign-launcher.py b/release/sign-launcher.py
new file mode 100755
index 00000000..ba5e490c
--- /dev/null
+++ b/release/sign-launcher.py
@@ -0,0 +1,114 @@
+#!/usr/bin/env python3
+# Copyright (C) 2020 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helper tool for signing repo launcher scripts correctly.
+
+This is intended to be run only by the official Repo release managers.
+"""
+
+import argparse
+import os
+import subprocess
+import sys
+
+import util
+
+
+def sign(opts):
+  """Sign the launcher!"""
+  output = ''
+  for key in opts.keys:
+    # We use ! at the end of the key so that gpg uses this specific key.
+    # Otherwise it uses the key as a lookup into the overall key and uses the
+    # default signing key.  i.e. It will see that KEYID_RSA is a subkey of
+    # another key, and use the primary key to sign instead of the subkey.
+    cmd = ['gpg', '--homedir', opts.gpgdir, '-u', f'{key}!', '--batch', '--yes',
+           '--armor', '--detach-sign', '--output', '-', opts.launcher]
+    ret = util.run(opts, cmd, encoding='utf-8', stdout=subprocess.PIPE)
+    output += ret.stdout
+
+  # Save the combined signatures into one file.
+  with open(f'{opts.launcher}.asc', 'w', encoding='utf-8') as fp:
+    fp.write(output)
+
+
+def check(opts):
+  """Check the signature."""
+  util.run(opts, ['gpg', '--verify', f'{opts.launcher}.asc'])
+
+
+def postmsg(opts):
+  """Helpful info to show at the end for release manager."""
+  print(f"""
+Repo launcher bucket:
+  gs://git-repo-downloads/
+
+To upload this launcher directly:
+  gsutil cp -a public-read {opts.launcher} {opts.launcher}.asc gs://git-repo-downloads/
+
+NB: You probably want to upload it with a specific version first, e.g.:
+  gsutil cp -a public-read {opts.launcher} gs://git-repo-downloads/repo-3.0
+  gsutil cp -a public-read {opts.launcher}.asc gs://git-repo-downloads/repo-3.0.asc
+""")
+
+
+def get_parser():
+  """Get a CLI parser."""
+  parser = argparse.ArgumentParser(description=__doc__)
+  parser.add_argument('-n', '--dry-run',
+                      dest='dryrun', action='store_true',
+                      help='show everything that would be done')
+  parser.add_argument('--gpgdir',
+                      default=os.path.join(util.HOMEDIR, '.gnupg', 'repo'),
+                      help='path to dedicated gpg dir with release keys '
+                           '(default: ~/.gnupg/repo/)')
+  parser.add_argument('--keyid', dest='keys', default=[], action='append',
+                      help='alternative signing keys to use')
+  parser.add_argument('launcher',
+                      default=os.path.join(util.TOPDIR, 'repo'), nargs='?',
+                      help='the launcher script to sign')
+  return parser
+
+
+def main(argv):
+  """The main func!"""
+  parser = get_parser()
+  opts = parser.parse_args(argv)
+
+  if not os.path.exists(opts.gpgdir):
+    parser.error(f'--gpgdir does not exist: {opts.gpgdir}')
+  if not os.path.exists(opts.launcher):
+    parser.error(f'launcher does not exist: {opts.launcher}')
+
+  opts.launcher = os.path.relpath(opts.launcher)
+  print(f'Signing "{opts.launcher}" launcher script and saving to '
+        f'"{opts.launcher}.asc"')
+
+  if opts.keys:
+    print(f'Using custom keys to sign: {" ".join(opts.keys)}')
+  else:
+    print('Using official Repo release keys to sign')
+    opts.keys = [util.KEYID_DSA, util.KEYID_RSA, util.KEYID_ECC]
+    util.import_release_key(opts)
+
+  sign(opts)
+  check(opts)
+  postmsg(opts)
+
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv[1:]))
diff --git a/release/sign-tag.py b/release/sign-tag.py
new file mode 100755
index 00000000..605437c9
--- /dev/null
+++ b/release/sign-tag.py
@@ -0,0 +1,140 @@
+#!/usr/bin/env python3
+# Copyright (C) 2020 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helper tool for signing repo release tags correctly.
+
+This is intended to be run only by the official Repo release managers, but it
+could be run by people maintaining their own fork of the project.
+
+NB: Check docs/release-process.md for production freeze information.
+"""
+
+import argparse
+import os
+import re
+import subprocess
+import sys
+
+import util
+
+
+# We currently sign with the old DSA key as it's been around the longest.
+# We should transition to RSA by Jun 2020, and ECC by Jun 2021.
+KEYID = util.KEYID_DSA
+
+# Regular expression to validate tag names.
+RE_VALID_TAG = r'^v([0-9]+[.])+[0-9]+$'
+
+
+def sign(opts):
+  """Tag the commit & sign it!"""
+  # We use ! at the end of the key so that gpg uses this specific key.
+  # Otherwise it uses the key as a lookup into the overall key and uses the
+  # default signing key.  i.e. It will see that KEYID_RSA is a subkey of
+  # another key, and use the primary key to sign instead of the subkey.
+  cmd = ['git', 'tag', '-s', opts.tag, '-u', f'{opts.key}!',
+         '-m', f'repo {opts.tag}', opts.commit]
+
+  key = 'GNUPGHOME'
+  print('+', f'export {key}="{opts.gpgdir}"')
+  oldvalue = os.getenv(key)
+  os.putenv(key, opts.gpgdir)
+  util.run(opts, cmd)
+  if oldvalue is None:
+    os.unsetenv(key)
+  else:
+    os.putenv(key, oldvalue)
+
+
+def check(opts):
+  """Check the signature."""
+  util.run(opts, ['git', 'tag', '--verify', opts.tag])
+
+
+def postmsg(opts):
+  """Helpful info to show at the end for release manager."""
+  cmd = ['git', 'rev-parse', 'remotes/origin/stable']
+  ret = util.run(opts, cmd, encoding='utf-8', stdout=subprocess.PIPE)
+  current_release = ret.stdout.strip()
+
+  cmd = ['git', 'log', '--format=%h (%aN) %s', '--no-merges',
+         f'remotes/origin/stable..{opts.tag}']
+  ret = util.run(opts, cmd, encoding='utf-8', stdout=subprocess.PIPE)
+  shortlog = ret.stdout.strip()
+
+  print(f"""
+Here's the short log since the last release.
+{shortlog}
+
+To push release to the public:
+  git push origin {opts.commit}:stable {opts.tag} -n
+NB: People will start upgrading to this version immediately.
+
+To roll back a release:
+  git push origin --force {current_release}:stable -n
+""")
+
+
+def get_parser():
+  """Get a CLI parser."""
+  parser = argparse.ArgumentParser(
+      description=__doc__,
+      formatter_class=argparse.RawDescriptionHelpFormatter)
+  parser.add_argument('-n', '--dry-run',
+                      dest='dryrun', action='store_true',
+                      help='show everything that would be done')
+  parser.add_argument('--gpgdir',
+                      default=os.path.join(util.HOMEDIR, '.gnupg', 'repo'),
+                      help='path to dedicated gpg dir with release keys '
+                           '(default: ~/.gnupg/repo/)')
+  parser.add_argument('-f', '--force', action='store_true',
+                      help='force signing of any tag')
+  parser.add_argument('--keyid', dest='key',
+                      help='alternative signing key to use')
+  parser.add_argument('tag',
+                      help='the tag to create (e.g. "v2.0")')
+  parser.add_argument('commit', default='HEAD', nargs='?',
+                      help='the commit to tag')
+  return parser
+
+
+def main(argv):
+  """The main func!"""
+  parser = get_parser()
+  opts = parser.parse_args(argv)
+
+  if not os.path.exists(opts.gpgdir):
+    parser.error(f'--gpgdir does not exist: {opts.gpgdir}')
+
+  if not opts.force and not re.match(RE_VALID_TAG, opts.tag):
+    parser.error(f'tag "{opts.tag}" does not match regex "{RE_VALID_TAG}"; '
+                 'use --force to sign anyways')
+
+  if opts.key:
+    print(f'Using custom key to sign: {opts.key}')
+  else:
+    print('Using official Repo release key to sign')
+    opts.key = KEYID
+    util.import_release_key(opts)
+
+  sign(opts)
+  check(opts)
+  postmsg(opts)
+
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv[1:]))
diff --git a/release/update-manpages b/release/update-manpages
new file mode 100755
index 00000000..ddbce0cc
--- /dev/null
+++ b/release/update-manpages
@@ -0,0 +1,102 @@
+#!/usr/bin/env python3
+# Copyright (C) 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helper tool for generating manual page for all repo commands.
+
+This is intended to be run before every official Repo release.
+"""
+
+from pathlib import Path
+from functools import partial
+import argparse
+import multiprocessing
+import os
+import re
+import shutil
+import subprocess
+import sys
+import tempfile
+
+TOPDIR = Path(__file__).resolve().parent.parent
+MANDIR = TOPDIR.joinpath('man')
+
+# Load repo local modules.
+sys.path.insert(0, str(TOPDIR))
+from git_command import RepoSourceVersion
+import subcmds
+
+def worker(cmd, **kwargs):
+  subprocess.run(cmd, **kwargs)
+
+def main(argv):
+  parser = argparse.ArgumentParser(description=__doc__)
+  opts = parser.parse_args(argv)
+
+  if not shutil.which('help2man'):
+    sys.exit('Please install help2man to continue.')
+
+  # Let repo know we're generating man pages so it can avoid some dynamic
+  # behavior (like probing active number of CPUs).  We use a weird name &
+  # value to make it less likely for users to set this var themselves.
+  os.environ['_REPO_GENERATE_MANPAGES_'] = ' indeed! '
+
+  # "repo branch" is an alias for "repo branches".
+  del subcmds.all_commands['branch']
+  (MANDIR / 'repo-branch.1').write_text('.so man1/repo-branches.1')
+
+  version = RepoSourceVersion()
+  cmdlist = [['help2man', '-N', '-n', f'repo {cmd} - manual page for repo {cmd}',
+    '-S', f'repo {cmd}', '-m', 'Repo Manual', f'--version-string={version}',
+    '-o', MANDIR.joinpath(f'repo-{cmd}.1.tmp'), TOPDIR.joinpath('repo'),
+    '-h', f'help {cmd}'] for cmd in subcmds.all_commands]
+  cmdlist.append(['help2man', '-N', '-n', 'repository management tool built on top of git',
+    '-S', 'repo', '-m', 'Repo Manual', f'--version-string={version}',
+    '-o', MANDIR.joinpath('repo.1.tmp'), TOPDIR.joinpath('repo'),
+    '-h', '--help-all'])
+
+  with tempfile.TemporaryDirectory() as tempdir:
+    repo_dir = Path(tempdir) / '.repo'
+    repo_dir.mkdir()
+    (repo_dir / 'repo').symlink_to(TOPDIR)
+
+    # Run all cmd in parallel, and wait for them to finish.
+    with multiprocessing.Pool() as pool:
+      pool.map(partial(worker, cwd=tempdir, check=True), cmdlist)
+
+  regex = (
+      (r'(It was generated by help2man) [0-9.]+', '\g<1>.'),
+      (r'^\.IP\n(.*:)\n', '.SS \g<1>\n'),
+      (r'^\.PP\nDescription', '.SH DETAILS'),
+  )
+  for tmp_path in MANDIR.glob('*.1.tmp'):
+    path = tmp_path.parent / tmp_path.stem
+    old_data = path.read_text() if path.exists() else ''
+
+    data = tmp_path.read_text()
+    tmp_path.unlink()
+
+    for pattern, replacement in regex:
+      data = re.sub(pattern, replacement, data, flags=re.M)
+
+    # If the only thing that changed was the date, don't refresh.  This avoids
+    # a lot of noise when only one file actually updates.
+    old_data = re.sub(r'^(\.TH REPO "1" ")([^"]+)', r'\1', old_data, flags=re.M)
+    new_data = re.sub(r'^(\.TH REPO "1" ")([^"]+)', r'\1', data, flags=re.M)
+    if old_data != new_data:
+      path.write_text(data)
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv[1:]))
diff --git a/release/util.py b/release/util.py
new file mode 100644
index 00000000..9d0eb1dc
--- /dev/null
+++ b/release/util.py
@@ -0,0 +1,73 @@
+# Copyright (C) 2020 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Random utility code for release tools."""
+
+import os
+import re
+import subprocess
+import sys
+
+
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
+TOPDIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+HOMEDIR = os.path.expanduser('~')
+
+
+# These are the release keys we sign with.
+KEYID_DSA = '8BB9AD793E8E6153AF0F9A4416530D5E920F5C65'
+KEYID_RSA = 'A34A13BE8E76BFF46A0C022DA2E75A824AAB9624'
+KEYID_ECC = 'E1F9040D7A3F6DAFAC897CD3D3B95DA243E48A39'
+
+
+def cmdstr(cmd):
+  """Get a nicely quoted shell command."""
+  ret = []
+  for arg in cmd:
+    if not re.match(r'^[a-zA-Z0-9/_.=-]+$', arg):
+      arg = f'"{arg}"'
+    ret.append(arg)
+  return ' '.join(ret)
+
+
+def run(opts, cmd, check=True, **kwargs):
+  """Helper around subprocess.run to include logging."""
+  print('+', cmdstr(cmd))
+  if opts.dryrun:
+    cmd = ['true', '--'] + cmd
+  try:
+    return subprocess.run(cmd, check=check, **kwargs)
+  except subprocess.CalledProcessError as e:
+    print(f'aborting: {e}', file=sys.stderr)
+    sys.exit(1)
+
+
+def import_release_key(opts):
+  """Import the public key of the official release repo signing key."""
+  # Extract the key from our repo launcher.
+  launcher = getattr(opts, 'launcher', os.path.join(TOPDIR, 'repo'))
+  print(f'Importing keys from "{launcher}" launcher script')
+  with open(launcher, encoding='utf-8') as fp:
+    data = fp.read()
+
+  keys = re.findall(
+      r'\n-----BEGIN PGP PUBLIC KEY BLOCK-----\n[^-]*'
+      r'\n-----END PGP PUBLIC KEY BLOCK-----\n', data, flags=re.M)
+  run(opts, ['gpg', '--import'], input='\n'.join(keys).encode('utf-8'))
+
+  print('Marking keys as fully trusted')
+  run(opts, ['gpg', '--import-ownertrust'],
+      input=f'{KEYID_DSA}:6:\n'.encode('utf-8'))
diff --git a/repo b/repo
index 15d2ff85..4cddbf1e 100755
--- a/repo
+++ b/repo
@@ -1,5 +1,19 @@
 #!/usr/bin/env python
 # -*- coding:utf-8 -*-
+#
+# Copyright (C) 2008 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
 
 """Repo launcher.
 
@@ -10,35 +24,135 @@ copy of repo in the checkout.
 
 from __future__ import print_function
 
+import datetime
+import os
+import platform
+import shlex
+import subprocess
+import sys
+
+
+# These should never be newer than the main.py version since this needs to be a
+# bit more flexible with older systems.  See that file for more details on the
+# versions we select.
+MIN_PYTHON_VERSION_SOFT = (3, 6)
+MIN_PYTHON_VERSION_HARD = (3, 5)
+
+
+# Keep basic logic in sync with repo_trace.py.
+class Trace(object):
+  """Trace helper logic."""
+
+  REPO_TRACE = 'REPO_TRACE'
+
+  def __init__(self):
+    self.set(os.environ.get(self.REPO_TRACE) == '1')
+
+  def set(self, value):
+    self.enabled = bool(value)
+
+  def print(self, *args, **kwargs):
+    if self.enabled:
+      print(*args, **kwargs)
+
+
+trace = Trace()
+
+
+def exec_command(cmd):
+  """Execute |cmd| or return None on failure."""
+  trace.print(':', ' '.join(cmd))
+  try:
+    if platform.system() == 'Windows':
+      ret = subprocess.call(cmd)
+      sys.exit(ret)
+    else:
+      os.execvp(cmd[0], cmd)
+  except Exception:
+    pass
+
+
+def check_python_version():
+  """Make sure the active Python version is recent enough."""
+  def reexec(prog):
+    exec_command([prog] + sys.argv)
+
+  ver = sys.version_info
+  major = ver.major
+  minor = ver.minor
+
+  # Abort on very old Python 2 versions.
+  if (major, minor) < (2, 7):
+    print('repo: error: Your Python version is too old. '
+          'Please use Python {}.{} or newer instead.'.format(
+              *MIN_PYTHON_VERSION_SOFT), file=sys.stderr)
+    sys.exit(1)
+
+  # Try to re-exec the version specific Python 3 if needed.
+  if (major, minor) < MIN_PYTHON_VERSION_SOFT:
+    # Python makes releases ~once a year, so try our min version +10 to help
+    # bridge the gap.  This is the fallback anyways so perf isn't critical.
+    min_major, min_minor = MIN_PYTHON_VERSION_SOFT
+    for inc in range(0, 10):
+      reexec('python{}.{}'.format(min_major, min_minor + inc))
+
+    # Fallback to older versions if possible.
+    for inc in range(MIN_PYTHON_VERSION_SOFT[1] - MIN_PYTHON_VERSION_HARD[1], 0, -1):
+      # Don't downgrade, and don't reexec ourselves (which would infinite loop).
+      if (min_major, min_minor - inc) <= (major, minor):
+        break
+      reexec('python{}.{}'.format(min_major, min_minor - inc))
+
+    # Try the generic Python 3 wrapper, but only if it's new enough.  If it
+    # isn't, we want to just give up below and make the user resolve things.
+    try:
+      proc = subprocess.Popen(
+          ['python3', '-c', 'import sys; '
+           'print(sys.version_info.major, sys.version_info.minor)'],
+          stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+      (output, _) = proc.communicate()
+      python3_ver = tuple(int(x) for x in output.decode('utf-8').split())
+    except (OSError, subprocess.CalledProcessError):
+      python3_ver = None
+
+    # If the python3 version looks like it's new enough, give it a try.
+    if (python3_ver and python3_ver >= MIN_PYTHON_VERSION_HARD
+            and python3_ver != (major, minor)):
+      reexec('python3')
+
+    # We're still here, so diagnose things for the user.
+    if major < 3:
+      print('repo: error: Python 2 is no longer supported; '
+            'Please upgrade to Python {}.{}+.'.format(*MIN_PYTHON_VERSION_HARD),
+            file=sys.stderr)
+      sys.exit(1)
+    elif (major, minor) < MIN_PYTHON_VERSION_HARD:
+      print('repo: error: Python 3 version is too old; '
+            'Please use Python {}.{} or newer.'.format(*MIN_PYTHON_VERSION_HARD),
+            file=sys.stderr)
+      sys.exit(1)
+
+
+if __name__ == '__main__':
+  check_python_version()
+
+
 # repo default configuration
 #
-import os
 REPO_URL = os.environ.get('REPO_URL', None)
 if not REPO_URL:
   REPO_URL = 'https://gerrit.googlesource.com/git-repo'
 REPO_REV = os.environ.get('REPO_REV')
 if not REPO_REV:
-  REPO_REV = 'repo-1'
-
-# Copyright (C) 2008 Google Inc.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#      http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
+  REPO_REV = 'stable'
+# URL to file bug reports for repo tool issues.
+BUG_URL = 'https://bugs.chromium.org/p/gerrit/issues/entry?template=Repo+tool+issue'
 
 # increment this whenever we make important changes to this script
-VERSION = (1, 27)
+VERSION = (2, 17)
 
 # increment this if the MAINTAINER_KEYS block is modified
-KEYRING_VERSION = (1, 2)
+KEYRING_VERSION = (2, 3)
 
 # Each individual key entry is created by using:
 # gpg --armor --export keyid
@@ -46,7 +160,6 @@ MAINTAINER_KEYS = """
 
      Repo Maintainer <repo@android.kernel.org>
 -----BEGIN PGP PUBLIC KEY BLOCK-----
-Version: GnuPG v1.4.2.2 (GNU/Linux)
 
 mQGiBEj3ugERBACrLJh/ZPyVSKeClMuznFIrsQ+hpNnmJGw1a9GXKYKk8qHPhAZf
 WKtrBqAVMNRLhL85oSlekRz98u41H5si5zcuv+IXJDF5MJYcB8f22wAy15lUqPWi
@@ -82,63 +195,64 @@ p3v5ILwfC7hVx4jHSnOgZ65L9s8EQdVr1ckN9243yta7rNgwfcqb60ILMFF1BRk/
 5xGrFy8tfAaeBMIQ17gvFSp/suc9DYO0ICK2BISzq+F+ZiAKsjMYOBNdH/h0zobQ
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-TACbBS+Up3RpfYVfd63c1cDdlru13pQAn3NQy/SN858MkxN+zym86UBgOad2
-=CMiZ
------END PGP PUBLIC KEY BLOCK-----
-
-     Conley Owens <cco3@android.com>
------BEGIN PGP PUBLIC KEY BLOCK-----
-Version: GnuPG v1.4.11 (GNU/Linux)
-
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+AgAgFiEEi7mteT6OYVOvD5pEFlMNXpIPXGUFAl5FqX0CGwIAgQkQFlMNXpIPXGV2
+IAQZFggAHRYhBOH5BA16P22vrIl809O5XaJD5Io5BQJeRal9AAoJENO5XaJD5Io5
+MEkA/3uLmiwANOcgE0zB9zga0T/KkYhYOWFx7zRyDhrTf9spAPwIfSBOAGtwxjLO
+DCce5OaQJl/YuGHvXq2yx5h7T8pdAZ+PAJ4qfIk2LLSidsplTDXOKhOQAuOqUQCf
+cZ7aFsJF4PtcDrfdejyAxbtsSHI=
+=82Tj
 -----END PGP PUBLIC KEY BLOCK-----
 """
 
 GIT = 'git'                      # our git command
+# NB: The version of git that the repo launcher requires may be much older than
+# the version of git that the main repo source tree requires.  Keeping this at
+# an older version also makes it easier for users to upgrade/rollback as needed.
+#
+# git-1.7 is in (EOL) Ubuntu Precise.
 MIN_GIT_VERSION = (1, 7, 2)      # minimum supported git version
 repodir = '.repo'                # name of repo's private directory
 S_repo = 'repo'                  # special repo repository
 S_manifests = 'manifests'        # special manifest repository
 REPO_MAIN = S_repo + '/main.py'  # main script
-MIN_PYTHON_VERSION = (2, 7)      # minimum supported python version
 GITC_CONFIG_FILE = '/gitc/.config'
 GITC_FS_ROOT_DIR = '/gitc/manifest-rw/'
 
 
 import collections
 import errno
+import json
 import optparse
-import platform
 import re
 import shutil
 import stat
-import subprocess
-import sys
 
 if sys.version_info[0] == 3:
   import urllib.request
@@ -151,116 +265,215 @@ else:
   urllib.error = urllib2
 
 
-# Python version check
-ver = sys.version_info
-if (ver[0], ver[1]) < MIN_PYTHON_VERSION:
-  print('error: Python version {} unsupported.\n'
-        'Please use Python {}.{} instead.'.format(
-            sys.version.split(' ')[0],
-            MIN_PYTHON_VERSION[0],
-            MIN_PYTHON_VERSION[1],
-        ), file=sys.stderr)
-  sys.exit(1)
-
 home_dot_repo = os.path.expanduser('~/.repoconfig')
 gpg_dir = os.path.join(home_dot_repo, 'gnupg')
 
-extra_args = []
-init_optparse = optparse.OptionParser(usage="repo init -u url [options]")
-
-# Logging
-group = init_optparse.add_option_group('Logging options')
-group.add_option('-q', '--quiet',
-                 dest="quiet", action="store_true", default=False,
-                 help="be quiet")
-
-# Manifest
-group = init_optparse.add_option_group('Manifest options')
-group.add_option('-u', '--manifest-url',
-                 dest='manifest_url',
-                 help='manifest repository location', metavar='URL')
-group.add_option('-b', '--manifest-branch',
-                 dest='manifest_branch',
-                 help='manifest branch or revision', metavar='REVISION')
-group.add_option('-m', '--manifest-name',
-                 dest='manifest_name',
-                 help='initial manifest file', metavar='NAME.xml')
-group.add_option('--current-branch',
-                 dest='current_branch_only', action='store_true',
-                 help='fetch only current manifest branch from server')
-group.add_option('--mirror',
-                 dest='mirror', action='store_true',
-                 help='create a replica of the remote repositories '
-                      'rather than a client working directory')
-group.add_option('--reference',
-                 dest='reference',
-                 help='location of mirror directory', metavar='DIR')
-group.add_option('--dissociate',
-                 dest='dissociate', action='store_true',
-                 help='dissociate from reference mirrors after clone')
-group.add_option('--depth', type='int', default=None,
-                 dest='depth',
-                 help='create a shallow clone with given depth; see git clone')
-group.add_option('--partial-clone', action='store_true',
-                 dest='partial_clone',
-                 help='perform partial clone (https://git-scm.com/'
-                 'docs/gitrepository-layout#_code_partialclone_code)')
-group.add_option('--clone-filter', action='store', default='blob:none',
-                 dest='clone_filter',
-                 help='filter for use with --partial-clone [default: %default]')
-group.add_option('--archive',
-                 dest='archive', action='store_true',
-                 help='checkout an archive instead of a git repository for '
-                      'each project. See git archive.')
-group.add_option('--submodules',
-                 dest='submodules', action='store_true',
-                 help='sync any submodules associated with the manifest repo')
-group.add_option('-g', '--groups',
-                 dest='groups', default='default',
-                 help='restrict manifest projects to ones with specified '
-                      'group(s) [default|all|G1,G2,G3|G4,-G5,-G6]',
-                 metavar='GROUP')
-group.add_option('-p', '--platform',
-                 dest='platform', default="auto",
-                 help='restrict manifest projects to ones with a specified '
-                      'platform group [auto|all|none|linux|darwin|...]',
-                 metavar='PLATFORM')
-group.add_option('--no-clone-bundle',
-                 dest='no_clone_bundle', action='store_true',
-                 help='disable use of /clone.bundle on HTTP/HTTPS')
-group.add_option('--no-tags',
-                 dest='no_tags', action='store_true',
-                 help="don't fetch tags in the manifest")
-
-
-# Tool
-group = init_optparse.add_option_group('repo Version options')
-group.add_option('--repo-url',
-                 dest='repo_url',
-                 help='repo repository location ($REPO_URL)', metavar='URL')
-group.add_option('--repo-branch',
-                 dest='repo_branch',
-                 help='repo branch or revision ($REPO_REV)', metavar='REVISION')
-group.add_option('--no-repo-verify',
-                 dest='no_repo_verify', action='store_true',
-                 help='do not verify repo source code')
-
-# Other
-group = init_optparse.add_option_group('Other options')
-group.add_option('--config-name',
-                 dest='config_name', action="store_true", default=False,
-                 help='Always prompt for name/e-mail')
-
-
-def _GitcInitOptions(init_optparse_arg):
-  init_optparse_arg.set_usage("repo gitc-init -u url -c client [options]")
-  g = init_optparse_arg.add_option_group('GITC options')
-  g.add_option('-f', '--manifest-file',
-               dest='manifest_file',
-               help='Optional manifest file to use for this GITC client.')
-  g.add_option('-c', '--gitc-client',
-               dest='gitc_client',
-               help='The name of the gitc_client instance to create or modify.')
+
+def GetParser(gitc_init=False):
+  """Setup the CLI parser."""
+  if gitc_init:
+    usage = 'repo gitc-init -c client [options] [-u] url'
+  else:
+    usage = 'repo init [options] [-u] url'
+
+  parser = optparse.OptionParser(usage=usage)
+  InitParser(parser, gitc_init=gitc_init)
+  return parser
+
+
+def InitParser(parser, gitc_init=False):
+  """Setup the CLI parser."""
+  # NB: Keep in sync with command.py:_CommonOptions().
+
+  # Logging.
+  group = parser.add_option_group('Logging options')
+  group.add_option('-v', '--verbose',
+                   dest='output_mode', action='store_true',
+                   help='show all output')
+  group.add_option('-q', '--quiet',
+                   dest='output_mode', action='store_false',
+                   help='only show errors')
+
+  # Manifest.
+  group = parser.add_option_group('Manifest options')
+  group.add_option('-u', '--manifest-url',
+                   help='manifest repository location', metavar='URL')
+  group.add_option('-b', '--manifest-branch', metavar='REVISION',
+                   help='manifest branch or revision (use HEAD for default)')
+  group.add_option('-m', '--manifest-name', default='default.xml',
+                   help='initial manifest file', metavar='NAME.xml')
+  group.add_option('-g', '--groups', default='default',
+                   help='restrict manifest projects to ones with specified '
+                        'group(s) [default|all|G1,G2,G3|G4,-G5,-G6]',
+                   metavar='GROUP')
+  group.add_option('-p', '--platform', default='auto',
+                   help='restrict manifest projects to ones with a specified '
+                        'platform group [auto|all|none|linux|darwin|...]',
+                   metavar='PLATFORM')
+  group.add_option('--submodules', action='store_true',
+                   help='sync any submodules associated with the manifest repo')
+  group.add_option('--standalone-manifest', action='store_true',
+                   help='download the manifest as a static file '
+                        'rather then create a git checkout of '
+                        'the manifest repo')
+
+  # Options that only affect manifest project, and not any of the projects
+  # specified in the manifest itself.
+  group = parser.add_option_group('Manifest (only) checkout options')
+  cbr_opts = ['--current-branch']
+  # The gitc-init subcommand allocates -c itself, but a lot of init users
+  # want -c, so try to satisfy both as best we can.
+  if not gitc_init:
+    cbr_opts += ['-c']
+  group.add_option(*cbr_opts,
+                   dest='current_branch_only', action='store_true',
+                   help='fetch only current manifest branch from server')
+  group.add_option('--no-current-branch',
+                   dest='current_branch_only', action='store_false',
+                   help='fetch all manifest branches from server')
+  group.add_option('--tags',
+                   action='store_true',
+                   help='fetch tags in the manifest')
+  group.add_option('--no-tags',
+                   dest='tags', action='store_false',
+                   help="don't fetch tags in the manifest")
+
+  # These are fundamentally different ways of structuring the checkout.
+  group = parser.add_option_group('Checkout modes')
+  group.add_option('--mirror', action='store_true',
+                   help='create a replica of the remote repositories '
+                        'rather than a client working directory')
+  group.add_option('--archive', action='store_true',
+                   help='checkout an archive instead of a git repository for '
+                        'each project. See git archive.')
+  group.add_option('--worktree', action='store_true',
+                   help='use git-worktree to manage projects')
+
+  # These are fundamentally different ways of structuring the checkout.
+  group = parser.add_option_group('Project checkout optimizations')
+  group.add_option('--reference',
+                   help='location of mirror directory', metavar='DIR')
+  group.add_option('--dissociate', action='store_true',
+                   help='dissociate from reference mirrors after clone')
+  group.add_option('--depth', type='int', default=None,
+                   help='create a shallow clone with given depth; '
+                        'see git clone')
+  group.add_option('--partial-clone', action='store_true',
+                   help='perform partial clone (https://git-scm.com/'
+                        'docs/gitrepository-layout#_code_partialclone_code)')
+  group.add_option('--no-partial-clone', action='store_false',
+                   help='disable use of partial clone (https://git-scm.com/'
+                        'docs/gitrepository-layout#_code_partialclone_code)')
+  group.add_option('--partial-clone-exclude', action='store',
+                   help='exclude the specified projects (a comma-delimited '
+                        'project names) from partial clone (https://git-scm.com'
+                        '/docs/gitrepository-layout#_code_partialclone_code)')
+  group.add_option('--clone-filter', action='store', default='blob:none',
+                   help='filter for use with --partial-clone '
+                        '[default: %default]')
+  group.add_option('--use-superproject', action='store_true', default=None,
+                   help='use the manifest superproject to sync projects')
+  group.add_option('--no-use-superproject', action='store_false',
+                   dest='use_superproject',
+                   help='disable use of manifest superprojects')
+  group.add_option('--clone-bundle', action='store_true',
+                   help='enable use of /clone.bundle on HTTP/HTTPS '
+                        '(default if not --partial-clone)')
+  group.add_option('--no-clone-bundle',
+                   dest='clone_bundle', action='store_false',
+                   help='disable use of /clone.bundle on HTTP/HTTPS (default if --partial-clone)')
+
+  # Tool.
+  group = parser.add_option_group('repo Version options')
+  group.add_option('--repo-url', metavar='URL',
+                   help='repo repository location ($REPO_URL)')
+  group.add_option('--repo-rev', metavar='REV',
+                   help='repo branch or revision ($REPO_REV)')
+  group.add_option('--repo-branch', dest='repo_rev',
+                   help=optparse.SUPPRESS_HELP)
+  group.add_option('--no-repo-verify',
+                   dest='repo_verify', default=True, action='store_false',
+                   help='do not verify repo source code')
+
+  # Other.
+  group = parser.add_option_group('Other options')
+  group.add_option('--config-name',
+                   action='store_true', default=False,
+                   help='Always prompt for name/e-mail')
+
+  # gitc-init specific settings.
+  if gitc_init:
+    group = parser.add_option_group('GITC options')
+    group.add_option('-f', '--manifest-file',
+                     help='Optional manifest file to use for this GITC client.')
+    group.add_option('-c', '--gitc-client',
+                     help='Name of the gitc_client instance to create or modify.')
+
+  return parser
+
+
+# This is a poor replacement for subprocess.run until we require Python 3.6+.
+RunResult = collections.namedtuple(
+    'RunResult', ('returncode', 'stdout', 'stderr'))
+
+
+class RunError(Exception):
+  """Error when running a command failed."""
+
+
+def run_command(cmd, **kwargs):
+  """Run |cmd| and return its output."""
+  check = kwargs.pop('check', False)
+  if kwargs.pop('capture_output', False):
+    kwargs.setdefault('stdout', subprocess.PIPE)
+    kwargs.setdefault('stderr', subprocess.PIPE)
+  cmd_input = kwargs.pop('input', None)
+
+  def decode(output):
+    """Decode |output| to text."""
+    if output is None:
+      return output
+    try:
+      return output.decode('utf-8')
+    except UnicodeError:
+      print('repo: warning: Invalid UTF-8 output:\ncmd: %r\n%r' % (cmd, output),
+            file=sys.stderr)
+      # TODO(vapier): Once we require Python 3, use 'backslashreplace'.
+      return output.decode('utf-8', 'replace')
+
+  # Run & package the results.
+  proc = subprocess.Popen(cmd, **kwargs)
+  (stdout, stderr) = proc.communicate(input=cmd_input)
+  dbg = ': ' + ' '.join(cmd)
+  if cmd_input is not None:
+    dbg += ' 0<|'
+  if stdout == subprocess.PIPE:
+    dbg += ' 1>|'
+  if stderr == subprocess.PIPE:
+    dbg += ' 2>|'
+  elif stderr == subprocess.STDOUT:
+    dbg += ' 2>&1'
+  trace.print(dbg)
+  ret = RunResult(proc.returncode, decode(stdout), decode(stderr))
+
+  # If things failed, print useful debugging output.
+  if check and ret.returncode:
+    print('repo: error: "%s" failed with exit status %s' %
+          (cmd[0], ret.returncode), file=sys.stderr)
+    print('  cwd: %s\n  cmd: %r' %
+          (kwargs.get('cwd', os.getcwd()), cmd), file=sys.stderr)
+
+    def _print_output(name, output):
+      if output:
+        print('  %s:\n  >> %s' % (name, '\n  >> '.join(output.splitlines())),
+              file=sys.stderr)
+
+    _print_output('stdout', ret.stdout)
+    _print_output('stderr', ret.stderr)
+    raise RunError(ret)
+
+  return ret
+
 
 _gitc_manifest_dir = None
 
@@ -283,9 +496,11 @@ def get_gitc_manifest_dir():
 def gitc_parse_clientdir(gitc_fs_path):
   """Parse a path in the GITC FS and return its client name.
 
-  @param gitc_fs_path: A subdirectory path within the GITC_FS_ROOT_DIR.
+  Args:
+    gitc_fs_path: A subdirectory path within the GITC_FS_ROOT_DIR.
 
-  @returns: The GITC client name
+  Returns:
+    The GITC client name.
   """
   if gitc_fs_path == GITC_FS_ROOT_DIR:
     return None
@@ -309,31 +524,53 @@ class CloneFailure(Exception):
   """
 
 
+def check_repo_verify(repo_verify, quiet=False):
+  """Check the --repo-verify state."""
+  if not repo_verify:
+    print('repo: warning: verification of repo code has been disabled;\n'
+          'repo will not be able to verify the integrity of itself.\n',
+          file=sys.stderr)
+    return False
+
+  if NeedSetupGnuPG():
+    return SetupGnuPG(quiet)
+
+  return True
+
+
+def check_repo_rev(dst, rev, repo_verify=True, quiet=False):
+  """Check that |rev| is valid."""
+  do_verify = check_repo_verify(repo_verify, quiet=quiet)
+  remote_ref, local_rev = resolve_repo_rev(dst, rev)
+  if not quiet and not remote_ref.startswith('refs/heads/'):
+    print('warning: repo is not tracking a remote branch, so it will not '
+          'receive updates', file=sys.stderr)
+  if do_verify:
+    rev = verify_rev(dst, remote_ref, local_rev, quiet)
+  else:
+    rev = local_rev
+  return (remote_ref, rev)
+
+
 def _Init(args, gitc_init=False):
   """Installs repo by cloning it over the network.
   """
-  if gitc_init:
-    _GitcInitOptions(init_optparse)
-  opt, args = init_optparse.parse_args(args)
+  parser = GetParser(gitc_init=gitc_init)
+  opt, args = parser.parse_args(args)
   if args:
-    init_optparse.print_usage()
-    sys.exit(1)
-
-  url = opt.repo_url
-  if not url:
-    url = REPO_URL
-    extra_args.append('--repo-url=%s' % url)
+    if not opt.manifest_url:
+      opt.manifest_url = args.pop(0)
+    if args:
+      parser.print_usage()
+      sys.exit(1)
+  opt.quiet = opt.output_mode is False
+  opt.verbose = opt.output_mode is True
 
-  branch = opt.repo_branch
-  if not branch:
-    branch = REPO_REV
-    extra_args.append('--repo-branch=%s' % branch)
+  if opt.clone_bundle is None:
+    opt.clone_bundle = False if opt.partial_clone else True
 
-  if branch.startswith('refs/heads/'):
-    branch = branch[len('refs/heads/'):]
-  if branch.startswith('refs/'):
-    print("fatal: invalid branch name '%s'" % branch, file=sys.stderr)
-    raise CloneFailure()
+  url = opt.repo_url or REPO_URL
+  rev = opt.repo_rev or REPO_REV
 
   try:
     if gitc_init:
@@ -368,23 +605,13 @@ def _Init(args, gitc_init=False):
 
   _CheckGitVersion()
   try:
-    if opt.no_repo_verify:
-      do_verify = False
-    else:
-      if NeedSetupGnuPG():
-        do_verify = SetupGnuPG(opt.quiet)
-      else:
-        do_verify = True
-
+    if not opt.quiet:
+      print('Downloading Repo source from', url)
     dst = os.path.abspath(os.path.join(repodir, S_repo))
-    _Clone(url, dst, opt.quiet, not opt.no_clone_bundle)
-
-    if do_verify:
-      rev = _Verify(dst, branch, opt.quiet)
-    else:
-      rev = 'refs/remotes/origin/%s^0' % branch
+    _Clone(url, dst, opt.clone_bundle, opt.quiet, opt.verbose)
 
-    _Checkout(dst, branch, rev, opt.quiet)
+    remote_ref, rev = check_repo_rev(dst, rev, opt.repo_verify, quiet=opt.quiet)
+    _Checkout(dst, remote_ref, rev, opt.quiet)
 
     if not os.path.isfile(os.path.join(dst, 'repo')):
       print("warning: '%s' does not look like a git-repo repository, is "
@@ -397,15 +624,34 @@ def _Init(args, gitc_init=False):
     raise
 
 
+def run_git(*args, **kwargs):
+  """Run git and return execution details."""
+  kwargs.setdefault('capture_output', True)
+  kwargs.setdefault('check', True)
+  try:
+    return run_command([GIT] + list(args), **kwargs)
+  except OSError as e:
+    print(file=sys.stderr)
+    print('repo: error: "%s" is not available' % GIT, file=sys.stderr)
+    print('repo: error: %s' % e, file=sys.stderr)
+    print(file=sys.stderr)
+    print('Please make sure %s is installed and in your path.' % GIT,
+          file=sys.stderr)
+    sys.exit(1)
+  except RunError:
+    raise CloneFailure()
+
+
 # The git version info broken down into components for easy analysis.
 # Similar to Python's sys.version_info.
 GitVersion = collections.namedtuple(
     'GitVersion', ('major', 'minor', 'micro', 'full'))
 
+
 def ParseGitVersion(ver_str=None):
   if ver_str is None:
     # Load the version ourselves.
-    ver_str = _GetGitVersion()
+    ver_str = run_git('--version').stdout
 
   if not ver_str.startswith('git version '):
     return None
@@ -422,41 +668,52 @@ def ParseGitVersion(ver_str=None):
   return GitVersion(*to_tuple)
 
 
-def _GetGitVersion():
-  cmd = [GIT, '--version']
-  try:
-    proc = subprocess.Popen(cmd, stdout=subprocess.PIPE)
-  except OSError as e:
-    print(file=sys.stderr)
-    print("fatal: '%s' is not available" % GIT, file=sys.stderr)
-    print('fatal: %s' % e, file=sys.stderr)
-    print(file=sys.stderr)
-    print('Please make sure %s is installed and in your path.' % GIT,
-          file=sys.stderr)
-    raise
-
-  ver_str = proc.stdout.read().strip()
-  proc.stdout.close()
-  proc.wait()
-  return ver_str.decode('utf-8')
-
-
 def _CheckGitVersion():
-  try:
-    ver_act = ParseGitVersion()
-  except OSError:
-    raise CloneFailure()
-
+  ver_act = ParseGitVersion()
   if ver_act is None:
     print('fatal: unable to detect git version', file=sys.stderr)
     raise CloneFailure()
 
   if ver_act < MIN_GIT_VERSION:
     need = '.'.join(map(str, MIN_GIT_VERSION))
-    print('fatal: git %s or later required' % need, file=sys.stderr)
+    print('fatal: git %s or later required; found %s' % (need, ver_act.full),
+          file=sys.stderr)
     raise CloneFailure()
 
 
+def SetGitTrace2ParentSid(env=None):
+  """Set up GIT_TRACE2_PARENT_SID for git tracing."""
+  # We roughly follow the format git itself uses in trace2/tr2_sid.c.
+  # (1) Be unique (2) be valid filename (3) be fixed length.
+  #
+  # Since we always export this variable, we try to avoid more expensive calls.
+  # e.g. We don't attempt hostname lookups or hashing the results.
+  if env is None:
+    env = os.environ
+
+  KEY = 'GIT_TRACE2_PARENT_SID'
+
+  now = datetime.datetime.utcnow()
+  value = 'repo-%s-P%08x' % (now.strftime('%Y%m%dT%H%M%SZ'), os.getpid())
+
+  # If it's already set, then append ourselves.
+  if KEY in env:
+    value = env[KEY] + '/' + value
+
+  _setenv(KEY, value, env=env)
+
+
+def _setenv(key, value, env=None):
+  """Set |key| in the OS environment |env| to |value|."""
+  if env is None:
+    env = os.environ
+  # Environment handling across systems is messy.
+  try:
+    env[key] = value
+  except UnicodeEncodeError:
+    env[key] = value.encode()
+
+
 def NeedSetupGnuPG():
   if not os.path.isdir(home_dot_repo):
     return True
@@ -492,43 +749,54 @@ def SetupGnuPG(quiet):
             file=sys.stderr)
       sys.exit(1)
 
-  env = os.environ.copy()
-  try:
-    env['GNUPGHOME'] = gpg_dir
-  except UnicodeEncodeError:
-    env['GNUPGHOME'] = gpg_dir.encode()
-
-  cmd = ['gpg', '--import']
+  if not quiet:
+    print('repo: Updating release signing keys to keyset ver %s' %
+          ('.'.join(str(x) for x in KEYRING_VERSION),))
+  # NB: We use --homedir (and cwd below) because some environments (Windows) do
+  # not correctly handle full native paths.  We avoid the issue by changing to
+  # the right dir with cwd=gpg_dir before executing gpg, and then telling gpg to
+  # use the cwd (.) as its homedir which leaves the path resolution logic to it.
+  cmd = ['gpg', '--homedir', '.', '--import']
   try:
-    proc = subprocess.Popen(cmd,
-                            env=env,
-                            stdin=subprocess.PIPE)
-  except OSError as e:
+    # gpg can be pretty chatty.  Always capture the output and if something goes
+    # wrong, the builtin check failure will dump stdout & stderr for debugging.
+    run_command(cmd, stdin=subprocess.PIPE, capture_output=True,
+                cwd=gpg_dir, check=True,
+                input=MAINTAINER_KEYS.encode('utf-8'))
+  except OSError:
     if not quiet:
       print('warning: gpg (GnuPG) is not available.', file=sys.stderr)
       print('warning: Installing it is strongly encouraged.', file=sys.stderr)
       print(file=sys.stderr)
     return False
 
-  proc.stdin.write(MAINTAINER_KEYS.encode('utf-8'))
-  proc.stdin.close()
-
-  if proc.wait() != 0:
-    print('fatal: registering repo maintainer keys failed', file=sys.stderr)
-    sys.exit(1)
-  print()
-
   with open(os.path.join(home_dot_repo, 'keyring-version'), 'w') as fd:
     fd.write('.'.join(map(str, KEYRING_VERSION)) + '\n')
   return True
 
 
-def _SetConfig(local, name, value):
+def _SetConfig(cwd, name, value):
   """Set a git configuration option to the specified value.
   """
-  cmd = [GIT, 'config', name, value]
-  if subprocess.Popen(cmd, cwd=local).wait() != 0:
-    raise CloneFailure()
+  run_git('config', name, value, cwd=cwd)
+
+
+def _GetRepoConfig(name):
+  """Read a repo configuration option."""
+  config = os.path.join(home_dot_repo, 'config')
+  if not os.path.exists(config):
+    return None
+
+  cmd = ['config', '--file', config, '--get', name]
+  ret = run_git(*cmd, check=False)
+  if ret.returncode == 0:
+    return ret.stdout
+  elif ret.returncode == 1:
+    return None
+  else:
+    print('repo: error: git %s failed:\n%s' % (' '.join(cmd), ret.stderr),
+          file=sys.stderr)
+    raise RunError()
 
 
 def _InitHttp():
@@ -542,7 +810,7 @@ def _InitHttp():
       p = n.hosts[host]
       mgr.add_password(p[1], 'http://%s/' % host, p[0], p[2])
       mgr.add_password(p[1], 'https://%s/' % host, p[0], p[2])
-  except:
+  except Exception:
     pass
   handlers.append(urllib.request.HTTPBasicAuthHandler(mgr))
   handlers.append(urllib.request.HTTPDigestAuthHandler(mgr))
@@ -556,39 +824,29 @@ def _InitHttp():
   urllib.request.install_opener(urllib.request.build_opener(*handlers))
 
 
-def _Fetch(url, local, src, quiet):
-  if not quiet:
-    print('Get %s' % url, file=sys.stderr)
-
-  cmd = [GIT, 'fetch']
-  if quiet:
+def _Fetch(url, cwd, src, quiet, verbose):
+  cmd = ['fetch']
+  if not verbose:
     cmd.append('--quiet')
+  err = None
+  if not quiet and sys.stdout.isatty():
+    cmd.append('--progress')
+  elif not verbose:
     err = subprocess.PIPE
-  else:
-    err = None
   cmd.append(src)
   cmd.append('+refs/heads/*:refs/remotes/origin/*')
   cmd.append('+refs/tags/*:refs/tags/*')
-
-  proc = subprocess.Popen(cmd, cwd=local, stderr=err)
-  if err:
-    proc.stderr.read()
-    proc.stderr.close()
-  if proc.wait() != 0:
-    raise CloneFailure()
+  run_git(*cmd, stderr=err, capture_output=False, cwd=cwd)
 
 
-def _DownloadBundle(url, local, quiet):
+def _DownloadBundle(url, cwd, quiet, verbose):
   if not url.endswith('/'):
     url += '/'
   url += 'clone.bundle'
 
-  proc = subprocess.Popen(
-      [GIT, 'config', '--get-regexp', 'url.*.insteadof'],
-      cwd=local,
-      stdout=subprocess.PIPE)
-  for line in proc.stdout:
-    line = line.decode('utf-8')
+  ret = run_git('config', '--get-regexp', 'url.*.insteadof', cwd=cwd,
+                check=False)
+  for line in ret.stdout.splitlines():
     m = re.compile(r'^url\.(.*)\.insteadof (.*)$').match(line)
     if m:
       new_url = m.group(1)
@@ -596,29 +854,26 @@ def _DownloadBundle(url, local, quiet):
       if url.startswith(old_url):
         url = new_url + url[len(old_url):]
         break
-  proc.stdout.close()
-  proc.wait()
 
   if not url.startswith('http:') and not url.startswith('https:'):
     return False
 
-  dest = open(os.path.join(local, '.git', 'clone.bundle'), 'w+b')
+  dest = open(os.path.join(cwd, '.git', 'clone.bundle'), 'w+b')
   try:
     try:
       r = urllib.request.urlopen(url)
     except urllib.error.HTTPError as e:
-      if e.code in [401, 403, 404, 501]:
-        return False
-      print('fatal: Cannot get %s' % url, file=sys.stderr)
-      print('fatal: HTTP error %s' % e.code, file=sys.stderr)
-      raise CloneFailure()
+      if e.code not in [400, 401, 403, 404, 501]:
+        print('warning: Cannot get %s' % url, file=sys.stderr)
+        print('warning: HTTP error %s' % e.code, file=sys.stderr)
+      return False
     except urllib.error.URLError as e:
       print('fatal: Cannot get %s' % url, file=sys.stderr)
       print('fatal: error %s' % e.reason, file=sys.stderr)
       raise CloneFailure()
     try:
-      if not quiet:
-        print('Get %s' % url, file=sys.stderr)
+      if verbose:
+        print('Downloading clone bundle %s' % url, file=sys.stderr)
       while True:
         buf = r.read(8192)
         if not buf:
@@ -630,124 +885,139 @@ def _DownloadBundle(url, local, quiet):
     dest.close()
 
 
-def _ImportBundle(local):
-  path = os.path.join(local, '.git', 'clone.bundle')
+def _ImportBundle(cwd):
+  path = os.path.join(cwd, '.git', 'clone.bundle')
   try:
-    _Fetch(local, local, path, True)
+    _Fetch(cwd, cwd, path, True, False)
   finally:
     os.remove(path)
 
 
-def _Clone(url, local, quiet, clone_bundle):
+def _Clone(url, cwd, clone_bundle, quiet, verbose):
   """Clones a git repository to a new subdirectory of repodir
   """
-  try:
-    os.mkdir(local)
-  except OSError as e:
-    print('fatal: cannot make %s directory: %s' % (local, e.strerror),
-          file=sys.stderr)
-    raise CloneFailure()
+  if verbose:
+    print('Cloning git repository', url)
 
-  cmd = [GIT, 'init', '--quiet']
   try:
-    proc = subprocess.Popen(cmd, cwd=local)
+    os.mkdir(cwd)
   except OSError as e:
-    print(file=sys.stderr)
-    print("fatal: '%s' is not available" % GIT, file=sys.stderr)
-    print('fatal: %s' % e, file=sys.stderr)
-    print(file=sys.stderr)
-    print('Please make sure %s is installed and in your path.' % GIT,
+    print('fatal: cannot make %s directory: %s' % (cwd, e.strerror),
           file=sys.stderr)
     raise CloneFailure()
-  if proc.wait() != 0:
-    print('fatal: could not create %s' % local, file=sys.stderr)
-    raise CloneFailure()
+
+  run_git('init', '--quiet', cwd=cwd)
 
   _InitHttp()
-  _SetConfig(local, 'remote.origin.url', url)
-  _SetConfig(local,
+  _SetConfig(cwd, 'remote.origin.url', url)
+  _SetConfig(cwd,
              'remote.origin.fetch',
              '+refs/heads/*:refs/remotes/origin/*')
-  if clone_bundle and _DownloadBundle(url, local, quiet):
-    _ImportBundle(local)
-  _Fetch(url, local, 'origin', quiet)
+  if clone_bundle and _DownloadBundle(url, cwd, quiet, verbose):
+    _ImportBundle(cwd)
+  _Fetch(url, cwd, 'origin', quiet, verbose)
+
+
+def resolve_repo_rev(cwd, committish):
+  """Figure out what REPO_REV represents.
 
+  We support:
+  * refs/heads/xxx: Branch.
+  * refs/tags/xxx: Tag.
+  * xxx: Branch or tag or commit.
 
-def _Verify(cwd, branch, quiet):
-  """Verify the branch has been signed by a tag.
+  Args:
+    cwd: The git checkout to run in.
+    committish: The REPO_REV argument to resolve.
+
+  Returns:
+    A tuple of (remote ref, commit) as makes sense for the committish.
+    For branches, this will look like ('refs/heads/stable', <revision>).
+    For tags, this will look like ('refs/tags/v1.0', <revision>).
+    For commits, this will be (<revision>, <revision>).
   """
-  cmd = [GIT, 'describe', 'origin/%s' % branch]
-  proc = subprocess.Popen(cmd,
-                          stdout=subprocess.PIPE,
-                          stderr=subprocess.PIPE,
-                          cwd=cwd)
-  cur = proc.stdout.read().strip().decode('utf-8')
-  proc.stdout.close()
-
-  proc.stderr.read()
-  proc.stderr.close()
-
-  if proc.wait() != 0 or not cur:
-    print(file=sys.stderr)
-    print("fatal: branch '%s' has not been signed" % branch, file=sys.stderr)
-    raise CloneFailure()
+  def resolve(committish):
+    ret = run_git('rev-parse', '--verify', '%s^{commit}' % (committish,),
+                  cwd=cwd, check=False)
+    return None if ret.returncode else ret.stdout.strip()
+
+  # An explicit branch.
+  if committish.startswith('refs/heads/'):
+    remote_ref = committish
+    committish = committish[len('refs/heads/'):]
+    rev = resolve('refs/remotes/origin/%s' % committish)
+    if rev is None:
+      print('repo: error: unknown branch "%s"' % (committish,),
+            file=sys.stderr)
+      raise CloneFailure()
+    return (remote_ref, rev)
+
+  # An explicit tag.
+  if committish.startswith('refs/tags/'):
+    remote_ref = committish
+    committish = committish[len('refs/tags/'):]
+    rev = resolve(remote_ref)
+    if rev is None:
+      print('repo: error: unknown tag "%s"' % (committish,),
+            file=sys.stderr)
+      raise CloneFailure()
+    return (remote_ref, rev)
+
+  # See if it's a short branch name.
+  rev = resolve('refs/remotes/origin/%s' % committish)
+  if rev:
+    return ('refs/heads/%s' % (committish,), rev)
+
+  # See if it's a tag.
+  rev = resolve('refs/tags/%s' % committish)
+  if rev:
+    return ('refs/tags/%s' % (committish,), rev)
+
+  # See if it's a commit.
+  rev = resolve(committish)
+  if rev and rev.lower().startswith(committish.lower()):
+    return (rev, rev)
+
+  # Give up!
+  print('repo: error: unable to resolve "%s"' % (committish,), file=sys.stderr)
+  raise CloneFailure()
+
+
+def verify_rev(cwd, remote_ref, rev, quiet):
+  """Verify the commit has been signed by a tag."""
+  ret = run_git('describe', rev, cwd=cwd)
+  cur = ret.stdout.strip()
 
   m = re.compile(r'^(.*)-[0-9]{1,}-g[0-9a-f]{1,}$').match(cur)
   if m:
     cur = m.group(1)
     if not quiet:
       print(file=sys.stderr)
-      print("info: Ignoring branch '%s'; using tagged release '%s'"
-            % (branch, cur), file=sys.stderr)
+      print("warning: '%s' is not signed; falling back to signed release '%s'"
+            % (remote_ref, cur), file=sys.stderr)
       print(file=sys.stderr)
 
   env = os.environ.copy()
-  try:
-    env['GNUPGHOME'] = gpg_dir
-  except UnicodeEncodeError:
-    env['GNUPGHOME'] = gpg_dir.encode()
-
-  cmd = [GIT, 'tag', '-v', cur]
-  proc = subprocess.Popen(cmd,
-                          stdout=subprocess.PIPE,
-                          stderr=subprocess.PIPE,
-                          cwd=cwd,
-                          env=env)
-  out = proc.stdout.read().decode('utf-8')
-  proc.stdout.close()
-
-  err = proc.stderr.read().decode('utf-8')
-  proc.stderr.close()
-
-  if proc.wait() != 0:
-    print(file=sys.stderr)
-    print(out, file=sys.stderr)
-    print(err, file=sys.stderr)
-    print(file=sys.stderr)
-    raise CloneFailure()
+  _setenv('GNUPGHOME', gpg_dir, env)
+  run_git('tag', '-v', cur, cwd=cwd, env=env)
   return '%s^0' % cur
 
 
-def _Checkout(cwd, branch, rev, quiet):
+def _Checkout(cwd, remote_ref, rev, quiet):
   """Checkout an upstream branch into the repository and track it.
   """
-  cmd = [GIT, 'update-ref', 'refs/heads/default', rev]
-  if subprocess.Popen(cmd, cwd=cwd).wait() != 0:
-    raise CloneFailure()
+  run_git('update-ref', 'refs/heads/default', rev, cwd=cwd)
 
   _SetConfig(cwd, 'branch.default.remote', 'origin')
-  _SetConfig(cwd, 'branch.default.merge', 'refs/heads/%s' % branch)
+  _SetConfig(cwd, 'branch.default.merge', remote_ref)
 
-  cmd = [GIT, 'symbolic-ref', 'HEAD', 'refs/heads/default']
-  if subprocess.Popen(cmd, cwd=cwd).wait() != 0:
-    raise CloneFailure()
+  run_git('symbolic-ref', 'HEAD', 'refs/heads/default', cwd=cwd)
 
-  cmd = [GIT, 'read-tree', '--reset', '-u']
+  cmd = ['read-tree', '--reset', '-u']
   if not quiet:
     cmd.append('-v')
   cmd.append('HEAD')
-  if subprocess.Popen(cmd, cwd=cwd).wait() != 0:
-    raise CloneFailure()
+  run_git(*cmd, cwd=cwd)
 
 
 def _FindRepo():
@@ -757,9 +1027,7 @@ def _FindRepo():
   repo = None
 
   olddir = None
-  while curdir != '/' \
-          and curdir != olddir \
-          and not repo:
+  while curdir != olddir and not repo:
     repo = os.path.join(curdir, repodir, REPO_MAIN)
     if not os.path.isfile(repo):
       repo = None
@@ -770,6 +1038,26 @@ def _FindRepo():
 
 class _Options(object):
   help = False
+  version = False
+
+
+def _ExpandAlias(name):
+  """Look up user registered aliases."""
+  # We don't resolve aliases for existing subcommands.  This matches git.
+  if name in {'gitc-init', 'help', 'init'}:
+    return name, []
+
+  alias = _GetRepoConfig('alias.%s' % (name,))
+  if alias is None:
+    return name, []
+
+  args = alias.strip().split(' ', 1)
+  name = args[0]
+  if len(args) == 2:
+    args = shlex.split(args[1])
+  else:
+    args = []
+  return name, args
 
 
 def _ParseArguments(args):
@@ -781,7 +1069,10 @@ def _ParseArguments(args):
     a = args[i]
     if a == '-h' or a == '--help':
       opt.help = True
-
+    elif a == '--version':
+      opt.version = True
+    elif a == '--trace':
+      trace.set(True)
     elif not a.startswith('-'):
       cmd = a
       arg = args[i + 1:]
@@ -789,6 +1080,90 @@ def _ParseArguments(args):
   return cmd, opt, arg
 
 
+class Requirements(object):
+  """Helper for checking repo's system requirements."""
+
+  REQUIREMENTS_NAME = 'requirements.json'
+
+  def __init__(self, requirements):
+    """Initialize.
+
+    Args:
+      requirements: A dictionary of settings.
+    """
+    self.requirements = requirements
+
+  @classmethod
+  def from_dir(cls, path):
+    return cls.from_file(os.path.join(path, cls.REQUIREMENTS_NAME))
+
+  @classmethod
+  def from_file(cls, path):
+    try:
+      with open(path, 'rb') as f:
+        data = f.read()
+    except EnvironmentError:
+      # NB: EnvironmentError is used for Python 2 & 3 compatibility.
+      # If we couldn't open the file, assume it's an old source tree.
+      return None
+
+    return cls.from_data(data)
+
+  @classmethod
+  def from_data(cls, data):
+    comment_line = re.compile(br'^ *#')
+    strip_data = b''.join(x for x in data.splitlines() if not comment_line.match(x))
+    try:
+      json_data = json.loads(strip_data)
+    except Exception:  # pylint: disable=broad-except
+      # If we couldn't parse it, assume it's incompatible.
+      return None
+
+    return cls(json_data)
+
+  def _get_soft_ver(self, pkg):
+    """Return the soft version for |pkg| if it exists."""
+    return self.requirements.get(pkg, {}).get('soft', ())
+
+  def _get_hard_ver(self, pkg):
+    """Return the hard version for |pkg| if it exists."""
+    return self.requirements.get(pkg, {}).get('hard', ())
+
+  @staticmethod
+  def _format_ver(ver):
+    """Return a dotted version from |ver|."""
+    return '.'.join(str(x) for x in ver)
+
+  def assert_ver(self, pkg, curr_ver):
+    """Verify |pkg|'s |curr_ver| is new enough."""
+    curr_ver = tuple(curr_ver)
+    soft_ver = tuple(self._get_soft_ver(pkg))
+    hard_ver = tuple(self._get_hard_ver(pkg))
+    if curr_ver < hard_ver:
+      print('repo: error: Your version of "%s" (%s) is unsupported; '
+            'Please upgrade to at least version %s to continue.' %
+            (pkg, self._format_ver(curr_ver), self._format_ver(soft_ver)),
+            file=sys.stderr)
+      sys.exit(1)
+
+    if curr_ver < soft_ver:
+      print('repo: warning: Your version of "%s" (%s) is no longer supported; '
+            'Please upgrade to at least version %s to avoid breakage.' %
+            (pkg, self._format_ver(curr_ver), self._format_ver(soft_ver)),
+            file=sys.stderr)
+
+  def assert_all(self):
+    """Assert all of the requirements are satisified."""
+    # See if we need a repo launcher upgrade first.
+    self.assert_ver('repo', VERSION)
+
+    # Check python before we try to import the repo code.
+    self.assert_ver('python', sys.version_info)
+
+    # Check git while we're at it.
+    self.assert_ver('git', ParseGitVersion())
+
+
 def _Usage():
   gitc_usage = ""
   if get_gitc_manifest_dir():
@@ -807,17 +1182,15 @@ The most commonly used repo commands are:
 
 For access to the full online help, install repo ("repo init").
 """)
+  print('Bug reports:', BUG_URL)
   sys.exit(0)
 
 
 def _Help(args):
   if args:
-    if args[0] == 'init':
-      init_optparse.print_help()
-      sys.exit(0)
-    elif args[0] == 'gitc-init':
-      _GitcInitOptions(init_optparse)
-      init_optparse.print_help()
+    if args[0] in {'init', 'gitc-init'}:
+      parser = GetParser(gitc_init=args[0] == 'gitc-init')
+      parser.print_help()
       sys.exit(0)
     else:
       print("error: '%s' is not a bootstrap command.\n"
@@ -828,6 +1201,25 @@ def _Help(args):
   sys.exit(1)
 
 
+def _Version():
+  """Show version information."""
+  print('<repo not installed>')
+  print('repo launcher version %s' % ('.'.join(str(x) for x in VERSION),))
+  print('       (from %s)' % (__file__,))
+  print('git %s' % (ParseGitVersion().full,))
+  print('Python %s' % sys.version)
+  uname = platform.uname()
+  if sys.version_info.major < 3:
+    # Python 3 returns a named tuple, but Python 2 is simpler.
+    print(uname)
+  else:
+    print('OS %s %s (%s)' % (uname.system, uname.release, uname.version))
+    print('CPU %s (%s)' %
+          (uname.machine, uname.processor if uname.processor else 'unknown'))
+  print('Bug reports:', BUG_URL)
+  sys.exit(0)
+
+
 def _NotInstalled():
   print('error: repo is not installed.  Use "repo init" to install it here.',
         file=sys.stderr)
@@ -860,26 +1252,26 @@ def _SetDefaultsTo(gitdir):
   global REPO_REV
 
   REPO_URL = gitdir
-  proc = subprocess.Popen([GIT,
-                           '--git-dir=%s' % gitdir,
-                           'symbolic-ref',
-                           'HEAD'],
-                          stdout=subprocess.PIPE,
-                          stderr=subprocess.PIPE)
-  REPO_REV = proc.stdout.read().strip().decode('utf-8')
-  proc.stdout.close()
-
-  proc.stderr.read()
-  proc.stderr.close()
-
-  if proc.wait() != 0:
-    print('fatal: %s has no current branch' % gitdir, file=sys.stderr)
-    sys.exit(1)
+  ret = run_git('--git-dir=%s' % gitdir, 'symbolic-ref', 'HEAD', check=False)
+  if ret.returncode:
+    # If we're not tracking a branch (bisect/etc...), then fall back to commit.
+    print('repo: warning: %s has no current branch; using HEAD' % gitdir,
+          file=sys.stderr)
+    try:
+      ret = run_git('rev-parse', 'HEAD', cwd=gitdir)
+    except CloneFailure:
+      print('fatal: %s has invalid HEAD' % gitdir, file=sys.stderr)
+      sys.exit(1)
+
+  REPO_REV = ret.stdout.strip()
 
 
 def main(orig_args):
   cmd, opt, args = _ParseArguments(orig_args)
 
+  # We run this early as we run some git commands ourselves.
+  SetGitTrace2ParentSid()
+
   repo_main, rel_repo_dir = None, None
   # Don't use the local repo copy, make sure to switch to the gitc client first.
   if cmd != 'gitc-init':
@@ -896,10 +1288,17 @@ def main(orig_args):
           file=sys.stderr)
     sys.exit(1)
   if not repo_main:
+    # Only expand aliases here since we'll be parsing the CLI ourselves.
+    # If we had repo_main, alias expansion would happen in main.py.
+    cmd, alias_args = _ExpandAlias(cmd)
+    args = alias_args + args
+
     if opt.help:
       _Usage()
     if cmd == 'help':
       _Help(args)
+    if opt.version or cmd == 'version':
+      _Version()
     if not cmd:
       _NotInstalled()
     if cmd == 'init' or cmd == 'gitc-init':
@@ -920,6 +1319,14 @@ def main(orig_args):
   if my_main:
     repo_main = my_main
 
+  if not repo_main:
+    print("fatal: unable to find repo entry point", file=sys.stderr)
+    sys.exit(1)
+
+  reqs = Requirements.from_dir(os.path.dirname(repo_main))
+  if reqs:
+    reqs.assert_all()
+
   ver_str = '.'.join(map(str, VERSION))
   me = [sys.executable, repo_main,
         '--repo-dir=%s' % rel_repo_dir,
@@ -927,16 +1334,9 @@ def main(orig_args):
         '--wrapper-path=%s' % wrapper_path,
         '--']
   me.extend(orig_args)
-  me.extend(extra_args)
-  try:
-    if platform.system() == "Windows":
-      sys.exit(subprocess.call(me))
-    else:
-      os.execv(sys.executable, me)
-  except OSError as e:
-    print("fatal: unable to start %s" % repo_main, file=sys.stderr)
-    print("fatal: %s" % e, file=sys.stderr)
-    sys.exit(148)
+  exec_command(me)
+  print("fatal: unable to start %s" % repo_main, file=sys.stderr)
+  sys.exit(148)
 
 
 if __name__ == '__main__':
diff --git a/repo_trace.py b/repo_trace.py
index f5bc76d4..7be0c045 100644
--- a/repo_trace.py
+++ b/repo_trace.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -19,7 +17,6 @@
 Activated via `repo --trace ...` or `REPO_TRACE=1 repo ...`.
 """
 
-from __future__ import print_function
 import sys
 import os
 
@@ -28,13 +25,16 @@ REPO_TRACE = 'REPO_TRACE'
 
 _TRACE = os.environ.get(REPO_TRACE) == '1'
 
+
 def IsTrace():
   return _TRACE
 
+
 def SetTrace():
   global _TRACE
   _TRACE = True
 
+
 def Trace(fmt, *args):
   if IsTrace():
     print(fmt % args, file=sys.stderr)
diff --git a/requirements.json b/requirements.json
new file mode 100644
index 00000000..cb55cd25
--- /dev/null
+++ b/requirements.json
@@ -0,0 +1,57 @@
+# This file declares various requirements for this version of repo.  The
+# launcher script will load it and check the constraints before trying to run
+# us.  This avoids issues of the launcher using an old version of Python (e.g.
+# 3.5) while the codebase has moved on to requiring something much newer (e.g.
+# 3.8).  If the launcher tried to import us, it would fail with syntax errors.
+
+# This is a JSON file with line-level comments allowed.
+
+# Always keep backwards compatibility in mine.  The launcher script is robust
+# against missing values, but when a field is renamed/removed, it means older
+# versions of the launcher script won't be able to enforce the constraint.
+
+# When requiring versions, always use lists as they are easy to parse & compare
+# in Python.  Strings would require futher processing to turn into a list.
+
+# Version constraints should be expressed in pairs: soft & hard.  Soft versions
+# are when we start warning users that their software too old and we're planning
+# on dropping support for it, so they need to start planning system upgrades.
+# Hard versions are when we refuse to work the tool.  Users will be shown an
+# error message before we abort entirely.
+
+# When deciding whether to upgrade a version requirement, check out the distro
+# lists to see who will be impacted:
+# https://gerrit.googlesource.com/git-repo/+/HEAD/docs/release-process.md#Project-References
+
+{
+  # The repo launcher itself.  This allows us to force people to upgrade as some
+  # ignore the warnings about it being out of date, or install ancient versions
+  # to start with for whatever reason.
+  #
+  # NB: Repo launchers started checking this file with repo-2.12, so listing
+  # versions older than that won't make a difference.
+  "repo": {
+    "hard": [2, 11],
+    "soft": [2, 11]
+  },
+
+  # Supported Python versions.
+  #
+  # python-3.6 is in Ubuntu Bionic.
+  # python-3.7 is in Debian Buster.
+  "python": {
+    "hard": [3, 6],
+    "soft": [3, 6]
+  },
+
+  # Supported git versions.
+  #
+  # git-1.7.2 is in Debian Squeeze.
+  # git-1.7.9 is in Ubuntu Precise.
+  # git-1.9.1 is in Ubuntu Trusty.
+  # git-1.7.10 is in Debian Wheezy.
+  "git": {
+    "hard": [1, 7, 2],
+    "soft": [1, 9, 1]
+  }
+}
diff --git a/run_tests b/run_tests
index d7144b3c..573dd446 100755
--- a/run_tests
+++ b/run_tests
@@ -1,5 +1,4 @@
-#!/usr/bin/env python
-# -*- coding:utf-8 -*-
+#!/usr/bin/env python3
 # Copyright 2019 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,37 +15,46 @@
 
 """Wrapper to run pytest with the right settings."""
 
-from __future__ import print_function
-
 import errno
 import os
+import shutil
 import subprocess
 import sys
 
 
-def run_pytest(cmd, argv):
-  """Run the unittests via |cmd|."""
-  try:
-    return subprocess.call([cmd] + argv)
-  except OSError as e:
-    if e.errno == errno.ENOENT:
-      print('%s: unable to run `%s`: %s' % (__file__, cmd, e), file=sys.stderr)
-      print('%s: Try installing pytest: sudo apt-get install python-pytest' %
-            (__file__,), file=sys.stderr)
-      return 127
-    else:
-      raise
+def find_pytest():
+  """Try to locate a good version of pytest."""
+  # If we're in a virtualenv, assume that it's provided the right pytest.
+  if 'VIRTUAL_ENV' in os.environ:
+    return 'pytest'
+
+  # Use the Python 3 version if available.
+  ret = shutil.which('pytest-3')
+  if ret:
+    return ret
+
+  # Hopefully this is a Python 3 version.
+  ret = shutil.which('pytest')
+  if ret:
+    return ret
+
+  print('%s: unable to find pytest.' % (__file__,), file=sys.stderr)
+  print('%s: Try installing: sudo apt-get install python-pytest' % (__file__,),
+        file=sys.stderr)
 
 
 def main(argv):
   """The main entry."""
   # Add the repo tree to PYTHONPATH as the tests expect to be able to import
   # modules directly.
-  topdir = os.path.dirname(os.path.realpath(__file__))
-  pythonpath = os.environ.get('PYTHONPATH', '')
-  os.environ['PYTHONPATH'] = '%s:%s' % (topdir, pythonpath)
-
-  return run_pytest('pytest', argv)
+  pythonpath = os.path.dirname(os.path.realpath(__file__))
+  oldpythonpath = os.environ.get('PYTHONPATH', None)
+  if oldpythonpath is not None:
+    pythonpath += os.pathsep + oldpythonpath
+  os.environ['PYTHONPATH'] = pythonpath
+
+  pytest = find_pytest()
+  return subprocess.run([pytest] + argv, check=False).returncode
 
 
 if __name__ == '__main__':
diff --git a/setup.py b/setup.py
index f4d7728d..17aeae22 100755
--- a/setup.py
+++ b/setup.py
@@ -1,5 +1,4 @@
-#!/usr/bin/env python
-# -*- coding:utf-8 -*-
+#!/usr/bin/env python3
 # Copyright 2019 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the 'License");
@@ -16,8 +15,6 @@
 
 """Python packaging for repo."""
 
-from __future__ import print_function
-
 import os
 import setuptools
 
@@ -35,7 +32,7 @@ with open(os.path.join(TOPDIR, 'README.md')) as fp:
 # https://packaging.python.org/tutorials/packaging-projects/
 setuptools.setup(
     name='repo',
-    version='1.13.8',
+    version='2',
     maintainer='Various',
     maintainer_email='repo-discuss@googlegroups.com',
     description='Repo helps manage many Git repositories',
@@ -55,9 +52,10 @@ setuptools.setup(
         'Operating System :: MacOS :: MacOS X',
         'Operating System :: Microsoft :: Windows :: Windows 10',
         'Operating System :: POSIX :: Linux',
+        'Programming Language :: Python :: 3',
+        'Programming Language :: Python :: 3 :: Only',
         'Topic :: Software Development :: Version Control :: Git',
     ],
-    # We support Python 2.7 and Python 3.6+.
-    python_requires='>=2.7, ' + ', '.join('!=3.%i.*' % x for x in range(0, 6)),
+    python_requires='>=3.6',
     packages=['subcmds'],
 )
diff --git a/ssh.py b/ssh.py
new file mode 100644
index 00000000..0ae8d120
--- /dev/null
+++ b/ssh.py
@@ -0,0 +1,277 @@
+# Copyright (C) 2008 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Common SSH management logic."""
+
+import functools
+import multiprocessing
+import os
+import re
+import signal
+import subprocess
+import sys
+import tempfile
+import time
+
+import platform_utils
+from repo_trace import Trace
+
+
+PROXY_PATH = os.path.join(os.path.dirname(__file__), 'git_ssh')
+
+
+def _run_ssh_version():
+  """run ssh -V to display the version number"""
+  return subprocess.check_output(['ssh', '-V'], stderr=subprocess.STDOUT).decode()
+
+
+def _parse_ssh_version(ver_str=None):
+  """parse a ssh version string into a tuple"""
+  if ver_str is None:
+    ver_str = _run_ssh_version()
+  m = re.match(r'^OpenSSH_([0-9.]+)(p[0-9]+)?\s', ver_str)
+  if m:
+    return tuple(int(x) for x in m.group(1).split('.'))
+  else:
+    return ()
+
+
+@functools.lru_cache(maxsize=None)
+def version():
+  """return ssh version as a tuple"""
+  try:
+    return _parse_ssh_version()
+  except subprocess.CalledProcessError:
+    print('fatal: unable to detect ssh version', file=sys.stderr)
+    sys.exit(1)
+
+
+URI_SCP = re.compile(r'^([^@:]*@?[^:/]{1,}):')
+URI_ALL = re.compile(r'^([a-z][a-z+-]*)://([^@/]*@?[^/]*)/')
+
+
+class ProxyManager:
+  """Manage various ssh clients & masters that we spawn.
+
+  This will take care of sharing state between multiprocessing children, and
+  make sure that if we crash, we don't leak any of the ssh sessions.
+
+  The code should work with a single-process scenario too, and not add too much
+  overhead due to the manager.
+  """
+
+  # Path to the ssh program to run which will pass our master settings along.
+  # Set here more as a convenience API.
+  proxy = PROXY_PATH
+
+  def __init__(self, manager):
+    # Protect access to the list of active masters.
+    self._lock = multiprocessing.Lock()
+    # List of active masters (pid).  These will be spawned on demand, and we are
+    # responsible for shutting them all down at the end.
+    self._masters = manager.list()
+    # Set of active masters indexed by "host:port" information.
+    # The value isn't used, but multiprocessing doesn't provide a set class.
+    self._master_keys = manager.dict()
+    # Whether ssh masters are known to be broken, so we give up entirely.
+    self._master_broken = manager.Value('b', False)
+    # List of active ssh sesssions.  Clients will be added & removed as
+    # connections finish, so this list is just for safety & cleanup if we crash.
+    self._clients = manager.list()
+    # Path to directory for holding master sockets.
+    self._sock_path = None
+
+  def __enter__(self):
+    """Enter a new context."""
+    return self
+
+  def __exit__(self, exc_type, exc_value, traceback):
+    """Exit a context & clean up all resources."""
+    self.close()
+
+  def add_client(self, proc):
+    """Track a new ssh session."""
+    self._clients.append(proc.pid)
+
+  def remove_client(self, proc):
+    """Remove a completed ssh session."""
+    try:
+      self._clients.remove(proc.pid)
+    except ValueError:
+      pass
+
+  def add_master(self, proc):
+    """Track a new master connection."""
+    self._masters.append(proc.pid)
+
+  def _terminate(self, procs):
+    """Kill all |procs|."""
+    for pid in procs:
+      try:
+        os.kill(pid, signal.SIGTERM)
+        os.waitpid(pid, 0)
+      except OSError:
+        pass
+
+    # The multiprocessing.list() API doesn't provide many standard list()
+    # methods, so we have to manually clear the list.
+    while True:
+      try:
+        procs.pop(0)
+      except:
+        break
+
+  def close(self):
+    """Close this active ssh session.
+
+    Kill all ssh clients & masters we created, and nuke the socket dir.
+    """
+    self._terminate(self._clients)
+    self._terminate(self._masters)
+
+    d = self.sock(create=False)
+    if d:
+      try:
+        platform_utils.rmdir(os.path.dirname(d))
+      except OSError:
+        pass
+
+  def _open_unlocked(self, host, port=None):
+    """Make sure a ssh master session exists for |host| & |port|.
+
+    If one doesn't exist already, we'll create it.
+
+    We won't grab any locks, so the caller has to do that.  This helps keep the
+    business logic of actually creating the master separate from grabbing locks.
+    """
+    # Check to see whether we already think that the master is running; if we
+    # think it's already running, return right away.
+    if port is not None:
+      key = '%s:%s' % (host, port)
+    else:
+      key = host
+
+    if key in self._master_keys:
+      return True
+
+    if self._master_broken.value or 'GIT_SSH' in os.environ:
+      # Failed earlier, so don't retry.
+      return False
+
+    # We will make two calls to ssh; this is the common part of both calls.
+    command_base = ['ssh', '-o', 'ControlPath %s' % self.sock(), host]
+    if port is not None:
+      command_base[1:1] = ['-p', str(port)]
+
+    # Since the key wasn't in _master_keys, we think that master isn't running.
+    # ...but before actually starting a master, we'll double-check.  This can
+    # be important because we can't tell that that 'git@myhost.com' is the same
+    # as 'myhost.com' where "User git" is setup in the user's ~/.ssh/config file.
+    check_command = command_base + ['-O', 'check']
+    try:
+      Trace(': %s', ' '.join(check_command))
+      check_process = subprocess.Popen(check_command,
+                                       stdout=subprocess.PIPE,
+                                       stderr=subprocess.PIPE)
+      check_process.communicate()  # read output, but ignore it...
+      isnt_running = check_process.wait()
+
+      if not isnt_running:
+        # Our double-check found that the master _was_ infact running.  Add to
+        # the list of keys.
+        self._master_keys[key] = True
+        return True
+    except Exception:
+      # Ignore excpetions.  We we will fall back to the normal command and print
+      # to the log there.
+      pass
+
+    command = command_base[:1] + ['-M', '-N'] + command_base[1:]
+    try:
+      Trace(': %s', ' '.join(command))
+      p = subprocess.Popen(command)
+    except Exception as e:
+      self._master_broken.value = True
+      print('\nwarn: cannot enable ssh control master for %s:%s\n%s'
+            % (host, port, str(e)), file=sys.stderr)
+      return False
+
+    time.sleep(1)
+    ssh_died = (p.poll() is not None)
+    if ssh_died:
+      return False
+
+    self.add_master(p)
+    self._master_keys[key] = True
+    return True
+
+  def _open(self, host, port=None):
+    """Make sure a ssh master session exists for |host| & |port|.
+
+    If one doesn't exist already, we'll create it.
+
+    This will obtain any necessary locks to avoid inter-process races.
+    """
+    # Bail before grabbing the lock if we already know that we aren't going to
+    # try creating new masters below.
+    if sys.platform in ('win32', 'cygwin'):
+      return False
+
+    # Acquire the lock.  This is needed to prevent opening multiple masters for
+    # the same host when we're running "repo sync -jN" (for N > 1) _and_ the
+    # manifest <remote fetch="ssh://xyz"> specifies a different host from the
+    # one that was passed to repo init.
+    with self._lock:
+      return self._open_unlocked(host, port)
+
+  def preconnect(self, url):
+    """If |uri| will create a ssh connection, setup the ssh master for it."""
+    m = URI_ALL.match(url)
+    if m:
+      scheme = m.group(1)
+      host = m.group(2)
+      if ':' in host:
+        host, port = host.split(':')
+      else:
+        port = None
+      if scheme in ('ssh', 'git+ssh', 'ssh+git'):
+        return self._open(host, port)
+      return False
+
+    m = URI_SCP.match(url)
+    if m:
+      host = m.group(1)
+      return self._open(host)
+
+    return False
+
+  def sock(self, create=True):
+    """Return the path to the ssh socket dir.
+
+    This has all the master sockets so clients can talk to them.
+    """
+    if self._sock_path is None:
+      if not create:
+        return None
+      tmp_dir = '/tmp'
+      if not os.path.exists(tmp_dir):
+        tmp_dir = tempfile.gettempdir()
+      if version() < (6, 7):
+        tokens = '%r@%h:%p'
+      else:
+        tokens = '%C'  # hash of %l%h%p%r
+      self._sock_path = os.path.join(
+          tempfile.mkdtemp('', 'ssh-', tmp_dir),
+          'master-' + tokens)
+    return self._sock_path
diff --git a/subcmds/__init__.py b/subcmds/__init__.py
index 27341038..051dda06 100644
--- a/subcmds/__init__.py
+++ b/subcmds/__init__.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,6 +14,7 @@
 
 import os
 
+# A mapping of the subcommand name to the class that implements it.
 all_commands = {}
 
 my_dir = os.path.dirname(__file__)
@@ -37,14 +36,14 @@ for py in os.listdir(my_dir):
                      ['%s' % name])
     mod = getattr(mod, name)
     try:
-      cmd = getattr(mod, clsn)()
+      cmd = getattr(mod, clsn)
     except AttributeError:
       raise SyntaxError('%s/%s does not define class %s' % (
-                         __name__, py, clsn))
+          __name__, py, clsn))
 
     name = name.replace('_', '-')
     cmd.NAME = name
     all_commands[name] = cmd
 
-if 'help' in all_commands:
-  all_commands['help'].commands = all_commands
+# Add 'branch' as an alias for 'branches'.
+all_commands['branch'] = all_commands['branches']
diff --git a/subcmds/abandon.py b/subcmds/abandon.py
index cd1d0c40..85d85f5a 100644
--- a/subcmds/abandon.py
+++ b/subcmds/abandon.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,15 +12,18 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-import sys
-from command import Command
 from collections import defaultdict
+import functools
+import itertools
+import sys
+
+from command import Command, DEFAULT_LOCAL_JOBS
 from git_command import git
 from progress import Progress
 
+
 class Abandon(Command):
-  common = True
+  COMMON = True
   helpSummary = "Permanently abandon a development branch"
   helpUsage = """
 %prog [--all | <branchname>] [<project>...]
@@ -32,6 +33,8 @@ deleting it (and all its history) from your local repository.
 
 It is equivalent to "git branch -D <branchname>".
 """
+  PARALLEL_JOBS = DEFAULT_LOCAL_JOBS
+
   def _Options(self, p):
     p.add_option('--all',
                  dest='all', action='store_true',
@@ -48,52 +51,64 @@ It is equivalent to "git branch -D <branchname>".
     else:
       args.insert(0, "'All local branches'")
 
+  def _ExecuteOne(self, all_branches, nb, project):
+    """Abandon one project."""
+    if all_branches:
+      branches = project.GetBranches()
+    else:
+      branches = [nb]
+
+    ret = {}
+    for name in branches:
+      status = project.AbandonBranch(name)
+      if status is not None:
+        ret[name] = status
+    return (ret, project)
+
   def Execute(self, opt, args):
     nb = args[0]
     err = defaultdict(list)
     success = defaultdict(list)
     all_projects = self.GetProjects(args[1:])
 
-    pm = Progress('Abandon %s' % nb, len(all_projects))
-    for project in all_projects:
-      pm.update()
-
-      if opt.all:
-        branches = list(project.GetBranches().keys())
-      else:
-        branches = [nb]
-
-      for name in branches:
-        status = project.AbandonBranch(name)
-        if status is not None:
+    def _ProcessResults(_pool, pm, states):
+      for (results, project) in states:
+        for branch, status in results.items():
           if status:
-            success[name].append(project)
+            success[branch].append(project)
           else:
-            err[name].append(project)
-    pm.end()
+            err[branch].append(project)
+        pm.update()
 
-    width = 25
-    for name in branches:
-      if width < len(name):
-        width = len(name)
+    self.ExecuteInParallel(
+        opt.jobs,
+        functools.partial(self._ExecuteOne, opt.all, nb),
+        all_projects,
+        callback=_ProcessResults,
+        output=Progress('Abandon %s' % (nb,), len(all_projects), quiet=opt.quiet))
 
+    width = max(itertools.chain(
+        [25], (len(x) for x in itertools.chain(success, err))))
     if err:
       for br in err.keys():
-        err_msg = "error: cannot abandon %s" %br
+        err_msg = "error: cannot abandon %s" % br
         print(err_msg, file=sys.stderr)
         for proj in err[br]:
-          print(' '*len(err_msg) + " | %s" % proj.relpath, file=sys.stderr)
+          print(' ' * len(err_msg) + " | %s" % proj.relpath, file=sys.stderr)
       sys.exit(1)
     elif not success:
       print('error: no project has local branch(es) : %s' % nb,
             file=sys.stderr)
       sys.exit(1)
     else:
-      print('Abandoned branches:', file=sys.stderr)
+      # Everything below here is displaying status.
+      if opt.quiet:
+        return
+      print('Abandoned branches:')
       for br in success.keys():
         if len(all_projects) > 1 and len(all_projects) == len(success[br]):
           result = "all project"
         else:
           result = "%s" % (
-            ('\n'+' '*width + '| ').join(p.relpath for p in success[br]))
-        print("%s%s| %s\n" % (br,' '*(width-len(br)), result),file=sys.stderr)
+              ('\n' + ' ' * width + '| ').join(p.relpath for p in success[br]))
+        print("%s%s| %s\n" % (br, ' ' * (width - len(br)), result))
diff --git a/subcmds/branches.py b/subcmds/branches.py
index fb60d7de..6d975ed4 100644
--- a/subcmds/branches.py
+++ b/subcmds/branches.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2009 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,18 +12,21 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
+import itertools
 import sys
+
 from color import Coloring
-from command import Command
+from command import Command, DEFAULT_LOCAL_JOBS
+
 
 class BranchColoring(Coloring):
   def __init__(self, config):
     Coloring.__init__(self, config, 'branch')
     self.current = self.printer('current', fg='green')
-    self.local   = self.printer('local')
+    self.local = self.printer('local')
     self.notinproject = self.printer('notinproject', fg='red')
 
+
 class BranchInfo(object):
   def __init__(self, name):
     self.name = name
@@ -61,7 +62,7 @@ class BranchInfo(object):
 
 
 class Branches(Command):
-  common = True
+  COMMON = True
   helpSummary = "View current topic branches"
   helpUsage = """
 %prog [<project>...]
@@ -94,6 +95,7 @@ the branch appears in, or does not appear in.  If no project list
 is shown, then the branch appears in all projects.
 
 """
+  PARALLEL_JOBS = DEFAULT_LOCAL_JOBS
 
   def Execute(self, opt, args):
     projects = self.GetProjects(args)
@@ -101,14 +103,19 @@ is shown, then the branch appears in all projects.
     all_branches = {}
     project_cnt = len(projects)
 
-    for project in projects:
-      for name, b in project.GetBranches().items():
-        b.project = project
+    def _ProcessResults(_pool, _output, results):
+      for name, b in itertools.chain.from_iterable(results):
         if name not in all_branches:
           all_branches[name] = BranchInfo(name)
         all_branches[name].add(b)
 
-    names = list(sorted(all_branches))
+    self.ExecuteInParallel(
+        opt.jobs,
+        expand_project_to_branches,
+        projects,
+        callback=_ProcessResults)
+
+    names = sorted(all_branches)
 
     if not names:
       print('   (no branches)', file=sys.stderr)
@@ -158,7 +165,7 @@ is shown, then the branch appears in all projects.
           for b in i.projects:
             have.add(b.project)
           for p in projects:
-            if not p in have:
+            if p not in have:
               paths.append(p.relpath)
 
         s = ' %s %s' % (in_type, ', '.join(paths))
@@ -170,11 +177,27 @@ is shown, then the branch appears in all projects.
           fmt = out.current if i.IsCurrent else out.write
           for p in paths:
             out.nl()
-            fmt(width*' ' + '          %s' % p)
+            fmt(width * ' ' + '          %s' % p)
           fmt = out.write
           for p in non_cur_paths:
             out.nl()
-            fmt(width*' ' + '          %s' % p)
+            fmt(width * ' ' + '          %s' % p)
       else:
         out.write(' in all projects')
       out.nl()
+
+
+def expand_project_to_branches(project):
+  """Expands a project into a list of branch names & associated information.
+
+  Args:
+    project: project.Project
+
+  Returns:
+    List[Tuple[str, git_config.Branch]]
+  """
+  branches = []
+  for name, b in project.GetBranches().items():
+    b.project = project
+    branches.append((name, b))
+  return branches
diff --git a/subcmds/checkout.py b/subcmds/checkout.py
index c8a09a8e..9b429489 100644
--- a/subcmds/checkout.py
+++ b/subcmds/checkout.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2009 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,13 +12,15 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
+import functools
 import sys
-from command import Command
+
+from command import Command, DEFAULT_LOCAL_JOBS
 from progress import Progress
 
+
 class Checkout(Command):
-  common = True
+  COMMON = True
   helpSummary = "Checkout a branch for development"
   helpUsage = """
 %prog <branchname> [<project>...]
@@ -33,28 +33,37 @@ The command is equivalent to:
 
   repo forall [<project>...] -c git checkout <branchname>
 """
+  PARALLEL_JOBS = DEFAULT_LOCAL_JOBS
 
   def ValidateOptions(self, opt, args):
     if not args:
       self.Usage()
 
+  def _ExecuteOne(self, nb, project):
+    """Checkout one project."""
+    return (project.CheckoutBranch(nb), project)
+
   def Execute(self, opt, args):
     nb = args[0]
     err = []
     success = []
     all_projects = self.GetProjects(args[1:])
 
-    pm = Progress('Checkout %s' % nb, len(all_projects))
-    for project in all_projects:
-      pm.update()
+    def _ProcessResults(_pool, pm, results):
+      for status, project in results:
+        if status is not None:
+          if status:
+            success.append(project)
+          else:
+            err.append(project)
+        pm.update()
 
-      status = project.CheckoutBranch(nb)
-      if status is not None:
-        if status:
-          success.append(project)
-        else:
-          err.append(project)
-    pm.end()
+    self.ExecuteInParallel(
+        opt.jobs,
+        functools.partial(self._ExecuteOne, nb),
+        all_projects,
+        callback=_ProcessResults,
+        output=Progress('Checkout %s' % (nb,), len(all_projects), quiet=opt.quiet))
 
     if err:
       for p in err:
diff --git a/subcmds/cherry_pick.py b/subcmds/cherry_pick.py
index a541a040..7bd858bf 100644
--- a/subcmds/cherry_pick.py
+++ b/subcmds/cherry_pick.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2010 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import re
 import sys
 from command import Command
@@ -22,8 +19,9 @@ from git_command import GitCommand
 
 CHANGE_ID_RE = re.compile(r'^\s*Change-Id: I([0-9a-f]{40})\s*$')
 
+
 class CherryPick(Command):
-  common = True
+  COMMON = True
   helpSummary = "Cherry-pick a change."
   helpUsage = """
 %prog <sha1>
@@ -34,9 +32,6 @@ The change id will be updated, and a reference to the old
 change id will be added.
 """
 
-  def _Options(self, p):
-    pass
-
   def ValidateOptions(self, opt, args):
     if len(args) != 1:
       self.Usage()
@@ -46,8 +41,8 @@ change id will be added.
 
     p = GitCommand(None,
                    ['rev-parse', '--verify', reference],
-                   capture_stdout = True,
-                   capture_stderr = True)
+                   capture_stdout=True,
+                   capture_stderr=True)
     if p.Wait() != 0:
       print(p.stderr, file=sys.stderr)
       sys.exit(1)
@@ -61,8 +56,8 @@ change id will be added.
 
     p = GitCommand(None,
                    ['cherry-pick', sha1],
-                   capture_stdout = True,
-                   capture_stderr = True)
+                   capture_stdout=True,
+                   capture_stderr=True)
     status = p.Wait()
 
     print(p.stdout, file=sys.stdout)
@@ -74,11 +69,9 @@ change id will be added.
       new_msg = self._Reformat(old_msg, sha1)
 
       p = GitCommand(None, ['commit', '--amend', '-F', '-'],
-                     provide_stdin = True,
-                     capture_stdout = True,
-                     capture_stderr = True)
-      p.stdin.write(new_msg)
-      p.stdin.close()
+                     input=new_msg,
+                     capture_stdout=True,
+                     capture_stderr=True)
       if p.Wait() != 0:
         print("error: Failed to update commit message", file=sys.stderr)
         sys.exit(1)
@@ -97,7 +90,7 @@ change id will be added.
 
   def _StripHeader(self, commit_msg):
     lines = commit_msg.splitlines()
-    return "\n".join(lines[lines.index("")+1:])
+    return "\n".join(lines[lines.index("") + 1:])
 
   def _Reformat(self, old_msg, sha1):
     new_msg = []
diff --git a/subcmds/diff.py b/subcmds/diff.py
index fa41e70e..00a7ec29 100644
--- a/subcmds/diff.py
+++ b/subcmds/diff.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,10 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from command import PagedCommand
+import functools
+import io
+
+from command import DEFAULT_LOCAL_JOBS, PagedCommand
+
 
 class Diff(PagedCommand):
-  common = True
+  COMMON = True
   helpSummary = "Show changes between commit and working tree"
   helpUsage = """
 %prog [<project>...]
@@ -26,19 +28,42 @@ The -u option causes '%prog' to generate diff output with file paths
 relative to the repository root, so the output can be applied
 to the Unix 'patch' command.
 """
+  PARALLEL_JOBS = DEFAULT_LOCAL_JOBS
 
   def _Options(self, p):
-    def cmd(option, opt_str, value, parser):
-      setattr(parser.values, option.dest, list(parser.rargs))
-      while parser.rargs:
-        del parser.rargs[0]
     p.add_option('-u', '--absolute',
                  dest='absolute', action='store_true',
-                 help='Paths are relative to the repository root')
+                 help='paths are relative to the repository root')
+
+  def _ExecuteOne(self, absolute, project):
+    """Obtains the diff for a specific project.
+
+    Args:
+      absolute: Paths are relative to the root.
+      project: Project to get status of.
+
+    Returns:
+      The status of the project.
+    """
+    buf = io.StringIO()
+    ret = project.PrintWorkTreeDiff(absolute, output_redir=buf)
+    return (ret, buf.getvalue())
 
   def Execute(self, opt, args):
-    ret = 0
-    for project in self.GetProjects(args):
-      if not project.PrintWorkTreeDiff(opt.absolute):
-        ret = 1
-    return ret
+    all_projects = self.GetProjects(args)
+
+    def _ProcessResults(_pool, _output, results):
+      ret = 0
+      for (state, output) in results:
+        if output:
+          print(output, end='')
+        if not state:
+          ret = 1
+      return ret
+
+    return self.ExecuteInParallel(
+        opt.jobs,
+        functools.partial(self._ExecuteOne, opt.absolute),
+        all_projects,
+        callback=_ProcessResults,
+        ordered=True)
diff --git a/subcmds/diffmanifests.py b/subcmds/diffmanifests.py
index b999699e..f6cc30a2 100644
--- a/subcmds/diffmanifests.py
+++ b/subcmds/diffmanifests.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2014 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,12 +14,14 @@
 
 from color import Coloring
 from command import PagedCommand
-from manifest_xml import XmlManifest
+from manifest_xml import RepoClient
+
 
 class _Coloring(Coloring):
   def __init__(self, config):
     Coloring.__init__(self, config, "status")
 
+
 class Diffmanifests(PagedCommand):
   """ A command to see logs in projects represented by manifests
 
@@ -31,7 +31,7 @@ class Diffmanifests(PagedCommand):
   deeper level.
   """
 
-  common = True
+  COMMON = True
   helpSummary = "Manifest diff utility"
   helpUsage = """%prog manifest1.xml [manifest2.xml] [options]"""
 
@@ -68,16 +68,16 @@ synced and their revisions won't be found.
   def _Options(self, p):
     p.add_option('--raw',
                  dest='raw', action='store_true',
-                 help='Display raw diff.')
+                 help='display raw diff')
     p.add_option('--no-color',
                  dest='color', action='store_false', default=True,
-                 help='does not display the diff in color.')
+                 help='does not display the diff in color')
     p.add_option('--pretty-format',
                  dest='pretty_format', action='store',
                  metavar='<FORMAT>',
                  help='print the log using a custom git pretty format string')
 
-  def _printRawDiff(self, diff):
+  def _printRawDiff(self, diff, pretty_format=None):
     for project in diff['added']:
       self.printText("A %s %s" % (project.relpath, project.revisionExpr))
       self.out.nl()
@@ -90,7 +90,7 @@ synced and their revisions won't be found.
       self.printText("C %s %s %s" % (project.relpath, project.revisionExpr,
                                      otherProject.revisionExpr))
       self.out.nl()
-      self._printLogs(project, otherProject, raw=True, color=False)
+      self._printLogs(project, otherProject, raw=True, color=False, pretty_format=pretty_format)
 
     for project, otherProject in diff['unreachable']:
       self.printText("U %s %s %s" % (project.relpath, project.revisionExpr,
@@ -181,26 +181,26 @@ synced and their revisions won't be found.
       self.OptionParser.error('missing manifests to diff')
 
   def Execute(self, opt, args):
-    self.out = _Coloring(self.manifest.globalConfig)
+    self.out = _Coloring(self.client.globalConfig)
     self.printText = self.out.nofmt_printer('text')
     if opt.color:
-      self.printProject = self.out.nofmt_printer('project', attr = 'bold')
-      self.printAdded = self.out.nofmt_printer('green', fg = 'green', attr = 'bold')
-      self.printRemoved = self.out.nofmt_printer('red', fg = 'red', attr = 'bold')
-      self.printRevision = self.out.nofmt_printer('revision', fg = 'yellow')
+      self.printProject = self.out.nofmt_printer('project', attr='bold')
+      self.printAdded = self.out.nofmt_printer('green', fg='green', attr='bold')
+      self.printRemoved = self.out.nofmt_printer('red', fg='red', attr='bold')
+      self.printRevision = self.out.nofmt_printer('revision', fg='yellow')
     else:
       self.printProject = self.printAdded = self.printRemoved = self.printRevision = self.printText
 
-    manifest1 = XmlManifest(self.manifest.repodir)
+    manifest1 = RepoClient(self.repodir)
     manifest1.Override(args[0], load_local_manifests=False)
     if len(args) == 1:
       manifest2 = self.manifest
     else:
-      manifest2 = XmlManifest(self.manifest.repodir)
+      manifest2 = RepoClient(self.repodir)
       manifest2.Override(args[1], load_local_manifests=False)
 
     diff = manifest1.projectsDiff(manifest2)
     if opt.raw:
-      self._printRawDiff(diff)
+      self._printRawDiff(diff, pretty_format=opt.pretty_format)
     else:
       self._printDiff(diff, color=opt.color, pretty_format=opt.pretty_format)
diff --git a/subcmds/download.py b/subcmds/download.py
index f746bc23..523f25e0 100644
--- a/subcmds/download.py
+++ b/subcmds/download.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,17 +12,17 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import re
 import sys
 
 from command import Command
-from error import GitError
+from error import GitError, NoSuchProjectError
 
 CHANGE_RE = re.compile(r'^([1-9][0-9]*)(?:[/\.-]([1-9][0-9]*))?$')
 
+
 class Download(Command):
-  common = True
+  COMMON = True
   helpSummary = "Download and checkout a change"
   helpUsage = """
 %prog {[project] change[/patchset]}...
@@ -36,9 +34,13 @@ If no project is specified try to use current directory as a project.
 """
 
   def _Options(self, p):
+    p.add_option('-b', '--branch',
+                 help='create a new branch first')
     p.add_option('-c', '--cherry-pick',
                  dest='cherrypick', action='store_true',
                  help="cherry-pick instead of checkout")
+    p.add_option('-x', '--record-origin', action='store_true',
+                 help='pass -x when cherry-picking')
     p.add_option('-r', '--revert',
                  dest='revert', action='store_true',
                  help="revert instead of checkout")
@@ -58,6 +60,7 @@ If no project is specified try to use current directory as a project.
       if m:
         if not project:
           project = self.GetProjects(".")[0]
+          print('Defaulting to cwd project', project.name)
         chg_id = int(m.group(1))
         if m.group(2):
           ps_id = int(m.group(2))
@@ -74,9 +77,33 @@ If no project is specified try to use current directory as a project.
                 ps_id = max(int(match.group(1)), ps_id)
         to_get.append((project, chg_id, ps_id))
       else:
-        project = self.GetProjects([a])[0]
+        projects = self.GetProjects([a])
+        if len(projects) > 1:
+          # If the cwd is one of the projects, assume they want that.
+          try:
+            project = self.GetProjects('.')[0]
+          except NoSuchProjectError:
+            project = None
+          if project not in projects:
+            print('error: %s matches too many projects; please re-run inside '
+                  'the project checkout.' % (a,), file=sys.stderr)
+            for project in projects:
+              print('  %s/ @ %s' % (project.relpath, project.revisionExpr),
+                    file=sys.stderr)
+            sys.exit(1)
+        else:
+          project = projects[0]
+          print('Defaulting to cwd project', project.name)
     return to_get
 
+  def ValidateOptions(self, opt, args):
+    if opt.record_origin:
+      if not opt.cherrypick:
+        self.OptionParser.error('-x only makes sense with --cherry-pick')
+
+      if opt.ffonly:
+        self.OptionParser.error('-x and --ff are mutually exclusive options')
+
   def Execute(self, opt, args):
     for project, change_id, ps_id in self._ParseChangeIds(args):
       dl = project.DownloadPatchSet(change_id, ps_id)
@@ -93,22 +120,41 @@ If no project is specified try to use current directory as a project.
         continue
 
       if len(dl.commits) > 1:
-        print('[%s] %d/%d depends on %d unmerged changes:' \
+        print('[%s] %d/%d depends on %d unmerged changes:'
               % (project.name, change_id, ps_id, len(dl.commits)),
               file=sys.stderr)
         for c in dl.commits:
           print('  %s' % (c), file=sys.stderr)
-      if opt.cherrypick:
-        try:
-          project._CherryPick(dl.commit)
-        except GitError:
-          print('[%s] Could not complete the cherry-pick of %s' \
-                % (project.name, dl.commit), file=sys.stderr)
-          sys.exit(1)
 
+      if opt.cherrypick:
+        mode = 'cherry-pick'
       elif opt.revert:
-        project._Revert(dl.commit)
+        mode = 'revert'
       elif opt.ffonly:
-        project._FastForward(dl.commit, ffonly=True)
+        mode = 'fast-forward merge'
       else:
-        project._Checkout(dl.commit)
+        mode = 'checkout'
+
+      # We'll combine the branch+checkout operation, but all the rest need a
+      # dedicated branch start.
+      if opt.branch and mode != 'checkout':
+        project.StartBranch(opt.branch)
+
+      try:
+        if opt.cherrypick:
+          project._CherryPick(dl.commit, ffonly=opt.ffonly,
+                              record_origin=opt.record_origin)
+        elif opt.revert:
+          project._Revert(dl.commit)
+        elif opt.ffonly:
+          project._FastForward(dl.commit, ffonly=True)
+        else:
+          if opt.branch:
+            project.StartBranch(opt.branch, revision=dl.commit)
+          else:
+            project._Checkout(dl.commit)
+
+      except GitError:
+        print('[%s] Could not complete the %s of %s'
+              % (project.name, mode, dl.commit), file=sys.stderr)
+        sys.exit(1)
diff --git a/subcmds/forall.py b/subcmds/forall.py
index 131ba676..7c1dea9e 100644
--- a/subcmds/forall.py
+++ b/subcmds/forall.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,8 +12,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import errno
+import functools
+import io
 import multiprocessing
 import re
 import os
@@ -24,14 +23,14 @@ import sys
 import subprocess
 
 from color import Coloring
-from command import Command, MirrorSafeCommand
-import platform_utils
+from command import DEFAULT_LOCAL_JOBS, Command, MirrorSafeCommand, WORKER_BATCH_SIZE
+from error import ManifestInvalidRevisionError
 
 _CAN_COLOR = [
-  'branch',
-  'diff',
-  'grep',
-  'log',
+    'branch',
+    'diff',
+    'grep',
+    'log',
 ]
 
 
@@ -42,11 +41,11 @@ class ForallColoring(Coloring):
 
 
 class Forall(Command, MirrorSafeCommand):
-  common = False
+  COMMON = False
   helpSummary = "Run a shell command in each project"
   helpUsage = """
 %prog [<project>...] -c <command> [<arg>...]
-%prog -r str1 [str2] ... -c <command> [<arg>...]"
+%prog -r str1 [str2] ... -c <command> [<arg>...]
 """
   helpDescription = """
 Executes the same shell command in each project.
@@ -54,6 +53,11 @@ Executes the same shell command in each project.
 The -r option allows running the command only on projects matching
 regex or wildcard expression.
 
+By default, projects are processed non-interactively in parallel.  If you want
+to run interactive commands, make sure to pass --interactive to force --jobs 1.
+While the processing order of projects is not guaranteed, the order of project
+output is stable.
+
 # Output Formatting
 
 The -p option causes '%prog' to bind pipes to the command's stdin,
@@ -116,70 +120,48 @@ terminal and are not redirected.
 If -e is used, when a command exits unsuccessfully, '%prog' will abort
 without iterating through the remaining projects.
 """
+  PARALLEL_JOBS = DEFAULT_LOCAL_JOBS
+
+  @staticmethod
+  def _cmd_option(option, _opt_str, _value, parser):
+    setattr(parser.values, option.dest, list(parser.rargs))
+    while parser.rargs:
+      del parser.rargs[0]
 
   def _Options(self, p):
-    def cmd(option, opt_str, value, parser):
-      setattr(parser.values, option.dest, list(parser.rargs))
-      while parser.rargs:
-        del parser.rargs[0]
     p.add_option('-r', '--regex',
                  dest='regex', action='store_true',
-                 help="Execute the command only on projects matching regex or wildcard expression")
+                 help='execute the command only on projects matching regex or wildcard expression')
     p.add_option('-i', '--inverse-regex',
                  dest='inverse_regex', action='store_true',
-                 help="Execute the command only on projects not matching regex or wildcard expression")
+                 help='execute the command only on projects not matching regex or '
+                      'wildcard expression')
     p.add_option('-g', '--groups',
                  dest='groups',
-                 help="Execute the command only on projects matching the specified groups")
+                 help='execute the command only on projects matching the specified groups')
     p.add_option('-c', '--command',
-                 help='Command (and arguments) to execute',
+                 help='command (and arguments) to execute',
                  dest='command',
                  action='callback',
-                 callback=cmd)
+                 callback=self._cmd_option)
     p.add_option('-e', '--abort-on-errors',
                  dest='abort_on_errors', action='store_true',
-                 help='Abort if a command exits unsuccessfully')
+                 help='abort if a command exits unsuccessfully')
     p.add_option('--ignore-missing', action='store_true',
-                 help='Silently skip & do not exit non-zero due missing '
+                 help='silently skip & do not exit non-zero due missing '
                       'checkouts')
 
-    g = p.add_option_group('Output')
+    g = p.get_option_group('--quiet')
     g.add_option('-p',
                  dest='project_header', action='store_true',
-                 help='Show project headers before output')
-    g.add_option('-v', '--verbose',
-                 dest='verbose', action='store_true',
-                 help='Show command error messages')
-    g.add_option('-j', '--jobs',
-                 dest='jobs', action='store', type='int', default=1,
-                 help='number of commands to execute simultaneously')
+                 help='show project headers before output')
+    p.add_option('--interactive',
+                 action='store_true',
+                 help='force interactive usage')
 
   def WantPager(self, opt):
     return opt.project_header and opt.jobs == 1
 
-  def _SerializeProject(self, project):
-    """ Serialize a project._GitGetByExec instance.
-
-    project._GitGetByExec is not pickle-able. Instead of trying to pass it
-    around between processes, make a dict ourselves containing only the
-    attributes that we need.
-
-    """
-    if not self.manifest.IsMirror:
-      lrev = project.GetRevisionId()
-    else:
-      lrev = None
-    return {
-      'name': project.name,
-      'relpath': project.relpath,
-      'remote_name': project.remote.name,
-      'lrev': lrev,
-      'rrev': project.revisionExpr,
-      'annotations': dict((a.name, a.value) for a in project.annotations),
-      'gitdir': project.gitdir,
-      'worktree': project.worktree,
-    }
-
   def ValidateOptions(self, opt, args):
     if not opt.command:
       self.Usage()
@@ -195,9 +177,14 @@ without iterating through the remaining projects.
       cmd.append(cmd[0])
     cmd.extend(opt.command[1:])
 
-    if  opt.project_header \
-    and not shell \
-    and cmd[0] == 'git':
+    # Historically, forall operated interactively, and in serial.  If the user
+    # has selected 1 job, then default to interacive mode.
+    if opt.jobs == 1:
+      opt.interactive = True
+
+    if opt.project_header \
+            and not shell \
+            and cmd[0] == 'git':
       # If this is a direct git command that can enable colorized
       # output and the user prefers coloring, add --color into the
       # command line because we are going to wrap the command into
@@ -220,7 +207,7 @@ without iterating through the remaining projects.
 
     smart_sync_manifest_name = "smart_sync_override.xml"
     smart_sync_manifest_path = os.path.join(
-      self.manifest.manifestProject.worktree, smart_sync_manifest_name)
+        self.manifest.manifestProject.worktree, smart_sync_manifest_name)
 
     if os.path.isfile(smart_sync_manifest_path):
       self.manifest.Override(smart_sync_manifest_path)
@@ -234,58 +221,50 @@ without iterating through the remaining projects.
 
     os.environ['REPO_COUNT'] = str(len(projects))
 
-    pool = multiprocessing.Pool(opt.jobs, InitWorker)
     try:
       config = self.manifest.manifestProject.config
-      results_it = pool.imap(
-         DoWorkWrapper,
-         self.ProjectArgs(projects, mirror, opt, cmd, shell, config))
-      pool.close()
-      for r in results_it:
-        rc = rc or r
-        if r != 0 and opt.abort_on_errors:
-          raise Exception('Aborting due to previous error')
+      with multiprocessing.Pool(opt.jobs, InitWorker) as pool:
+        results_it = pool.imap(
+            functools.partial(DoWorkWrapper, mirror, opt, cmd, shell, config),
+            enumerate(projects),
+            chunksize=WORKER_BATCH_SIZE)
+        first = True
+        for (r, output) in results_it:
+          if output:
+            if first:
+              first = False
+            elif opt.project_header:
+              print()
+            # To simplify the DoWorkWrapper, take care of automatic newlines.
+            end = '\n'
+            if output[-1] == '\n':
+              end = ''
+            print(output, end=end)
+          rc = rc or r
+          if r != 0 and opt.abort_on_errors:
+            raise Exception('Aborting due to previous error')
     except (KeyboardInterrupt, WorkerKeyboardInterrupt):
       # Catch KeyboardInterrupt raised inside and outside of workers
-      print('Interrupted - terminating the pool')
-      pool.terminate()
       rc = rc or errno.EINTR
     except Exception as e:
       # Catch any other exceptions raised
-      print('Got an error, terminating the pool: %s: %s' %
-              (type(e).__name__, e),
+      print('forall: unhandled error, terminating the pool: %s: %s' %
+            (type(e).__name__, e),
             file=sys.stderr)
-      pool.terminate()
       rc = rc or getattr(e, 'errno', 1)
-    finally:
-      pool.join()
     if rc != 0:
       sys.exit(rc)
 
-  def ProjectArgs(self, projects, mirror, opt, cmd, shell, config):
-    for cnt, p in enumerate(projects):
-      try:
-        project = self._SerializeProject(p)
-      except Exception as e:
-        print('Project list error on project %s: %s: %s' %
-                (p.name, type(e).__name__, e),
-              file=sys.stderr)
-        return
-      except KeyboardInterrupt:
-        print('Project list interrupted',
-              file=sys.stderr)
-        return
-      yield [mirror, opt, cmd, shell, cnt, config, project]
 
 class WorkerKeyboardInterrupt(Exception):
   """ Keyboard interrupt exception for worker processes. """
-  pass
 
 
 def InitWorker():
   signal.signal(signal.SIGINT, signal.SIG_IGN)
 
-def DoWorkWrapper(args):
+
+def DoWorkWrapper(mirror, opt, cmd, shell, config, args):
   """ A wrapper around the DoWork() method.
 
   Catch the KeyboardInterrupt exceptions here and re-raise them as a different,
@@ -293,109 +272,81 @@ def DoWorkWrapper(args):
   and making the parent hang indefinitely.
 
   """
-  project = args.pop()
+  cnt, project = args
   try:
-    return DoWork(project, *args)
+    return DoWork(project, mirror, opt, cmd, shell, cnt, config)
   except KeyboardInterrupt:
-    print('%s: Worker interrupted' % project['name'])
+    print('%s: Worker interrupted' % project.name)
     raise WorkerKeyboardInterrupt()
 
 
 def DoWork(project, mirror, opt, cmd, shell, cnt, config):
   env = os.environ.copy()
+
   def setenv(name, val):
     if val is None:
       val = ''
-    if hasattr(val, 'encode'):
-      val = val.encode()
     env[name] = val
 
-  setenv('REPO_PROJECT', project['name'])
-  setenv('REPO_PATH', project['relpath'])
-  setenv('REPO_REMOTE', project['remote_name'])
-  setenv('REPO_LREV', project['lrev'])
-  setenv('REPO_RREV', project['rrev'])
+  setenv('REPO_PROJECT', project.name)
+  setenv('REPO_PATH', project.relpath)
+  setenv('REPO_REMOTE', project.remote.name)
+  try:
+    # If we aren't in a fully synced state and we don't have the ref the manifest
+    # wants, then this will fail.  Ignore it for the purposes of this code.
+    lrev = '' if mirror else project.GetRevisionId()
+  except ManifestInvalidRevisionError:
+    lrev = ''
+  setenv('REPO_LREV', lrev)
+  setenv('REPO_RREV', project.revisionExpr)
+  setenv('REPO_UPSTREAM', project.upstream)
+  setenv('REPO_DEST_BRANCH', project.dest_branch)
   setenv('REPO_I', str(cnt + 1))
-  for name in project['annotations']:
-    setenv("REPO__%s" % (name), project['annotations'][name])
+  for annotation in project.annotations:
+    setenv("REPO__%s" % (annotation.name), annotation.value)
 
   if mirror:
-    setenv('GIT_DIR', project['gitdir'])
-    cwd = project['gitdir']
+    setenv('GIT_DIR', project.gitdir)
+    cwd = project.gitdir
   else:
-    cwd = project['worktree']
+    cwd = project.worktree
 
   if not os.path.exists(cwd):
     # Allow the user to silently ignore missing checkouts so they can run on
     # partial checkouts (good for infra recovery tools).
     if opt.ignore_missing:
-      return 0
+      return (0, '')
+
+    output = ''
     if ((opt.project_header and opt.verbose)
-        or not opt.project_header):
-      print('skipping %s/' % project['relpath'], file=sys.stderr)
-    return 1
+            or not opt.project_header):
+      output = 'skipping %s/' % project.relpath
+    return (1, output)
 
-  if opt.project_header:
-    stdin = subprocess.PIPE
-    stdout = subprocess.PIPE
-    stderr = subprocess.PIPE
+  if opt.verbose:
+    stderr = subprocess.STDOUT
   else:
-    stdin = None
-    stdout = None
-    stderr = None
-
-  p = subprocess.Popen(cmd,
-                       cwd=cwd,
-                       shell=shell,
-                       env=env,
-                       stdin=stdin,
-                       stdout=stdout,
-                       stderr=stderr)
+    stderr = subprocess.DEVNULL
+
+  stdin = None if opt.interactive else subprocess.DEVNULL
 
+  result = subprocess.run(
+      cmd, cwd=cwd, shell=shell, env=env, check=False,
+      encoding='utf-8', errors='replace',
+      stdin=stdin, stdout=subprocess.PIPE, stderr=stderr)
+
+  output = result.stdout
   if opt.project_header:
-    out = ForallColoring(config)
-    out.redirect(sys.stdout)
-    empty = True
-    errbuf = ''
-
-    p.stdin.close()
-    s_in = platform_utils.FileDescriptorStreams.create()
-    s_in.add(p.stdout, sys.stdout, 'stdout')
-    s_in.add(p.stderr, sys.stderr, 'stderr')
-
-    while not s_in.is_done:
-      in_ready = s_in.select()
-      for s in in_ready:
-        buf = s.read().decode()
-        if not buf:
-          s.close()
-          s_in.remove(s)
-          continue
-
-        if not opt.verbose:
-          if s.std_name == 'stderr':
-            errbuf += buf
-            continue
-
-        if empty and out:
-          if not cnt == 0:
-            out.nl()
-
-          if mirror:
-            project_header_path = project['name']
-          else:
-            project_header_path = project['relpath']
-          out.project('project %s/', project_header_path)
-          out.nl()
-          out.flush()
-          if errbuf:
-            sys.stderr.write(errbuf)
-            sys.stderr.flush()
-            errbuf = ''
-          empty = False
-
-        s.dest.write(buf)
-        s.dest.flush()
-
-  r = p.wait()
-  return r
+    if output:
+      buf = io.StringIO()
+      out = ForallColoring(config)
+      out.redirect(buf)
+      if mirror:
+        project_header_path = project.name
+      else:
+        project_header_path = project.relpath
+      out.project('project %s/' % project_header_path)
+      out.nl()
+      buf.write(output)
+      output = buf.getvalue()
+  return (result.returncode, output)
diff --git a/subcmds/gitc_delete.py b/subcmds/gitc_delete.py
index e5214b8e..df749469 100644
--- a/subcmds/gitc_delete.py
+++ b/subcmds/gitc_delete.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2015 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,18 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import sys
 
 from command import Command, GitcClientCommand
 import platform_utils
 
-from pyversion import is_python3
-if not is_python3():
-  input = raw_input
 
 class GitcDelete(Command, GitcClientCommand):
-  common = True
+  COMMON = True
   visible_everywhere = False
   helpSummary = "Delete a GITC Client."
   helpUsage = """
@@ -39,7 +33,7 @@ and all locally downloaded sources.
   def _Options(self, p):
     p.add_option('-f', '--force',
                  dest='force', action='store_true',
-                 help='Force the deletion (no prompt).')
+                 help='force the deletion (no prompt)')
 
   def Execute(self, opt, args):
     if not opt.force:
diff --git a/subcmds/gitc_init.py b/subcmds/gitc_init.py
index 378f9236..e705b613 100644
--- a/subcmds/gitc_init.py
+++ b/subcmds/gitc_init.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2015 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import os
 import sys
 
@@ -26,7 +23,7 @@ import wrapper
 
 
 class GitcInit(init.Init, GitcAvailableCommand):
-  common = True
+  COMMON = True
   helpSummary = "Initialize a GITC Client."
   helpUsage = """
 %prog [options] [client name]
@@ -50,23 +47,17 @@ use for this GITC client.
 """
 
   def _Options(self, p):
-    super(GitcInit, self)._Options(p, gitc_init=True)
-    g = p.add_option_group('GITC options')
-    g.add_option('-f', '--manifest-file',
-                 dest='manifest_file',
-                 help='Optional manifest file to use for this GITC client.')
-    g.add_option('-c', '--gitc-client',
-                 dest='gitc_client',
-                 help='The name of the gitc_client instance to create or modify.')
+    super()._Options(p, gitc_init=True)
 
   def Execute(self, opt, args):
     gitc_client = gitc_utils.parse_clientdir(os.getcwd())
     if not gitc_client or (opt.gitc_client and gitc_client != opt.gitc_client):
-      print('fatal: Please update your repo command. See go/gitc for instructions.', file=sys.stderr)
+      print('fatal: Please update your repo command. See go/gitc for instructions.',
+            file=sys.stderr)
       sys.exit(1)
     self.client_dir = os.path.join(gitc_utils.get_gitc_manifest_dir(),
                                    gitc_client)
-    super(GitcInit, self).Execute(opt, args)
+    super().Execute(opt, args)
 
     manifest_file = self.manifest.manifestFile
     if opt.manifest_file:
diff --git a/subcmds/grep.py b/subcmds/grep.py
index 4dd85d57..8ac4ba14 100644
--- a/subcmds/grep.py
+++ b/subcmds/grep.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2009 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,14 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
+import functools
 import sys
 
 from color import Coloring
-from command import PagedCommand
+from command import DEFAULT_LOCAL_JOBS, PagedCommand
 from error import GitError
-from git_command import git_require, GitCommand
+from git_command import GitCommand
+
 
 class GrepColoring(Coloring):
   def __init__(self, config):
@@ -29,8 +27,9 @@ class GrepColoring(Coloring):
     self.project = self.printer('project', attr='bold')
     self.fail = self.printer('fail', fg='red')
 
+
 class Grep(PagedCommand):
-  common = True
+  COMMON = True
   helpSummary = "Print lines matching a pattern"
   helpUsage = """
 %prog {pattern | -e pattern} [<project>...]
@@ -63,30 +62,33 @@ contain a line that matches both expressions:
   repo grep --all-match -e NODE -e Unexpected
 
 """
+  PARALLEL_JOBS = DEFAULT_LOCAL_JOBS
+
+  @staticmethod
+  def _carry_option(_option, opt_str, value, parser):
+    pt = getattr(parser.values, 'cmd_argv', None)
+    if pt is None:
+      pt = []
+      setattr(parser.values, 'cmd_argv', pt)
+
+    if opt_str == '-(':
+      pt.append('(')
+    elif opt_str == '-)':
+      pt.append(')')
+    else:
+      pt.append(opt_str)
 
-  def _Options(self, p):
-    def carry(option,
-              opt_str,
-              value,
-              parser):
-      pt = getattr(parser.values, 'cmd_argv', None)
-      if pt is None:
-        pt = []
-        setattr(parser.values, 'cmd_argv', pt)
-
-      if opt_str == '-(':
-        pt.append('(')
-      elif opt_str == '-)':
-        pt.append(')')
-      else:
-        pt.append(opt_str)
+    if value is not None:
+      pt.append(value)
 
-      if value is not None:
-        pt.append(value)
+  def _CommonOptions(self, p):
+    """Override common options slightly."""
+    super()._CommonOptions(p, opt_v=False)
 
+  def _Options(self, p):
     g = p.add_option_group('Sources')
     g.add_option('--cached',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Search the index, instead of the work tree')
     g.add_option('-r', '--revision',
                  dest='revision', action='append', metavar='TREEish',
@@ -94,136 +96,111 @@ contain a line that matches both expressions:
 
     g = p.add_option_group('Pattern')
     g.add_option('-e',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  metavar='PATTERN', type='str',
                  help='Pattern to search for')
     g.add_option('-i', '--ignore-case',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Ignore case differences')
     g.add_option('-a', '--text',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help="Process binary files as if they were text")
     g.add_option('-I',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help="Don't match the pattern in binary files")
     g.add_option('-w', '--word-regexp',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Match the pattern only at word boundaries')
     g.add_option('-v', '--invert-match',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Select non-matching lines')
     g.add_option('-G', '--basic-regexp',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Use POSIX basic regexp for patterns (default)')
     g.add_option('-E', '--extended-regexp',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Use POSIX extended regexp for patterns')
     g.add_option('-F', '--fixed-strings',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Use fixed strings (not regexp) for pattern')
 
     g = p.add_option_group('Pattern Grouping')
     g.add_option('--all-match',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Limit match to lines that have all patterns')
     g.add_option('--and', '--or', '--not',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Boolean operators to combine patterns')
     g.add_option('-(', '-)',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Boolean operator grouping')
 
     g = p.add_option_group('Output')
     g.add_option('-n',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Prefix the line number to matching lines')
     g.add_option('-C',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  metavar='CONTEXT', type='str',
                  help='Show CONTEXT lines around match')
     g.add_option('-B',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  metavar='CONTEXT', type='str',
                  help='Show CONTEXT lines before match')
     g.add_option('-A',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  metavar='CONTEXT', type='str',
                  help='Show CONTEXT lines after match')
     g.add_option('-l', '--name-only', '--files-with-matches',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Show only file names containing matching lines')
     g.add_option('-L', '--files-without-match',
-                 action='callback', callback=carry,
+                 action='callback', callback=self._carry_option,
                  help='Show only file names not containing matching lines')
 
-
-  def Execute(self, opt, args):
-    out = GrepColoring(self.manifest.manifestProject.config)
-
-    cmd_argv = ['grep']
-    if out.is_on and git_require((1, 6, 3)):
-      cmd_argv.append('--color')
-    cmd_argv.extend(getattr(opt, 'cmd_argv', []))
-
-    if '-e' not in cmd_argv:
-      if not args:
-        self.Usage()
-      cmd_argv.append('-e')
-      cmd_argv.append(args[0])
-      args = args[1:]
-
-    projects = self.GetProjects(args)
-
-    full_name = False
-    if len(projects) > 1:
-      cmd_argv.append('--full-name')
-      full_name = True
-
-    have_rev = False
-    if opt.revision:
-      if '--cached' in cmd_argv:
-        print('fatal: cannot combine --cached and --revision', file=sys.stderr)
-        sys.exit(1)
-      have_rev = True
-      cmd_argv.extend(opt.revision)
-    cmd_argv.append('--')
-
+  def _ExecuteOne(self, cmd_argv, project):
+    """Process one project."""
+    try:
+      p = GitCommand(project,
+                     cmd_argv,
+                     bare=False,
+                     capture_stdout=True,
+                     capture_stderr=True)
+    except GitError as e:
+      return (project, -1, None, str(e))
+
+    return (project, p.Wait(), p.stdout, p.stderr)
+
+  @staticmethod
+  def _ProcessResults(full_name, have_rev, _pool, out, results):
     git_failed = False
     bad_rev = False
     have_match = False
 
-    for project in projects:
-      try:
-        p = GitCommand(project,
-                       cmd_argv,
-                       bare=False,
-                       capture_stdout=True,
-                       capture_stderr=True)
-      except GitError as e:
+    for project, rc, stdout, stderr in results:
+      if rc < 0:
         git_failed = True
         out.project('--- project %s ---' % project.relpath)
         out.nl()
-        out.fail('%s', str(e))
+        out.fail('%s', stderr)
         out.nl()
         continue
 
-      if p.Wait() != 0:
+      if rc:
         # no results
-        #
-        if p.stderr:
-          if have_rev and 'fatal: ambiguous argument' in p.stderr:
+        if stderr:
+          if have_rev and 'fatal: ambiguous argument' in stderr:
             bad_rev = True
           else:
             out.project('--- project %s ---' % project.relpath)
             out.nl()
-            out.fail('%s', p.stderr.strip())
+            out.fail('%s', stderr.strip())
             out.nl()
         continue
       have_match = True
 
       # We cut the last element, to avoid a blank line.
-      #
-      r = p.stdout.split('\n')
+      r = stdout.split('\n')
       r = r[0:-1]
 
       if have_rev and full_name:
@@ -245,6 +222,47 @@ contain a line that matches both expressions:
         for line in r:
           print(line)
 
+    return (git_failed, bad_rev, have_match)
+
+  def Execute(self, opt, args):
+    out = GrepColoring(self.manifest.manifestProject.config)
+
+    cmd_argv = ['grep']
+    if out.is_on:
+      cmd_argv.append('--color')
+    cmd_argv.extend(getattr(opt, 'cmd_argv', []))
+
+    if '-e' not in cmd_argv:
+      if not args:
+        self.Usage()
+      cmd_argv.append('-e')
+      cmd_argv.append(args[0])
+      args = args[1:]
+
+    projects = self.GetProjects(args)
+
+    full_name = False
+    if len(projects) > 1:
+      cmd_argv.append('--full-name')
+      full_name = True
+
+    have_rev = False
+    if opt.revision:
+      if '--cached' in cmd_argv:
+        print('fatal: cannot combine --cached and --revision', file=sys.stderr)
+        sys.exit(1)
+      have_rev = True
+      cmd_argv.extend(opt.revision)
+    cmd_argv.append('--')
+
+    git_failed, bad_rev, have_match = self.ExecuteInParallel(
+        opt.jobs,
+        functools.partial(self._ExecuteOne, cmd_argv),
+        projects,
+        callback=functools.partial(self._ProcessResults, full_name, have_rev),
+        output=out,
+        ordered=True)
+
     if git_failed:
       sys.exit(1)
     elif have_match:
diff --git a/subcmds/help.py b/subcmds/help.py
index 78930502..1a60ef45 100644
--- a/subcmds/help.py
+++ b/subcmds/help.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,17 +12,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import re
 import sys
-from formatter import AbstractFormatter, DumbWriter
+import textwrap
 
+from subcmds import all_commands
 from color import Coloring
 from command import PagedCommand, MirrorSafeCommand, GitcAvailableCommand, GitcClientCommand
 import gitc_utils
+from wrapper import Wrapper
+
 
 class Help(PagedCommand, MirrorSafeCommand):
-  common = False
+  COMMON = False
   helpSummary = "Display detailed help on a command"
   helpUsage = """
 %prog [--all|command]
@@ -41,7 +41,7 @@ Displays detailed usage information about a command.
     fmt = '  %%-%ds  %%s' % maxlen
 
     for name in commandNames:
-      command = self.commands[name]
+      command = all_commands[name]()
       try:
         summary = command.helpSummary.strip()
       except AttributeError:
@@ -50,20 +50,27 @@ Displays detailed usage information about a command.
 
   def _PrintAllCommands(self):
     print('usage: repo COMMAND [ARGS]')
+    self.PrintAllCommandsBody()
+
+  def PrintAllCommandsBody(self):
     print('The complete list of recognized repo commands are:')
-    commandNames = list(sorted(self.commands))
+    commandNames = list(sorted(all_commands))
     self._PrintCommands(commandNames)
     print("See 'repo help <command>' for more information on a "
           'specific command.')
+    print('Bug reports:', Wrapper().BUG_URL)
 
   def _PrintCommonCommands(self):
     print('usage: repo COMMAND [ARGS]')
+    self.PrintCommonCommandsBody()
+
+  def PrintCommonCommandsBody(self):
     print('The most commonly used repo commands are:')
 
     def gitc_supported(cmd):
       if not isinstance(cmd, GitcAvailableCommand) and not isinstance(cmd, GitcClientCommand):
         return True
-      if self.manifest.isGitcClient:
+      if self.client.isGitcClient:
         return True
       if isinstance(cmd, GitcClientCommand):
         return False
@@ -72,21 +79,21 @@ Displays detailed usage information about a command.
       return False
 
     commandNames = list(sorted([name
-                    for name, command in self.commands.items()
-                    if command.common and gitc_supported(command)]))
+                                for name, command in all_commands.items()
+                                if command.COMMON and gitc_supported(command)]))
     self._PrintCommands(commandNames)
 
     print(
-"See 'repo help <command>' for more information on a specific command.\n"
-"See 'repo help --all' for a complete list of recognized commands.")
+        "See 'repo help <command>' for more information on a specific command.\n"
+        "See 'repo help --all' for a complete list of recognized commands.")
+    print('Bug reports:', Wrapper().BUG_URL)
 
   def _PrintCommandHelp(self, cmd, header_prefix=''):
     class _Out(Coloring):
       def __init__(self, gc):
         Coloring.__init__(self, gc, 'help')
         self.heading = self.printer('heading', attr='bold')
-
-        self.wrap = AbstractFormatter(DumbWriter())
+        self._first = True
 
       def _PrintSection(self, heading, bodyAttr):
         try:
@@ -96,7 +103,9 @@ Displays detailed usage information about a command.
         if body == '' or body is None:
           return
 
-        self.nl()
+        if not self._first:
+          self.nl()
+        self._first = False
 
         self.heading('%s%s', header_prefix, heading)
         self.nl()
@@ -106,7 +115,8 @@ Displays detailed usage information about a command.
         body = body.strip()
         body = body.replace('%prog', me)
 
-        asciidoc_hdr = re.compile(r'^\n?#+ (.+)$')
+        # Extract the title, but skip any trailing {#anchors}.
+        asciidoc_hdr = re.compile(r'^\n?#+ ([^{]+)(\{#.+\})?$')
         for para in body.split("\n\n"):
           if para.startswith(' '):
             self.write('%s', para)
@@ -121,19 +131,21 @@ Displays detailed usage information about a command.
             self.nl()
             continue
 
-          self.wrap.add_flowing_data(para)
-          self.wrap.end_paragraph(1)
-        self.wrap.end_paragraph(0)
+          lines = textwrap.wrap(para.replace('  ', ' '), width=80,
+                                break_long_words=False, break_on_hyphens=False)
+          for line in lines:
+            self.write('%s', line)
+            self.nl()
+          self.nl()
 
-    out = _Out(self.manifest.globalConfig)
+    out = _Out(self.client.globalConfig)
     out._PrintSection('Summary', 'helpSummary')
     cmd.OptionParser.print_help()
     out._PrintSection('Description', 'helpDescription')
 
   def _PrintAllCommandHelp(self):
-    for name in sorted(self.commands):
-      cmd = self.commands[name]
-      cmd.manifest = self.manifest
+    for name in sorted(all_commands):
+      cmd = all_commands[name](manifest=self.manifest)
       self._PrintCommandHelp(cmd, header_prefix='[%s] ' % (name,))
 
   def _Options(self, p):
@@ -157,12 +169,11 @@ Displays detailed usage information about a command.
       name = args[0]
 
       try:
-        cmd = self.commands[name]
+        cmd = all_commands[name](manifest=self.manifest)
       except KeyError:
         print("repo: '%s' is not a repo command." % name, file=sys.stderr)
         sys.exit(1)
 
-      cmd.manifest = self.manifest
       self._PrintCommandHelp(cmd)
 
     else:
diff --git a/subcmds/info.py b/subcmds/info.py
index d62e1e64..6c1246ef 100644
--- a/subcmds/info.py
+++ b/subcmds/info.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2012 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,18 +12,22 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import optparse
+
 from command import PagedCommand
 from color import Coloring
-from git_refs import R_M
+from git_refs import R_M, R_HEADS
+
 
 class _Coloring(Coloring):
   def __init__(self, config):
     Coloring.__init__(self, config, "status")
 
+
 class Info(PagedCommand):
-  common = True
+  COMMON = True
   helpSummary = "Get info on the manifest branch, current branch or unmerged branches"
-  helpUsage = "%prog [-dl] [-o [-b]] [<project>...]"
+  helpUsage = "%prog [-dl] [-o [-c]] [<project>...]"
 
   def _Options(self, p):
     p.add_option('-d', '--diff',
@@ -34,22 +36,28 @@ class Info(PagedCommand):
     p.add_option('-o', '--overview',
                  dest='overview', action='store_true',
                  help='show overview of all local commits')
-    p.add_option('-b', '--current-branch',
+    p.add_option('-c', '--current-branch',
                  dest="current_branch", action="store_true",
                  help="consider only checked out branches")
+    p.add_option('--no-current-branch',
+                 dest='current_branch', action='store_false',
+                 help='consider all local branches')
+    # Turn this into a warning & remove this someday.
+    p.add_option('-b',
+                 dest='current_branch', action='store_true',
+                 help=optparse.SUPPRESS_HELP)
     p.add_option('-l', '--local-only',
                  dest="local", action="store_true",
-                 help="Disable all remote operations")
-
+                 help="disable all remote operations")
 
   def Execute(self, opt, args):
-    self.out = _Coloring(self.manifest.globalConfig)
-    self.heading = self.out.printer('heading', attr = 'bold')
-    self.headtext = self.out.nofmt_printer('headtext', fg = 'yellow')
-    self.redtext = self.out.printer('redtext', fg = 'red')
-    self.sha = self.out.printer("sha", fg = 'yellow')
+    self.out = _Coloring(self.client.globalConfig)
+    self.heading = self.out.printer('heading', attr='bold')
+    self.headtext = self.out.nofmt_printer('headtext', fg='yellow')
+    self.redtext = self.out.printer('redtext', fg='red')
+    self.sha = self.out.printer("sha", fg='yellow')
     self.text = self.out.nofmt_printer('text')
-    self.dimtext = self.out.printer('dimtext', attr = 'dim')
+    self.dimtext = self.out.printer('dimtext', attr='dim')
 
     self.opt = opt
 
@@ -122,11 +130,14 @@ class Info(PagedCommand):
       self.printSeparator()
 
   def findRemoteLocalDiff(self, project):
-    #Fetch all the latest commits
+    # Fetch all the latest commits.
     if not self.opt.local:
       project.Sync_NetworkHalf(quiet=True, current_branch_only=True)
 
-    logTarget = R_M + self.manifest.manifestProject.config.GetBranch("default").merge
+    branch = self.manifest.manifestProject.config.GetBranch('default').merge
+    if branch.startswith(R_HEADS):
+      branch = branch[len(R_HEADS):]
+    logTarget = R_M + branch
 
     bareTmp = project.bare_git._bare
     project.bare_git._bare = False
@@ -195,16 +206,16 @@ class Info(PagedCommand):
       commits = branch.commits
       date = branch.date
       self.text('%s %-33s (%2d commit%s, %s)' % (
-        branch.name == project.CurrentBranch and '*' or ' ',
-        branch.name,
-        len(commits),
-        len(commits) != 1 and 's' or '',
-        date))
+          branch.name == project.CurrentBranch and '*' or ' ',
+          branch.name,
+          len(commits),
+          len(commits) != 1 and 's' or '',
+          date))
       self.out.nl()
 
       for commit in commits:
         split = commit.split()
-        self.text('{0:38}{1} '.format('','-'))
+        self.text('{0:38}{1} '.format('', '-'))
         self.sha(split[0] + " ")
         self.text(" ".join(split[1:]))
         self.out.nl()
diff --git a/subcmds/init.py b/subcmds/init.py
index 6594a602..9c6b2ad9 100644
--- a/subcmds/init.py
+++ b/subcmds/init.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,34 +12,30 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import os
 import platform
 import re
+import subprocess
 import sys
-
-from pyversion import is_python3
-if is_python3():
-  import urllib.parse
-else:
-  import imp
-  import urlparse
-  urllib = imp.new_module('urllib')
-  urllib.parse = urlparse
+import urllib.parse
 
 from color import Coloring
 from command import InteractiveCommand, MirrorSafeCommand
 from error import ManifestParseError
 from project import SyncBuffer
 from git_config import GitConfig
-from git_command import git_require, MIN_GIT_VERSION
+from git_command import git_require, MIN_GIT_VERSION_SOFT, MIN_GIT_VERSION_HARD
+import fetch
+import git_superproject
 import platform_utils
+from wrapper import Wrapper
+
 
 class Init(InteractiveCommand, MirrorSafeCommand):
-  common = True
-  helpSummary = "Initialize repo in the current directory"
+  COMMON = True
+  helpSummary = "Initialize a repo client checkout in the current directory"
   helpUsage = """
-%prog [options]
+%prog [options] [manifest url]
 """
   helpDescription = """
 The '%prog' command is run once to install and initialize repo.
@@ -49,13 +43,24 @@ The latest repo source code and manifest collection is downloaded
 from the server and is installed in the .repo/ directory in the
 current working directory.
 
+When creating a new checkout, the manifest URL is the only required setting.
+It may be specified using the --manifest-url option, or as the first optional
+argument.
+
 The optional -b argument can be used to select the manifest branch
-to checkout and use.  If no branch is specified, master is assumed.
+to checkout and use.  If no branch is specified, the remote's default
+branch is used.  This is equivalent to using -b HEAD.
 
 The optional -m argument can be used to specify an alternate manifest
 to be used. If no manifest is specified, the manifest default.xml
 will be used.
 
+If the --standalone-manifest argument is set, the manifest will be downloaded
+directly from the specified --manifest-url as a static file (rather than
+setting up a manifest git checkout). With --standalone-manifest, the manifest
+will be fully static and will not be re-downloaded during subsesquent
+`repo init` and `repo sync` calls.
+
 The --reference option can be used to point to a directory that
 has the content of a --mirror sync. This will make the working
 directory use as much data as possible from the local reference
@@ -81,109 +86,64 @@ manifest, a subsequent `repo sync` (or `repo sync -d`) is necessary
 to update the working directory files.
 """
 
+  def _CommonOptions(self, p):
+    """Disable due to re-use of Wrapper()."""
+
   def _Options(self, p, gitc_init=False):
-    # Logging
-    g = p.add_option_group('Logging options')
-    g.add_option('-q', '--quiet',
-                 dest="quiet", action="store_true", default=False,
-                 help="be quiet")
-
-    # Manifest
-    g = p.add_option_group('Manifest options')
-    g.add_option('-u', '--manifest-url',
-                 dest='manifest_url',
-                 help='manifest repository location', metavar='URL')
-    g.add_option('-b', '--manifest-branch',
-                 dest='manifest_branch',
-                 help='manifest branch or revision', metavar='REVISION')
-    cbr_opts = ['--current-branch']
-    # The gitc-init subcommand allocates -c itself, but a lot of init users
-    # want -c, so try to satisfy both as best we can.
-    if not gitc_init:
-      cbr_opts += ['-c']
-    g.add_option(*cbr_opts,
-                 dest='current_branch_only', action='store_true',
-                 help='fetch only current manifest branch from server')
-    g.add_option('-m', '--manifest-name',
-                 dest='manifest_name', default='default.xml',
-                 help='initial manifest file', metavar='NAME.xml')
-    g.add_option('--mirror',
-                 dest='mirror', action='store_true',
-                 help='create a replica of the remote repositories '
-                      'rather than a client working directory')
-    g.add_option('--reference',
-                 dest='reference',
-                 help='location of mirror directory', metavar='DIR')
-    g.add_option('--dissociate',
-                 dest='dissociate', action='store_true',
-                 help='dissociate from reference mirrors after clone')
-    g.add_option('--depth', type='int', default=None,
-                 dest='depth',
-                 help='create a shallow clone with given depth; see git clone')
-    g.add_option('--partial-clone', action='store_true',
-                 dest='partial_clone',
-                 help='perform partial clone (https://git-scm.com/'
-                 'docs/gitrepository-layout#_code_partialclone_code)')
-    g.add_option('--clone-filter', action='store', default='blob:none',
-                 dest='clone_filter',
-                 help='filter for use with --partial-clone [default: %default]')
-    g.add_option('--archive',
-                 dest='archive', action='store_true',
-                 help='checkout an archive instead of a git repository for '
-                      'each project. See git archive.')
-    g.add_option('--submodules',
-                 dest='submodules', action='store_true',
-                 help='sync any submodules associated with the manifest repo')
-    g.add_option('-g', '--groups',
-                 dest='groups', default='default',
-                 help='restrict manifest projects to ones with specified '
-                      'group(s) [default|all|G1,G2,G3|G4,-G5,-G6]',
-                 metavar='GROUP')
-    g.add_option('-p', '--platform',
-                 dest='platform', default='auto',
-                 help='restrict manifest projects to ones with a specified '
-                      'platform group [auto|all|none|linux|darwin|...]',
-                 metavar='PLATFORM')
-    g.add_option('--no-clone-bundle',
-                 dest='no_clone_bundle', action='store_true',
-                 help='disable use of /clone.bundle on HTTP/HTTPS')
-    g.add_option('--no-tags',
-                 dest='no_tags', action='store_true',
-                 help="don't fetch tags in the manifest")
-
-    # Tool
-    g = p.add_option_group('repo Version options')
-    g.add_option('--repo-url',
-                 dest='repo_url',
-                 help='repo repository location', metavar='URL')
-    g.add_option('--repo-branch',
-                 dest='repo_branch',
-                 help='repo branch or revision', metavar='REVISION')
-    g.add_option('--no-repo-verify',
-                 dest='no_repo_verify', action='store_true',
-                 help='do not verify repo source code')
-
-    # Other
-    g = p.add_option_group('Other options')
-    g.add_option('--config-name',
-                 dest='config_name', action="store_true", default=False,
-                 help='Always prompt for name/e-mail')
+    Wrapper().InitParser(p, gitc_init=gitc_init)
 
   def _RegisteredEnvironmentOptions(self):
     return {'REPO_MANIFEST_URL': 'manifest_url',
             'REPO_MIRROR_LOCATION': 'reference'}
 
+  def _CloneSuperproject(self, opt):
+    """Clone the superproject based on the superproject's url and branch.
+
+    Args:
+      opt: Program options returned from optparse.  See _Options().
+    """
+    superproject = git_superproject.Superproject(self.manifest,
+                                                 self.repodir,
+                                                 self.git_event_log,
+                                                 quiet=opt.quiet)
+    sync_result = superproject.Sync()
+    if not sync_result.success:
+      print('warning: git update of superproject failed, repo sync will not '
+            'use superproject to fetch source; while this error is not fatal, '
+            'and you can continue to run repo sync, please run repo init with '
+            'the --no-use-superproject option to stop seeing this warning',
+            file=sys.stderr)
+      if sync_result.fatal and opt.use_superproject is not None:
+        sys.exit(1)
+
   def _SyncManifest(self, opt):
     m = self.manifest.manifestProject
     is_new = not m.Exists
 
+    # If repo has already been initialized, we take -u with the absence of
+    # --standalone-manifest to mean "transition to a standard repo set up",
+    # which necessitates starting fresh.
+    # If --standalone-manifest is set, we always tear everything down and start
+    # anew.
+    if not is_new:
+      was_standalone_manifest = m.config.GetString('manifest.standalone')
+      if opt.standalone_manifest or (
+          was_standalone_manifest and opt.manifest_url):
+        m.config.ClearCache()
+        if m.gitdir and os.path.exists(m.gitdir):
+          platform_utils.rmtree(m.gitdir)
+        if m.worktree and os.path.exists(m.worktree):
+          platform_utils.rmtree(m.worktree)
+
+    is_new = not m.Exists
     if is_new:
       if not opt.manifest_url:
-        print('fatal: manifest url (-u) is required.', file=sys.stderr)
+        print('fatal: manifest url is required.', file=sys.stderr)
         sys.exit(1)
 
       if not opt.quiet:
-        print('Get %s' % GitConfig.ForUser().UrlInsteadOf(opt.manifest_url),
+        print('Downloading manifest from %s' %
+              (GitConfig.ForUser().UrlInsteadOf(opt.manifest_url),),
               file=sys.stderr)
 
       # The manifest project object doesn't keep track of the path on the
@@ -200,30 +160,52 @@ to update the working directory files.
 
       m._InitGitDir(mirror_git=mirrored_manifest_git)
 
-      if opt.manifest_branch:
-        m.revisionExpr = opt.manifest_branch
-      else:
-        m.revisionExpr = 'refs/heads/master'
-    else:
-      if opt.manifest_branch:
-        m.revisionExpr = opt.manifest_branch
-      else:
-        m.PreSync()
+    # If standalone_manifest is set, mark the project as "standalone" -- we'll
+    # still do much of the manifests.git set up, but will avoid actual syncs to
+    # a remote.
+    standalone_manifest = False
+    if opt.standalone_manifest:
+      standalone_manifest = True
+    elif not opt.manifest_url:
+      # If -u is set and --standalone-manifest is not, then we're not in
+      # standalone mode. Otherwise, use config to infer what we were in the last
+      # init.
+      standalone_manifest = bool(m.config.GetString('manifest.standalone'))
+    m.config.SetString('manifest.standalone', opt.manifest_url)
 
     self._ConfigureDepth(opt)
 
+    # Set the remote URL before the remote branch as we might need it below.
     if opt.manifest_url:
       r = m.GetRemote(m.remote.name)
       r.url = opt.manifest_url
       r.ResetFetch()
       r.Save()
 
+    if not standalone_manifest:
+      if opt.manifest_branch:
+        if opt.manifest_branch == 'HEAD':
+          opt.manifest_branch = m.ResolveRemoteHead()
+          if opt.manifest_branch is None:
+            print('fatal: unable to resolve HEAD', file=sys.stderr)
+            sys.exit(1)
+        m.revisionExpr = opt.manifest_branch
+      else:
+        if is_new:
+          default_branch = m.ResolveRemoteHead()
+          if default_branch is None:
+            # If the remote doesn't have HEAD configured, default to master.
+            default_branch = 'refs/heads/master'
+          m.revisionExpr = default_branch
+        else:
+          m.PreSync()
+
     groups = re.split(r'[,\s]+', opt.groups)
     all_platforms = ['linux', 'darwin', 'windows']
     platformize = lambda x: 'platform-' + x
     if opt.platform == 'auto':
       if (not opt.mirror and
-          not m.config.GetString('repo.mirror') == 'true'):
+              not m.config.GetString('repo.mirror') == 'true'):
         groups.append(platformize(platform.system().lower()))
     elif opt.platform == 'all':
       groups.extend(map(platformize, all_platforms))
@@ -235,7 +217,7 @@ to update the working directory files.
 
     groups = [x for x in groups if x]
     groupstr = ','.join(groups)
-    if opt.platform == 'auto' and groupstr == 'default,platform-' + platform.system().lower():
+    if opt.platform == 'auto' and groupstr == self.manifest.GetDefaultGroupsStr():
       groupstr = None
     m.config.SetString('manifest.groups', groupstr)
 
@@ -243,11 +225,25 @@ to update the working directory files.
       m.config.SetString('repo.reference', opt.reference)
 
     if opt.dissociate:
-      m.config.SetString('repo.dissociate', 'true')
+      m.config.SetBoolean('repo.dissociate', opt.dissociate)
+
+    if opt.worktree:
+      if opt.mirror:
+        print('fatal: --mirror and --worktree are incompatible',
+              file=sys.stderr)
+        sys.exit(1)
+      if opt.submodules:
+        print('fatal: --submodules and --worktree are incompatible',
+              file=sys.stderr)
+        sys.exit(1)
+      m.config.SetBoolean('repo.worktree', opt.worktree)
+      if is_new:
+        m.use_git_worktrees = True
+      print('warning: --worktree is experimental!', file=sys.stderr)
 
     if opt.archive:
       if is_new:
-        m.config.SetString('repo.archive', 'true')
+        m.config.SetBoolean('repo.archive', opt.archive)
       else:
         print('fatal: --archive is only supported when initializing a new '
               'workspace.', file=sys.stderr)
@@ -257,7 +253,7 @@ to update the working directory files.
 
     if opt.mirror:
       if is_new:
-        m.config.SetString('repo.mirror', 'true')
+        m.config.SetBoolean('repo.mirror', opt.mirror)
       else:
         print('fatal: --mirror is only supported when initializing a new '
               'workspace.', file=sys.stderr)
@@ -265,25 +261,49 @@ to update the working directory files.
               'in another location.', file=sys.stderr)
         sys.exit(1)
 
-    if opt.partial_clone:
+    if opt.partial_clone is not None:
       if opt.mirror:
         print('fatal: --mirror and --partial-clone are mutually exclusive',
               file=sys.stderr)
         sys.exit(1)
-      m.config.SetString('repo.partialclone', 'true')
+      m.config.SetBoolean('repo.partialclone', opt.partial_clone)
       if opt.clone_filter:
         m.config.SetString('repo.clonefilter', opt.clone_filter)
+    elif m.config.GetBoolean('repo.partialclone'):
+      opt.clone_filter = m.config.GetString('repo.clonefilter')
     else:
       opt.clone_filter = None
 
+    if opt.partial_clone_exclude is not None:
+      m.config.SetString('repo.partialcloneexclude', opt.partial_clone_exclude)
+
+    if opt.clone_bundle is None:
+      opt.clone_bundle = False if opt.partial_clone else True
+    else:
+      m.config.SetBoolean('repo.clonebundle', opt.clone_bundle)
+
     if opt.submodules:
-      m.config.SetString('repo.submodules', 'true')
+      m.config.SetBoolean('repo.submodules', opt.submodules)
+
+    if opt.use_superproject is not None:
+      m.config.SetBoolean('repo.superproject', opt.use_superproject)
+
+    if standalone_manifest:
+      if is_new:
+        manifest_name = 'default.xml'
+        manifest_data = fetch.fetch_file(opt.manifest_url)
+        dest = os.path.join(m.worktree, manifest_name)
+        os.makedirs(os.path.dirname(dest), exist_ok=True)
+        with open(dest, 'wb') as f:
+          f.write(manifest_data)
+      return
 
-    if not m.Sync_NetworkHalf(is_new=is_new, quiet=opt.quiet,
-        clone_bundle=not opt.no_clone_bundle,
-        current_branch_only=opt.current_branch_only,
-        no_tags=opt.no_tags, submodules=opt.submodules,
-        clone_filter=opt.clone_filter):
+    if not m.Sync_NetworkHalf(is_new=is_new, quiet=opt.quiet, verbose=opt.verbose,
+                              clone_bundle=opt.clone_bundle,
+                              current_branch_only=opt.current_branch_only,
+                              tags=opt.tags, submodules=opt.submodules,
+                              clone_filter=opt.clone_filter,
+                              partial_clone_exclude=self.manifest.PartialCloneExclude):
       r = m.GetRemote(m.remote.name)
       print('fatal: cannot obtain manifest %s' % r.url, file=sys.stderr)
 
@@ -326,8 +346,8 @@ to update the working directory files.
       return value
     return a
 
-  def _ShouldConfigureUser(self):
-    gc = self.manifest.globalConfig
+  def _ShouldConfigureUser(self, opt):
+    gc = self.client.globalConfig
     mp = self.manifest.manifestProject
 
     # If we don't have local settings, get from global.
@@ -338,21 +358,24 @@ to update the working directory files.
       mp.config.SetString('user.name', gc.GetString('user.name'))
       mp.config.SetString('user.email', gc.GetString('user.email'))
 
-    print()
-    print('Your identity is: %s <%s>' % (mp.config.GetString('user.name'),
-                                         mp.config.GetString('user.email')))
-    print('If you want to change this, please re-run \'repo init\' with --config-name')
+    if not opt.quiet:
+      print()
+      print('Your identity is: %s <%s>' % (mp.config.GetString('user.name'),
+                                           mp.config.GetString('user.email')))
+      print("If you want to change this, please re-run 'repo init' with --config-name")
     return False
 
-  def _ConfigureUser(self):
+  def _ConfigureUser(self, opt):
     mp = self.manifest.manifestProject
 
     while True:
-      print()
-      name  = self._Prompt('Your Name', mp.UserName)
+      if not opt.quiet:
+        print()
+      name = self._Prompt('Your Name', mp.UserName)
       email = self._Prompt('Your Email', mp.UserEmail)
 
-      print()
+      if not opt.quiet:
+        print()
       print('Your identity is: %s <%s>' % (name, email))
       print('is this correct [y/N]? ', end='')
       # TODO: When we require Python 3, use flush=True w/print above.
@@ -373,7 +396,7 @@ to update the working directory files.
     return False
 
   def _ConfigureColor(self):
-    gc = self.manifest.globalConfig
+    gc = self.client.globalConfig
     if self._HasColorSet(gc):
       return
 
@@ -424,15 +447,16 @@ to update the working directory files.
       # We store the depth in the main manifest project.
       self.manifest.manifestProject.config.SetString('repo.depth', depth)
 
-  def _DisplayResult(self):
+  def _DisplayResult(self, opt):
     if self.manifest.IsMirror:
       init_type = 'mirror '
     else:
       init_type = ''
 
-    print()
-    print('repo %shas been initialized in %s'
-          % (init_type, self.manifest.topdir))
+    if not opt.quiet:
+      print()
+      print('repo %shas been initialized in %s' %
+            (init_type, self.manifest.topdir))
 
     current_dir = os.getcwd()
     if current_dir != self.manifest.topdir:
@@ -450,15 +474,61 @@ to update the working directory files.
     if opt.archive and opt.mirror:
       self.OptionParser.error('--mirror and --archive cannot be used together.')
 
+    if opt.standalone_manifest and (
+        opt.manifest_branch or opt.manifest_name != 'default.xml'):
+      self.OptionParser.error('--manifest-branch and --manifest-name cannot'
+                              ' be used with --standalone-manifest.')
+
+    if args:
+      if opt.manifest_url:
+        self.OptionParser.error(
+            '--manifest-url option and URL argument both specified: only use '
+            'one to select the manifest URL.')
+
+      opt.manifest_url = args.pop(0)
+
+      if args:
+        self.OptionParser.error('too many arguments to init')
+
   def Execute(self, opt, args):
-    git_require(MIN_GIT_VERSION, fail=True)
+    git_require(MIN_GIT_VERSION_HARD, fail=True)
+    if not git_require(MIN_GIT_VERSION_SOFT):
+      print('repo: warning: git-%s+ will soon be required; please upgrade your '
+            'version of git to maintain support.'
+            % ('.'.join(str(x) for x in MIN_GIT_VERSION_SOFT),),
+            file=sys.stderr)
+
+    rp = self.manifest.repoProject
+
+    # Handle new --repo-url requests.
+    if opt.repo_url:
+      remote = rp.GetRemote('origin')
+      remote.url = opt.repo_url
+      remote.Save()
+
+    # Handle new --repo-rev requests.
+    if opt.repo_rev:
+      wrapper = Wrapper()
+      remote_ref, rev = wrapper.check_repo_rev(
+          rp.gitdir, opt.repo_rev, repo_verify=opt.repo_verify, quiet=opt.quiet)
+      branch = rp.GetBranch('default')
+      branch.merge = remote_ref
+      rp.work_git.reset('--hard', rev)
+      branch.Save()
+
+    if opt.worktree:
+      # Older versions of git supported worktree, but had dangerous gc bugs.
+      git_require((2, 15, 0), fail=True, msg='git gc worktree corruption')
 
     self._SyncManifest(opt)
     self._LinkManifest(opt.manifest_name)
 
+    if self.manifest.manifestProject.config.GetBoolean('repo.superproject'):
+      self._CloneSuperproject(opt)
+
     if os.isatty(0) and os.isatty(1) and not self.manifest.IsMirror:
-      if opt.config_name or self._ShouldConfigureUser():
-        self._ConfigureUser()
+      if opt.config_name or self._ShouldConfigureUser(opt):
+        self._ConfigureUser(opt)
       self._ConfigureColor()
 
-    self._DisplayResult()
+    self._DisplayResult(opt)
diff --git a/subcmds/list.py b/subcmds/list.py
index 00172f0e..6adf85b7 100644
--- a/subcmds/list.py
+++ b/subcmds/list.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2011 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,45 +12,59 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-import sys
+import os
 
 from command import Command, MirrorSafeCommand
 
+
 class List(Command, MirrorSafeCommand):
-  common = True
+  COMMON = True
   helpSummary = "List projects and their associated directories"
   helpUsage = """
 %prog [-f] [<project>...]
-%prog [-f] -r str1 [str2]..."
+%prog [-f] -r str1 [str2]...
 """
   helpDescription = """
 List all projects; pass '.' to list the project for the cwd.
 
+By default, only projects that currently exist in the checkout are shown.  If
+you want to list all projects (using the specified filter settings), use the
+--all option.  If you want to show all projects regardless of the manifest
+groups, then also pass --groups all.
+
 This is similar to running: repo forall -c 'echo "$REPO_PATH : $REPO_PROJECT"'.
 """
 
   def _Options(self, p):
     p.add_option('-r', '--regex',
                  dest='regex', action='store_true',
-                 help="Filter the project list based on regex or wildcard matching of strings")
+                 help='filter the project list based on regex or wildcard matching of strings')
     p.add_option('-g', '--groups',
                  dest='groups',
-                 help="Filter the project list based on the groups the project is in")
-    p.add_option('-f', '--fullpath',
-                 dest='fullpath', action='store_true',
-                 help="Display the full work tree path instead of the relative path")
+                 help='filter the project list based on the groups the project is in')
+    p.add_option('-a', '--all',
+                 action='store_true',
+                 help='show projects regardless of checkout state')
     p.add_option('-n', '--name-only',
                  dest='name_only', action='store_true',
-                 help="Display only the name of the repository")
+                 help='display only the name of the repository')
     p.add_option('-p', '--path-only',
                  dest='path_only', action='store_true',
-                 help="Display only the path of the repository")
+                 help='display only the path of the repository')
+    p.add_option('-f', '--fullpath',
+                 dest='fullpath', action='store_true',
+                 help='display the full work tree path instead of the relative path')
+    p.add_option('--relative-to', metavar='PATH',
+                 help='display paths relative to this one (default: top of repo client checkout)')
 
   def ValidateOptions(self, opt, args):
     if opt.fullpath and opt.name_only:
       self.OptionParser.error('cannot combine -f and -n')
 
+    # Resolve any symlinks so the output is stable.
+    if opt.relative_to:
+      opt.relative_to = os.path.realpath(opt.relative_to)
+
   def Execute(self, opt, args):
     """List all projects and the associated directories.
 
@@ -65,23 +77,26 @@ This is similar to running: repo forall -c 'echo "$REPO_PATH : $REPO_PROJECT"'.
       args: Positional args.  Can be a list of projects to list, or empty.
     """
     if not opt.regex:
-      projects = self.GetProjects(args, groups=opt.groups)
+      projects = self.GetProjects(args, groups=opt.groups, missing_ok=opt.all)
     else:
       projects = self.FindProjects(args)
 
     def _getpath(x):
       if opt.fullpath:
         return x.worktree
+      if opt.relative_to:
+        return os.path.relpath(x.worktree, opt.relative_to)
       return x.relpath
 
     lines = []
     for project in projects:
       if opt.name_only and not opt.path_only:
-        lines.append("%s" % ( project.name))
+        lines.append("%s" % (project.name))
       elif opt.path_only and not opt.name_only:
         lines.append("%s" % (_getpath(project)))
       else:
         lines.append("%s : %s" % (_getpath(project), project.name))
 
-    lines.sort()
-    print('\n'.join(lines))
+    if lines:
+      lines.sort()
+      print('\n'.join(lines))
diff --git a/subcmds/manifest.py b/subcmds/manifest.py
index 9c1b3f0c..0fbdeac0 100644
--- a/subcmds/manifest.py
+++ b/subcmds/manifest.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2009 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,25 +12,32 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
+import json
 import os
 import sys
 
 from command import PagedCommand
 
+
 class Manifest(PagedCommand):
-  common = False
+  COMMON = False
   helpSummary = "Manifest inspection utility"
   helpUsage = """
-%prog [-o {-|NAME.xml} [-r]]
+%prog [-o {-|NAME.xml}] [-m MANIFEST.xml] [-r]
 """
   _helpDescription = """
 
 With the -o option, exports the current manifest for inspection.
-The manifest and (if present) local_manifest.xml are combined
+The manifest and (if present) local_manifests/ are combined
 together to produce a single manifest file.  This file can be stored
 in a Git repository for use during future 'repo init' invocations.
 
+The -r option can be used to generate a manifest file with project
+revisions set to the current commit hash.  These are known as
+"revision locked manifests", as they don't follow a particular branch.
+In this case, the 'upstream' attribute is set to the ref we were on
+when the manifest was generated.  The 'dest-branch' attribute is set
+to indicate the remote ref to push changes to via 'repo upload'.
 """
 
   @property
@@ -48,26 +53,63 @@ in a Git repository for use during future 'repo init' invocations.
   def _Options(self, p):
     p.add_option('-r', '--revision-as-HEAD',
                  dest='peg_rev', action='store_true',
-                 help='Save revisions as current HEAD')
+                 help='save revisions as current HEAD')
+    p.add_option('-m', '--manifest-name',
+                 help='temporary manifest to use for this sync', metavar='NAME.xml')
     p.add_option('--suppress-upstream-revision', dest='peg_rev_upstream',
                  default=True, action='store_false',
-                 help='If in -r mode, do not write the upstream field.  '
-                 'Only of use if the branch names for a sha1 manifest are '
-                 'sensitive.')
+                 help='if in -r mode, do not write the upstream field '
+                 '(only of use if the branch names for a sha1 manifest are '
+                 'sensitive)')
+    p.add_option('--suppress-dest-branch', dest='peg_rev_dest_branch',
+                 default=True, action='store_false',
+                 help='if in -r mode, do not write the dest-branch field '
+                 '(only of use if the branch names for a sha1 manifest are '
+                 'sensitive)')
+    p.add_option('--json', default=False, action='store_true',
+                 help='output manifest in JSON format (experimental)')
+    p.add_option('--pretty', default=False, action='store_true',
+                 help='format output for humans to read')
+    p.add_option('--no-local-manifests', default=False, action='store_true',
+                 dest='ignore_local_manifests', help='ignore local manifests')
     p.add_option('-o', '--output-file',
                  dest='output_file',
                  default='-',
-                 help='File to save the manifest to',
+                 help='file to save the manifest to',
                  metavar='-|NAME.xml')
 
   def _Output(self, opt):
+    # If alternate manifest is specified, override the manifest file that we're using.
+    if opt.manifest_name:
+      self.manifest.Override(opt.manifest_name, False)
+
     if opt.output_file == '-':
       fd = sys.stdout
     else:
       fd = open(opt.output_file, 'w')
-    self.manifest.Save(fd,
-                       peg_rev = opt.peg_rev,
-                       peg_rev_upstream = opt.peg_rev_upstream)
+
+    self.manifest.SetUseLocalManifests(not opt.ignore_local_manifests)
+
+    if opt.json:
+      print('warning: --json is experimental!', file=sys.stderr)
+      doc = self.manifest.ToDict(peg_rev=opt.peg_rev,
+                                 peg_rev_upstream=opt.peg_rev_upstream,
+                                 peg_rev_dest_branch=opt.peg_rev_dest_branch)
+
+      json_settings = {
+          # JSON style guide says Uunicode characters are fully allowed.
+          'ensure_ascii': False,
+          # We use 2 space indent to match JSON style guide.
+          'indent': 2 if opt.pretty else None,
+          'separators': (',', ': ') if opt.pretty else (',', ':'),
+          'sort_keys': True,
+      }
+      fd.write(json.dumps(doc, **json_settings))
+    else:
+      self.manifest.Save(fd,
+                         peg_rev=opt.peg_rev,
+                         peg_rev_upstream=opt.peg_rev_upstream,
+                         peg_rev_dest_branch=opt.peg_rev_dest_branch)
     fd.close()
     if opt.output_file != '-':
       print('Saved manifest to %s' % opt.output_file, file=sys.stderr)
diff --git a/subcmds/overview.py b/subcmds/overview.py
index 08b58a6c..63f5a79e 100644
--- a/subcmds/overview.py
+++ b/subcmds/overview.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2012 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,13 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
+import optparse
+
 from color import Coloring
 from command import PagedCommand
 
 
 class Overview(PagedCommand):
-  common = True
+  COMMON = True
   helpSummary = "Display overview of unmerged project branches"
   helpUsage = """
 %prog [--current-branch] [<project>...]
@@ -29,15 +28,22 @@ class Overview(PagedCommand):
 The '%prog' command is used to display an overview of the projects branches,
 and list any local commits that have not yet been merged into the project.
 
-The -b/--current-branch option can be used to restrict the output to only
+The -c/--current-branch option can be used to restrict the output to only
 branches currently checked out in each project.  By default, all branches
 are displayed.
 """
 
   def _Options(self, p):
-    p.add_option('-b', '--current-branch',
+    p.add_option('-c', '--current-branch',
                  dest="current_branch", action="store_true",
-                 help="Consider only checked out branches")
+                 help="consider only checked out branches")
+    p.add_option('--no-current-branch',
+                 dest='current_branch', action='store_false',
+                 help='consider all local branches')
+    # Turn this into a warning & remove this someday.
+    p.add_option('-b',
+                 dest='current_branch', action='store_true',
+                 help=optparse.SUPPRESS_HELP)
 
   def Execute(self, opt, args):
     all_branches = []
diff --git a/subcmds/prune.py b/subcmds/prune.py
index ff2fba1d..584ee7ed 100644
--- a/subcmds/prune.py
+++ b/subcmds/prune.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,21 +12,38 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
+import itertools
+
 from color import Coloring
-from command import PagedCommand
+from command import DEFAULT_LOCAL_JOBS, PagedCommand
+
 
 class Prune(PagedCommand):
-  common = True
+  COMMON = True
   helpSummary = "Prune (delete) already merged topics"
   helpUsage = """
 %prog [<project>...]
 """
+  PARALLEL_JOBS = DEFAULT_LOCAL_JOBS
+
+  def _ExecuteOne(self, project):
+    """Process one project."""
+    return project.PruneHeads()
 
   def Execute(self, opt, args):
-    all_branches = []
-    for project in self.GetProjects(args):
-      all_branches.extend(project.PruneHeads())
+    projects = self.GetProjects(args)
+
+    # NB: Should be able to refactor this module to display summary as results
+    # come back from children.
+    def _ProcessResults(_pool, _output, results):
+      return list(itertools.chain.from_iterable(results))
+
+    all_branches = self.ExecuteInParallel(
+        opt.jobs,
+        self._ExecuteOne,
+        projects,
+        callback=_ProcessResults,
+        ordered=True)
 
     if not all_branches:
       return
diff --git a/subcmds/rebase.py b/subcmds/rebase.py
index dcb8b2a3..7c53eb7a 100644
--- a/subcmds/rebase.py
+++ b/subcmds/rebase.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2010 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import sys
 
 from color import Coloring
@@ -30,7 +27,7 @@ class RebaseColoring(Coloring):
 
 
 class Rebase(Command):
-  common = True
+  COMMON = True
   helpSummary = "Rebase local branches on upstream branch"
   helpUsage = """
 %prog {[<project>...] | -i <project>...}
@@ -42,36 +39,34 @@ branch but need to incorporate new upstream changes "underneath" them.
 """
 
   def _Options(self, p):
-    p.add_option('-i', '--interactive',
-                dest="interactive", action="store_true",
-                help="interactive rebase (single project only)")
+    g = p.get_option_group('--quiet')
+    g.add_option('-i', '--interactive',
+                 dest="interactive", action="store_true",
+                 help="interactive rebase (single project only)")
 
     p.add_option('--fail-fast',
                  dest='fail_fast', action='store_true',
-                 help='Stop rebasing after first error is hit')
+                 help='stop rebasing after first error is hit')
     p.add_option('-f', '--force-rebase',
                  dest='force_rebase', action='store_true',
-                 help='Pass --force-rebase to git rebase')
+                 help='pass --force-rebase to git rebase')
     p.add_option('--no-ff',
-                 dest='no_ff', action='store_true',
-                 help='Pass --no-ff to git rebase')
-    p.add_option('-q', '--quiet',
-                 dest='quiet', action='store_true',
-                 help='Pass --quiet to git rebase')
+                 dest='ff', default=True, action='store_false',
+                 help='pass --no-ff to git rebase')
     p.add_option('--autosquash',
                  dest='autosquash', action='store_true',
-                 help='Pass --autosquash to git rebase')
+                 help='pass --autosquash to git rebase')
     p.add_option('--whitespace',
                  dest='whitespace', action='store', metavar='WS',
-                 help='Pass --whitespace to git rebase')
+                 help='pass --whitespace to git rebase')
     p.add_option('--auto-stash',
                  dest='auto_stash', action='store_true',
-                 help='Stash local modifications before starting')
+                 help='stash local modifications before starting')
     p.add_option('-m', '--onto-manifest',
                  dest='onto_manifest', action='store_true',
-                 help='Rebase onto the manifest version instead of upstream '
-                      'HEAD.  This helps to make sure the local tree stays '
-                      'consistent if you previously synced to a manifest.')
+                 help='rebase onto the manifest version instead of upstream '
+                      'HEAD (this helps to make sure the local tree stays '
+                      'consistent if you previously synced to a manifest)')
 
   def Execute(self, opt, args):
     all_projects = self.GetProjects(args)
@@ -82,7 +77,7 @@ branch but need to incorporate new upstream changes "underneath" them.
             file=sys.stderr)
       if len(args) == 1:
         print('note: project %s is mapped to more than one path' % (args[0],),
-            file=sys.stderr)
+              file=sys.stderr)
       return 1
 
     # Setup the common git rebase args that we use for all projects.
@@ -93,7 +88,7 @@ branch but need to incorporate new upstream changes "underneath" them.
       common_args.append('--quiet')
     if opt.force_rebase:
       common_args.append('--force-rebase')
-    if opt.no_ff:
+    if not opt.ff:
       common_args.append('--no-ff')
     if opt.autosquash:
       common_args.append('--autosquash')
diff --git a/subcmds/selfupdate.py b/subcmds/selfupdate.py
index a8a09b64..282f518e 100644
--- a/subcmds/selfupdate.py
+++ b/subcmds/selfupdate.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2009 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 from optparse import SUPPRESS_HELP
 import sys
 
@@ -22,8 +19,9 @@ from command import Command, MirrorSafeCommand
 from subcmds.sync import _PostRepoUpgrade
 from subcmds.sync import _PostRepoFetch
 
+
 class Selfupdate(Command, MirrorSafeCommand):
-  common = False
+  COMMON = False
   helpSummary = "Update repo to the latest version"
   helpUsage = """
 %prog
@@ -39,7 +37,7 @@ need to be performed by an end-user.
   def _Options(self, p):
     g = p.add_option_group('repo Version options')
     g.add_option('--no-repo-verify',
-                 dest='no_repo_verify', action='store_true',
+                 dest='repo_verify', default=True, action='store_false',
                  help='do not verify repo source code')
     g.add_option('--repo-upgraded',
                  dest='repo_upgraded', action='store_true',
@@ -59,5 +57,5 @@ need to be performed by an end-user.
 
       rp.bare_git.gc('--auto')
       _PostRepoFetch(rp,
-                     no_repo_verify = opt.no_repo_verify,
-                     verbose = True)
+                     repo_verify=opt.repo_verify,
+                     verbose=True)
diff --git a/subcmds/smartsync.py b/subcmds/smartsync.py
index 675b9834..d91d59c6 100644
--- a/subcmds/smartsync.py
+++ b/subcmds/smartsync.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2010 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,8 +14,9 @@
 
 from subcmds.sync import Sync
 
+
 class Smartsync(Sync):
-  common = True
+  COMMON = True
   helpSummary = "Update working tree to the latest known good revision"
   helpUsage = """
 %prog [<project>...]
diff --git a/subcmds/stage.py b/subcmds/stage.py
index aeb49513..0389a4ff 100644
--- a/subcmds/stage.py
+++ b/subcmds/stage.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,13 +12,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import sys
 
 from color import Coloring
 from command import InteractiveCommand
 from git_command import GitCommand
 
+
 class _ProjectList(Coloring):
   def __init__(self, gc):
     Coloring.__init__(self, gc, 'interactive')
@@ -28,8 +26,9 @@ class _ProjectList(Coloring):
     self.header = self.printer('header', attr='bold')
     self.help = self.printer('help', fg='red', attr='bold')
 
+
 class Stage(InteractiveCommand):
-  common = True
+  COMMON = True
   helpSummary = "Stage file(s) for commit"
   helpUsage = """
 %prog -i [<project>...]
@@ -39,7 +38,8 @@ The '%prog' command stages files to prepare the next commit.
 """
 
   def _Options(self, p):
-    p.add_option('-i', '--interactive',
+    g = p.get_option_group('--quiet')
+    g.add_option('-i', '--interactive',
                  dest='interactive', action='store_true',
                  help='use interactive staging')
 
@@ -105,6 +105,7 @@ The '%prog' command stages files to prepare the next commit.
         continue
     print('Bye.')
 
+
 def _AddI(project):
   p = GitCommand(project, ['add', '--interactive'], bare=False)
   p.Wait()
diff --git a/subcmds/start.py b/subcmds/start.py
index 6ec0b2ce..2addaf2e 100644
--- a/subcmds/start.py
+++ b/subcmds/start.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,19 +12,20 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
+import functools
 import os
 import sys
 
-from command import Command
+from command import Command, DEFAULT_LOCAL_JOBS
 from git_config import IsImmutable
 from git_command import git
 import gitc_utils
 from progress import Progress
 from project import SyncBuffer
 
+
 class Start(Command):
-  common = True
+  COMMON = True
   helpSummary = "Start a new branch for development"
   helpUsage = """
 %prog <newbranchname> [--all | <project>...]
@@ -35,6 +34,7 @@ class Start(Command):
 '%prog' begins a new branch of development, starting from the
 revision specified in the manifest.
 """
+  PARALLEL_JOBS = DEFAULT_LOCAL_JOBS
 
   def _Options(self, p):
     p.add_option('--all',
@@ -42,7 +42,8 @@ revision specified in the manifest.
                  help='begin branch in all projects')
     p.add_option('-r', '--rev', '--revision', dest='revision',
                  help='point branch at this revision instead of upstream')
-    p.add_option('--head', dest='revision', action='store_const', const='HEAD',
+    p.add_option('--head', '--HEAD',
+                 dest='revision', action='store_const', const='HEAD',
                  help='abbreviation for --rev HEAD')
 
   def ValidateOptions(self, opt, args):
@@ -53,6 +54,26 @@ revision specified in the manifest.
     if not git.check_ref_format('heads/%s' % nb):
       self.OptionParser.error("'%s' is not a valid name" % nb)
 
+  def _ExecuteOne(self, revision, nb, project):
+    """Start one project."""
+    # If the current revision is immutable, such as a SHA1, a tag or
+    # a change, then we can't push back to it. Substitute with
+    # dest_branch, if defined; or with manifest default revision instead.
+    branch_merge = ''
+    if IsImmutable(project.revisionExpr):
+      if project.dest_branch:
+        branch_merge = project.dest_branch
+      else:
+        branch_merge = self.manifest.default.revisionExpr
+
+    try:
+      ret = project.StartBranch(
+          nb, branch_merge=branch_merge, revision=revision)
+    except Exception as e:
+      print('error: unable to checkout %s: %s' % (project.name, e), file=sys.stderr)
+      ret = False
+    return (ret, project)
+
   def Execute(self, opt, args):
     nb = args[0]
     err = []
@@ -60,7 +81,7 @@ revision specified in the manifest.
     if not opt.all:
       projects = args[1:]
       if len(projects) < 1:
-        projects = ['.',]  # start it in the local project by default
+        projects = ['.']  # start it in the local project by default
 
     all_projects = self.GetProjects(projects,
                                     missing_ok=bool(self.gitc_manifest))
@@ -84,11 +105,8 @@ revision specified in the manifest.
       if not os.path.exists(os.getcwd()):
         os.chdir(self.manifest.topdir)
 
-    pm = Progress('Starting %s' % nb, len(all_projects))
-    for project in all_projects:
-      pm.update()
-
-      if self.gitc_manifest:
+      pm = Progress('Syncing %s' % nb, len(all_projects), quiet=opt.quiet)
+      for project in all_projects:
         gitc_project = self.gitc_manifest.paths[project.relpath]
         # Sync projects that have not been opened.
         if not gitc_project.already_synced:
@@ -101,21 +119,21 @@ revision specified in the manifest.
           sync_buf = SyncBuffer(self.manifest.manifestProject.config)
           project.Sync_LocalHalf(sync_buf)
           project.revisionId = gitc_project.old_revision
+        pm.update()
+      pm.end()
 
-      # If the current revision is immutable, such as a SHA1, a tag or
-      # a change, then we can't push back to it. Substitute with
-      # dest_branch, if defined; or with manifest default revision instead.
-      branch_merge = ''
-      if IsImmutable(project.revisionExpr):
-        if project.dest_branch:
-          branch_merge = project.dest_branch
-        else:
-          branch_merge = self.manifest.default.revisionExpr
+    def _ProcessResults(_pool, pm, results):
+      for (result, project) in results:
+        if not result:
+          err.append(project)
+        pm.update()
 
-      if not project.StartBranch(
-          nb, branch_merge=branch_merge, revision=opt.revision):
-        err.append(project)
-    pm.end()
+    self.ExecuteInParallel(
+        opt.jobs,
+        functools.partial(self._ExecuteOne, opt.revision, nb),
+        all_projects,
+        callback=_ProcessResults,
+        output=Progress('Starting %s' % (nb,), len(all_projects), quiet=opt.quiet))
 
     if err:
       for p in err:
diff --git a/subcmds/status.py b/subcmds/status.py
index 63972d72..5b669547 100644
--- a/subcmds/status.py
+++ b/subcmds/status.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,25 +12,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
-
-from command import PagedCommand
-
-try:
-  import threading as _threading
-except ImportError:
-  import dummy_threading as _threading
-
+import functools
 import glob
-
-import itertools
+import io
 import os
 
+from command import DEFAULT_LOCAL_JOBS, PagedCommand
+
 from color import Coloring
 import platform_utils
 
+
 class Status(PagedCommand):
-  common = True
+  COMMON = True
   helpSummary = "Show the working tree status"
   helpUsage = """
 %prog [<project>...]
@@ -84,36 +76,29 @@ the following meanings:
  d:  deleted       (    in index, not in work tree                )
 
 """
+  PARALLEL_JOBS = DEFAULT_LOCAL_JOBS
 
   def _Options(self, p):
-    p.add_option('-j', '--jobs',
-                 dest='jobs', action='store', type='int', default=2,
-                 help="number of projects to check simultaneously")
     p.add_option('-o', '--orphans',
                  dest='orphans', action='store_true',
                  help="include objects in working directory outside of repo projects")
-    p.add_option('-q', '--quiet', action='store_true',
-                 help="only print the name of modified projects")
 
-  def _StatusHelper(self, project, clean_counter, sem, quiet):
+  def _StatusHelper(self, quiet, project):
     """Obtains the status for a specific project.
 
     Obtains the status for a project, redirecting the output to
-    the specified object. It will release the semaphore
-    when done.
+    the specified object.
 
     Args:
+      quiet: Where to output the status.
       project: Project to get status of.
-      clean_counter: Counter for clean projects.
-      sem: Semaphore, will call release() when complete.
-      output: Where to output the status.
+
+    Returns:
+      The status of the project.
     """
-    try:
-      state = project.PrintWorkTreeStatus(quiet=quiet)
-      if state == 'CLEAN':
-        next(clean_counter)
-    finally:
-      sem.release()
+    buf = io.StringIO()
+    ret = project.PrintWorkTreeStatus(quiet=quiet, output_redir=buf)
+    return (ret, buf.getvalue())
 
   def _FindOrphans(self, dirs, proj_dirs, proj_dirs_parents, outstring):
     """find 'dirs' that are present in 'proj_dirs_parents' but not in 'proj_dirs'"""
@@ -126,34 +111,31 @@ the following meanings:
         continue
       if item in proj_dirs_parents:
         self._FindOrphans(glob.glob('%s/.*' % item) +
-            glob.glob('%s/*' % item),
-            proj_dirs, proj_dirs_parents, outstring)
+                          glob.glob('%s/*' % item),
+                          proj_dirs, proj_dirs_parents, outstring)
         continue
       outstring.append(''.join([status_header, item, '/']))
 
   def Execute(self, opt, args):
     all_projects = self.GetProjects(args)
-    counter = itertools.count()
 
-    if opt.jobs == 1:
-      for project in all_projects:
-        state = project.PrintWorkTreeStatus(quiet=opt.quiet)
+    def _ProcessResults(_pool, _output, results):
+      ret = 0
+      for (state, output) in results:
+        if output:
+          print(output, end='')
         if state == 'CLEAN':
-          next(counter)
-    else:
-      sem = _threading.Semaphore(opt.jobs)
-      threads = []
-      for project in all_projects:
-        sem.acquire()
-
-        t = _threading.Thread(target=self._StatusHelper,
-                              args=(project, counter, sem, opt.quiet))
-        threads.append(t)
-        t.daemon = True
-        t.start()
-      for t in threads:
-        t.join()
-    if not opt.quiet and len(all_projects) == next(counter):
+          ret += 1
+      return ret
+
+    counter = self.ExecuteInParallel(
+        opt.jobs,
+        functools.partial(self._StatusHelper, opt.quiet),
+        all_projects,
+        callback=_ProcessResults,
+        ordered=True)
+
+    if not opt.quiet and len(all_projects) == counter:
       print('nothing to commit (working directory clean)')
 
     if opt.orphans:
@@ -170,8 +152,8 @@ the following meanings:
       class StatusColoring(Coloring):
         def __init__(self, config):
           Coloring.__init__(self, config, 'status')
-          self.project = self.printer('header', attr = 'bold')
-          self.untracked = self.printer('untracked', fg = 'red')
+          self.project = self.printer('header', attr='bold')
+          self.untracked = self.printer('untracked', fg='red')
 
       orig_path = os.getcwd()
       try:
@@ -179,11 +161,11 @@ the following meanings:
 
         outstring = []
         self._FindOrphans(glob.glob('.*') +
-            glob.glob('*'),
-            proj_dirs, proj_dirs_parents, outstring)
+                          glob.glob('*'),
+                          proj_dirs, proj_dirs_parents, outstring)
 
         if outstring:
-          output = StatusColoring(self.manifest.globalConfig)
+          output = StatusColoring(self.client.globalConfig)
           output.project('Objects not within a project (orphans)')
           output.nl()
           for entry in outstring:
diff --git a/subcmds/sync.py b/subcmds/sync.py
index 2973a16e..3211cbb1 100644
--- a/subcmds/sync.py
+++ b/subcmds/sync.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,37 +12,23 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
+import errno
+import functools
+import http.cookiejar as cookielib
+import io
 import json
+import multiprocessing
 import netrc
 from optparse import SUPPRESS_HELP
 import os
-import re
 import socket
-import subprocess
 import sys
 import tempfile
 import time
-
-from pyversion import is_python3
-if is_python3():
-  import http.cookiejar as cookielib
-  import urllib.error
-  import urllib.parse
-  import urllib.request
-  import xmlrpc.client
-else:
-  import cookielib
-  import imp
-  import urllib2
-  import urlparse
-  import xmlrpclib
-  urllib = imp.new_module('urllib')
-  urllib.error = urllib2
-  urllib.parse = urlparse
-  urllib.request = urllib2
-  xmlrpc = imp.new_module('xmlrpc')
-  xmlrpc.client = xmlrpclib
+import urllib.error
+import urllib.parse
+import urllib.request
+import xmlrpc.client
 
 try:
   import threading as _threading
@@ -53,44 +37,36 @@ except ImportError:
 
 try:
   import resource
+
   def _rlimit_nofile():
     return resource.getrlimit(resource.RLIMIT_NOFILE)
 except ImportError:
   def _rlimit_nofile():
     return (256, 256)
 
-try:
-  import multiprocessing
-except ImportError:
-  multiprocessing = None
-
 import event_log
-from git_command import GIT, git_require
+from git_command import git_require
 from git_config import GetUrlCookieFile
 from git_refs import R_HEADS, HEAD
+import git_superproject
 import gitc_utils
 from project import Project
 from project import RemoteSpec
-from command import Command, MirrorSafeCommand
+from command import Command, MirrorSafeCommand, WORKER_BATCH_SIZE
 from error import RepoChangedException, GitError, ManifestParseError
 import platform_utils
 from project import SyncBuffer
 from progress import Progress
+import ssh
 from wrapper import Wrapper
 from manifest_xml import GitcManifest
 
 _ONE_DAY_S = 24 * 60 * 60
 
-class _FetchError(Exception):
-  """Internal error thrown in _FetchHelper() when we don't want stack trace."""
-  pass
-
-class _CheckoutError(Exception):
-  """Internal error thrown in _CheckoutOne() when we don't want stack trace."""
 
 class Sync(Command, MirrorSafeCommand):
   jobs = 1
-  common = True
+  COMMON = True
   helpSummary = "Update working tree to the latest revision"
   helpUsage = """
 %prog [<project>...]
@@ -133,11 +109,11 @@ if the manifest server specified in the manifest file already includes
 credentials.
 
 By default, all projects will be synced. The --fail-fast option can be used
-to halt syncing as soon as possible when the the first project fails to sync.
+to halt syncing as soon as possible when the first project fails to sync.
 
 The --force-sync option can be used to overwrite existing git
 directories if they have previously been linked to a different
-object direcotry. WARNING: This may cause data to be lost since
+object directory. WARNING: This may cause data to be lost since
 refs may be removed when overwriting.
 
 The --force-remove-dirty option can be used to remove previously used
@@ -191,12 +167,21 @@ If the remote SSH daemon is Gerrit Code Review, version 2.0.10 or
 later is required to fix a server side protocol bug.
 
 """
+  PARALLEL_JOBS = 1
+
+  def _CommonOptions(self, p):
+    if self.manifest:
+      try:
+        self.PARALLEL_JOBS = self.manifest.default.sync_j
+      except ManifestParseError:
+        pass
+    super()._CommonOptions(p)
 
   def _Options(self, p, show_smart=True):
-    try:
-      self.jobs = self.manifest.default.sync_j
-    except ManifestParseError:
-      self.jobs = 1
+    p.add_option('--jobs-network', default=None, type=int, metavar='JOBS',
+                 help='number of network jobs to run in parallel (defaults to --jobs)')
+    p.add_option('--jobs-checkout', default=None, type=int, metavar='JOBS',
+                 help='number of local checkout jobs to run in parallel (defaults to --jobs)')
 
     p.add_option('-f', '--force-broken',
                  dest='force_broken', action='store_true',
@@ -217,6 +202,10 @@ later is required to fix a server side protocol bug.
     p.add_option('-l', '--local-only',
                  dest='local_only', action='store_true',
                  help="only update working tree, don't fetch")
+    p.add_option('--no-manifest-update', '--nmu',
+                 dest='mp_update', action='store_false', default='true',
+                 help='use the existing manifest checkout as-is. '
+                      '(do not update to the latest revision)')
     p.add_option('-n', '--network-only',
                  dest='network_only', action='store_true',
                  help="fetch only, don't update working tree")
@@ -226,17 +215,15 @@ later is required to fix a server side protocol bug.
     p.add_option('-c', '--current-branch',
                  dest='current_branch_only', action='store_true',
                  help='fetch only current branch from server')
-    p.add_option('-q', '--quiet',
-                 dest='quiet', action='store_true',
-                 help='be more quiet')
-    p.add_option('-j', '--jobs',
-                 dest='jobs', action='store', type='int',
-                 help="projects to fetch simultaneously (default %d)" % self.jobs)
+    p.add_option('--no-current-branch',
+                 dest='current_branch_only', action='store_false',
+                 help='fetch all branches from server')
     p.add_option('-m', '--manifest-name',
                  dest='manifest_name',
                  help='temporary manifest to use for this sync', metavar='NAME.xml')
-    p.add_option('--no-clone-bundle',
-                 dest='no_clone_bundle', action='store_true',
+    p.add_option('--clone-bundle', action='store_true',
+                 help='enable use of /clone.bundle on HTTP/HTTPS')
+    p.add_option('--no-clone-bundle', dest='clone_bundle', action='store_false',
                  help='disable use of /clone.bundle on HTTP/HTTPS')
     p.add_option('-u', '--manifest-server-username', action='store',
                  dest='manifest_server_username',
@@ -247,12 +234,23 @@ later is required to fix a server side protocol bug.
     p.add_option('--fetch-submodules',
                  dest='fetch_submodules', action='store_true',
                  help='fetch submodules from server')
+    p.add_option('--use-superproject', action='store_true',
+                 help='use the manifest superproject to sync projects')
+    p.add_option('--no-use-superproject', action='store_false',
+                 dest='use_superproject',
+                 help='disable use of manifest superprojects')
+    p.add_option('--tags',
+                 action='store_false',
+                 help='fetch tags')
     p.add_option('--no-tags',
-                 dest='no_tags', action='store_true',
+                 dest='tags', action='store_false',
                  help="don't fetch tags")
     p.add_option('--optimized-fetch',
                  dest='optimized_fetch', action='store_true',
                  help='only fetch projects fixed to sha1 if revision does not exist locally')
+    p.add_option('--retry-fetches',
+                 default=0, action='store', type='int',
+                 help='number of times to retry fetches on transient errors')
     p.add_option('--prune', dest='prune', action='store_true',
                  help='delete refs that no longer exist on the remote')
     if show_smart:
@@ -265,345 +263,400 @@ later is required to fix a server side protocol bug.
 
     g = p.add_option_group('repo Version options')
     g.add_option('--no-repo-verify',
-                 dest='no_repo_verify', action='store_true',
+                 dest='repo_verify', default=True, action='store_false',
                  help='do not verify repo source code')
     g.add_option('--repo-upgraded',
                  dest='repo_upgraded', action='store_true',
                  help=SUPPRESS_HELP)
 
-  def _FetchProjectList(self, opt, projects, sem, *args, **kwargs):
-    """Main function of the fetch threads.
+  def _GetBranch(self):
+    """Returns the branch name for getting the approved manifest."""
+    p = self.manifest.manifestProject
+    b = p.GetBranch(p.CurrentBranch)
+    branch = b.merge
+    if branch.startswith(R_HEADS):
+      branch = branch[len(R_HEADS):]
+    return branch
+
+  def _GetCurrentBranchOnly(self, opt):
+    """Returns True if current-branch or use-superproject options are enabled."""
+    return opt.current_branch_only or git_superproject.UseSuperproject(opt, self.manifest)
+
+  def _UpdateProjectsRevisionId(self, opt, args, load_local_manifests, superproject_logging_data):
+    """Update revisionId of every project with the SHA from superproject.
+
+    This function updates each project's revisionId with SHA from superproject.
+    It writes the updated manifest into a file and reloads the manifest from it.
+
+    Args:
+      opt: Program options returned from optparse.  See _Options().
+      args: Arguments to pass to GetProjects. See the GetProjects
+          docstring for details.
+      load_local_manifests: Whether to load local manifests.
+      superproject_logging_data: A dictionary of superproject data that is to be logged.
+
+    Returns:
+      Returns path to the overriding manifest file instead of None.
+    """
+    print_messages = git_superproject.PrintMessages(opt, self.manifest)
+    superproject = git_superproject.Superproject(self.manifest,
+                                                 self.repodir,
+                                                 self.git_event_log,
+                                                 quiet=opt.quiet,
+                                                 print_messages=print_messages)
+    if opt.local_only:
+      manifest_path = superproject.manifest_path
+      if manifest_path:
+        self._ReloadManifest(manifest_path, load_local_manifests)
+      return manifest_path
+
+    all_projects = self.GetProjects(args,
+                                    missing_ok=True,
+                                    submodules_ok=opt.fetch_submodules)
+    update_result = superproject.UpdateProjectsRevisionId(all_projects)
+    manifest_path = update_result.manifest_path
+    superproject_logging_data['updatedrevisionid'] = bool(manifest_path)
+    if manifest_path:
+      self._ReloadManifest(manifest_path, load_local_manifests)
+    else:
+      if print_messages:
+        print('warning: Update of revisionId from superproject has failed, '
+              'repo sync will not use superproject to fetch the source. ',
+              'Please resync with the --no-use-superproject option to avoid this repo warning.',
+              file=sys.stderr)
+      if update_result.fatal and opt.use_superproject is not None:
+        sys.exit(1)
+    return manifest_path
+
+  def _FetchProjectList(self, opt, projects):
+    """Main function of the fetch worker.
+
+    The projects we're given share the same underlying git object store, so we
+    have to fetch them in serial.
 
     Delegates most of the work to _FetchHelper.
 
     Args:
       opt: Program options returned from optparse.  See _Options().
       projects: Projects to fetch.
-      sem: We'll release() this semaphore when we exit so that another thread
-          can be started up.
-      *args, **kwargs: Remaining arguments to pass to _FetchHelper. See the
-          _FetchHelper docstring for details.
     """
-    try:
-        for project in projects:
-          success = self._FetchHelper(opt, project, *args, **kwargs)
-          if not success and opt.fail_fast:
-            break
-    finally:
-        sem.release()
+    return [self._FetchOne(opt, x) for x in projects]
 
-  def _FetchHelper(self, opt, project, lock, fetched, pm, err_event,
-                   clone_filter):
+  def _FetchOne(self, opt, project):
     """Fetch git objects for a single project.
 
     Args:
       opt: Program options returned from optparse.  See _Options().
       project: Project object for the project to fetch.
-      lock: Lock for accessing objects that are shared amongst multiple
-          _FetchHelper() threads.
-      fetched: set object that we will add project.gitdir to when we're done
-          (with our lock held).
-      pm: Instance of a Project object.  We will call pm.update() (with our
-          lock held).
-      err_event: We'll set this event in the case of an error (after printing
-          out info about the error).
-      clone_filter: Filter for use in a partial clone.
 
     Returns:
       Whether the fetch was successful.
     """
-    # We'll set to true once we've locked the lock.
-    did_lock = False
-
-    # Encapsulate everything in a try/except/finally so that:
-    # - We always set err_event in the case of an exception.
-    # - We always make sure we unlock the lock if we locked it.
     start = time.time()
     success = False
+    buf = io.StringIO()
     try:
-      try:
-        success = project.Sync_NetworkHalf(
+      success = project.Sync_NetworkHalf(
           quiet=opt.quiet,
-          current_branch_only=opt.current_branch_only,
+          verbose=opt.verbose,
+          output_redir=buf,
+          current_branch_only=self._GetCurrentBranchOnly(opt),
           force_sync=opt.force_sync,
-          clone_bundle=not opt.no_clone_bundle,
-          no_tags=opt.no_tags, archive=self.manifest.IsArchive,
+          clone_bundle=opt.clone_bundle,
+          tags=opt.tags, archive=self.manifest.IsArchive,
           optimized_fetch=opt.optimized_fetch,
+          retry_fetches=opt.retry_fetches,
           prune=opt.prune,
-          clone_filter=clone_filter)
-        self._fetch_times.Set(project, time.time() - start)
+          ssh_proxy=self.ssh_proxy,
+          clone_filter=self.manifest.CloneFilter,
+          partial_clone_exclude=self.manifest.PartialCloneExclude)
 
-        # Lock around all the rest of the code, since printing, updating a set
-        # and Progress.update() are not thread safe.
-        lock.acquire()
-        did_lock = True
+      output = buf.getvalue()
+      if (opt.verbose or not success) and output:
+        print('\n' + output.rstrip())
 
-        if not success:
-          err_event.set()
-          print('error: Cannot fetch %s from %s'
-                % (project.name, project.remote.url),
-                file=sys.stderr)
-          if opt.fail_fast:
-            raise _FetchError()
-
-        fetched.add(project.gitdir)
-        pm.update(msg=project.name)
-      except _FetchError:
-        pass
-      except Exception as e:
-        print('error: Cannot fetch %s (%s: %s)' \
+      if not success:
+        print('error: Cannot fetch %s from %s'
+              % (project.name, project.remote.url),
+              file=sys.stderr)
+    except GitError as e:
+      print('error.GitError: Cannot fetch %s' % str(e), file=sys.stderr)
+    except Exception as e:
+      print('error: Cannot fetch %s (%s: %s)'
             % (project.name, type(e).__name__, str(e)), file=sys.stderr)
-        err_event.set()
-        raise
-    finally:
-      if did_lock:
-        lock.release()
-      finish = time.time()
-      self.event_log.AddSync(project, event_log.TASK_SYNC_NETWORK,
-                             start, finish, success)
+      raise
+
+    finish = time.time()
+    return (success, project, start, finish)
 
-    return success
+  @classmethod
+  def _FetchInitChild(cls, ssh_proxy):
+    cls.ssh_proxy = ssh_proxy
 
-  def _Fetch(self, projects, opt):
+  def _Fetch(self, projects, opt, err_event, ssh_proxy):
+    ret = True
+
+    jobs = opt.jobs_network if opt.jobs_network else self.jobs
     fetched = set()
-    lock = _threading.Lock()
-    pm = Progress('Fetching projects', len(projects),
-                  always_print_percentage=opt.quiet)
+    pm = Progress('Fetching', len(projects), delay=False, quiet=opt.quiet)
 
     objdir_project_map = dict()
     for project in projects:
       objdir_project_map.setdefault(project.objdir, []).append(project)
-
-    threads = set()
-    sem = _threading.Semaphore(self.jobs)
-    err_event = _threading.Event()
-    for project_list in objdir_project_map.values():
-      # Check for any errors before running any more tasks.
-      # ...we'll let existing threads finish, though.
-      if err_event.isSet() and opt.fail_fast:
-        break
-
-      sem.acquire()
-      kwargs = dict(opt=opt,
-                    projects=project_list,
-                    sem=sem,
-                    lock=lock,
-                    fetched=fetched,
-                    pm=pm,
-                    err_event=err_event,
-                    clone_filter=self.manifest.CloneFilter)
-      if self.jobs > 1:
-        t = _threading.Thread(target = self._FetchProjectList,
-                              kwargs = kwargs)
-        # Ensure that Ctrl-C will not freeze the repo process.
-        t.daemon = True
-        threads.add(t)
-        t.start()
+    projects_list = list(objdir_project_map.values())
+
+    def _ProcessResults(results_sets):
+      ret = True
+      for results in results_sets:
+        for (success, project, start, finish) in results:
+          self._fetch_times.Set(project, finish - start)
+          self.event_log.AddSync(project, event_log.TASK_SYNC_NETWORK,
+                                 start, finish, success)
+          # Check for any errors before running any more tasks.
+          # ...we'll let existing jobs finish, though.
+          if not success:
+            ret = False
+          else:
+            fetched.add(project.gitdir)
+          pm.update(msg=project.name)
+        if not ret and opt.fail_fast:
+          break
+      return ret
+
+    # We pass the ssh proxy settings via the class.  This allows multiprocessing
+    # to pickle it up when spawning children.  We can't pass it as an argument
+    # to _FetchProjectList below as multiprocessing is unable to pickle those.
+    Sync.ssh_proxy = None
+
+    # NB: Multiprocessing is heavy, so don't spin it up for one job.
+    if len(projects_list) == 1 or jobs == 1:
+      self._FetchInitChild(ssh_proxy)
+      if not _ProcessResults(self._FetchProjectList(opt, x) for x in projects_list):
+        ret = False
+    else:
+      # Favor throughput over responsiveness when quiet.  It seems that imap()
+      # will yield results in batches relative to chunksize, so even as the
+      # children finish a sync, we won't see the result until one child finishes
+      # ~chunksize jobs.  When using a large --jobs with large chunksize, this
+      # can be jarring as there will be a large initial delay where repo looks
+      # like it isn't doing anything and sits at 0%, but then suddenly completes
+      # a lot of jobs all at once.  Since this code is more network bound, we
+      # can accept a bit more CPU overhead with a smaller chunksize so that the
+      # user sees more immediate & continuous feedback.
+      if opt.quiet:
+        chunksize = WORKER_BATCH_SIZE
       else:
-        self._FetchProjectList(**kwargs)
-
-    for t in threads:
-      t.join()
-
-    # If we saw an error, exit with code 1 so that other scripts can check.
-    if err_event.isSet() and opt.fail_fast:
-      print('\nerror: Exited sync due to fetch errors', file=sys.stderr)
-      sys.exit(1)
+        pm.update(inc=0, msg='warming up')
+        chunksize = 4
+      with multiprocessing.Pool(
+          jobs, initializer=self._FetchInitChild, initargs=(ssh_proxy,)) as pool:
+        results = pool.imap_unordered(
+            functools.partial(self._FetchProjectList, opt),
+            projects_list,
+            chunksize=chunksize)
+        if not _ProcessResults(results):
+          ret = False
+          pool.close()
+
+    # Cleanup the reference now that we're done with it, and we're going to
+    # release any resources it points to.  If we don't, later multiprocessing
+    # usage (e.g. checkouts) will try to pickle and then crash.
+    del Sync.ssh_proxy
 
     pm.end()
     self._fetch_times.Save()
 
     if not self.manifest.IsArchive:
-      self._GCProjects(projects)
+      self._GCProjects(projects, opt, err_event)
 
-    return fetched
+    return (ret, fetched)
 
-  def _CheckoutWorker(self, opt, sem, project, *args, **kwargs):
-    """Main function of the fetch threads.
-
-    Delegates most of the work to _CheckoutOne.
+  def _FetchMain(self, opt, args, all_projects, err_event, manifest_name,
+                 load_local_manifests, ssh_proxy):
+    """The main network fetch loop.
 
     Args:
       opt: Program options returned from optparse.  See _Options().
-      projects: Projects to fetch.
-      sem: We'll release() this semaphore when we exit so that another thread
-          can be started up.
-      *args, **kwargs: Remaining arguments to pass to _CheckoutOne. See the
-          _CheckoutOne docstring for details.
+      args: Command line args used to filter out projects.
+      all_projects: List of all projects that should be fetched.
+      err_event: Whether an error was hit while processing.
+      manifest_name: Manifest file to be reloaded.
+      load_local_manifests: Whether to load local manifests.
+      ssh_proxy: SSH manager for clients & masters.
+
+    Returns:
+      List of all projects that should be checked out.
     """
-    try:
-      return self._CheckoutOne(opt, project, *args, **kwargs)
-    finally:
-      sem.release()
+    rp = self.manifest.repoProject
 
-  def _CheckoutOne(self, opt, project, lock, pm, err_event, err_results):
+    to_fetch = []
+    now = time.time()
+    if _ONE_DAY_S <= (now - rp.LastFetch):
+      to_fetch.append(rp)
+    to_fetch.extend(all_projects)
+    to_fetch.sort(key=self._fetch_times.Get, reverse=True)
+
+    success, fetched = self._Fetch(to_fetch, opt, err_event, ssh_proxy)
+    if not success:
+      err_event.set()
+
+    _PostRepoFetch(rp, opt.repo_verify)
+    if opt.network_only:
+      # bail out now; the rest touches the working tree
+      if err_event.is_set():
+        print('\nerror: Exited sync due to fetch errors.\n', file=sys.stderr)
+        sys.exit(1)
+      return
+
+    # Iteratively fetch missing and/or nested unregistered submodules
+    previously_missing_set = set()
+    while True:
+      self._ReloadManifest(manifest_name, load_local_manifests)
+      all_projects = self.GetProjects(args,
+                                      missing_ok=True,
+                                      submodules_ok=opt.fetch_submodules)
+      missing = []
+      for project in all_projects:
+        if project.gitdir not in fetched:
+          missing.append(project)
+      if not missing:
+        break
+      # Stop us from non-stopped fetching actually-missing repos: If set of
+      # missing repos has not been changed from last fetch, we break.
+      missing_set = set(p.name for p in missing)
+      if previously_missing_set == missing_set:
+        break
+      previously_missing_set = missing_set
+      success, new_fetched = self._Fetch(missing, opt, err_event, ssh_proxy)
+      if not success:
+        err_event.set()
+      fetched.update(new_fetched)
+
+    return all_projects
+
+  def _CheckoutOne(self, detach_head, force_sync, project):
     """Checkout work tree for one project
 
     Args:
-      opt: Program options returned from optparse.  See _Options().
+      detach_head: Whether to leave a detached HEAD.
+      force_sync: Force checking out of the repo.
       project: Project object for the project to checkout.
-      lock: Lock for accessing objects that are shared amongst multiple
-          _CheckoutWorker() threads.
-      pm: Instance of a Project object.  We will call pm.update() (with our
-          lock held).
-      err_event: We'll set this event in the case of an error (after printing
-          out info about the error).
-      err_results: A list of strings, paths to git repos where checkout
-          failed.
 
     Returns:
       Whether the fetch was successful.
     """
-    # We'll set to true once we've locked the lock.
-    did_lock = False
-
-    # Encapsulate everything in a try/except/finally so that:
-    # - We always set err_event in the case of an exception.
-    # - We always make sure we unlock the lock if we locked it.
     start = time.time()
     syncbuf = SyncBuffer(self.manifest.manifestProject.config,
-                         detach_head=opt.detach_head)
+                         detach_head=detach_head)
     success = False
     try:
-      try:
-        project.Sync_LocalHalf(syncbuf, force_sync=opt.force_sync)
-
-        # Lock around all the rest of the code, since printing, updating a set
-        # and Progress.update() are not thread safe.
-        lock.acquire()
-        success = syncbuf.Finish()
-        did_lock = True
-
-        if not success:
-          err_event.set()
-          print('error: Cannot checkout %s' % (project.name),
-                file=sys.stderr)
-          raise _CheckoutError()
-
-        pm.update(msg=project.name)
-      except _CheckoutError:
-        pass
-      except Exception as e:
-        print('error: Cannot checkout %s: %s: %s' %
-              (project.name, type(e).__name__, str(e)),
-              file=sys.stderr)
-        err_event.set()
-        raise
-    finally:
-      if did_lock:
-        if not success:
-          err_results.append(project.relpath)
-        lock.release()
-      finish = time.time()
-      self.event_log.AddSync(project, event_log.TASK_SYNC_LOCAL,
-                             start, finish, success)
+      project.Sync_LocalHalf(syncbuf, force_sync=force_sync)
+      success = syncbuf.Finish()
+    except GitError as e:
+      print('error.GitError: Cannot checkout %s: %s' %
+            (project.name, str(e)), file=sys.stderr)
+    except Exception as e:
+      print('error: Cannot checkout %s: %s: %s' %
+            (project.name, type(e).__name__, str(e)),
+            file=sys.stderr)
+      raise
 
-    return success
+    if not success:
+      print('error: Cannot checkout %s' % (project.name), file=sys.stderr)
+    finish = time.time()
+    return (success, project, start, finish)
 
-  def _Checkout(self, all_projects, opt):
+  def _Checkout(self, all_projects, opt, err_results):
     """Checkout projects listed in all_projects
 
     Args:
       all_projects: List of all projects that should be checked out.
       opt: Program options returned from optparse.  See _Options().
+      err_results: A list of strings, paths to git repos where checkout failed.
     """
+    # Only checkout projects with worktrees.
+    all_projects = [x for x in all_projects if x.worktree]
+
+    def _ProcessResults(pool, pm, results):
+      ret = True
+      for (success, project, start, finish) in results:
+        self.event_log.AddSync(project, event_log.TASK_SYNC_LOCAL,
+                               start, finish, success)
+        # Check for any errors before running any more tasks.
+        # ...we'll let existing jobs finish, though.
+        if not success:
+          ret = False
+          err_results.append(project.relpath)
+          if opt.fail_fast:
+            if pool:
+              pool.close()
+            return ret
+        pm.update(msg=project.name)
+      return ret
 
-    # Perform checkouts in multiple threads when we are using partial clone.
-    # Without partial clone, all needed git objects are already downloaded,
-    # in this situation it's better to use only one process because the checkout
-    # would be mostly disk I/O; with partial clone, the objects are only
-    # downloaded when demanded (at checkout time), which is similar to the
-    # Sync_NetworkHalf case and parallelism would be helpful.
-    if self.manifest.CloneFilter:
-      syncjobs = self.jobs
-    else:
-      syncjobs = 1
-
-    lock = _threading.Lock()
-    pm = Progress('Checking out projects', len(all_projects))
-
-    threads = set()
-    sem = _threading.Semaphore(syncjobs)
-    err_event = _threading.Event()
-    err_results = []
-
-    for project in all_projects:
-      # Check for any errors before running any more tasks.
-      # ...we'll let existing threads finish, though.
-      if err_event.isSet() and opt.fail_fast:
-        break
-
-      sem.acquire()
-      if project.worktree:
-        kwargs = dict(opt=opt,
-                      sem=sem,
-                      project=project,
-                      lock=lock,
-                      pm=pm,
-                      err_event=err_event,
-                      err_results=err_results)
-        if syncjobs > 1:
-          t = _threading.Thread(target=self._CheckoutWorker,
-                                kwargs=kwargs)
-          # Ensure that Ctrl-C will not freeze the repo process.
-          t.daemon = True
-          threads.add(t)
-          t.start()
-        else:
-          self._CheckoutWorker(**kwargs)
-
-    for t in threads:
-      t.join()
+    return self.ExecuteInParallel(
+        opt.jobs_checkout if opt.jobs_checkout else self.jobs,
+        functools.partial(self._CheckoutOne, opt.detach_head, opt.force_sync),
+        all_projects,
+        callback=_ProcessResults,
+        output=Progress('Checking out', len(all_projects), quiet=opt.quiet)) and not err_results
 
-    pm.end()
-    # If we saw an error, exit with code 1 so that other scripts can check.
-    if err_event.isSet():
-      print('\nerror: Exited sync due to checkout errors', file=sys.stderr)
-      if err_results:
-        print('Failing repos:\n%s' % '\n'.join(err_results),
-              file=sys.stderr)
-      sys.exit(1)
+  def _GCProjects(self, projects, opt, err_event):
+    pm = Progress('Garbage collecting', len(projects), delay=False, quiet=opt.quiet)
+    pm.update(inc=0, msg='prescan')
 
-  def _GCProjects(self, projects):
     gc_gitdirs = {}
     for project in projects:
-      if len(project.manifest.GetProjectsWithName(project.name)) > 1:
-        print('Shared project %s found, disabling pruning.' % project.name)
-        project.bare_git.config('--replace-all', 'gc.pruneExpire', 'never')
+      # Make sure pruning never kicks in with shared projects.
+      if (not project.use_git_worktrees and
+              len(project.manifest.GetProjectsWithName(project.name)) > 1):
+        if not opt.quiet:
+          print('\r%s: Shared project %s found, disabling pruning.' %
+                (project.relpath, project.name))
+        if git_require((2, 7, 0)):
+          project.EnableRepositoryExtension('preciousObjects')
+        else:
+          # This isn't perfect, but it's the best we can do with old git.
+          print('\r%s: WARNING: shared projects are unreliable when using old '
+                'versions of git; please upgrade to git-2.7.0+.'
+                % (project.relpath,),
+                file=sys.stderr)
+          project.config.SetString('gc.pruneExpire', 'never')
       gc_gitdirs[project.gitdir] = project.bare_git
 
-    has_dash_c = git_require((1, 7, 2))
-    if multiprocessing and has_dash_c:
-      cpu_count = multiprocessing.cpu_count()
-    else:
-      cpu_count = 1
+    pm.update(inc=len(projects) - len(gc_gitdirs), msg='warming up')
+
+    cpu_count = os.cpu_count()
     jobs = min(self.jobs, cpu_count)
 
     if jobs < 2:
       for bare_git in gc_gitdirs.values():
+        pm.update(msg=bare_git._project.name)
         bare_git.gc('--auto')
+      pm.end()
       return
 
     config = {'pack.threads': cpu_count // jobs if cpu_count > jobs else 1}
 
     threads = set()
     sem = _threading.Semaphore(jobs)
-    err_event = _threading.Event()
 
     def GC(bare_git):
+      pm.start(bare_git._project.name)
       try:
         try:
           bare_git.gc('--auto', config=config)
         except GitError:
           err_event.set()
-        except:
+        except Exception:
           err_event.set()
           raise
       finally:
+        pm.finish(bare_git._project.name)
         sem.release()
 
     for bare_git in gc_gitdirs.values():
-      if err_event.isSet():
+      if err_event.is_set() and opt.fail_fast:
         break
       sem.acquire()
       t = _threading.Thread(target=GC, args=(bare_git,))
@@ -613,84 +666,30 @@ later is required to fix a server side protocol bug.
 
     for t in threads:
       t.join()
+    pm.end()
 
-    if err_event.isSet():
-      print('\nerror: Exited sync due to gc errors', file=sys.stderr)
-      sys.exit(1)
+  def _ReloadManifest(self, manifest_name=None, load_local_manifests=True):
+    """Reload the manfiest from the file specified by the |manifest_name|.
+
+    It unloads the manifest if |manifest_name| is None.
 
-  def _ReloadManifest(self, manifest_name=None):
+    Args:
+      manifest_name: Manifest file to be reloaded.
+      load_local_manifests: Whether to load local manifests.
+    """
     if manifest_name:
       # Override calls _Unload already
-      self.manifest.Override(manifest_name)
+      self.manifest.Override(manifest_name, load_local_manifests=load_local_manifests)
     else:
       self.manifest._Unload()
 
-  def _DeleteProject(self, path):
-    print('Deleting obsolete path %s' % path, file=sys.stderr)
-
-    # Delete the .git directory first, so we're less likely to have a partially
-    # working git repository around. There shouldn't be any git projects here,
-    # so rmtree works.
-    try:
-      platform_utils.rmtree(os.path.join(path, '.git'))
-    except OSError as e:
-      print('Failed to remove %s (%s)' % (os.path.join(path, '.git'), str(e)), file=sys.stderr)
-      print('error: Failed to delete obsolete path %s' % path, file=sys.stderr)
-      print('       remove manually, then run sync again', file=sys.stderr)
-      return 1
-
-    # Delete everything under the worktree, except for directories that contain
-    # another git project
-    dirs_to_remove = []
-    failed = False
-    for root, dirs, files in platform_utils.walk(path):
-      for f in files:
-        try:
-          platform_utils.remove(os.path.join(root, f))
-        except OSError as e:
-          print('Failed to remove %s (%s)' % (os.path.join(root, f), str(e)), file=sys.stderr)
-          failed = True
-      dirs[:] = [d for d in dirs
-                 if not os.path.lexists(os.path.join(root, d, '.git'))]
-      dirs_to_remove += [os.path.join(root, d) for d in dirs
-                         if os.path.join(root, d) not in dirs_to_remove]
-    for d in reversed(dirs_to_remove):
-      if platform_utils.islink(d):
-        try:
-          platform_utils.remove(d)
-        except OSError as e:
-          print('Failed to remove %s (%s)' % (os.path.join(root, d), str(e)), file=sys.stderr)
-          failed = True
-      elif len(platform_utils.listdir(d)) == 0:
-        try:
-          platform_utils.rmdir(d)
-        except OSError as e:
-          print('Failed to remove %s (%s)' % (os.path.join(root, d), str(e)), file=sys.stderr)
-          failed = True
-          continue
-    if failed:
-      print('error: Failed to delete obsolete path %s' % path, file=sys.stderr)
-      print('       remove manually, then run sync again', file=sys.stderr)
-      return 1
-
-    # Try deleting parent dirs if they are empty
-    project_dir = path
-    while project_dir != self.manifest.topdir:
-      if len(platform_utils.listdir(project_dir)) == 0:
-        platform_utils.rmdir(project_dir)
-      else:
-        break
-      project_dir = os.path.dirname(project_dir)
-
-    return 0
-
   def UpdateProjectList(self, opt):
     new_project_paths = []
     for project in self.GetProjects(None, missing_ok=True):
       if project.relpath:
         new_project_paths.append(project.relpath)
     file_name = 'project.list'
-    file_path = os.path.join(self.manifest.repodir, file_name)
+    file_path = os.path.join(self.repodir, file_name)
     old_project_paths = []
 
     if os.path.exists(file_path):
@@ -705,28 +704,20 @@ later is required to fix a server side protocol bug.
           gitdir = os.path.join(self.manifest.topdir, path, '.git')
           if os.path.exists(gitdir):
             project = Project(
-                           manifest = self.manifest,
-                           name = path,
-                           remote = RemoteSpec('origin'),
-                           gitdir = gitdir,
-                           objdir = gitdir,
-                           worktree = os.path.join(self.manifest.topdir, path),
-                           relpath = path,
-                           revisionExpr = 'HEAD',
-                           revisionId = None,
-                           groups = None)
-
-            if project.IsDirty() and opt.force_remove_dirty:
-              print('WARNING: Removing dirty project "%s": uncommitted changes '
-                    'erased' % project.relpath, file=sys.stderr)
-              self._DeleteProject(project.worktree)
-            elif project.IsDirty():
-              print('error: Cannot remove project "%s": uncommitted changes '
-                    'are present' % project.relpath, file=sys.stderr)
-              print('       commit changes, then run sync again',
-                    file=sys.stderr)
-              return 1
-            elif self._DeleteProject(project.worktree):
+                manifest=self.manifest,
+                name=path,
+                remote=RemoteSpec('origin'),
+                gitdir=gitdir,
+                objdir=gitdir,
+                use_git_worktrees=os.path.isfile(gitdir),
+                worktree=os.path.join(self.manifest.topdir, path),
+                relpath=path,
+                revisionExpr='HEAD',
+                revisionId=None,
+                groups=None)
+            if not project.DeleteWorktree(
+                    quiet=opt.quiet,
+                    force=opt.force_remove_dirty):
               return 1
 
     new_project_paths.sort()
@@ -735,6 +726,56 @@ later is required to fix a server side protocol bug.
       fd.write('\n')
     return 0
 
+  def UpdateCopyLinkfileList(self):
+    """Save all dests of copyfile and linkfile, and update them if needed.
+
+    Returns:
+      Whether update was successful.
+    """
+    new_paths = {}
+    new_linkfile_paths = []
+    new_copyfile_paths = []
+    for project in self.GetProjects(None, missing_ok=True):
+      new_linkfile_paths.extend(x.dest for x in project.linkfiles)
+      new_copyfile_paths.extend(x.dest for x in project.copyfiles)
+
+    new_paths = {
+        'linkfile': new_linkfile_paths,
+        'copyfile': new_copyfile_paths,
+    }
+
+    copylinkfile_name = 'copy-link-files.json'
+    copylinkfile_path = os.path.join(self.manifest.repodir, copylinkfile_name)
+    old_copylinkfile_paths = {}
+
+    if os.path.exists(copylinkfile_path):
+      with open(copylinkfile_path, 'rb') as fp:
+        try:
+          old_copylinkfile_paths = json.load(fp)
+        except:
+          print('error: %s is not a json formatted file.' %
+                copylinkfile_path, file=sys.stderr)
+          platform_utils.remove(copylinkfile_path)
+          return False
+
+      need_remove_files = []
+      need_remove_files.extend(
+          set(old_copylinkfile_paths.get('linkfile', [])) -
+          set(new_linkfile_paths))
+      need_remove_files.extend(
+          set(old_copylinkfile_paths.get('copyfile', [])) -
+          set(new_copyfile_paths))
+
+      for need_remove_file in need_remove_files:
+        # Try to remove the updated copyfile or linkfile.
+        # So, if the file is not exist, nothing need to do.
+        platform_utils.remove(need_remove_file, missing_ok=True)
+
+    # Create copy-link-files.json, save dest path of "copyfile" and "linkfile".
+    with open(copylinkfile_path, 'w', encoding='utf-8') as fp:
+      json.dump(new_paths, fp)
+    return True
+
   def _SmartSyncSetup(self, opt, smart_sync_manifest_path):
     if not self.manifest.manifest_server:
       print('error: cannot smart sync: no manifest server defined in '
@@ -745,7 +786,7 @@ later is required to fix a server side protocol bug.
     if not opt.quiet:
       print('Using manifest server %s' % manifest_server)
 
-    if not '@' in manifest_server:
+    if '@' not in manifest_server:
       username = None
       password = None
       if opt.manifest_server_username and opt.manifest_server_password:
@@ -782,19 +823,15 @@ later is required to fix a server side protocol bug.
     try:
       server = xmlrpc.client.Server(manifest_server, transport=transport)
       if opt.smart_sync:
-        p = self.manifest.manifestProject
-        b = p.GetBranch(p.CurrentBranch)
-        branch = b.merge
-        if branch.startswith(R_HEADS):
-          branch = branch[len(R_HEADS):]
-
-        env = os.environ.copy()
-        if 'SYNC_TARGET' in env:
-          target = env['SYNC_TARGET']
+        branch = self._GetBranch()
+
+        if 'SYNC_TARGET' in os.environ:
+          target = os.environ['SYNC_TARGET']
           [success, manifest_str] = server.GetApprovedManifest(branch, target)
-        elif 'TARGET_PRODUCT' in env and 'TARGET_BUILD_VARIANT' in env:
-          target = '%s-%s' % (env['TARGET_PRODUCT'],
-                              env['TARGET_BUILD_VARIANT'])
+        elif ('TARGET_PRODUCT' in os.environ and
+              'TARGET_BUILD_VARIANT' in os.environ):
+          target = '%s-%s' % (os.environ['TARGET_PRODUCT'],
+                              os.environ['TARGET_BUILD_VARIANT'])
           [success, manifest_str] = server.GetApprovedManifest(branch, target)
         else:
           [success, manifest_str] = server.GetApprovedManifest(branch)
@@ -833,12 +870,15 @@ later is required to fix a server side protocol bug.
     """Fetch & update the local manifest project."""
     if not opt.local_only:
       start = time.time()
-      success = mp.Sync_NetworkHalf(quiet=opt.quiet,
-                                    current_branch_only=opt.current_branch_only,
-                                    no_tags=opt.no_tags,
+      success = mp.Sync_NetworkHalf(quiet=opt.quiet, verbose=opt.verbose,
+                                    current_branch_only=self._GetCurrentBranchOnly(opt),
+                                    force_sync=opt.force_sync,
+                                    tags=opt.tags,
                                     optimized_fetch=opt.optimized_fetch,
+                                    retry_fetches=opt.retry_fetches,
                                     submodules=self.manifest.HasSubmodules,
-                                    clone_filter=self.manifest.CloneFilter)
+                                    clone_filter=self.manifest.CloneFilter,
+                                    partial_clone_exclude=self.manifest.PartialCloneExclude)
       finish = time.time()
       self.event_log.AddSync(mp, event_log.TASK_SYNC_NETWORK,
                              start, finish, success)
@@ -852,7 +892,7 @@ later is required to fix a server side protocol bug.
                              start, time.time(), clean)
       if not clean:
         sys.exit(1)
-      self._ReloadManifest(opt.manifest_name)
+      self._ReloadManifest(manifest_name)
       if opt.jobs is None:
         self.jobs = self.manifest.default.sync_j
 
@@ -886,7 +926,10 @@ later is required to fix a server side protocol bug.
 
     manifest_name = opt.manifest_name
     smart_sync_manifest_path = os.path.join(
-      self.manifest.manifestProject.worktree, 'smart_sync_override.xml')
+        self.manifest.manifestProject.worktree, 'smart_sync_override.xml')
+
+    if opt.clone_bundle is None:
+      opt.clone_bundle = self.manifest.CloneBundle
 
     if opt.smart_sync or opt.smart_tag:
       manifest_name = self._SmartSyncSetup(opt, smart_sync_manifest_path)
@@ -898,8 +941,17 @@ later is required to fix a server side protocol bug.
           print('error: failed to remove existing smart sync override manifest: %s' %
                 e, file=sys.stderr)
 
+    err_event = multiprocessing.Event()
+
     rp = self.manifest.repoProject
     rp.PreSync()
+    cb = rp.CurrentBranch
+    if cb:
+      base = rp.GetBranch(cb).merge
+      if not base or not base.startswith('refs/heads/'):
+        print('warning: repo is not tracking a remote branch, so it will not '
+              'receive updates; run `repo init --repo-rev=stable` to fix.',
+              file=sys.stderr)
 
     mp = self.manifest.manifestProject
     mp.PreSync()
@@ -907,7 +959,21 @@ later is required to fix a server side protocol bug.
     if opt.repo_upgraded:
       _PostRepoUpgrade(self.manifest, quiet=opt.quiet)
 
-    self._UpdateManifestProject(opt, mp, manifest_name)
+    if not opt.mp_update:
+      print('Skipping update of local manifest project.')
+    else:
+      self._UpdateManifestProject(opt, mp, manifest_name)
+
+    load_local_manifests = not self.manifest.HasLocalManifests
+    use_superproject = git_superproject.UseSuperproject(opt, self.manifest)
+    superproject_logging_data = {
+        'superproject': use_superproject,
+        'haslocalmanifests': bool(self.manifest.HasLocalManifests),
+        'hassuperprojecttag': bool(self.manifest.superproject),
+    }
+    if use_superproject:
+      manifest_name = self._UpdateProjectsRevisionId(
+          opt, args, load_local_manifests, superproject_logging_data) or opt.manifest_name
 
     if self.gitc_manifest:
       gitc_manifest_projects = self.GetProjects(args,
@@ -948,56 +1014,92 @@ later is required to fix a server side protocol bug.
                                     missing_ok=True,
                                     submodules_ok=opt.fetch_submodules)
 
+    err_network_sync = False
+    err_update_projects = False
+
     self._fetch_times = _FetchTimes(self.manifest)
     if not opt.local_only:
-      to_fetch = []
-      now = time.time()
-      if _ONE_DAY_S <= (now - rp.LastFetch):
-        to_fetch.append(rp)
-      to_fetch.extend(all_projects)
-      to_fetch.sort(key=self._fetch_times.Get, reverse=True)
-
-      fetched = self._Fetch(to_fetch, opt)
-      _PostRepoFetch(rp, opt.no_repo_verify)
+      with multiprocessing.Manager() as manager:
+        with ssh.ProxyManager(manager) as ssh_proxy:
+          # Initialize the socket dir once in the parent.
+          ssh_proxy.sock()
+          all_projects = self._FetchMain(opt, args, all_projects, err_event,
+                                         manifest_name, load_local_manifests,
+                                         ssh_proxy)
+
       if opt.network_only:
-        # bail out now; the rest touches the working tree
         return
 
-      # Iteratively fetch missing and/or nested unregistered submodules
-      previously_missing_set = set()
-      while True:
-        self._ReloadManifest(manifest_name)
-        all_projects = self.GetProjects(args,
-                                        missing_ok=True,
-                                        submodules_ok=opt.fetch_submodules)
-        missing = []
-        for project in all_projects:
-          if project.gitdir not in fetched:
-            missing.append(project)
-        if not missing:
-          break
-        # Stop us from non-stopped fetching actually-missing repos: If set of
-        # missing repos has not been changed from last fetch, we break.
-        missing_set = set(p.name for p in missing)
-        if previously_missing_set == missing_set:
-          break
-        previously_missing_set = missing_set
-        fetched.update(self._Fetch(missing, opt))
+      # If we saw an error, exit with code 1 so that other scripts can check.
+      if err_event.is_set():
+        err_network_sync = True
+        if opt.fail_fast:
+          print('\nerror: Exited sync due to fetch errors.\n'
+                'Local checkouts *not* updated. Resolve network issues & '
+                'retry.\n'
+                '`repo sync -l` will update some local checkouts.',
+                file=sys.stderr)
+          sys.exit(1)
 
     if self.manifest.IsMirror or self.manifest.IsArchive:
       # bail out now, we have no working tree
       return
 
     if self.UpdateProjectList(opt):
-      sys.exit(1)
+      err_event.set()
+      err_update_projects = True
+      if opt.fail_fast:
+        print('\nerror: Local checkouts *not* updated.', file=sys.stderr)
+        sys.exit(1)
 
-    self._Checkout(all_projects, opt)
+    err_update_linkfiles = not self.UpdateCopyLinkfileList()
+    if err_update_linkfiles:
+      err_event.set()
+      if opt.fail_fast:
+        print('\nerror: Local update copyfile or linkfile failed.', file=sys.stderr)
+        sys.exit(1)
+
+    err_results = []
+    # NB: We don't exit here because this is the last step.
+    err_checkout = not self._Checkout(all_projects, opt, err_results)
+    if err_checkout:
+      err_event.set()
 
     # If there's a notice that's supposed to print at the end of the sync, print
     # it now...
     if self.manifest.notice:
       print(self.manifest.notice)
 
+    # If we saw an error, exit with code 1 so that other scripts can check.
+    if err_event.is_set():
+      print('\nerror: Unable to fully sync the tree.', file=sys.stderr)
+      if err_network_sync:
+        print('error: Downloading network changes failed.', file=sys.stderr)
+      if err_update_projects:
+        print('error: Updating local project lists failed.', file=sys.stderr)
+      if err_update_linkfiles:
+        print('error: Updating copyfiles or linkfiles failed.', file=sys.stderr)
+      if err_checkout:
+        print('error: Checking out local projects failed.', file=sys.stderr)
+        if err_results:
+          print('Failing repos:\n%s' % '\n'.join(err_results), file=sys.stderr)
+      print('Try re-running with "-j1 --fail-fast" to exit at the first error.',
+            file=sys.stderr)
+      sys.exit(1)
+
+    # Log the previous sync analysis state from the config.
+    self.git_event_log.LogDataConfigEvents(mp.config.GetSyncAnalysisStateData(),
+                                           'previous_sync_state')
+
+    # Update and log with the new sync analysis state.
+    mp.config.UpdateSyncAnalysisState(opt, superproject_logging_data)
+    self.git_event_log.LogDataConfigEvents(mp.config.GetSyncAnalysisStateData(),
+                                           'current_sync_state')
+
+    if not opt.quiet:
+      print('repo sync has finished successfully.')
+
+
 def _PostRepoUpgrade(manifest, quiet=False):
   wrapper = Wrapper()
   if wrapper.NeedSetupGnuPG():
@@ -1006,15 +1108,29 @@ def _PostRepoUpgrade(manifest, quiet=False):
     if project.Exists:
       project.PostRepoUpgrade()
 
-def _PostRepoFetch(rp, no_repo_verify=False, verbose=False):
+
+def _PostRepoFetch(rp, repo_verify=True, verbose=False):
   if rp.HasChanges:
     print('info: A new version of repo is available', file=sys.stderr)
-    print(file=sys.stderr)
-    if no_repo_verify or _VerifyTag(rp):
-      syncbuf = SyncBuffer(rp.config)
-      rp.Sync_LocalHalf(syncbuf)
-      if not syncbuf.Finish():
-        sys.exit(1)
+    wrapper = Wrapper()
+    try:
+      rev = rp.bare_git.describe(rp.GetRevisionId())
+    except GitError:
+      rev = None
+    _, new_rev = wrapper.check_repo_rev(rp.gitdir, rev, repo_verify=repo_verify)
+    # See if we're held back due to missing signed tag.
+    current_revid = rp.bare_git.rev_parse('HEAD')
+    new_revid = rp.bare_git.rev_parse('--verify', new_rev)
+    if current_revid != new_revid:
+      # We want to switch to the new rev, but also not trash any uncommitted
+      # changes.  This helps with local testing/hacking.
+      # If a local change has been made, we will throw that away.
+      # We also have to make sure this will switch to an older commit if that's
+      # the latest tag in order to support release rollback.
+      try:
+        rp.work_git.reset('--keep', new_rev)
+      except GitError as e:
+        sys.exit(str(e))
       print('info: Restarting repo with latest version', file=sys.stderr)
       raise RepoChangedException(['--repo-upgraded'])
     else:
@@ -1024,53 +1140,6 @@ def _PostRepoFetch(rp, no_repo_verify=False, verbose=False):
       print('repo version %s is current' % rp.work_git.describe(HEAD),
             file=sys.stderr)
 
-def _VerifyTag(project):
-  gpg_dir = os.path.expanduser('~/.repoconfig/gnupg')
-  if not os.path.exists(gpg_dir):
-    print('warning: GnuPG was not available during last "repo init"\n'
-          'warning: Cannot automatically authenticate repo."""',
-          file=sys.stderr)
-    return True
-
-  try:
-    cur = project.bare_git.describe(project.GetRevisionId())
-  except GitError:
-    cur = None
-
-  if not cur \
-     or re.compile(r'^.*-[0-9]{1,}-g[0-9a-f]{1,}$').match(cur):
-    rev = project.revisionExpr
-    if rev.startswith(R_HEADS):
-      rev = rev[len(R_HEADS):]
-
-    print(file=sys.stderr)
-    print("warning: project '%s' branch '%s' is not signed"
-          % (project.name, rev), file=sys.stderr)
-    return False
-
-  env = os.environ.copy()
-  env['GIT_DIR'] = project.gitdir.encode()
-  env['GNUPGHOME'] = gpg_dir.encode()
-
-  cmd = [GIT, 'tag', '-v', cur]
-  proc = subprocess.Popen(cmd,
-                          stdout = subprocess.PIPE,
-                          stderr = subprocess.PIPE,
-                          env = env)
-  out = proc.stdout.read()
-  proc.stdout.close()
-
-  err = proc.stderr.read()
-  proc.stderr.close()
-
-  if proc.wait() != 0:
-    print(file=sys.stderr)
-    print(out, file=sys.stderr)
-    print(err, file=sys.stderr)
-    print(file=sys.stderr)
-    return False
-  return True
-
 
 class _FetchTimes(object):
   _ALPHA = 0.5
@@ -1090,7 +1159,7 @@ class _FetchTimes(object):
     old = self._times.get(name, t)
     self._seen.add(name)
     a = self._ALPHA
-    self._times[name] = (a*t) + ((1-a) * old)
+    self._times[name] = (a * t) + ((1 - a) * old)
 
   def _Load(self):
     if self._times is None:
@@ -1098,10 +1167,7 @@ class _FetchTimes(object):
         with open(self._path) as f:
           self._times = json.load(f)
       except (IOError, ValueError):
-        try:
-          platform_utils.remove(self._path)
-        except OSError:
-          pass
+        platform_utils.remove(self._path, missing_ok=True)
         self._times = {}
 
   def Save(self):
@@ -1119,15 +1185,14 @@ class _FetchTimes(object):
       with open(self._path, 'w') as f:
         json.dump(self._times, f, indent=2)
     except (IOError, TypeError):
-      try:
-        platform_utils.remove(self._path)
-      except OSError:
-        pass
+      platform_utils.remove(self._path, missing_ok=True)
 
 # This is a replacement for xmlrpc.client.Transport using urllib2
 # and supporting persistent-http[s]. It cannot change hosts from
 # request to request like the normal transport, the real url
 # is passed during initialization.
+
+
 class PersistentTransport(xmlrpc.client.Transport):
   def __init__(self, orig_host):
     self.orig_host = orig_host
@@ -1138,7 +1203,7 @@ class PersistentTransport(xmlrpc.client.Transport):
       # Since we're only using them for HTTP, copy the file temporarily,
       # stripping those prefixes away.
       if cookiefile:
-        tmpcookiefile = tempfile.NamedTemporaryFile()
+        tmpcookiefile = tempfile.NamedTemporaryFile(mode='w')
         tmpcookiefile.write("# HTTP Cookie File")
         try:
           with open(cookiefile) as f:
@@ -1162,7 +1227,7 @@ class PersistentTransport(xmlrpc.client.Transport):
       if proxy:
         proxyhandler = urllib.request.ProxyHandler({
             "http": proxy,
-            "https": proxy })
+            "https": proxy})
 
       opener = urllib.request.build_opener(
           urllib.request.HTTPCookieProcessor(cookiejar),
@@ -1219,4 +1284,3 @@ class PersistentTransport(xmlrpc.client.Transport):
 
   def close(self):
     pass
-
diff --git a/subcmds/upload.py b/subcmds/upload.py
index 5c12aaee..c48deab6 100644
--- a/subcmds/upload.py
+++ b/subcmds/upload.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2008 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,25 +12,23 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 import copy
+import functools
+import optparse
 import re
 import sys
 
-from command import InteractiveCommand
+from command import DEFAULT_LOCAL_JOBS, InteractiveCommand
 from editor import Editor
-from error import HookError, UploadError
+from error import UploadError
 from git_command import GitCommand
-from project import RepoHook
+from git_refs import R_HEADS
+from hooks import RepoHook
 
-from pyversion import is_python3
-if not is_python3():
-  input = raw_input
-else:
-  unicode = str
 
 UNUSUAL_COMMIT_THRESHOLD = 5
 
+
 def _ConfirmManyUploads(multiple_branches=False):
   if multiple_branches:
     print('ATTENTION: One or more branches has an unusually high number '
@@ -44,19 +40,22 @@ def _ConfirmManyUploads(multiple_branches=False):
   answer = input("If you are sure you intend to do this, type 'yes': ").strip()
   return answer == "yes"
 
+
 def _die(fmt, *args):
   msg = fmt % args
   print('error: %s' % msg, file=sys.stderr)
   sys.exit(1)
 
+
 def _SplitEmails(values):
   result = []
   for value in values:
     result.extend([s.strip() for s in value.split(',')])
   return result
 
+
 class Upload(InteractiveCommand):
-  common = True
+  COMMON = True
   helpSummary = "Upload changes for code review"
   helpUsage = """
 %prog [--re --cc] [<project>]...
@@ -126,74 +125,89 @@ is set to "true" then repo will assume you always want the equivalent
 of the -t option to the repo command. If unset or set to "false" then
 repo will make use of only the command line option.
 
+review.URL.uploadhashtags:
+
+To add hashtags whenever uploading a commit, you can set a per-project
+or global Git option to do so. The value of review.URL.uploadhashtags
+will be used as comma delimited hashtags like the --hashtag option.
+
+review.URL.uploadlabels:
+
+To add labels whenever uploading a commit, you can set a per-project
+or global Git option to do so. The value of review.URL.uploadlabels
+will be used as comma delimited labels like the --label option.
+
+review.URL.uploadnotify:
+
+Control e-mail notifications when uploading.
+https://gerrit-review.googlesource.com/Documentation/user-upload.html#notify
+
 # References
 
 Gerrit Code Review:  https://www.gerritcodereview.com/
 
 """
+  PARALLEL_JOBS = DEFAULT_LOCAL_JOBS
 
   def _Options(self, p):
     p.add_option('-t',
                  dest='auto_topic', action='store_true',
-                 help='Send local branch name to Gerrit Code Review')
+                 help='send local branch name to Gerrit Code Review')
+    p.add_option('--hashtag', '--ht',
+                 dest='hashtags', action='append', default=[],
+                 help='add hashtags (comma delimited) to the review')
+    p.add_option('--hashtag-branch', '--htb',
+                 action='store_true',
+                 help='add local branch name as a hashtag')
+    p.add_option('-l', '--label',
+                 dest='labels', action='append', default=[],
+                 help='add a label when uploading')
     p.add_option('--re', '--reviewers',
-                 type='string',  action='append', dest='reviewers',
-                 help='Request reviews from these people.')
+                 type='string', action='append', dest='reviewers',
+                 help='request reviews from these people')
     p.add_option('--cc',
-                 type='string',  action='append', dest='cc',
-                 help='Also send email to these email addresses.')
-    p.add_option('--br',
-                 type='string',  action='store', dest='branch',
-                 help='Branch to upload.')
-    p.add_option('--cbr', '--current-branch',
+                 type='string', action='append', dest='cc',
+                 help='also send email to these email addresses')
+    p.add_option('--br', '--branch',
+                 type='string', action='store', dest='branch',
+                 help='(local) branch to upload')
+    p.add_option('-c', '--current-branch',
+                 dest='current_branch', action='store_true',
+                 help='upload current git branch')
+    p.add_option('--no-current-branch',
+                 dest='current_branch', action='store_false',
+                 help='upload all git branches')
+    # Turn this into a warning & remove this someday.
+    p.add_option('--cbr',
                  dest='current_branch', action='store_true',
-                 help='Upload current git branch.')
-    p.add_option('-d', '--draft',
-                 action='store_true', dest='draft', default=False,
-                 help='If specified, upload as a draft.')
+                 help=optparse.SUPPRESS_HELP)
     p.add_option('--ne', '--no-emails',
                  action='store_false', dest='notify', default=True,
-                 help='If specified, do not send emails on upload.')
+                 help='do not send e-mails on upload')
     p.add_option('-p', '--private',
                  action='store_true', dest='private', default=False,
-                 help='If specified, upload as a private change.')
+                 help='upload as a private change (deprecated; use --wip)')
     p.add_option('-w', '--wip',
                  action='store_true', dest='wip', default=False,
-                 help='If specified, upload as a work-in-progress change.')
+                 help='upload as a work-in-progress change')
     p.add_option('-o', '--push-option',
                  type='string', action='append', dest='push_options',
                  default=[],
-                 help='Additional push options to transmit')
+                 help='additional push options to transmit')
     p.add_option('-D', '--destination', '--dest',
                  type='string', action='store', dest='dest_branch',
                  metavar='BRANCH',
-                 help='Submit for review on this target branch.')
-
-    # Options relating to upload hook.  Note that verify and no-verify are NOT
-    # opposites of each other, which is why they store to different locations.
-    # We are using them to match 'git commit' syntax.
-    #
-    # Combinations:
-    # - no-verify=False, verify=False (DEFAULT):
-    #   If stdout is a tty, can prompt about running upload hooks if needed.
-    #   If user denies running hooks, the upload is cancelled.  If stdout is
-    #   not a tty and we would need to prompt about upload hooks, upload is
-    #   cancelled.
-    # - no-verify=False, verify=True:
-    #   Always run upload hooks with no prompt.
-    # - no-verify=True, verify=False:
-    #   Never run upload hooks, but upload anyway (AKA bypass hooks).
-    # - no-verify=True, verify=True:
-    #   Invalid
+                 help='submit for review on this target branch')
+    p.add_option('-n', '--dry-run',
+                 dest='dryrun', default=False, action='store_true',
+                 help='do everything except actually upload the CL')
+    p.add_option('-y', '--yes',
+                 default=False, action='store_true',
+                 help='answer yes to all safe prompts')
     p.add_option('--no-cert-checks',
                  dest='validate_certs', action='store_false', default=True,
-                 help='Disable verifying ssl certs (unsafe).')
-    p.add_option('--no-verify',
-                 dest='bypass_hooks', action='store_true',
-                 help='Do not run the upload hook.')
-    p.add_option('--verify',
-                 dest='allow_all_hooks', action='store_true',
-                 help='Run the upload hook without prompting.')
+                 help='disable verifying ssl certs (unsafe)')
+    RepoHook.AddOptionGroup(p, 'pre-upload')
 
   def _SingleBranch(self, opt, branch, people):
     project = branch.project
@@ -212,20 +226,24 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
 
       destination = opt.dest_branch or project.dest_branch or project.revisionExpr
       print('Upload project %s/ to remote branch %s%s:' %
-            (project.relpath, destination, ' (draft)' if opt.draft else ''))
+            (project.relpath, destination, ' (private)' if opt.private else ''))
       print('  branch %s (%2d commit%s, %s):' % (
-                    name,
-                    len(commit_list),
-                    len(commit_list) != 1 and 's' or '',
-                    date))
+          name,
+          len(commit_list),
+          len(commit_list) != 1 and 's' or '',
+          date))
       for commit in commit_list:
         print('         %s' % commit)
 
       print('to %s (y/N)? ' % remote.review, end='')
       # TODO: When we require Python 3, use flush=True w/print above.
       sys.stdout.flush()
-      answer = sys.stdin.readline().strip().lower()
-      answer = answer in ('y', 'yes', '1', 'true', 't')
+      if opt.yes:
+        print('<--yes>')
+        answer = True
+      else:
+        answer = sys.stdin.readline().strip().lower()
+        answer = answer in ('y', 'yes', '1', 'true', 't')
 
     if answer:
       if len(branch.commits) > UNUSUAL_COMMIT_THRESHOLD:
@@ -322,12 +340,12 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
 
     key = 'review.%s.autoreviewer' % project.GetBranch(name).remote.review
     raw_list = project.config.GetString(key)
-    if not raw_list is None:
+    if raw_list is not None:
       people[0].extend([entry.strip() for entry in raw_list.split(',')])
 
     key = 'review.%s.autocopy' % project.GetBranch(name).remote.review
     raw_list = project.config.GetString(key)
-    if not raw_list is None and len(people[0]) > 0:
+    if raw_list is not None and len(people[0]) > 0:
       people[1].extend([entry.strip() for entry in raw_list.split(',')])
 
   def _FindGerritChange(self, branch):
@@ -364,7 +382,11 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
             print('Continue uploading? (y/N) ', end='')
             # TODO: When we require Python 3, use flush=True w/print above.
             sys.stdout.flush()
-            a = sys.stdin.readline().strip().lower()
+            if opt.yes:
+              print('<--yes>')
+              a = 'yes'
+            else:
+              a = sys.stdin.readline().strip().lower()
             if a not in ('y', 'yes', 't', 'true', 'on'):
               print("skipping upload", file=sys.stderr)
               branch.uploaded = False
@@ -376,12 +398,51 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
           key = 'review.%s.uploadtopic' % branch.project.remote.review
           opt.auto_topic = branch.project.config.GetBoolean(key)
 
+        def _ExpandCommaList(value):
+          """Split |value| up into comma delimited entries."""
+          if not value:
+            return
+          for ret in value.split(','):
+            ret = ret.strip()
+            if ret:
+              yield ret
+
+        # Check if hashtags should be included.
+        key = 'review.%s.uploadhashtags' % branch.project.remote.review
+        hashtags = set(_ExpandCommaList(branch.project.config.GetString(key)))
+        for tag in opt.hashtags:
+          hashtags.update(_ExpandCommaList(tag))
+        if opt.hashtag_branch:
+          hashtags.add(branch.name)
+
+        # Check if labels should be included.
+        key = 'review.%s.uploadlabels' % branch.project.remote.review
+        labels = set(_ExpandCommaList(branch.project.config.GetString(key)))
+        for label in opt.labels:
+          labels.update(_ExpandCommaList(label))
+        # Basic sanity check on label syntax.
+        for label in labels:
+          if not re.match(r'^.+[+-][0-9]+$', label):
+            print('repo: error: invalid label syntax "%s": labels use forms '
+                  'like CodeReview+1 or Verified-1' % (label,), file=sys.stderr)
+            sys.exit(1)
+
+        # Handle e-mail notifications.
+        if opt.notify is False:
+          notify = 'NONE'
+        else:
+          key = 'review.%s.uploadnotify' % branch.project.remote.review
+          notify = branch.project.config.GetString(key)
+
         destination = opt.dest_branch or branch.project.dest_branch
 
         # Make sure our local branch is not setup to track a different remote branch
         merge_branch = self._GetMergeBranch(branch.project)
         if destination:
-          full_dest = 'refs/heads/%s' % destination
+          full_dest = destination
+          if not full_dest.startswith(R_HEADS):
+            full_dest = R_HEADS + full_dest
+
           if not opt.dest_branch and merge_branch and merge_branch != full_dest:
             print('merge branch %s does not match destination branch %s'
                   % (merge_branch, full_dest))
@@ -392,10 +453,12 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
             continue
 
         branch.UploadForReview(people,
+                               dryrun=opt.dryrun,
                                auto_topic=opt.auto_topic,
-                               draft=opt.draft,
+                               hashtags=hashtags,
+                               labels=labels,
                                private=opt.private,
-                               notify=None if opt.notify else 'NONE',
+                               notify=notify,
                                wip=opt.wip,
                                dest_branch=destination,
                                validate_certs=opt.validate_certs,
@@ -418,18 +481,18 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
           else:
             fmt = '\n       (%s)'
           print(('[FAILED] %-15s %-15s' + fmt) % (
-                 branch.project.relpath + '/', \
-                 branch.name, \
-                 str(branch.error)),
-                 file=sys.stderr)
+              branch.project.relpath + '/',
+              branch.name,
+              str(branch.error)),
+              file=sys.stderr)
       print()
 
     for branch in todo:
       if branch.uploaded:
         print('[OK    ] %-15s %s' % (
-               branch.project.relpath + '/',
-               branch.name),
-               file=sys.stderr)
+            branch.project.relpath + '/',
+            branch.name),
+            file=sys.stderr)
 
     if have_errors:
       sys.exit(1)
@@ -437,68 +500,72 @@ Gerrit Code Review:  https://www.gerritcodereview.com/
   def _GetMergeBranch(self, project):
     p = GitCommand(project,
                    ['rev-parse', '--abbrev-ref', 'HEAD'],
-                   capture_stdout = True,
-                   capture_stderr = True)
+                   capture_stdout=True,
+                   capture_stderr=True)
     p.Wait()
     local_branch = p.stdout.strip()
     p = GitCommand(project,
                    ['config', '--get', 'branch.%s.merge' % local_branch],
-                   capture_stdout = True,
-                   capture_stderr = True)
+                   capture_stdout=True,
+                   capture_stderr=True)
     p.Wait()
     merge_branch = p.stdout.strip()
     return merge_branch
 
+  @staticmethod
+  def _GatherOne(opt, project):
+    """Figure out the upload status for |project|."""
+    if opt.current_branch:
+      cbr = project.CurrentBranch
+      up_branch = project.GetUploadableBranch(cbr)
+      avail = [up_branch] if up_branch else None
+    else:
+      avail = project.GetUploadableBranches(opt.branch)
+    return (project, avail)
+
   def Execute(self, opt, args):
-    project_list = self.GetProjects(args)
-    pending = []
-    reviewers = []
-    cc = []
-    branch = None
-
-    if opt.branch:
-      branch = opt.branch
-
-    for project in project_list:
-      if opt.current_branch:
-        cbr = project.CurrentBranch
-        up_branch = project.GetUploadableBranch(cbr)
-        if up_branch:
-          avail = [up_branch]
-        else:
-          avail = None
-          print('ERROR: Current branch (%s) not uploadable. '
-                'You may be able to type '
-                '"git branch --set-upstream-to m/master" to fix '
-                'your branch.' % str(cbr),
+    projects = self.GetProjects(args)
+
+    def _ProcessResults(_pool, _out, results):
+      pending = []
+      for result in results:
+        project, avail = result
+        if avail is None:
+          print('repo: error: %s: Unable to upload branch "%s". '
+                'You might be able to fix the branch by running:\n'
+                '  git branch --set-upstream-to m/%s' %
+                (project.relpath, project.CurrentBranch, self.manifest.branch),
                 file=sys.stderr)
-      else:
-        avail = project.GetUploadableBranches(branch)
-      if avail:
-        pending.append((project, avail))
+        elif avail:
+          pending.append(result)
+      return pending
+
+    pending = self.ExecuteInParallel(
+        opt.jobs,
+        functools.partial(self._GatherOne, opt),
+        projects,
+        callback=_ProcessResults)
 
     if not pending:
-      print("no branches ready for upload", file=sys.stderr)
-      return
-
-    if not opt.bypass_hooks:
-      hook = RepoHook('pre-upload', self.manifest.repo_hooks_project,
-                      self.manifest.topdir,
-                      self.manifest.manifestProject.GetRemote('origin').url,
-                      abort_if_user_denies=True)
-      pending_proj_names = [project.name for (project, available) in pending]
-      pending_worktrees = [project.worktree for (project, available) in pending]
-      try:
-        hook.Run(opt.allow_all_hooks, project_list=pending_proj_names,
-                 worktree_list=pending_worktrees)
-      except HookError as e:
-        print("ERROR: %s" % str(e), file=sys.stderr)
-        return
-
-    if opt.reviewers:
-      reviewers = _SplitEmails(opt.reviewers)
-    if opt.cc:
-      cc = _SplitEmails(opt.cc)
+      if opt.branch is None:
+        print('repo: error: no branches ready for upload', file=sys.stderr)
+      else:
+        print('repo: error: no branches named "%s" ready for upload' %
+              (opt.branch,), file=sys.stderr)
+      return 1
+
+    pending_proj_names = [project.name for (project, available) in pending]
+    pending_worktrees = [project.worktree for (project, available) in pending]
+    hook = RepoHook.FromSubcmd(
+        hook_type='pre-upload', manifest=self.manifest,
+        opt=opt, abort_if_user_denies=True)
+    if not hook.Run(
+        project_list=pending_proj_names,
+        worktree_list=pending_worktrees):
+      return 1
+
+    reviewers = _SplitEmails(opt.reviewers) if opt.reviewers else []
+    cc = _SplitEmails(opt.cc) if opt.cc else []
     people = (reviewers, cc)
 
     if len(pending) == 1 and len(pending[0][1]) == 1:
diff --git a/subcmds/version.py b/subcmds/version.py
index 761172b7..09b053ea 100644
--- a/subcmds/version.py
+++ b/subcmds/version.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2009 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,17 +12,20 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
+import platform
 import sys
+
 from command import Command, MirrorSafeCommand
 from git_command import git, RepoSourceVersion, user_agent
 from git_refs import HEAD
+from wrapper import Wrapper
+
 
 class Version(Command, MirrorSafeCommand):
   wrapper_version = None
   wrapper_path = None
 
-  common = False
+  COMMON = False
   helpSummary = "Display the version of repo"
   helpUsage = """
 %prog
@@ -33,16 +34,19 @@ class Version(Command, MirrorSafeCommand):
   def Execute(self, opt, args):
     rp = self.manifest.repoProject
     rem = rp.GetRemote(rp.remote.name)
+    branch = rp.GetBranch('default')
 
     # These might not be the same.  Report them both.
     src_ver = RepoSourceVersion()
     rp_ver = rp.bare_git.describe(HEAD)
     print('repo version %s' % rp_ver)
     print('       (from %s)' % rem.url)
+    print('       (tracking %s)' % branch.merge)
+    print('       (%s)' % rp.bare_git.log('-1', '--format=%cD', HEAD))
 
-    if Version.wrapper_path is not None:
-      print('repo launcher version %s' % Version.wrapper_version)
-      print('       (from %s)' % Version.wrapper_path)
+    if self.wrapper_path is not None:
+      print('repo launcher version %s' % self.wrapper_version)
+      print('       (from %s)' % self.wrapper_path)
 
       if src_ver != rp_ver:
         print('       (currently at %s)' % src_ver)
@@ -51,3 +55,12 @@ class Version(Command, MirrorSafeCommand):
     print('git %s' % git.version_tuple().full)
     print('git User-Agent %s' % user_agent.git)
     print('Python %s' % sys.version)
+    uname = platform.uname()
+    if sys.version_info.major < 3:
+      # Python 3 returns a named tuple, but Python 2 is simpler.
+      print(uname)
+    else:
+      print('OS %s %s (%s)' % (uname.system, uname.release, uname.version))
+      print('CPU %s (%s)' %
+            (uname.machine, uname.processor if uname.processor else 'unknown'))
+    print('Bug reports:', Wrapper().BUG_URL)
diff --git a/tests/fixtures/test.gitconfig b/tests/fixtures/test.gitconfig
index 3c573c9e..b178cf60 100644
--- a/tests/fixtures/test.gitconfig
+++ b/tests/fixtures/test.gitconfig
@@ -1,3 +1,23 @@
 [section]
         empty
         nonempty = true
+        boolinvalid = oops
+        booltrue = true
+        boolfalse = false
+        intinvalid = oops
+        inthex = 0x10
+        inthexk = 0x10k
+        int = 10
+        intk = 10k
+        intm = 10m
+        intg = 10g
+[repo "syncstate.main"]
+        synctime = 2021-09-14T17:23:43.537338Z
+        version = 1
+[repo "syncstate.sys"]
+        argv = ['/usr/bin/pytest-3']
+[repo "syncstate.superproject"]
+        test = false
+[repo "syncstate.options"]
+        verbose = true
+        mpupdate = false
diff --git a/tests/test_editor.py b/tests/test_editor.py
index fbcfcdbd..cfd4f5ed 100644
--- a/tests/test_editor.py
+++ b/tests/test_editor.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2019 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,8 +14,6 @@
 
 """Unittests for the editor.py module."""
 
-from __future__ import print_function
-
 import unittest
 
 from editor import Editor
diff --git a/tests/test_error.py b/tests/test_error.py
new file mode 100644
index 00000000..82b00c24
--- /dev/null
+++ b/tests/test_error.py
@@ -0,0 +1,53 @@
+# Copyright 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for the error.py module."""
+
+import inspect
+import pickle
+import unittest
+
+import error
+
+
+class PickleTests(unittest.TestCase):
+  """Make sure all our custom exceptions can be pickled."""
+
+  def getExceptions(self):
+    """Return all our custom exceptions."""
+    for name in dir(error):
+      cls = getattr(error, name)
+      if isinstance(cls, type) and issubclass(cls, Exception):
+        yield cls
+
+  def testExceptionLookup(self):
+    """Make sure our introspection logic works."""
+    classes = list(self.getExceptions())
+    self.assertIn(error.HookError, classes)
+    # Don't assert the exact number to avoid being a change-detector test.
+    self.assertGreater(len(classes), 10)
+
+  def testPickle(self):
+    """Try to pickle all the exceptions."""
+    for cls in self.getExceptions():
+      args = inspect.getfullargspec(cls.__init__).args[1:]
+      obj = cls(*args)
+      p = pickle.dumps(obj)
+      try:
+        newobj = pickle.loads(p)
+      except Exception as e:  # pylint: disable=broad-except
+        self.fail('Class %s is unable to be pickled: %s\n'
+                  'Incomplete super().__init__(...) call?' % (cls, e))
+      self.assertIsInstance(newobj, cls)
+      self.assertEqual(str(obj), str(newobj))
diff --git a/tests/test_git_command.py b/tests/test_git_command.py
index 51171a32..93300a6f 100644
--- a/tests/test_git_command.py
+++ b/tests/test_git_command.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright 2019 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,12 +14,16 @@
 
 """Unittests for the git_command.py module."""
 
-from __future__ import print_function
-
 import re
 import unittest
 
+try:
+  from unittest import mock
+except ImportError:
+  import mock
+
 import git_command
+import wrapper
 
 
 class GitCallUnitTest(unittest.TestCase):
@@ -35,7 +37,7 @@ class GitCallUnitTest(unittest.TestCase):
     # We don't dive too deep into the values here to avoid having to update
     # whenever git versions change.  We do check relative to this min version
     # as this is what `repo` itself requires via MIN_GIT_VERSION.
-    MIN_GIT_VERSION = (1, 7, 2)
+    MIN_GIT_VERSION = (2, 10, 2)
     self.assertTrue(isinstance(ver.major, int))
     self.assertTrue(isinstance(ver.minor, int))
     self.assertTrue(isinstance(ver.micro, int))
@@ -76,3 +78,45 @@ class UserAgentUnitTest(unittest.TestCase):
     # the general form.
     m = re.match(r'^git/[^ ]+ ([^ ]+) git-repo/[^ ]+', ua)
     self.assertIsNotNone(m)
+
+
+class GitRequireTests(unittest.TestCase):
+  """Test the git_require helper."""
+
+  def setUp(self):
+    ver = wrapper.GitVersion(1, 2, 3, 4)
+    mock.patch.object(git_command.git, 'version_tuple', return_value=ver).start()
+
+  def tearDown(self):
+    mock.patch.stopall()
+
+  def test_older_nonfatal(self):
+    """Test non-fatal require calls with old versions."""
+    self.assertFalse(git_command.git_require((2,)))
+    self.assertFalse(git_command.git_require((1, 3)))
+    self.assertFalse(git_command.git_require((1, 2, 4)))
+    self.assertFalse(git_command.git_require((1, 2, 3, 5)))
+
+  def test_newer_nonfatal(self):
+    """Test non-fatal require calls with newer versions."""
+    self.assertTrue(git_command.git_require((0,)))
+    self.assertTrue(git_command.git_require((1, 0)))
+    self.assertTrue(git_command.git_require((1, 2, 0)))
+    self.assertTrue(git_command.git_require((1, 2, 3, 0)))
+
+  def test_equal_nonfatal(self):
+    """Test require calls with equal values."""
+    self.assertTrue(git_command.git_require((1, 2, 3, 4), fail=False))
+    self.assertTrue(git_command.git_require((1, 2, 3, 4), fail=True))
+
+  def test_older_fatal(self):
+    """Test fatal require calls with old versions."""
+    with self.assertRaises(SystemExit) as e:
+      git_command.git_require((2,), fail=True)
+      self.assertNotEqual(0, e.code)
+
+  def test_older_fatal_msg(self):
+    """Test fatal require calls with old versions and message."""
+    with self.assertRaises(SystemExit) as e:
+      git_command.git_require((2,), fail=True, msg='so sad')
+      self.assertNotEqual(0, e.code)
diff --git a/tests/test_git_config.py b/tests/test_git_config.py
index b735f27f..faf12a2e 100644
--- a/tests/test_git_config.py
+++ b/tests/test_git_config.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2009 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,21 +14,22 @@
 
 """Unittests for the git_config.py module."""
 
-from __future__ import print_function
-
 import os
+import tempfile
 import unittest
 
 import git_config
 
+
 def fixture(*paths):
   """Return a path relative to test/fixtures.
   """
   return os.path.join(os.path.dirname(__file__), 'fixtures', *paths)
 
-class GitConfigUnitTest(unittest.TestCase):
-  """Tests the GitConfig class.
-  """
+
+class GitConfigReadOnlyTests(unittest.TestCase):
+  """Read-only tests of the GitConfig class."""
+
   def setUp(self):
     """Create a GitConfig object using the test.gitconfig fixture.
     """
@@ -68,5 +67,126 @@ class GitConfigUnitTest(unittest.TestCase):
     val = config.GetString('empty')
     self.assertEqual(val, None)
 
+  def test_GetBoolean_undefined(self):
+    """Test GetBoolean on key that doesn't exist."""
+    self.assertIsNone(self.config.GetBoolean('section.missing'))
+
+  def test_GetBoolean_invalid(self):
+    """Test GetBoolean on invalid boolean value."""
+    self.assertIsNone(self.config.GetBoolean('section.boolinvalid'))
+
+  def test_GetBoolean_true(self):
+    """Test GetBoolean on valid true boolean."""
+    self.assertTrue(self.config.GetBoolean('section.booltrue'))
+
+  def test_GetBoolean_false(self):
+    """Test GetBoolean on valid false boolean."""
+    self.assertFalse(self.config.GetBoolean('section.boolfalse'))
+
+  def test_GetInt_undefined(self):
+    """Test GetInt on key that doesn't exist."""
+    self.assertIsNone(self.config.GetInt('section.missing'))
+
+  def test_GetInt_invalid(self):
+    """Test GetInt on invalid integer value."""
+    self.assertIsNone(self.config.GetBoolean('section.intinvalid'))
+
+  def test_GetInt_valid(self):
+    """Test GetInt on valid integers."""
+    TESTS = (
+        ('inthex', 16),
+        ('inthexk', 16384),
+        ('int', 10),
+        ('intk', 10240),
+        ('intm', 10485760),
+        ('intg', 10737418240),
+    )
+    for key, value in TESTS:
+      self.assertEqual(value, self.config.GetInt('section.%s' % (key,)))
+
+  def test_GetSyncAnalysisStateData(self):
+    """Test config entries with a sync state analysis data."""
+    superproject_logging_data = {}
+    superproject_logging_data['test'] = False
+    options = type('options', (object,), {})()
+    options.verbose = 'true'
+    options.mp_update = 'false'
+    TESTS = (
+        ('superproject.test', 'false'),
+        ('options.verbose', 'true'),
+        ('options.mpupdate', 'false'),
+        ('main.version', '1'),
+    )
+    self.config.UpdateSyncAnalysisState(options, superproject_logging_data)
+    sync_data = self.config.GetSyncAnalysisStateData()
+    for key, value in TESTS:
+      self.assertEqual(sync_data[f'{git_config.SYNC_STATE_PREFIX}{key}'], value)
+    self.assertTrue(sync_data[f'{git_config.SYNC_STATE_PREFIX}main.synctime'])
+
+
+class GitConfigReadWriteTests(unittest.TestCase):
+  """Read/write tests of the GitConfig class."""
+
+  def setUp(self):
+    self.tmpfile = tempfile.NamedTemporaryFile()
+    self.config = self.get_config()
+
+  def get_config(self):
+    """Get a new GitConfig instance."""
+    return git_config.GitConfig(self.tmpfile.name)
+
+  def test_SetString(self):
+    """Test SetString behavior."""
+    # Set a value.
+    self.assertIsNone(self.config.GetString('foo.bar'))
+    self.config.SetString('foo.bar', 'val')
+    self.assertEqual('val', self.config.GetString('foo.bar'))
+
+    # Make sure the value was actually written out.
+    config = self.get_config()
+    self.assertEqual('val', config.GetString('foo.bar'))
+
+    # Update the value.
+    self.config.SetString('foo.bar', 'valll')
+    self.assertEqual('valll', self.config.GetString('foo.bar'))
+    config = self.get_config()
+    self.assertEqual('valll', config.GetString('foo.bar'))
+
+    # Delete the value.
+    self.config.SetString('foo.bar', None)
+    self.assertIsNone(self.config.GetString('foo.bar'))
+    config = self.get_config()
+    self.assertIsNone(config.GetString('foo.bar'))
+
+  def test_SetBoolean(self):
+    """Test SetBoolean behavior."""
+    # Set a true value.
+    self.assertIsNone(self.config.GetBoolean('foo.bar'))
+    for val in (True, 1):
+      self.config.SetBoolean('foo.bar', val)
+      self.assertTrue(self.config.GetBoolean('foo.bar'))
+
+    # Make sure the value was actually written out.
+    config = self.get_config()
+    self.assertTrue(config.GetBoolean('foo.bar'))
+    self.assertEqual('true', config.GetString('foo.bar'))
+
+    # Set a false value.
+    for val in (False, 0):
+      self.config.SetBoolean('foo.bar', val)
+      self.assertFalse(self.config.GetBoolean('foo.bar'))
+
+    # Make sure the value was actually written out.
+    config = self.get_config()
+    self.assertFalse(config.GetBoolean('foo.bar'))
+    self.assertEqual('false', config.GetString('foo.bar'))
+
+    # Delete the value.
+    self.config.SetBoolean('foo.bar', None)
+    self.assertIsNone(self.config.GetBoolean('foo.bar'))
+    config = self.get_config()
+    self.assertIsNone(config.GetBoolean('foo.bar'))
+
+
 if __name__ == '__main__':
   unittest.main()
diff --git a/tests/test_git_superproject.py b/tests/test_git_superproject.py
new file mode 100644
index 00000000..a24fc7f0
--- /dev/null
+++ b/tests/test_git_superproject.py
@@ -0,0 +1,376 @@
+# Copyright (C) 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for the git_superproject.py module."""
+
+import json
+import os
+import platform
+import tempfile
+import unittest
+from unittest import mock
+
+import git_superproject
+import git_trace2_event_log
+import manifest_xml
+import platform_utils
+from test_manifest_xml import sort_attributes
+
+
+class SuperprojectTestCase(unittest.TestCase):
+  """TestCase for the Superproject module."""
+
+  PARENT_SID_KEY = 'GIT_TRACE2_PARENT_SID'
+  PARENT_SID_VALUE = 'parent_sid'
+  SELF_SID_REGEX = r'repo-\d+T\d+Z-.*'
+  FULL_SID_REGEX = r'^%s/%s' % (PARENT_SID_VALUE, SELF_SID_REGEX)
+
+  def setUp(self):
+    """Set up superproject every time."""
+    self.tempdir = tempfile.mkdtemp(prefix='repo_tests')
+    self.repodir = os.path.join(self.tempdir, '.repo')
+    self.manifest_file = os.path.join(
+        self.repodir, manifest_xml.MANIFEST_FILE_NAME)
+    os.mkdir(self.repodir)
+    self.platform = platform.system().lower()
+
+    # By default we initialize with the expected case where
+    # repo launches us (so GIT_TRACE2_PARENT_SID is set).
+    env = {
+        self.PARENT_SID_KEY: self.PARENT_SID_VALUE,
+    }
+    self.git_event_log = git_trace2_event_log.EventLog(env=env)
+
+    # The manifest parsing really wants a git repo currently.
+    gitdir = os.path.join(self.repodir, 'manifests.git')
+    os.mkdir(gitdir)
+    with open(os.path.join(gitdir, 'config'), 'w') as fp:
+      fp.write("""[remote "origin"]
+        url = https://localhost:0/manifest
+""")
+
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <superproject name="superproject"/>
+  <project path="art" name="platform/art" groups="notdefault,platform-""" + self.platform + """
+  " /></manifest>
+""")
+    self._superproject = git_superproject.Superproject(manifest, self.repodir,
+                                                       self.git_event_log)
+
+  def tearDown(self):
+    """Tear down superproject every time."""
+    platform_utils.rmtree(self.tempdir)
+
+  def getXmlManifest(self, data):
+    """Helper to initialize a manifest for testing."""
+    with open(self.manifest_file, 'w') as fp:
+      fp.write(data)
+    return manifest_xml.XmlManifest(self.repodir, self.manifest_file)
+
+  def verifyCommonKeys(self, log_entry, expected_event_name, full_sid=True):
+    """Helper function to verify common event log keys."""
+    self.assertIn('event', log_entry)
+    self.assertIn('sid', log_entry)
+    self.assertIn('thread', log_entry)
+    self.assertIn('time', log_entry)
+
+    # Do basic data format validation.
+    self.assertEqual(expected_event_name, log_entry['event'])
+    if full_sid:
+      self.assertRegex(log_entry['sid'], self.FULL_SID_REGEX)
+    else:
+      self.assertRegex(log_entry['sid'], self.SELF_SID_REGEX)
+    self.assertRegex(log_entry['time'], r'^\d+-\d+-\d+T\d+:\d+:\d+\.\d+Z$')
+
+  def readLog(self, log_path):
+    """Helper function to read log data into a list."""
+    log_data = []
+    with open(log_path, mode='rb') as f:
+      for line in f:
+        log_data.append(json.loads(line))
+    return log_data
+
+  def verifyErrorEvent(self):
+    """Helper to verify that error event is written."""
+
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      log_path = self.git_event_log.Write(path=tempdir)
+      self.log_data = self.readLog(log_path)
+
+    self.assertEqual(len(self.log_data), 2)
+    error_event = self.log_data[1]
+    self.verifyCommonKeys(self.log_data[0], expected_event_name='version')
+    self.verifyCommonKeys(error_event, expected_event_name='error')
+    # Check for 'error' event specific fields.
+    self.assertIn('msg', error_event)
+    self.assertIn('fmt', error_event)
+
+  def test_superproject_get_superproject_no_superproject(self):
+    """Test with no url."""
+    manifest = self.getXmlManifest("""
+<manifest>
+</manifest>
+""")
+    superproject = git_superproject.Superproject(manifest, self.repodir, self.git_event_log)
+    # Test that exit condition is false when there is no superproject tag.
+    sync_result = superproject.Sync()
+    self.assertFalse(sync_result.success)
+    self.assertFalse(sync_result.fatal)
+    self.verifyErrorEvent()
+
+  def test_superproject_get_superproject_invalid_url(self):
+    """Test with an invalid url."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="localhost" />
+  <default remote="test-remote" revision="refs/heads/main" />
+  <superproject name="superproject"/>
+</manifest>
+""")
+    superproject = git_superproject.Superproject(manifest, self.repodir, self.git_event_log)
+    sync_result = superproject.Sync()
+    self.assertFalse(sync_result.success)
+    self.assertTrue(sync_result.fatal)
+
+  def test_superproject_get_superproject_invalid_branch(self):
+    """Test with an invalid branch."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="localhost" />
+  <default remote="test-remote" revision="refs/heads/main" />
+  <superproject name="superproject"/>
+</manifest>
+""")
+    self._superproject = git_superproject.Superproject(manifest, self.repodir,
+                                                       self.git_event_log)
+    with mock.patch.object(self._superproject, '_branch', 'junk'):
+      sync_result = self._superproject.Sync()
+      self.assertFalse(sync_result.success)
+      self.assertTrue(sync_result.fatal)
+
+  def test_superproject_get_superproject_mock_init(self):
+    """Test with _Init failing."""
+    with mock.patch.object(self._superproject, '_Init', return_value=False):
+      sync_result = self._superproject.Sync()
+      self.assertFalse(sync_result.success)
+      self.assertTrue(sync_result.fatal)
+
+  def test_superproject_get_superproject_mock_fetch(self):
+    """Test with _Fetch failing."""
+    with mock.patch.object(self._superproject, '_Init', return_value=True):
+      os.mkdir(self._superproject._superproject_path)
+      with mock.patch.object(self._superproject, '_Fetch', return_value=False):
+        sync_result = self._superproject.Sync()
+        self.assertFalse(sync_result.success)
+        self.assertTrue(sync_result.fatal)
+
+  def test_superproject_get_all_project_commit_ids_mock_ls_tree(self):
+    """Test with LsTree being a mock."""
+    data = ('120000 blob 158258bdf146f159218e2b90f8b699c4d85b5804\tAndroid.bp\x00'
+            '160000 commit 2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea\tart\x00'
+            '160000 commit e9d25da64d8d365dbba7c8ee00fe8c4473fe9a06\tbootable/recovery\x00'
+            '120000 blob acc2cbdf438f9d2141f0ae424cec1d8fc4b5d97f\tbootstrap.bash\x00'
+            '160000 commit ade9b7a0d874e25fff4bf2552488825c6f111928\tbuild/bazel\x00')
+    with mock.patch.object(self._superproject, '_Init', return_value=True):
+      with mock.patch.object(self._superproject, '_Fetch', return_value=True):
+        with mock.patch.object(self._superproject, '_LsTree', return_value=data):
+          commit_ids_result = self._superproject._GetAllProjectsCommitIds()
+          self.assertEqual(commit_ids_result.commit_ids, {
+              'art': '2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea',
+              'bootable/recovery': 'e9d25da64d8d365dbba7c8ee00fe8c4473fe9a06',
+              'build/bazel': 'ade9b7a0d874e25fff4bf2552488825c6f111928'
+          })
+          self.assertFalse(commit_ids_result.fatal)
+
+  def test_superproject_write_manifest_file(self):
+    """Test with writing manifest to a file after setting revisionId."""
+    self.assertEqual(len(self._superproject._manifest.projects), 1)
+    project = self._superproject._manifest.projects[0]
+    project.SetRevisionId('ABCDEF')
+    # Create temporary directory so that it can write the file.
+    os.mkdir(self._superproject._superproject_path)
+    manifest_path = self._superproject._WriteManifestFile()
+    self.assertIsNotNone(manifest_path)
+    with open(manifest_path, 'r') as fp:
+      manifest_xml_data = fp.read()
+    self.assertEqual(
+        sort_attributes(manifest_xml_data),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="default-remote"/>'
+        '<default remote="default-remote" revision="refs/heads/main"/>'
+        '<project groups="notdefault,platform-' + self.platform + '" '
+        'name="platform/art" path="art" revision="ABCDEF" upstream="refs/heads/main"/>'
+        '<superproject name="superproject"/>'
+        '</manifest>')
+
+  def test_superproject_update_project_revision_id(self):
+    """Test with LsTree being a mock."""
+    self.assertEqual(len(self._superproject._manifest.projects), 1)
+    projects = self._superproject._manifest.projects
+    data = ('160000 commit 2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea\tart\x00'
+            '160000 commit e9d25da64d8d365dbba7c8ee00fe8c4473fe9a06\tbootable/recovery\x00')
+    with mock.patch.object(self._superproject, '_Init', return_value=True):
+      with mock.patch.object(self._superproject, '_Fetch', return_value=True):
+        with mock.patch.object(self._superproject,
+                               '_LsTree',
+                               return_value=data):
+          # Create temporary directory so that it can write the file.
+          os.mkdir(self._superproject._superproject_path)
+          update_result = self._superproject.UpdateProjectsRevisionId(projects)
+          self.assertIsNotNone(update_result.manifest_path)
+          self.assertFalse(update_result.fatal)
+          with open(update_result.manifest_path, 'r') as fp:
+            manifest_xml_data = fp.read()
+          self.assertEqual(
+              sort_attributes(manifest_xml_data),
+              '<?xml version="1.0" ?><manifest>'
+              '<remote fetch="http://localhost" name="default-remote"/>'
+              '<default remote="default-remote" revision="refs/heads/main"/>'
+              '<project groups="notdefault,platform-' + self.platform + '" '
+              'name="platform/art" path="art" '
+              'revision="2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea" upstream="refs/heads/main"/>'
+              '<superproject name="superproject"/>'
+              '</manifest>')
+
+  def test_superproject_update_project_revision_id_no_superproject_tag(self):
+    """Test update of commit ids of a manifest without superproject tag."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="test-name"/>
+</manifest>
+""")
+    self.maxDiff = None
+    self._superproject = git_superproject.Superproject(manifest, self.repodir,
+                                                       self.git_event_log)
+    self.assertEqual(len(self._superproject._manifest.projects), 1)
+    projects = self._superproject._manifest.projects
+    project = projects[0]
+    project.SetRevisionId('ABCDEF')
+    update_result = self._superproject.UpdateProjectsRevisionId(projects)
+    self.assertIsNone(update_result.manifest_path)
+    self.assertFalse(update_result.fatal)
+    self.verifyErrorEvent()
+    self.assertEqual(
+        sort_attributes(manifest.ToXml().toxml()),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="default-remote"/>'
+        '<default remote="default-remote" revision="refs/heads/main"/>'
+        '<project name="test-name" revision="ABCDEF" upstream="refs/heads/main"/>'
+        '</manifest>')
+
+  def test_superproject_update_project_revision_id_from_local_manifest_group(self):
+    """Test update of commit ids of a manifest that have local manifest no superproject group."""
+    local_group = manifest_xml.LOCAL_MANIFEST_GROUP_PREFIX + ':local'
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <remote name="goog" fetch="http://localhost2" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <superproject name="superproject"/>
+  <project path="vendor/x" name="platform/vendor/x" remote="goog"
+           groups=\"""" + local_group + """
+         " revision="master-with-vendor" clone-depth="1" />
+  <project path="art" name="platform/art" groups="notdefault,platform-""" + self.platform + """
+  " /></manifest>
+""")
+    self.maxDiff = None
+    self._superproject = git_superproject.Superproject(manifest, self.repodir,
+                                                       self.git_event_log)
+    self.assertEqual(len(self._superproject._manifest.projects), 2)
+    projects = self._superproject._manifest.projects
+    data = ('160000 commit 2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea\tart\x00')
+    with mock.patch.object(self._superproject, '_Init', return_value=True):
+      with mock.patch.object(self._superproject, '_Fetch', return_value=True):
+        with mock.patch.object(self._superproject,
+                               '_LsTree',
+                               return_value=data):
+          # Create temporary directory so that it can write the file.
+          os.mkdir(self._superproject._superproject_path)
+          update_result = self._superproject.UpdateProjectsRevisionId(projects)
+          self.assertIsNotNone(update_result.manifest_path)
+          self.assertFalse(update_result.fatal)
+          with open(update_result.manifest_path, 'r') as fp:
+            manifest_xml_data = fp.read()
+          # Verify platform/vendor/x's project revision hasn't changed.
+          self.assertEqual(
+              sort_attributes(manifest_xml_data),
+              '<?xml version="1.0" ?><manifest>'
+              '<remote fetch="http://localhost" name="default-remote"/>'
+              '<remote fetch="http://localhost2" name="goog"/>'
+              '<default remote="default-remote" revision="refs/heads/main"/>'
+              '<project groups="notdefault,platform-' + self.platform + '" '
+              'name="platform/art" path="art" '
+              'revision="2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea" upstream="refs/heads/main"/>'
+              '<project clone-depth="1" groups="' + local_group + '" '
+              'name="platform/vendor/x" path="vendor/x" remote="goog" '
+              'revision="master-with-vendor"/>'
+              '<superproject name="superproject"/>'
+              '</manifest>')
+
+  def test_superproject_update_project_revision_id_with_pinned_manifest(self):
+    """Test update of commit ids of a pinned manifest."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <superproject name="superproject"/>
+  <project path="vendor/x" name="platform/vendor/x" revision="" />
+  <project path="vendor/y" name="platform/vendor/y"
+           revision="52d3c9f7c107839ece2319d077de0cd922aa9d8f" />
+  <project path="art" name="platform/art" groups="notdefault,platform-""" + self.platform + """
+  " /></manifest>
+""")
+    self.maxDiff = None
+    self._superproject = git_superproject.Superproject(manifest, self.repodir,
+                                                       self.git_event_log)
+    self.assertEqual(len(self._superproject._manifest.projects), 3)
+    projects = self._superproject._manifest.projects
+    data = ('160000 commit 2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea\tart\x00'
+            '160000 commit e9d25da64d8d365dbba7c8ee00fe8c4473fe9a06\tvendor/x\x00')
+    with mock.patch.object(self._superproject, '_Init', return_value=True):
+      with mock.patch.object(self._superproject, '_Fetch', return_value=True):
+        with mock.patch.object(self._superproject,
+                               '_LsTree',
+                               return_value=data):
+          # Create temporary directory so that it can write the file.
+          os.mkdir(self._superproject._superproject_path)
+          update_result = self._superproject.UpdateProjectsRevisionId(projects)
+          self.assertIsNotNone(update_result.manifest_path)
+          self.assertFalse(update_result.fatal)
+          with open(update_result.manifest_path, 'r') as fp:
+            manifest_xml_data = fp.read()
+          # Verify platform/vendor/x's project revision hasn't changed.
+          self.assertEqual(
+              sort_attributes(manifest_xml_data),
+              '<?xml version="1.0" ?><manifest>'
+              '<remote fetch="http://localhost" name="default-remote"/>'
+              '<default remote="default-remote" revision="refs/heads/main"/>'
+              '<project groups="notdefault,platform-' + self.platform + '" '
+              'name="platform/art" path="art" '
+              'revision="2c2724cb36cd5a9cec6c852c681efc3b7c6b86ea" upstream="refs/heads/main"/>'
+              '<project name="platform/vendor/x" path="vendor/x" '
+              'revision="e9d25da64d8d365dbba7c8ee00fe8c4473fe9a06" upstream="refs/heads/main"/>'
+              '<project name="platform/vendor/y" path="vendor/y" '
+              'revision="52d3c9f7c107839ece2319d077de0cd922aa9d8f"/>'
+              '<superproject name="superproject"/>'
+              '</manifest>')
+
+
+if __name__ == '__main__':
+  unittest.main()
diff --git a/tests/test_git_trace2_event_log.py b/tests/test_git_trace2_event_log.py
new file mode 100644
index 00000000..89dcfb92
--- /dev/null
+++ b/tests/test_git_trace2_event_log.py
@@ -0,0 +1,329 @@
+# Copyright (C) 2020 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for the git_trace2_event_log.py module."""
+
+import json
+import os
+import tempfile
+import unittest
+from unittest import mock
+
+import git_trace2_event_log
+
+
+class EventLogTestCase(unittest.TestCase):
+  """TestCase for the EventLog module."""
+
+  PARENT_SID_KEY = 'GIT_TRACE2_PARENT_SID'
+  PARENT_SID_VALUE = 'parent_sid'
+  SELF_SID_REGEX = r'repo-\d+T\d+Z-.*'
+  FULL_SID_REGEX = r'^%s/%s' % (PARENT_SID_VALUE, SELF_SID_REGEX)
+
+  def setUp(self):
+    """Load the event_log module every time."""
+    self._event_log_module = None
+    # By default we initialize with the expected case where
+    # repo launches us (so GIT_TRACE2_PARENT_SID is set).
+    env = {
+        self.PARENT_SID_KEY: self.PARENT_SID_VALUE,
+    }
+    self._event_log_module = git_trace2_event_log.EventLog(env=env)
+    self._log_data = None
+
+  def verifyCommonKeys(self, log_entry, expected_event_name=None, full_sid=True):
+    """Helper function to verify common event log keys."""
+    self.assertIn('event', log_entry)
+    self.assertIn('sid', log_entry)
+    self.assertIn('thread', log_entry)
+    self.assertIn('time', log_entry)
+
+    # Do basic data format validation.
+    if expected_event_name:
+      self.assertEqual(expected_event_name, log_entry['event'])
+    if full_sid:
+      self.assertRegex(log_entry['sid'], self.FULL_SID_REGEX)
+    else:
+      self.assertRegex(log_entry['sid'], self.SELF_SID_REGEX)
+    self.assertRegex(log_entry['time'], r'^\d+-\d+-\d+T\d+:\d+:\d+\.\d+Z$')
+
+  def readLog(self, log_path):
+    """Helper function to read log data into a list."""
+    log_data = []
+    with open(log_path, mode='rb') as f:
+      for line in f:
+        log_data.append(json.loads(line))
+    return log_data
+
+  def remove_prefix(self, s, prefix):
+    """Return a copy string after removing |prefix| from |s|, if present or the original string."""
+    if s.startswith(prefix):
+        return s[len(prefix):]
+    else:
+        return s
+
+  def test_initial_state_with_parent_sid(self):
+    """Test initial state when 'GIT_TRACE2_PARENT_SID' is set by parent."""
+    self.assertRegex(self._event_log_module.full_sid, self.FULL_SID_REGEX)
+
+  def test_initial_state_no_parent_sid(self):
+    """Test initial state when 'GIT_TRACE2_PARENT_SID' is not set."""
+    # Setup an empty environment dict (no parent sid).
+    self._event_log_module = git_trace2_event_log.EventLog(env={})
+    self.assertRegex(self._event_log_module.full_sid, self.SELF_SID_REGEX)
+
+  def test_version_event(self):
+    """Test 'version' event data is valid.
+
+    Verify that the 'version' event is written even when no other
+    events are addded.
+
+    Expected event log:
+    <version event>
+    """
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      log_path = self._event_log_module.Write(path=tempdir)
+      self._log_data = self.readLog(log_path)
+
+    # A log with no added events should only have the version entry.
+    self.assertEqual(len(self._log_data), 1)
+    version_event = self._log_data[0]
+    self.verifyCommonKeys(version_event, expected_event_name='version')
+    # Check for 'version' event specific fields.
+    self.assertIn('evt', version_event)
+    self.assertIn('exe', version_event)
+    # Verify "evt" version field is a string.
+    self.assertIsInstance(version_event['evt'], str)
+
+  def test_start_event(self):
+    """Test and validate 'start' event data is valid.
+
+    Expected event log:
+    <version event>
+    <start event>
+    """
+    self._event_log_module.StartEvent()
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      log_path = self._event_log_module.Write(path=tempdir)
+      self._log_data = self.readLog(log_path)
+
+    self.assertEqual(len(self._log_data), 2)
+    start_event = self._log_data[1]
+    self.verifyCommonKeys(self._log_data[0], expected_event_name='version')
+    self.verifyCommonKeys(start_event, expected_event_name='start')
+    # Check for 'start' event specific fields.
+    self.assertIn('argv', start_event)
+    self.assertTrue(isinstance(start_event['argv'], list))
+
+  def test_exit_event_result_none(self):
+    """Test 'exit' event data is valid when result is None.
+
+    We expect None result to be converted to 0 in the exit event data.
+
+    Expected event log:
+    <version event>
+    <exit event>
+    """
+    self._event_log_module.ExitEvent(None)
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      log_path = self._event_log_module.Write(path=tempdir)
+      self._log_data = self.readLog(log_path)
+
+    self.assertEqual(len(self._log_data), 2)
+    exit_event = self._log_data[1]
+    self.verifyCommonKeys(self._log_data[0], expected_event_name='version')
+    self.verifyCommonKeys(exit_event, expected_event_name='exit')
+    # Check for 'exit' event specific fields.
+    self.assertIn('code', exit_event)
+    # 'None' result should convert to 0 (successful) return code.
+    self.assertEqual(exit_event['code'], 0)
+
+  def test_exit_event_result_integer(self):
+    """Test 'exit' event data is valid when result is an integer.
+
+    Expected event log:
+    <version event>
+    <exit event>
+    """
+    self._event_log_module.ExitEvent(2)
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      log_path = self._event_log_module.Write(path=tempdir)
+      self._log_data = self.readLog(log_path)
+
+    self.assertEqual(len(self._log_data), 2)
+    exit_event = self._log_data[1]
+    self.verifyCommonKeys(self._log_data[0], expected_event_name='version')
+    self.verifyCommonKeys(exit_event, expected_event_name='exit')
+    # Check for 'exit' event specific fields.
+    self.assertIn('code', exit_event)
+    self.assertEqual(exit_event['code'], 2)
+
+  def test_command_event(self):
+    """Test and validate 'command' event data is valid.
+
+    Expected event log:
+    <version event>
+    <command event>
+    """
+    name = 'repo'
+    subcommands = ['init' 'this']
+    self._event_log_module.CommandEvent(name='repo', subcommands=subcommands)
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      log_path = self._event_log_module.Write(path=tempdir)
+      self._log_data = self.readLog(log_path)
+
+    self.assertEqual(len(self._log_data), 2)
+    command_event = self._log_data[1]
+    self.verifyCommonKeys(self._log_data[0], expected_event_name='version')
+    self.verifyCommonKeys(command_event, expected_event_name='command')
+    # Check for 'command' event specific fields.
+    self.assertIn('name', command_event)
+    self.assertIn('subcommands', command_event)
+    self.assertEqual(command_event['name'], name)
+    self.assertEqual(command_event['subcommands'], subcommands)
+
+  def test_def_params_event_repo_config(self):
+    """Test 'def_params' event data outputs only repo config keys.
+
+    Expected event log:
+    <version event>
+    <def_param event>
+    <def_param event>
+    """
+    config = {
+        'git.foo': 'bar',
+        'repo.partialclone': 'true',
+        'repo.partialclonefilter': 'blob:none',
+    }
+    self._event_log_module.DefParamRepoEvents(config)
+
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      log_path = self._event_log_module.Write(path=tempdir)
+      self._log_data = self.readLog(log_path)
+
+    self.assertEqual(len(self._log_data), 3)
+    def_param_events = self._log_data[1:]
+    self.verifyCommonKeys(self._log_data[0], expected_event_name='version')
+
+    for event in def_param_events:
+      self.verifyCommonKeys(event, expected_event_name='def_param')
+      # Check for 'def_param' event specific fields.
+      self.assertIn('param', event)
+      self.assertIn('value', event)
+      self.assertTrue(event['param'].startswith('repo.'))
+
+  def test_def_params_event_no_repo_config(self):
+    """Test 'def_params' event data won't output non-repo config keys.
+
+    Expected event log:
+    <version event>
+    """
+    config = {
+        'git.foo': 'bar',
+        'git.core.foo2': 'baz',
+    }
+    self._event_log_module.DefParamRepoEvents(config)
+
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      log_path = self._event_log_module.Write(path=tempdir)
+      self._log_data = self.readLog(log_path)
+
+    self.assertEqual(len(self._log_data), 1)
+    self.verifyCommonKeys(self._log_data[0], expected_event_name='version')
+
+  def test_data_event_config(self):
+    """Test 'data' event data outputs all config keys.
+
+    Expected event log:
+    <version event>
+    <data event>
+    <data event>
+    """
+    config = {
+        'git.foo': 'bar',
+        'repo.partialclone': 'false',
+        'repo.syncstate.superproject.hassuperprojecttag': 'true',
+        'repo.syncstate.superproject.sys.argv': ['--', 'sync', 'protobuf'],
+    }
+    prefix_value = 'prefix'
+    self._event_log_module.LogDataConfigEvents(config, prefix_value)
+
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      log_path = self._event_log_module.Write(path=tempdir)
+      self._log_data = self.readLog(log_path)
+
+    self.assertEqual(len(self._log_data), 5)
+    data_events = self._log_data[1:]
+    self.verifyCommonKeys(self._log_data[0], expected_event_name='version')
+
+    for event in data_events:
+      self.verifyCommonKeys(event)
+      # Check for 'data' event specific fields.
+      self.assertIn('key', event)
+      self.assertIn('value', event)
+      key = event['key']
+      key = self.remove_prefix(key, f'{prefix_value}/')
+      value = event['value']
+      self.assertEqual(self._event_log_module.GetDataEventName(value), event['event'])
+      self.assertTrue(key in config and value == config[key])
+
+  def test_error_event(self):
+    """Test and validate 'error' event data is valid.
+
+    Expected event log:
+    <version event>
+    <error event>
+    """
+    msg = 'invalid option: --cahced'
+    fmt = 'invalid option: %s'
+    self._event_log_module.ErrorEvent(msg, fmt)
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      log_path = self._event_log_module.Write(path=tempdir)
+      self._log_data = self.readLog(log_path)
+
+    self.assertEqual(len(self._log_data), 2)
+    error_event = self._log_data[1]
+    self.verifyCommonKeys(self._log_data[0], expected_event_name='version')
+    self.verifyCommonKeys(error_event, expected_event_name='error')
+    # Check for 'error' event specific fields.
+    self.assertIn('msg', error_event)
+    self.assertIn('fmt', error_event)
+    self.assertEqual(error_event['msg'], msg)
+    self.assertEqual(error_event['fmt'], fmt)
+
+  def test_write_with_filename(self):
+    """Test Write() with a path to a file exits with None."""
+    self.assertIsNone(self._event_log_module.Write(path='path/to/file'))
+
+  def test_write_with_git_config(self):
+    """Test Write() uses the git config path when 'git config' call succeeds."""
+    with tempfile.TemporaryDirectory(prefix='event_log_tests') as tempdir:
+      with mock.patch.object(self._event_log_module,
+                             '_GetEventTargetPath', return_value=tempdir):
+        self.assertEqual(os.path.dirname(self._event_log_module.Write()), tempdir)
+
+  def test_write_no_git_config(self):
+    """Test Write() with no git config variable present exits with None."""
+    with mock.patch.object(self._event_log_module,
+                           '_GetEventTargetPath', return_value=None):
+      self.assertIsNone(self._event_log_module.Write())
+
+  def test_write_non_string(self):
+    """Test Write() with non-string type for |path| throws TypeError."""
+    with self.assertRaises(TypeError):
+      self._event_log_module.Write(path=1234)
+
+
+if __name__ == '__main__':
+  unittest.main()
diff --git a/tests/test_hooks.py b/tests/test_hooks.py
new file mode 100644
index 00000000..6632b3e5
--- /dev/null
+++ b/tests/test_hooks.py
@@ -0,0 +1,55 @@
+# Copyright (C) 2019 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for the hooks.py module."""
+
+import hooks
+import unittest
+
+class RepoHookShebang(unittest.TestCase):
+  """Check shebang parsing in RepoHook."""
+
+  def test_no_shebang(self):
+    """Lines w/out shebangs should be rejected."""
+    DATA = (
+        '',
+        '#\n# foo\n',
+        '# Bad shebang in script\n#!/foo\n'
+    )
+    for data in DATA:
+      self.assertIsNone(hooks.RepoHook._ExtractInterpFromShebang(data))
+
+  def test_direct_interp(self):
+    """Lines whose shebang points directly to the interpreter."""
+    DATA = (
+        ('#!/foo', '/foo'),
+        ('#! /foo', '/foo'),
+        ('#!/bin/foo ', '/bin/foo'),
+        ('#! /usr/foo ', '/usr/foo'),
+        ('#! /usr/foo -args', '/usr/foo'),
+    )
+    for shebang, interp in DATA:
+      self.assertEqual(hooks.RepoHook._ExtractInterpFromShebang(shebang),
+                       interp)
+
+  def test_env_interp(self):
+    """Lines whose shebang launches through `env`."""
+    DATA = (
+        ('#!/usr/bin/env foo', 'foo'),
+        ('#!/bin/env foo', 'foo'),
+        ('#! /bin/env /bin/foo ', '/bin/foo'),
+    )
+    for shebang, interp in DATA:
+      self.assertEqual(hooks.RepoHook._ExtractInterpFromShebang(shebang),
+                       interp)
diff --git a/tests/test_manifest_xml.py b/tests/test_manifest_xml.py
new file mode 100644
index 00000000..cb3eb855
--- /dev/null
+++ b/tests/test_manifest_xml.py
@@ -0,0 +1,845 @@
+# Copyright (C) 2019 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for the manifest_xml.py module."""
+
+import os
+import platform
+import re
+import shutil
+import tempfile
+import unittest
+import xml.dom.minidom
+
+import error
+import manifest_xml
+
+
+# Invalid paths that we don't want in the filesystem.
+INVALID_FS_PATHS = (
+    '',
+    '.',
+    '..',
+    '../',
+    './',
+    './/',
+    'foo/',
+    './foo',
+    '../foo',
+    'foo/./bar',
+    'foo/../../bar',
+    '/foo',
+    './../foo',
+    '.git/foo',
+    # Check case folding.
+    '.GIT/foo',
+    'blah/.git/foo',
+    '.repo/foo',
+    '.repoconfig',
+    # Block ~ due to 8.3 filenames on Windows filesystems.
+    '~',
+    'foo~',
+    'blah/foo~',
+    # Block Unicode characters that get normalized out by filesystems.
+    u'foo\u200Cbar',
+    # Block newlines.
+    'f\n/bar',
+    'f\r/bar',
+)
+
+# Make sure platforms that use path separators (e.g. Windows) are also
+# rejected properly.
+if os.path.sep != '/':
+  INVALID_FS_PATHS += tuple(x.replace('/', os.path.sep) for x in INVALID_FS_PATHS)
+
+
+def sort_attributes(manifest):
+  """Sort the attributes of all elements alphabetically.
+
+  This is needed because different versions of the toxml() function from
+  xml.dom.minidom outputs the attributes of elements in different orders.
+  Before Python 3.8 they were output alphabetically, later versions preserve
+  the order specified by the user.
+
+  Args:
+    manifest: String containing an XML manifest.
+
+  Returns:
+    The XML manifest with the attributes of all elements sorted alphabetically.
+  """
+  new_manifest = ''
+  # This will find every element in the XML manifest, whether they have
+  # attributes or not. This simplifies recreating the manifest below.
+  matches = re.findall(r'(<[/?]?[a-z-]+\s*)((?:\S+?="[^"]+"\s*?)*)(\s*[/?]?>)', manifest)
+  for head, attrs, tail in matches:
+    m = re.findall(r'\S+?="[^"]+"', attrs)
+    new_manifest += head + ' '.join(sorted(m)) + tail
+  return new_manifest
+
+
+class ManifestParseTestCase(unittest.TestCase):
+  """TestCase for parsing manifests."""
+
+  def setUp(self):
+    self.tempdir = tempfile.mkdtemp(prefix='repo_tests')
+    self.repodir = os.path.join(self.tempdir, '.repo')
+    self.manifest_dir = os.path.join(self.repodir, 'manifests')
+    self.manifest_file = os.path.join(
+        self.repodir, manifest_xml.MANIFEST_FILE_NAME)
+    self.local_manifest_dir = os.path.join(
+        self.repodir, manifest_xml.LOCAL_MANIFESTS_DIR_NAME)
+    os.mkdir(self.repodir)
+    os.mkdir(self.manifest_dir)
+
+    # The manifest parsing really wants a git repo currently.
+    gitdir = os.path.join(self.repodir, 'manifests.git')
+    os.mkdir(gitdir)
+    with open(os.path.join(gitdir, 'config'), 'w') as fp:
+      fp.write("""[remote "origin"]
+        url = https://localhost:0/manifest
+""")
+
+  def tearDown(self):
+    shutil.rmtree(self.tempdir, ignore_errors=True)
+
+  def getXmlManifest(self, data):
+    """Helper to initialize a manifest for testing."""
+    with open(self.manifest_file, 'w') as fp:
+      fp.write(data)
+    return manifest_xml.XmlManifest(self.repodir, self.manifest_file)
+
+  @staticmethod
+  def encodeXmlAttr(attr):
+    """Encode |attr| using XML escape rules."""
+    return attr.replace('\r', '&#x000d;').replace('\n', '&#x000a;')
+
+
+class ManifestValidateFilePaths(unittest.TestCase):
+  """Check _ValidateFilePaths helper.
+
+  This doesn't access a real filesystem.
+  """
+
+  def check_both(self, *args):
+    manifest_xml.XmlManifest._ValidateFilePaths('copyfile', *args)
+    manifest_xml.XmlManifest._ValidateFilePaths('linkfile', *args)
+
+  def test_normal_path(self):
+    """Make sure good paths are accepted."""
+    self.check_both('foo', 'bar')
+    self.check_both('foo/bar', 'bar')
+    self.check_both('foo', 'bar/bar')
+    self.check_both('foo/bar', 'bar/bar')
+
+  def test_symlink_targets(self):
+    """Some extra checks for symlinks."""
+    def check(*args):
+      manifest_xml.XmlManifest._ValidateFilePaths('linkfile', *args)
+
+    # We allow symlinks to end in a slash since we allow them to point to dirs
+    # in general.  Technically the slash isn't necessary.
+    check('foo/', 'bar')
+    # We allow a single '.' to get a reference to the project itself.
+    check('.', 'bar')
+
+  def test_bad_paths(self):
+    """Make sure bad paths (src & dest) are rejected."""
+    for path in INVALID_FS_PATHS:
+      self.assertRaises(
+          error.ManifestInvalidPathError, self.check_both, path, 'a')
+      self.assertRaises(
+          error.ManifestInvalidPathError, self.check_both, 'a', path)
+
+
+class ValueTests(unittest.TestCase):
+  """Check utility parsing code."""
+
+  def _get_node(self, text):
+    return xml.dom.minidom.parseString(text).firstChild
+
+  def test_bool_default(self):
+    """Check XmlBool default handling."""
+    node = self._get_node('<node/>')
+    self.assertIsNone(manifest_xml.XmlBool(node, 'a'))
+    self.assertIsNone(manifest_xml.XmlBool(node, 'a', None))
+    self.assertEqual(123, manifest_xml.XmlBool(node, 'a', 123))
+
+    node = self._get_node('<node a=""/>')
+    self.assertIsNone(manifest_xml.XmlBool(node, 'a'))
+
+  def test_bool_invalid(self):
+    """Check XmlBool invalid handling."""
+    node = self._get_node('<node a="moo"/>')
+    self.assertEqual(123, manifest_xml.XmlBool(node, 'a', 123))
+
+  def test_bool_true(self):
+    """Check XmlBool true values."""
+    for value in ('yes', 'true', '1'):
+      node = self._get_node('<node a="%s"/>' % (value,))
+      self.assertTrue(manifest_xml.XmlBool(node, 'a'))
+
+  def test_bool_false(self):
+    """Check XmlBool false values."""
+    for value in ('no', 'false', '0'):
+      node = self._get_node('<node a="%s"/>' % (value,))
+      self.assertFalse(manifest_xml.XmlBool(node, 'a'))
+
+  def test_int_default(self):
+    """Check XmlInt default handling."""
+    node = self._get_node('<node/>')
+    self.assertIsNone(manifest_xml.XmlInt(node, 'a'))
+    self.assertIsNone(manifest_xml.XmlInt(node, 'a', None))
+    self.assertEqual(123, manifest_xml.XmlInt(node, 'a', 123))
+
+    node = self._get_node('<node a=""/>')
+    self.assertIsNone(manifest_xml.XmlInt(node, 'a'))
+
+  def test_int_good(self):
+    """Check XmlInt numeric handling."""
+    for value in (-1, 0, 1, 50000):
+      node = self._get_node('<node a="%s"/>' % (value,))
+      self.assertEqual(value, manifest_xml.XmlInt(node, 'a'))
+
+  def test_int_invalid(self):
+    """Check XmlInt invalid handling."""
+    with self.assertRaises(error.ManifestParseError):
+      node = self._get_node('<node a="xx"/>')
+      manifest_xml.XmlInt(node, 'a')
+
+
+class XmlManifestTests(ManifestParseTestCase):
+  """Check manifest processing."""
+
+  def test_empty(self):
+    """Parse an 'empty' manifest file."""
+    manifest = self.getXmlManifest(
+        '<?xml version="1.0" encoding="UTF-8"?>'
+        '<manifest></manifest>')
+    self.assertEqual(manifest.remotes, {})
+    self.assertEqual(manifest.projects, [])
+
+  def test_link(self):
+    """Verify Link handling with new names."""
+    manifest = manifest_xml.XmlManifest(self.repodir, self.manifest_file)
+    with open(os.path.join(self.manifest_dir, 'foo.xml'), 'w') as fp:
+      fp.write('<manifest></manifest>')
+    manifest.Link('foo.xml')
+    with open(self.manifest_file) as fp:
+      self.assertIn('<include name="foo.xml" />', fp.read())
+
+  def test_toxml_empty(self):
+    """Verify the ToXml() helper."""
+    manifest = self.getXmlManifest(
+        '<?xml version="1.0" encoding="UTF-8"?>'
+        '<manifest></manifest>')
+    self.assertEqual(manifest.ToXml().toxml(), '<?xml version="1.0" ?><manifest/>')
+
+  def test_todict_empty(self):
+    """Verify the ToDict() helper."""
+    manifest = self.getXmlManifest(
+        '<?xml version="1.0" encoding="UTF-8"?>'
+        '<manifest></manifest>')
+    self.assertEqual(manifest.ToDict(), {})
+
+  def test_repo_hooks(self):
+    """Check repo-hooks settings."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="http://localhost" />
+  <default remote="test-remote" revision="refs/heads/main" />
+  <project name="repohooks" path="src/repohooks"/>
+  <repo-hooks in-project="repohooks" enabled-list="a, b"/>
+</manifest>
+""")
+    self.assertEqual(manifest.repo_hooks_project.name, 'repohooks')
+    self.assertEqual(manifest.repo_hooks_project.enabled_repo_hooks, ['a', 'b'])
+
+  def test_repo_hooks_unordered(self):
+    """Check repo-hooks settings work even if the project def comes second."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="http://localhost" />
+  <default remote="test-remote" revision="refs/heads/main" />
+  <repo-hooks in-project="repohooks" enabled-list="a, b"/>
+  <project name="repohooks" path="src/repohooks"/>
+</manifest>
+""")
+    self.assertEqual(manifest.repo_hooks_project.name, 'repohooks')
+    self.assertEqual(manifest.repo_hooks_project.enabled_repo_hooks, ['a', 'b'])
+
+  def test_unknown_tags(self):
+    """Check superproject settings."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="http://localhost" />
+  <default remote="test-remote" revision="refs/heads/main" />
+  <superproject name="superproject"/>
+  <iankaz value="unknown (possible) future tags are ignored"/>
+  <x-custom-tag>X tags are always ignored</x-custom-tag>
+</manifest>
+""")
+    self.assertEqual(manifest.superproject['name'], 'superproject')
+    self.assertEqual(manifest.superproject['remote'].name, 'test-remote')
+    self.assertEqual(
+        sort_attributes(manifest.ToXml().toxml()),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="test-remote"/>'
+        '<default remote="test-remote" revision="refs/heads/main"/>'
+        '<superproject name="superproject"/>'
+        '</manifest>')
+
+  def test_remote_annotations(self):
+    """Check remote settings."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="http://localhost">
+    <annotation name="foo" value="bar"/>
+  </remote>
+</manifest>
+""")
+    self.assertEqual(manifest.remotes['test-remote'].annotations[0].name, 'foo')
+    self.assertEqual(manifest.remotes['test-remote'].annotations[0].value, 'bar')
+    self.assertEqual(
+        sort_attributes(manifest.ToXml().toxml()),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="test-remote">'
+        '<annotation name="foo" value="bar"/>'
+        '</remote>'
+        '</manifest>')
+
+
+class IncludeElementTests(ManifestParseTestCase):
+  """Tests for <include>."""
+
+  def test_group_levels(self):
+    root_m = os.path.join(self.manifest_dir, 'root.xml')
+    with open(root_m, 'w') as fp:
+      fp.write("""
+<manifest>
+  <remote name="test-remote" fetch="http://localhost" />
+  <default remote="test-remote" revision="refs/heads/main" />
+  <include name="level1.xml" groups="level1-group" />
+  <project name="root-name1" path="root-path1" />
+  <project name="root-name2" path="root-path2" groups="r2g1,r2g2" />
+</manifest>
+""")
+    with open(os.path.join(self.manifest_dir, 'level1.xml'), 'w') as fp:
+      fp.write("""
+<manifest>
+  <include name="level2.xml" groups="level2-group" />
+  <project name="level1-name1" path="level1-path1" />
+</manifest>
+""")
+    with open(os.path.join(self.manifest_dir, 'level2.xml'), 'w') as fp:
+      fp.write("""
+<manifest>
+  <project name="level2-name1" path="level2-path1" groups="l2g1,l2g2" />
+</manifest>
+""")
+    include_m = manifest_xml.XmlManifest(self.repodir, root_m)
+    for proj in include_m.projects:
+      if proj.name == 'root-name1':
+        # Check include group not set on root level proj.
+        self.assertNotIn('level1-group', proj.groups)
+      if proj.name == 'root-name2':
+        # Check root proj group not removed.
+        self.assertIn('r2g1', proj.groups)
+      if proj.name == 'level1-name1':
+        # Check level1 proj has inherited group level 1.
+        self.assertIn('level1-group', proj.groups)
+      if proj.name == 'level2-name1':
+        # Check level2 proj has inherited group levels 1 and 2.
+        self.assertIn('level1-group', proj.groups)
+        self.assertIn('level2-group', proj.groups)
+        # Check level2 proj group not removed.
+        self.assertIn('l2g1', proj.groups)
+
+  def test_allow_bad_name_from_user(self):
+    """Check handling of bad name attribute from the user's input."""
+    def parse(name):
+      name = self.encodeXmlAttr(name)
+      manifest = self.getXmlManifest(f"""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <include name="{name}" />
+</manifest>
+""")
+      # Force the manifest to be parsed.
+      manifest.ToXml()
+
+    # Setup target of the include.
+    target = os.path.join(self.tempdir, 'target.xml')
+    with open(target, 'w') as fp:
+      fp.write('<manifest></manifest>')
+
+    # Include with absolute path.
+    parse(os.path.abspath(target))
+
+    # Include with relative path.
+    parse(os.path.relpath(target, self.manifest_dir))
+
+  def test_bad_name_checks(self):
+    """Check handling of bad name attribute."""
+    def parse(name):
+      name = self.encodeXmlAttr(name)
+      # Setup target of the include.
+      with open(os.path.join(self.manifest_dir, 'target.xml'), 'w') as fp:
+        fp.write(f'<manifest><include name="{name}"/></manifest>')
+
+      manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <include name="target.xml" />
+</manifest>
+""")
+      # Force the manifest to be parsed.
+      manifest.ToXml()
+
+    # Handle empty name explicitly because a different codepath rejects it.
+    with self.assertRaises(error.ManifestParseError):
+      parse('')
+
+    for path in INVALID_FS_PATHS:
+      if not path:
+        continue
+
+      with self.assertRaises(error.ManifestInvalidPathError):
+        parse(path)
+
+
+class ProjectElementTests(ManifestParseTestCase):
+  """Tests for <project>."""
+
+  def test_group(self):
+    """Check project group settings."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="http://localhost" />
+  <default remote="test-remote" revision="refs/heads/main" />
+  <project name="test-name" path="test-path"/>
+  <project name="extras" path="path" groups="g1,g2,g1"/>
+</manifest>
+""")
+    self.assertEqual(len(manifest.projects), 2)
+    # Ordering isn't guaranteed.
+    result = {
+        manifest.projects[0].name: manifest.projects[0].groups,
+        manifest.projects[1].name: manifest.projects[1].groups,
+    }
+    project = manifest.projects[0]
+    self.assertCountEqual(
+        result['test-name'],
+        ['name:test-name', 'all', 'path:test-path'])
+    self.assertCountEqual(
+        result['extras'],
+        ['g1', 'g2', 'g1', 'name:extras', 'all', 'path:path'])
+    groupstr = 'default,platform-' + platform.system().lower()
+    self.assertEqual(groupstr, manifest.GetGroupsStr())
+    groupstr = 'g1,g2,g1'
+    manifest.manifestProject.config.SetString('manifest.groups', groupstr)
+    self.assertEqual(groupstr, manifest.GetGroupsStr())
+
+  def test_set_revision_id(self):
+    """Check setting of project's revisionId."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="test-name"/>
+</manifest>
+""")
+    self.assertEqual(len(manifest.projects), 1)
+    project = manifest.projects[0]
+    project.SetRevisionId('ABCDEF')
+    self.assertEqual(
+        sort_attributes(manifest.ToXml().toxml()),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="default-remote"/>'
+        '<default remote="default-remote" revision="refs/heads/main"/>'
+        '<project name="test-name" revision="ABCDEF" upstream="refs/heads/main"/>'
+        '</manifest>')
+
+  def test_trailing_slash(self):
+    """Check handling of trailing slashes in attributes."""
+    def parse(name, path):
+      name = self.encodeXmlAttr(name)
+      path = self.encodeXmlAttr(path)
+      return self.getXmlManifest(f"""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="{name}" path="{path}" />
+</manifest>
+""")
+
+    manifest = parse('a/path/', 'foo')
+    self.assertEqual(manifest.projects[0].gitdir,
+                     os.path.join(self.tempdir, '.repo/projects/foo.git'))
+    self.assertEqual(manifest.projects[0].objdir,
+                     os.path.join(self.tempdir, '.repo/project-objects/a/path.git'))
+
+    manifest = parse('a/path', 'foo/')
+    self.assertEqual(manifest.projects[0].gitdir,
+                     os.path.join(self.tempdir, '.repo/projects/foo.git'))
+    self.assertEqual(manifest.projects[0].objdir,
+                     os.path.join(self.tempdir, '.repo/project-objects/a/path.git'))
+
+    manifest = parse('a/path', 'foo//////')
+    self.assertEqual(manifest.projects[0].gitdir,
+                     os.path.join(self.tempdir, '.repo/projects/foo.git'))
+    self.assertEqual(manifest.projects[0].objdir,
+                     os.path.join(self.tempdir, '.repo/project-objects/a/path.git'))
+
+  def test_toplevel_path(self):
+    """Check handling of path=. specially."""
+    def parse(name, path):
+      name = self.encodeXmlAttr(name)
+      path = self.encodeXmlAttr(path)
+      return self.getXmlManifest(f"""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="{name}" path="{path}" />
+</manifest>
+""")
+
+    for path in ('.', './', './/', './//'):
+      manifest = parse('server/path', path)
+      self.assertEqual(manifest.projects[0].gitdir,
+                       os.path.join(self.tempdir, '.repo/projects/..git'))
+
+  def test_bad_path_name_checks(self):
+    """Check handling of bad path & name attributes."""
+    def parse(name, path):
+      name = self.encodeXmlAttr(name)
+      path = self.encodeXmlAttr(path)
+      manifest = self.getXmlManifest(f"""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="{name}" path="{path}" />
+</manifest>
+""")
+      # Force the manifest to be parsed.
+      manifest.ToXml()
+
+    # Verify the parser is valid by default to avoid buggy tests below.
+    parse('ok', 'ok')
+
+    # Handle empty name explicitly because a different codepath rejects it.
+    # Empty path is OK because it defaults to the name field.
+    with self.assertRaises(error.ManifestParseError):
+      parse('', 'ok')
+
+    for path in INVALID_FS_PATHS:
+      if not path or path.endswith('/'):
+        continue
+
+      with self.assertRaises(error.ManifestInvalidPathError):
+        parse(path, 'ok')
+
+      # We have a dedicated test for path=".".
+      if path not in {'.'}:
+        with self.assertRaises(error.ManifestInvalidPathError):
+          parse('ok', path)
+
+
+class SuperProjectElementTests(ManifestParseTestCase):
+  """Tests for <superproject>."""
+
+  def test_superproject(self):
+    """Check superproject settings."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="http://localhost" />
+  <default remote="test-remote" revision="refs/heads/main" />
+  <superproject name="superproject"/>
+</manifest>
+""")
+    self.assertEqual(manifest.superproject['name'], 'superproject')
+    self.assertEqual(manifest.superproject['remote'].name, 'test-remote')
+    self.assertEqual(manifest.superproject['remote'].url, 'http://localhost/superproject')
+    self.assertEqual(manifest.superproject['revision'], 'refs/heads/main')
+    self.assertEqual(
+        sort_attributes(manifest.ToXml().toxml()),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="test-remote"/>'
+        '<default remote="test-remote" revision="refs/heads/main"/>'
+        '<superproject name="superproject"/>'
+        '</manifest>')
+
+  def test_superproject_revision(self):
+    """Check superproject settings with a different revision attribute"""
+    self.maxDiff = None
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="http://localhost" />
+  <default remote="test-remote" revision="refs/heads/main" />
+  <superproject name="superproject" revision="refs/heads/stable" />
+</manifest>
+""")
+    self.assertEqual(manifest.superproject['name'], 'superproject')
+    self.assertEqual(manifest.superproject['remote'].name, 'test-remote')
+    self.assertEqual(manifest.superproject['remote'].url, 'http://localhost/superproject')
+    self.assertEqual(manifest.superproject['revision'], 'refs/heads/stable')
+    self.assertEqual(
+        sort_attributes(manifest.ToXml().toxml()),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="test-remote"/>'
+        '<default remote="test-remote" revision="refs/heads/main"/>'
+        '<superproject name="superproject" revision="refs/heads/stable"/>'
+        '</manifest>')
+
+  def test_superproject_revision_default_negative(self):
+    """Check superproject settings with a same revision attribute"""
+    self.maxDiff = None
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="http://localhost" />
+  <default remote="test-remote" revision="refs/heads/stable" />
+  <superproject name="superproject" revision="refs/heads/stable" />
+</manifest>
+""")
+    self.assertEqual(manifest.superproject['name'], 'superproject')
+    self.assertEqual(manifest.superproject['remote'].name, 'test-remote')
+    self.assertEqual(manifest.superproject['remote'].url, 'http://localhost/superproject')
+    self.assertEqual(manifest.superproject['revision'], 'refs/heads/stable')
+    self.assertEqual(
+        sort_attributes(manifest.ToXml().toxml()),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="test-remote"/>'
+        '<default remote="test-remote" revision="refs/heads/stable"/>'
+        '<superproject name="superproject"/>'
+        '</manifest>')
+
+  def test_superproject_revision_remote(self):
+    """Check superproject settings with a same revision attribute"""
+    self.maxDiff = None
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="test-remote" fetch="http://localhost" revision="refs/heads/main" />
+  <default remote="test-remote" />
+  <superproject name="superproject" revision="refs/heads/stable" />
+</manifest>
+""")
+    self.assertEqual(manifest.superproject['name'], 'superproject')
+    self.assertEqual(manifest.superproject['remote'].name, 'test-remote')
+    self.assertEqual(manifest.superproject['remote'].url, 'http://localhost/superproject')
+    self.assertEqual(manifest.superproject['revision'], 'refs/heads/stable')
+    self.assertEqual(
+        sort_attributes(manifest.ToXml().toxml()),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="test-remote" revision="refs/heads/main"/>'
+        '<default remote="test-remote"/>'
+        '<superproject name="superproject" revision="refs/heads/stable"/>'
+        '</manifest>')
+
+  def test_remote(self):
+    """Check superproject settings with a remote."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <remote name="superproject-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <superproject name="platform/superproject" remote="superproject-remote"/>
+</manifest>
+""")
+    self.assertEqual(manifest.superproject['name'], 'platform/superproject')
+    self.assertEqual(manifest.superproject['remote'].name, 'superproject-remote')
+    self.assertEqual(manifest.superproject['remote'].url, 'http://localhost/platform/superproject')
+    self.assertEqual(manifest.superproject['revision'], 'refs/heads/main')
+    self.assertEqual(
+        sort_attributes(manifest.ToXml().toxml()),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="default-remote"/>'
+        '<remote fetch="http://localhost" name="superproject-remote"/>'
+        '<default remote="default-remote" revision="refs/heads/main"/>'
+        '<superproject name="platform/superproject" remote="superproject-remote"/>'
+        '</manifest>')
+
+  def test_defalut_remote(self):
+    """Check superproject settings with a default remote."""
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <superproject name="superproject" remote="default-remote"/>
+</manifest>
+""")
+    self.assertEqual(manifest.superproject['name'], 'superproject')
+    self.assertEqual(manifest.superproject['remote'].name, 'default-remote')
+    self.assertEqual(manifest.superproject['revision'], 'refs/heads/main')
+    self.assertEqual(
+        sort_attributes(manifest.ToXml().toxml()),
+        '<?xml version="1.0" ?><manifest>'
+        '<remote fetch="http://localhost" name="default-remote"/>'
+        '<default remote="default-remote" revision="refs/heads/main"/>'
+        '<superproject name="superproject"/>'
+        '</manifest>')
+
+
+class ContactinfoElementTests(ManifestParseTestCase):
+  """Tests for <contactinfo>."""
+
+  def test_contactinfo(self):
+    """Check contactinfo settings."""
+    bugurl = 'http://localhost/contactinfo'
+    manifest = self.getXmlManifest(f"""
+<manifest>
+  <contactinfo bugurl="{bugurl}"/>
+</manifest>
+""")
+    self.assertEqual(manifest.contactinfo.bugurl, bugurl)
+    self.assertEqual(
+        manifest.ToXml().toxml(),
+        '<?xml version="1.0" ?><manifest>'
+        f'<contactinfo bugurl="{bugurl}"/>'
+        '</manifest>')
+
+
+class DefaultElementTests(ManifestParseTestCase):
+  """Tests for <default>."""
+
+  def test_default(self):
+    """Check default settings."""
+    a = manifest_xml._Default()
+    a.revisionExpr = 'foo'
+    a.remote = manifest_xml._XmlRemote(name='remote')
+    b = manifest_xml._Default()
+    b.revisionExpr = 'bar'
+    self.assertEqual(a, a)
+    self.assertNotEqual(a, b)
+    self.assertNotEqual(b, a.remote)
+    self.assertNotEqual(a, 123)
+    self.assertNotEqual(a, None)
+
+
+class RemoteElementTests(ManifestParseTestCase):
+  """Tests for <remote>."""
+
+  def test_remote(self):
+    """Check remote settings."""
+    a = manifest_xml._XmlRemote(name='foo')
+    a.AddAnnotation('key1', 'value1', 'true')
+    b = manifest_xml._XmlRemote(name='foo')
+    b.AddAnnotation('key2', 'value1', 'true')
+    c = manifest_xml._XmlRemote(name='foo')
+    c.AddAnnotation('key1', 'value2', 'true')
+    d = manifest_xml._XmlRemote(name='foo')
+    d.AddAnnotation('key1', 'value1', 'false')
+    self.assertEqual(a, a)
+    self.assertNotEqual(a, b)
+    self.assertNotEqual(a, c)
+    self.assertNotEqual(a, d)
+    self.assertNotEqual(a, manifest_xml._Default())
+    self.assertNotEqual(a, 123)
+    self.assertNotEqual(a, None)
+
+
+class RemoveProjectElementTests(ManifestParseTestCase):
+  """Tests for <remove-project>."""
+
+  def test_remove_one_project(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="myproject" />
+  <remove-project name="myproject" />
+</manifest>
+""")
+    self.assertEqual(manifest.projects, [])
+
+  def test_remove_one_project_one_remains(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="myproject" />
+  <project name="yourproject" />
+  <remove-project name="myproject" />
+</manifest>
+""")
+
+    self.assertEqual(len(manifest.projects), 1)
+    self.assertEqual(manifest.projects[0].name, 'yourproject')
+
+  def test_remove_one_project_doesnt_exist(self):
+    with self.assertRaises(manifest_xml.ManifestParseError):
+      manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <remove-project name="myproject" />
+</manifest>
+""")
+      manifest.projects
+
+  def test_remove_one_optional_project_doesnt_exist(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <remove-project name="myproject" optional="true" />
+</manifest>
+""")
+    self.assertEqual(manifest.projects, [])
+
+
+class ExtendProjectElementTests(ManifestParseTestCase):
+  """Tests for <extend-project>."""
+
+  def test_extend_project_dest_path_single_match(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="myproject" />
+  <extend-project name="myproject" dest-path="bar" />
+</manifest>
+""")
+    self.assertEqual(len(manifest.projects), 1)
+    self.assertEqual(manifest.projects[0].relpath, 'bar')
+
+  def test_extend_project_dest_path_multi_match(self):
+    with self.assertRaises(manifest_xml.ManifestParseError):
+      manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="myproject" path="x" />
+  <project name="myproject" path="y" />
+  <extend-project name="myproject" dest-path="bar" />
+</manifest>
+""")
+      manifest.projects
+
+  def test_extend_project_dest_path_multi_match_path_specified(self):
+    manifest = self.getXmlManifest("""
+<manifest>
+  <remote name="default-remote" fetch="http://localhost" />
+  <default remote="default-remote" revision="refs/heads/main" />
+  <project name="myproject" path="x" />
+  <project name="myproject" path="y" />
+  <extend-project name="myproject" path="x" dest-path="bar" />
+</manifest>
+""")
+    self.assertEqual(len(manifest.projects), 2)
+    if manifest.projects[0].relpath == 'y':
+      self.assertEqual(manifest.projects[1].relpath, 'bar')
+    else:
+      self.assertEqual(manifest.projects[0].relpath, 'bar')
+      self.assertEqual(manifest.projects[1].relpath, 'y')
diff --git a/tests/test_platform_utils.py b/tests/test_platform_utils.py
new file mode 100644
index 00000000..55b7805c
--- /dev/null
+++ b/tests/test_platform_utils.py
@@ -0,0 +1,50 @@
+# Copyright 2021 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for the platform_utils.py module."""
+
+import os
+import tempfile
+import unittest
+
+import platform_utils
+
+
+class RemoveTests(unittest.TestCase):
+  """Check remove() helper."""
+
+  def testMissingOk(self):
+    """Check missing_ok handling."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+      path = os.path.join(tmpdir, 'test')
+
+      # Should not fail.
+      platform_utils.remove(path, missing_ok=True)
+
+      # Should fail.
+      self.assertRaises(OSError, platform_utils.remove, path)
+      self.assertRaises(OSError, platform_utils.remove, path, missing_ok=False)
+
+      # Should not fail if it exists.
+      open(path, 'w').close()
+      platform_utils.remove(path, missing_ok=True)
+      self.assertFalse(os.path.exists(path))
+
+      open(path, 'w').close()
+      platform_utils.remove(path)
+      self.assertFalse(os.path.exists(path))
+
+      open(path, 'w').close()
+      platform_utils.remove(path, missing_ok=False)
+      self.assertFalse(os.path.exists(path))
diff --git a/tests/test_project.py b/tests/test_project.py
index 77126dff..9b2cc4e9 100644
--- a/tests/test_project.py
+++ b/tests/test_project.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2019 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,8 +14,6 @@
 
 """Unittests for the project.py module."""
 
-from __future__ import print_function
-
 import contextlib
 import os
 import shutil
@@ -25,7 +21,10 @@ import subprocess
 import tempfile
 import unittest
 
+import error
+import git_command
 import git_config
+import platform_utils
 import project
 
 
@@ -36,49 +35,22 @@ def TempGitTree():
   # Python 2 support entirely.
   try:
     tempdir = tempfile.mkdtemp(prefix='repo-tests')
-    subprocess.check_call(['git', 'init'], cwd=tempdir)
+
+    # Tests need to assume, that main is default branch at init,
+    # which is not supported in config until 2.28.
+    cmd = ['git', 'init']
+    if git_command.git_require((2, 28, 0)):
+      cmd += ['--initial-branch=main']
+    else:
+      # Use template dir for init.
+      templatedir = tempfile.mkdtemp(prefix='.test-template')
+      with open(os.path.join(templatedir, 'HEAD'), 'w') as fp:
+        fp.write('ref: refs/heads/main\n')
+      cmd += ['--template', templatedir]
+    subprocess.check_call(cmd, cwd=tempdir)
     yield tempdir
   finally:
-    shutil.rmtree(tempdir)
-
-
-class RepoHookShebang(unittest.TestCase):
-  """Check shebang parsing in RepoHook."""
-
-  def test_no_shebang(self):
-    """Lines w/out shebangs should be rejected."""
-    DATA = (
-        '',
-        '# -*- coding:utf-8 -*-\n',
-        '#\n# foo\n',
-        '# Bad shebang in script\n#!/foo\n'
-    )
-    for data in DATA:
-      self.assertIsNone(project.RepoHook._ExtractInterpFromShebang(data))
-
-  def test_direct_interp(self):
-    """Lines whose shebang points directly to the interpreter."""
-    DATA = (
-        ('#!/foo', '/foo'),
-        ('#! /foo', '/foo'),
-        ('#!/bin/foo ', '/bin/foo'),
-        ('#! /usr/foo ', '/usr/foo'),
-        ('#! /usr/foo -args', '/usr/foo'),
-    )
-    for shebang, interp in DATA:
-      self.assertEqual(project.RepoHook._ExtractInterpFromShebang(shebang),
-                       interp)
-
-  def test_env_interp(self):
-    """Lines whose shebang launches through `env`."""
-    DATA = (
-        ('#!/usr/bin/env foo', 'foo'),
-        ('#!/bin/env foo', 'foo'),
-        ('#! /bin/env /bin/foo ', '/bin/foo'),
-    )
-    for shebang, interp in DATA:
-      self.assertEqual(project.RepoHook._ExtractInterpFromShebang(shebang),
-                       interp)
+    platform_utils.rmtree(tempdir)
 
 
 class FakeProject(object):
@@ -114,7 +86,7 @@ class ReviewableBranchTests(unittest.TestCase):
 
       # Start off with the normal details.
       rb = project.ReviewableBranch(
-          fakeproj, fakeproj.config.GetBranch('work'), 'master')
+          fakeproj, fakeproj.config.GetBranch('work'), 'main')
       self.assertEqual('work', rb.name)
       self.assertEqual(1, len(rb.commits))
       self.assertIn('Del file', rb.commits[0])
@@ -127,10 +99,239 @@ class ReviewableBranchTests(unittest.TestCase):
       self.assertTrue(rb.date)
 
       # Now delete the tracking branch!
-      fakeproj.work_git.branch('-D', 'master')
+      fakeproj.work_git.branch('-D', 'main')
       rb = project.ReviewableBranch(
-          fakeproj, fakeproj.config.GetBranch('work'), 'master')
+          fakeproj, fakeproj.config.GetBranch('work'), 'main')
       self.assertEqual(0, len(rb.commits))
       self.assertFalse(rb.base_exists)
       # Hard to assert anything useful about this.
       self.assertTrue(rb.date)
+
+
+class CopyLinkTestCase(unittest.TestCase):
+  """TestCase for stub repo client checkouts.
+
+  It'll have a layout like:
+    tempdir/          # self.tempdir
+      checkout/       # self.topdir
+        git-project/  # self.worktree
+
+  Attributes:
+    tempdir: A dedicated temporary directory.
+    worktree: The top of the repo client checkout.
+    topdir: The top of a project checkout.
+  """
+
+  def setUp(self):
+    self.tempdir = tempfile.mkdtemp(prefix='repo_tests')
+    self.topdir = os.path.join(self.tempdir, 'checkout')
+    self.worktree = os.path.join(self.topdir, 'git-project')
+    os.makedirs(self.topdir)
+    os.makedirs(self.worktree)
+
+  def tearDown(self):
+    shutil.rmtree(self.tempdir, ignore_errors=True)
+
+  @staticmethod
+  def touch(path):
+    with open(path, 'w'):
+      pass
+
+  def assertExists(self, path, msg=None):
+    """Make sure |path| exists."""
+    if os.path.exists(path):
+      return
+
+    if msg is None:
+      msg = ['path is missing: %s' % path]
+      while path != '/':
+        path = os.path.dirname(path)
+        if not path:
+          # If we're given something like "foo", abort once we get to "".
+          break
+        result = os.path.exists(path)
+        msg.append('\tos.path.exists(%s): %s' % (path, result))
+        if result:
+          msg.append('\tcontents: %r' % os.listdir(path))
+          break
+      msg = '\n'.join(msg)
+
+    raise self.failureException(msg)
+
+
+class CopyFile(CopyLinkTestCase):
+  """Check _CopyFile handling."""
+
+  def CopyFile(self, src, dest):
+    return project._CopyFile(self.worktree, src, self.topdir, dest)
+
+  def test_basic(self):
+    """Basic test of copying a file from a project to the toplevel."""
+    src = os.path.join(self.worktree, 'foo.txt')
+    self.touch(src)
+    cf = self.CopyFile('foo.txt', 'foo')
+    cf._Copy()
+    self.assertExists(os.path.join(self.topdir, 'foo'))
+
+  def test_src_subdir(self):
+    """Copy a file from a subdir of a project."""
+    src = os.path.join(self.worktree, 'bar', 'foo.txt')
+    os.makedirs(os.path.dirname(src))
+    self.touch(src)
+    cf = self.CopyFile('bar/foo.txt', 'new.txt')
+    cf._Copy()
+    self.assertExists(os.path.join(self.topdir, 'new.txt'))
+
+  def test_dest_subdir(self):
+    """Copy a file to a subdir of a checkout."""
+    src = os.path.join(self.worktree, 'foo.txt')
+    self.touch(src)
+    cf = self.CopyFile('foo.txt', 'sub/dir/new.txt')
+    self.assertFalse(os.path.exists(os.path.join(self.topdir, 'sub')))
+    cf._Copy()
+    self.assertExists(os.path.join(self.topdir, 'sub', 'dir', 'new.txt'))
+
+  def test_update(self):
+    """Make sure changed files get copied again."""
+    src = os.path.join(self.worktree, 'foo.txt')
+    dest = os.path.join(self.topdir, 'bar')
+    with open(src, 'w') as f:
+      f.write('1st')
+    cf = self.CopyFile('foo.txt', 'bar')
+    cf._Copy()
+    self.assertExists(dest)
+    with open(dest) as f:
+      self.assertEqual(f.read(), '1st')
+
+    with open(src, 'w') as f:
+      f.write('2nd!')
+    cf._Copy()
+    with open(dest) as f:
+      self.assertEqual(f.read(), '2nd!')
+
+  def test_src_block_symlink(self):
+    """Do not allow reading from a symlinked path."""
+    src = os.path.join(self.worktree, 'foo.txt')
+    sym = os.path.join(self.worktree, 'sym')
+    self.touch(src)
+    platform_utils.symlink('foo.txt', sym)
+    self.assertExists(sym)
+    cf = self.CopyFile('sym', 'foo')
+    self.assertRaises(error.ManifestInvalidPathError, cf._Copy)
+
+  def test_src_block_symlink_traversal(self):
+    """Do not allow reading through a symlink dir."""
+    realfile = os.path.join(self.tempdir, 'file.txt')
+    self.touch(realfile)
+    src = os.path.join(self.worktree, 'bar', 'file.txt')
+    platform_utils.symlink(self.tempdir, os.path.join(self.worktree, 'bar'))
+    self.assertExists(src)
+    cf = self.CopyFile('bar/file.txt', 'foo')
+    self.assertRaises(error.ManifestInvalidPathError, cf._Copy)
+
+  def test_src_block_copy_from_dir(self):
+    """Do not allow copying from a directory."""
+    src = os.path.join(self.worktree, 'dir')
+    os.makedirs(src)
+    cf = self.CopyFile('dir', 'foo')
+    self.assertRaises(error.ManifestInvalidPathError, cf._Copy)
+
+  def test_dest_block_symlink(self):
+    """Do not allow writing to a symlink."""
+    src = os.path.join(self.worktree, 'foo.txt')
+    self.touch(src)
+    platform_utils.symlink('dest', os.path.join(self.topdir, 'sym'))
+    cf = self.CopyFile('foo.txt', 'sym')
+    self.assertRaises(error.ManifestInvalidPathError, cf._Copy)
+
+  def test_dest_block_symlink_traversal(self):
+    """Do not allow writing through a symlink dir."""
+    src = os.path.join(self.worktree, 'foo.txt')
+    self.touch(src)
+    platform_utils.symlink(tempfile.gettempdir(),
+                           os.path.join(self.topdir, 'sym'))
+    cf = self.CopyFile('foo.txt', 'sym/foo.txt')
+    self.assertRaises(error.ManifestInvalidPathError, cf._Copy)
+
+  def test_src_block_copy_to_dir(self):
+    """Do not allow copying to a directory."""
+    src = os.path.join(self.worktree, 'foo.txt')
+    self.touch(src)
+    os.makedirs(os.path.join(self.topdir, 'dir'))
+    cf = self.CopyFile('foo.txt', 'dir')
+    self.assertRaises(error.ManifestInvalidPathError, cf._Copy)
+
+
+class LinkFile(CopyLinkTestCase):
+  """Check _LinkFile handling."""
+
+  def LinkFile(self, src, dest):
+    return project._LinkFile(self.worktree, src, self.topdir, dest)
+
+  def test_basic(self):
+    """Basic test of linking a file from a project into the toplevel."""
+    src = os.path.join(self.worktree, 'foo.txt')
+    self.touch(src)
+    lf = self.LinkFile('foo.txt', 'foo')
+    lf._Link()
+    dest = os.path.join(self.topdir, 'foo')
+    self.assertExists(dest)
+    self.assertTrue(os.path.islink(dest))
+    self.assertEqual(os.path.join('git-project', 'foo.txt'), os.readlink(dest))
+
+  def test_src_subdir(self):
+    """Link to a file in a subdir of a project."""
+    src = os.path.join(self.worktree, 'bar', 'foo.txt')
+    os.makedirs(os.path.dirname(src))
+    self.touch(src)
+    lf = self.LinkFile('bar/foo.txt', 'foo')
+    lf._Link()
+    self.assertExists(os.path.join(self.topdir, 'foo'))
+
+  def test_src_self(self):
+    """Link to the project itself."""
+    dest = os.path.join(self.topdir, 'foo', 'bar')
+    lf = self.LinkFile('.', 'foo/bar')
+    lf._Link()
+    self.assertExists(dest)
+    self.assertEqual(os.path.join('..', 'git-project'), os.readlink(dest))
+
+  def test_dest_subdir(self):
+    """Link a file to a subdir of a checkout."""
+    src = os.path.join(self.worktree, 'foo.txt')
+    self.touch(src)
+    lf = self.LinkFile('foo.txt', 'sub/dir/foo/bar')
+    self.assertFalse(os.path.exists(os.path.join(self.topdir, 'sub')))
+    lf._Link()
+    self.assertExists(os.path.join(self.topdir, 'sub', 'dir', 'foo', 'bar'))
+
+  def test_src_block_relative(self):
+    """Do not allow relative symlinks."""
+    BAD_SOURCES = (
+        './',
+        '..',
+        '../',
+        'foo/.',
+        'foo/./bar',
+        'foo/..',
+        'foo/../foo',
+    )
+    for src in BAD_SOURCES:
+      lf = self.LinkFile(src, 'foo')
+      self.assertRaises(error.ManifestInvalidPathError, lf._Link)
+
+  def test_update(self):
+    """Make sure changed targets get updated."""
+    dest = os.path.join(self.topdir, 'sym')
+
+    src = os.path.join(self.worktree, 'foo.txt')
+    self.touch(src)
+    lf = self.LinkFile('foo.txt', 'sym')
+    lf._Link()
+    self.assertEqual(os.path.join('git-project', 'foo.txt'), os.readlink(dest))
+
+    # Point the symlink somewhere else.
+    os.unlink(dest)
+    platform_utils.symlink(self.tempdir, dest)
+    lf._Link()
+    self.assertEqual(os.path.join('git-project', 'foo.txt'), os.readlink(dest))
diff --git a/tests/test_ssh.py b/tests/test_ssh.py
new file mode 100644
index 00000000..ffb5cb94
--- /dev/null
+++ b/tests/test_ssh.py
@@ -0,0 +1,74 @@
+# Copyright 2019 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for the ssh.py module."""
+
+import multiprocessing
+import subprocess
+import unittest
+from unittest import mock
+
+import ssh
+
+
+class SshTests(unittest.TestCase):
+  """Tests the ssh functions."""
+
+  def test_parse_ssh_version(self):
+    """Check _parse_ssh_version() handling."""
+    ver = ssh._parse_ssh_version('Unknown\n')
+    self.assertEqual(ver, ())
+    ver = ssh._parse_ssh_version('OpenSSH_1.0\n')
+    self.assertEqual(ver, (1, 0))
+    ver = ssh._parse_ssh_version('OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.13, OpenSSL 1.0.1f 6 Jan 2014\n')
+    self.assertEqual(ver, (6, 6, 1))
+    ver = ssh._parse_ssh_version('OpenSSH_7.6p1 Ubuntu-4ubuntu0.3, OpenSSL 1.0.2n  7 Dec 2017\n')
+    self.assertEqual(ver, (7, 6))
+
+  def test_version(self):
+    """Check version() handling."""
+    with mock.patch('ssh._run_ssh_version', return_value='OpenSSH_1.2\n'):
+      self.assertEqual(ssh.version(), (1, 2))
+
+  def test_context_manager_empty(self):
+    """Verify context manager with no clients works correctly."""
+    with multiprocessing.Manager() as manager:
+      with ssh.ProxyManager(manager):
+        pass
+
+  def test_context_manager_child_cleanup(self):
+    """Verify orphaned clients & masters get cleaned up."""
+    with multiprocessing.Manager() as manager:
+      with ssh.ProxyManager(manager) as ssh_proxy:
+        client = subprocess.Popen(['sleep', '964853320'])
+        ssh_proxy.add_client(client)
+        master = subprocess.Popen(['sleep', '964853321'])
+        ssh_proxy.add_master(master)
+    # If the process still exists, these will throw timeout errors.
+    client.wait(0)
+    master.wait(0)
+
+  def test_ssh_sock(self):
+    """Check sock() function."""
+    manager = multiprocessing.Manager()
+    proxy = ssh.ProxyManager(manager)
+    with mock.patch('tempfile.mkdtemp', return_value='/tmp/foo'):
+      # old ssh version uses port
+      with mock.patch('ssh.version', return_value=(6, 6)):
+        self.assertTrue(proxy.sock().endswith('%p'))
+
+      proxy._sock_path = None
+      # new ssh version uses hash
+      with mock.patch('ssh.version', return_value=(6, 7)):
+        self.assertTrue(proxy.sock().endswith('%C'))
diff --git a/tests/test_subcmds.py b/tests/test_subcmds.py
new file mode 100644
index 00000000..bc53051a
--- /dev/null
+++ b/tests/test_subcmds.py
@@ -0,0 +1,73 @@
+# Copyright (C) 2020 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for the subcmds module (mostly __init__.py than subcommands)."""
+
+import optparse
+import unittest
+
+import subcmds
+
+
+class AllCommands(unittest.TestCase):
+  """Check registered all_commands."""
+
+  def test_required_basic(self):
+    """Basic checking of registered commands."""
+    # NB: We don't test all subcommands as we want to avoid "change detection"
+    # tests, so we just look for the most common/important ones here that are
+    # unlikely to ever change.
+    for cmd in {'cherry-pick', 'help', 'init', 'start', 'sync', 'upload'}:
+      self.assertIn(cmd, subcmds.all_commands)
+
+  def test_naming(self):
+    """Verify we don't add things that we shouldn't."""
+    for cmd in subcmds.all_commands:
+      # Reject filename suffixes like "help.py".
+      self.assertNotIn('.', cmd)
+
+      # Make sure all '_' were converted to '-'.
+      self.assertNotIn('_', cmd)
+
+      # Reject internal python paths like "__init__".
+      self.assertFalse(cmd.startswith('__'))
+
+  def test_help_desc_style(self):
+    """Force some consistency in option descriptions.
+
+    Python's optparse & argparse has a few default options like --help.  Their
+    option description text uses lowercase sentence fragments, so enforce our
+    options follow the same style so UI is consistent.
+
+    We enforce:
+    * Text starts with lowercase.
+    * Text doesn't end with period.
+    """
+    for name, cls in subcmds.all_commands.items():
+      cmd = cls()
+      parser = cmd.OptionParser
+      for option in parser.option_list:
+        if option.help == optparse.SUPPRESS_HELP:
+          continue
+
+        c = option.help[0]
+        self.assertEqual(
+            c.lower(), c,
+            msg=f'subcmds/{name}.py: {option.get_opt_string()}: help text '
+                f'should start with lowercase: "{option.help}"')
+
+        self.assertNotEqual(
+            option.help[-1], '.',
+            msg=f'subcmds/{name}.py: {option.get_opt_string()}: help text '
+                f'should not end in a period: "{option.help}"')
diff --git a/tests/test_subcmds_init.py b/tests/test_subcmds_init.py
new file mode 100644
index 00000000..af4346de
--- /dev/null
+++ b/tests/test_subcmds_init.py
@@ -0,0 +1,49 @@
+# Copyright (C) 2020 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Unittests for the subcmds/init.py module."""
+
+import unittest
+
+from subcmds import init
+
+
+class InitCommand(unittest.TestCase):
+  """Check registered all_commands."""
+
+  def setUp(self):
+    self.cmd = init.Init()
+
+  def test_cli_parser_good(self):
+    """Check valid command line options."""
+    ARGV = (
+        [],
+    )
+    for argv in ARGV:
+      opts, args = self.cmd.OptionParser.parse_args(argv)
+      self.cmd.ValidateOptions(opts, args)
+
+  def test_cli_parser_bad(self):
+    """Check invalid command line options."""
+    ARGV = (
+        # Too many arguments.
+        ['url', 'asdf'],
+
+        # Conflicting options.
+        ['--mirror', '--archive'],
+    )
+    for argv in ARGV:
+      opts, args = self.cmd.OptionParser.parse_args(argv)
+      with self.assertRaises(SystemExit):
+        self.cmd.ValidateOptions(opts, args)
diff --git a/tests/test_wrapper.py b/tests/test_wrapper.py
index 8ef8d48d..e9a1f64a 100644
--- a/tests/test_wrapper.py
+++ b/tests/test_wrapper.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2015 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,27 +14,87 @@
 
 """Unittests for the wrapper.py module."""
 
-from __future__ import print_function
-
+import contextlib
+from io import StringIO
 import os
+import re
+import shutil
+import sys
+import tempfile
 import unittest
+from unittest import mock
 
+import git_command
+import main
+import platform_utils
 import wrapper
 
+
+@contextlib.contextmanager
+def TemporaryDirectory():
+  """Create a new empty git checkout for testing."""
+  # TODO(vapier): Convert this to tempfile.TemporaryDirectory once we drop
+  # Python 2 support entirely.
+  try:
+    tempdir = tempfile.mkdtemp(prefix='repo-tests')
+    yield tempdir
+  finally:
+    platform_utils.rmtree(tempdir)
+
+
 def fixture(*paths):
   """Return a path relative to tests/fixtures.
   """
   return os.path.join(os.path.dirname(__file__), 'fixtures', *paths)
 
-class RepoWrapperUnitTest(unittest.TestCase):
-  """Tests helper functions in the repo wrapper
-  """
+
+class RepoWrapperTestCase(unittest.TestCase):
+  """TestCase for the wrapper module."""
+
   def setUp(self):
-    """Load the wrapper module every time
-    """
+    """Load the wrapper module every time."""
     wrapper._wrapper_module = None
     self.wrapper = wrapper.Wrapper()
 
+
+class RepoWrapperUnitTest(RepoWrapperTestCase):
+  """Tests helper functions in the repo wrapper
+  """
+
+  def test_version(self):
+    """Make sure _Version works."""
+    with self.assertRaises(SystemExit) as e:
+      with mock.patch('sys.stdout', new_callable=StringIO) as stdout:
+        with mock.patch('sys.stderr', new_callable=StringIO) as stderr:
+          self.wrapper._Version()
+    self.assertEqual(0, e.exception.code)
+    self.assertEqual('', stderr.getvalue())
+    self.assertIn('repo launcher version', stdout.getvalue())
+
+  def test_python_constraints(self):
+    """The launcher should never require newer than main.py."""
+    self.assertGreaterEqual(main.MIN_PYTHON_VERSION_HARD,
+                            wrapper.MIN_PYTHON_VERSION_HARD)
+    self.assertGreaterEqual(main.MIN_PYTHON_VERSION_SOFT,
+                            wrapper.MIN_PYTHON_VERSION_SOFT)
+    # Make sure the versions are themselves in sync.
+    self.assertGreaterEqual(wrapper.MIN_PYTHON_VERSION_SOFT,
+                            wrapper.MIN_PYTHON_VERSION_HARD)
+
+  def test_init_parser(self):
+    """Make sure 'init' GetParser works."""
+    parser = self.wrapper.GetParser(gitc_init=False)
+    opts, args = parser.parse_args([])
+    self.assertEqual([], args)
+    self.assertIsNone(opts.manifest_url)
+
+  def test_gitc_init_parser(self):
+    """Make sure 'gitc-init' GetParser works."""
+    parser = self.wrapper.GetParser(gitc_init=True)
+    opts, args = parser.parse_args([])
+    self.assertEqual([], args)
+    self.assertIsNone(opts.manifest_file)
+
   def test_get_gitc_manifest_dir_no_gitc(self):
     """
     Test reading a missing gitc config file
@@ -72,9 +130,442 @@ class RepoWrapperUnitTest(unittest.TestCase):
     self.assertEqual(self.wrapper.gitc_parse_clientdir('/gitc/manifest-rw/test/extra'), 'test')
     self.assertEqual(self.wrapper.gitc_parse_clientdir('/test/usr/local/google/gitc/test'), 'test')
     self.assertEqual(self.wrapper.gitc_parse_clientdir('/test/usr/local/google/gitc/test/'), 'test')
-    self.assertEqual(self.wrapper.gitc_parse_clientdir('/test/usr/local/google/gitc/test/extra'), 'test')
+    self.assertEqual(self.wrapper.gitc_parse_clientdir('/test/usr/local/google/gitc/test/extra'),
+                     'test')
     self.assertEqual(self.wrapper.gitc_parse_clientdir('/gitc/manifest-rw/'), None)
     self.assertEqual(self.wrapper.gitc_parse_clientdir('/test/usr/local/google/gitc/'), None)
 
+
+class SetGitTrace2ParentSid(RepoWrapperTestCase):
+  """Check SetGitTrace2ParentSid behavior."""
+
+  KEY = 'GIT_TRACE2_PARENT_SID'
+  VALID_FORMAT = re.compile(r'^repo-[0-9]{8}T[0-9]{6}Z-P[0-9a-f]{8}$')
+
+  def test_first_set(self):
+    """Test env var not yet set."""
+    env = {}
+    self.wrapper.SetGitTrace2ParentSid(env)
+    self.assertIn(self.KEY, env)
+    value = env[self.KEY]
+    self.assertRegex(value, self.VALID_FORMAT)
+
+  def test_append(self):
+    """Test env var is appended."""
+    env = {self.KEY: 'pfx'}
+    self.wrapper.SetGitTrace2ParentSid(env)
+    self.assertIn(self.KEY, env)
+    value = env[self.KEY]
+    self.assertTrue(value.startswith('pfx/'))
+    self.assertRegex(value[4:], self.VALID_FORMAT)
+
+  def test_global_context(self):
+    """Check os.environ gets updated by default."""
+    os.environ.pop(self.KEY, None)
+    self.wrapper.SetGitTrace2ParentSid()
+    self.assertIn(self.KEY, os.environ)
+    value = os.environ[self.KEY]
+    self.assertRegex(value, self.VALID_FORMAT)
+
+
+class RunCommand(RepoWrapperTestCase):
+  """Check run_command behavior."""
+
+  def test_capture(self):
+    """Check capture_output handling."""
+    ret = self.wrapper.run_command(['echo', 'hi'], capture_output=True)
+    self.assertEqual(ret.stdout, 'hi\n')
+
+  def test_check(self):
+    """Check check handling."""
+    self.wrapper.run_command(['true'], check=False)
+    self.wrapper.run_command(['true'], check=True)
+    self.wrapper.run_command(['false'], check=False)
+    with self.assertRaises(self.wrapper.RunError):
+      self.wrapper.run_command(['false'], check=True)
+
+
+class RunGit(RepoWrapperTestCase):
+  """Check run_git behavior."""
+
+  def test_capture(self):
+    """Check capture_output handling."""
+    ret = self.wrapper.run_git('--version')
+    self.assertIn('git', ret.stdout)
+
+  def test_check(self):
+    """Check check handling."""
+    with self.assertRaises(self.wrapper.CloneFailure):
+      self.wrapper.run_git('--version-asdfasdf')
+    self.wrapper.run_git('--version-asdfasdf', check=False)
+
+
+class ParseGitVersion(RepoWrapperTestCase):
+  """Check ParseGitVersion behavior."""
+
+  def test_autoload(self):
+    """Check we can load the version from the live git."""
+    ret = self.wrapper.ParseGitVersion()
+    self.assertIsNotNone(ret)
+
+  def test_bad_ver(self):
+    """Check handling of bad git versions."""
+    ret = self.wrapper.ParseGitVersion(ver_str='asdf')
+    self.assertIsNone(ret)
+
+  def test_normal_ver(self):
+    """Check handling of normal git versions."""
+    ret = self.wrapper.ParseGitVersion(ver_str='git version 2.25.1')
+    self.assertEqual(2, ret.major)
+    self.assertEqual(25, ret.minor)
+    self.assertEqual(1, ret.micro)
+    self.assertEqual('2.25.1', ret.full)
+
+  def test_extended_ver(self):
+    """Check handling of extended distro git versions."""
+    ret = self.wrapper.ParseGitVersion(
+        ver_str='git version 1.30.50.696.g5e7596f4ac-goog')
+    self.assertEqual(1, ret.major)
+    self.assertEqual(30, ret.minor)
+    self.assertEqual(50, ret.micro)
+    self.assertEqual('1.30.50.696.g5e7596f4ac-goog', ret.full)
+
+
+class CheckGitVersion(RepoWrapperTestCase):
+  """Check _CheckGitVersion behavior."""
+
+  def test_unknown(self):
+    """Unknown versions should abort."""
+    with mock.patch.object(self.wrapper, 'ParseGitVersion', return_value=None):
+      with self.assertRaises(self.wrapper.CloneFailure):
+        self.wrapper._CheckGitVersion()
+
+  def test_old(self):
+    """Old versions should abort."""
+    with mock.patch.object(
+        self.wrapper, 'ParseGitVersion',
+        return_value=self.wrapper.GitVersion(1, 0, 0, '1.0.0')):
+      with self.assertRaises(self.wrapper.CloneFailure):
+        self.wrapper._CheckGitVersion()
+
+  def test_new(self):
+    """Newer versions should run fine."""
+    with mock.patch.object(
+        self.wrapper, 'ParseGitVersion',
+        return_value=self.wrapper.GitVersion(100, 0, 0, '100.0.0')):
+      self.wrapper._CheckGitVersion()
+
+
+class Requirements(RepoWrapperTestCase):
+  """Check Requirements handling."""
+
+  def test_missing_file(self):
+    """Don't crash if the file is missing (old version)."""
+    testdir = os.path.dirname(os.path.realpath(__file__))
+    self.assertIsNone(self.wrapper.Requirements.from_dir(testdir))
+    self.assertIsNone(self.wrapper.Requirements.from_file(
+        os.path.join(testdir, 'xxxxxxxxxxxxxxxxxxxxxxxx')))
+
+  def test_corrupt_data(self):
+    """If the file can't be parsed, don't blow up."""
+    self.assertIsNone(self.wrapper.Requirements.from_file(__file__))
+    self.assertIsNone(self.wrapper.Requirements.from_data(b'x'))
+
+  def test_valid_data(self):
+    """Make sure we can parse the file we ship."""
+    self.assertIsNotNone(self.wrapper.Requirements.from_data(b'{}'))
+    rootdir = os.path.dirname(os.path.dirname(os.path.realpath(__file__)))
+    self.assertIsNotNone(self.wrapper.Requirements.from_dir(rootdir))
+    self.assertIsNotNone(self.wrapper.Requirements.from_file(os.path.join(
+        rootdir, 'requirements.json')))
+
+  def test_format_ver(self):
+    """Check format_ver can format."""
+    self.assertEqual('1.2.3', self.wrapper.Requirements._format_ver((1, 2, 3)))
+    self.assertEqual('1', self.wrapper.Requirements._format_ver([1]))
+
+  def test_assert_all_unknown(self):
+    """Check assert_all works with incompatible file."""
+    reqs = self.wrapper.Requirements({})
+    reqs.assert_all()
+
+  def test_assert_all_new_repo(self):
+    """Check assert_all accepts new enough repo."""
+    reqs = self.wrapper.Requirements({'repo': {'hard': [1, 0]}})
+    reqs.assert_all()
+
+  def test_assert_all_old_repo(self):
+    """Check assert_all rejects old repo."""
+    reqs = self.wrapper.Requirements({'repo': {'hard': [99999, 0]}})
+    with self.assertRaises(SystemExit):
+      reqs.assert_all()
+
+  def test_assert_all_new_python(self):
+    """Check assert_all accepts new enough python."""
+    reqs = self.wrapper.Requirements({'python': {'hard': sys.version_info}})
+    reqs.assert_all()
+
+  def test_assert_all_old_python(self):
+    """Check assert_all rejects old python."""
+    reqs = self.wrapper.Requirements({'python': {'hard': [99999, 0]}})
+    with self.assertRaises(SystemExit):
+      reqs.assert_all()
+
+  def test_assert_ver_unknown(self):
+    """Check assert_ver works with incompatible file."""
+    reqs = self.wrapper.Requirements({})
+    reqs.assert_ver('xxx', (1, 0))
+
+  def test_assert_ver_new(self):
+    """Check assert_ver allows new enough versions."""
+    reqs = self.wrapper.Requirements({'git': {'hard': [1, 0], 'soft': [2, 0]}})
+    reqs.assert_ver('git', (1, 0))
+    reqs.assert_ver('git', (1, 5))
+    reqs.assert_ver('git', (2, 0))
+    reqs.assert_ver('git', (2, 5))
+
+  def test_assert_ver_old(self):
+    """Check assert_ver rejects old versions."""
+    reqs = self.wrapper.Requirements({'git': {'hard': [1, 0], 'soft': [2, 0]}})
+    with self.assertRaises(SystemExit):
+      reqs.assert_ver('git', (0, 5))
+
+
+class NeedSetupGnuPG(RepoWrapperTestCase):
+  """Check NeedSetupGnuPG behavior."""
+
+  def test_missing_dir(self):
+    """The ~/.repoconfig tree doesn't exist yet."""
+    with TemporaryDirectory() as tempdir:
+      self.wrapper.home_dot_repo = os.path.join(tempdir, 'foo')
+      self.assertTrue(self.wrapper.NeedSetupGnuPG())
+
+  def test_missing_keyring(self):
+    """The keyring-version file doesn't exist yet."""
+    with TemporaryDirectory() as tempdir:
+      self.wrapper.home_dot_repo = tempdir
+      self.assertTrue(self.wrapper.NeedSetupGnuPG())
+
+  def test_empty_keyring(self):
+    """The keyring-version file exists, but is empty."""
+    with TemporaryDirectory() as tempdir:
+      self.wrapper.home_dot_repo = tempdir
+      with open(os.path.join(tempdir, 'keyring-version'), 'w'):
+        pass
+      self.assertTrue(self.wrapper.NeedSetupGnuPG())
+
+  def test_old_keyring(self):
+    """The keyring-version file exists, but it's old."""
+    with TemporaryDirectory() as tempdir:
+      self.wrapper.home_dot_repo = tempdir
+      with open(os.path.join(tempdir, 'keyring-version'), 'w') as fp:
+        fp.write('1.0\n')
+      self.assertTrue(self.wrapper.NeedSetupGnuPG())
+
+  def test_new_keyring(self):
+    """The keyring-version file exists, and is up-to-date."""
+    with TemporaryDirectory() as tempdir:
+      self.wrapper.home_dot_repo = tempdir
+      with open(os.path.join(tempdir, 'keyring-version'), 'w') as fp:
+        fp.write('1000.0\n')
+      self.assertFalse(self.wrapper.NeedSetupGnuPG())
+
+
+class SetupGnuPG(RepoWrapperTestCase):
+  """Check SetupGnuPG behavior."""
+
+  def test_full(self):
+    """Make sure it works completely."""
+    with TemporaryDirectory() as tempdir:
+      self.wrapper.home_dot_repo = tempdir
+      self.wrapper.gpg_dir = os.path.join(self.wrapper.home_dot_repo, 'gnupg')
+      self.assertTrue(self.wrapper.SetupGnuPG(True))
+      with open(os.path.join(tempdir, 'keyring-version'), 'r') as fp:
+        data = fp.read()
+      self.assertEqual('.'.join(str(x) for x in self.wrapper.KEYRING_VERSION),
+                       data.strip())
+
+
+class VerifyRev(RepoWrapperTestCase):
+  """Check verify_rev behavior."""
+
+  def test_verify_passes(self):
+    """Check when we have a valid signed tag."""
+    desc_result = self.wrapper.RunResult(0, 'v1.0\n', '')
+    gpg_result = self.wrapper.RunResult(0, '', '')
+    with mock.patch.object(self.wrapper, 'run_git',
+                           side_effect=(desc_result, gpg_result)):
+      ret = self.wrapper.verify_rev('/', 'refs/heads/stable', '1234', True)
+      self.assertEqual('v1.0^0', ret)
+
+  def test_unsigned_commit(self):
+    """Check we fall back to signed tag when we have an unsigned commit."""
+    desc_result = self.wrapper.RunResult(0, 'v1.0-10-g1234\n', '')
+    gpg_result = self.wrapper.RunResult(0, '', '')
+    with mock.patch.object(self.wrapper, 'run_git',
+                           side_effect=(desc_result, gpg_result)):
+      ret = self.wrapper.verify_rev('/', 'refs/heads/stable', '1234', True)
+      self.assertEqual('v1.0^0', ret)
+
+  def test_verify_fails(self):
+    """Check we fall back to signed tag when we have an unsigned commit."""
+    desc_result = self.wrapper.RunResult(0, 'v1.0-10-g1234\n', '')
+    gpg_result = Exception
+    with mock.patch.object(self.wrapper, 'run_git',
+                           side_effect=(desc_result, gpg_result)):
+      with self.assertRaises(Exception):
+        self.wrapper.verify_rev('/', 'refs/heads/stable', '1234', True)
+
+
+class GitCheckoutTestCase(RepoWrapperTestCase):
+  """Tests that use a real/small git checkout."""
+
+  GIT_DIR = None
+  REV_LIST = None
+
+  @classmethod
+  def setUpClass(cls):
+    # Create a repo to operate on, but do it once per-class.
+    cls.GIT_DIR = tempfile.mkdtemp(prefix='repo-rev-tests')
+    run_git = wrapper.Wrapper().run_git
+
+    remote = os.path.join(cls.GIT_DIR, 'remote')
+    os.mkdir(remote)
+
+    # Tests need to assume, that main is default branch at init,
+    # which is not supported in config until 2.28.
+    if git_command.git_require((2, 28, 0)):
+      initstr = '--initial-branch=main'
+    else:
+      # Use template dir for init.
+      templatedir = tempfile.mkdtemp(prefix='.test-template')
+      with open(os.path.join(templatedir, 'HEAD'), 'w') as fp:
+        fp.write('ref: refs/heads/main\n')
+      initstr = '--template=' + templatedir
+
+    run_git('init', initstr, cwd=remote)
+    run_git('commit', '--allow-empty', '-minit', cwd=remote)
+    run_git('branch', 'stable', cwd=remote)
+    run_git('tag', 'v1.0', cwd=remote)
+    run_git('commit', '--allow-empty', '-m2nd commit', cwd=remote)
+    cls.REV_LIST = run_git('rev-list', 'HEAD', cwd=remote).stdout.splitlines()
+
+    run_git('init', cwd=cls.GIT_DIR)
+    run_git('fetch', remote, '+refs/heads/*:refs/remotes/origin/*', cwd=cls.GIT_DIR)
+
+  @classmethod
+  def tearDownClass(cls):
+    if not cls.GIT_DIR:
+      return
+
+    shutil.rmtree(cls.GIT_DIR)
+
+
+class ResolveRepoRev(GitCheckoutTestCase):
+  """Check resolve_repo_rev behavior."""
+
+  def test_explicit_branch(self):
+    """Check refs/heads/branch argument."""
+    rrev, lrev = self.wrapper.resolve_repo_rev(self.GIT_DIR, 'refs/heads/stable')
+    self.assertEqual('refs/heads/stable', rrev)
+    self.assertEqual(self.REV_LIST[1], lrev)
+
+    with self.assertRaises(wrapper.CloneFailure):
+      self.wrapper.resolve_repo_rev(self.GIT_DIR, 'refs/heads/unknown')
+
+  def test_explicit_tag(self):
+    """Check refs/tags/tag argument."""
+    rrev, lrev = self.wrapper.resolve_repo_rev(self.GIT_DIR, 'refs/tags/v1.0')
+    self.assertEqual('refs/tags/v1.0', rrev)
+    self.assertEqual(self.REV_LIST[1], lrev)
+
+    with self.assertRaises(wrapper.CloneFailure):
+      self.wrapper.resolve_repo_rev(self.GIT_DIR, 'refs/tags/unknown')
+
+  def test_branch_name(self):
+    """Check branch argument."""
+    rrev, lrev = self.wrapper.resolve_repo_rev(self.GIT_DIR, 'stable')
+    self.assertEqual('refs/heads/stable', rrev)
+    self.assertEqual(self.REV_LIST[1], lrev)
+
+    rrev, lrev = self.wrapper.resolve_repo_rev(self.GIT_DIR, 'main')
+    self.assertEqual('refs/heads/main', rrev)
+    self.assertEqual(self.REV_LIST[0], lrev)
+
+  def test_tag_name(self):
+    """Check tag argument."""
+    rrev, lrev = self.wrapper.resolve_repo_rev(self.GIT_DIR, 'v1.0')
+    self.assertEqual('refs/tags/v1.0', rrev)
+    self.assertEqual(self.REV_LIST[1], lrev)
+
+  def test_full_commit(self):
+    """Check specific commit argument."""
+    commit = self.REV_LIST[0]
+    rrev, lrev = self.wrapper.resolve_repo_rev(self.GIT_DIR, commit)
+    self.assertEqual(commit, rrev)
+    self.assertEqual(commit, lrev)
+
+  def test_partial_commit(self):
+    """Check specific (partial) commit argument."""
+    commit = self.REV_LIST[0][0:20]
+    rrev, lrev = self.wrapper.resolve_repo_rev(self.GIT_DIR, commit)
+    self.assertEqual(self.REV_LIST[0], rrev)
+    self.assertEqual(self.REV_LIST[0], lrev)
+
+  def test_unknown(self):
+    """Check unknown ref/commit argument."""
+    with self.assertRaises(wrapper.CloneFailure):
+      self.wrapper.resolve_repo_rev(self.GIT_DIR, 'boooooooya')
+
+
+class CheckRepoVerify(RepoWrapperTestCase):
+  """Check check_repo_verify behavior."""
+
+  def test_no_verify(self):
+    """Always fail with --no-repo-verify."""
+    self.assertFalse(self.wrapper.check_repo_verify(False))
+
+  def test_gpg_initialized(self):
+    """Should pass if gpg is setup already."""
+    with mock.patch.object(self.wrapper, 'NeedSetupGnuPG', return_value=False):
+      self.assertTrue(self.wrapper.check_repo_verify(True))
+
+  def test_need_gpg_setup(self):
+    """Should pass/fail based on gpg setup."""
+    with mock.patch.object(self.wrapper, 'NeedSetupGnuPG', return_value=True):
+      with mock.patch.object(self.wrapper, 'SetupGnuPG') as m:
+        m.return_value = True
+        self.assertTrue(self.wrapper.check_repo_verify(True))
+
+        m.return_value = False
+        self.assertFalse(self.wrapper.check_repo_verify(True))
+
+
+class CheckRepoRev(GitCheckoutTestCase):
+  """Check check_repo_rev behavior."""
+
+  def test_verify_works(self):
+    """Should pass when verification passes."""
+    with mock.patch.object(self.wrapper, 'check_repo_verify', return_value=True):
+      with mock.patch.object(self.wrapper, 'verify_rev', return_value='12345'):
+        rrev, lrev = self.wrapper.check_repo_rev(self.GIT_DIR, 'stable')
+    self.assertEqual('refs/heads/stable', rrev)
+    self.assertEqual('12345', lrev)
+
+  def test_verify_fails(self):
+    """Should fail when verification fails."""
+    with mock.patch.object(self.wrapper, 'check_repo_verify', return_value=True):
+      with mock.patch.object(self.wrapper, 'verify_rev', side_effect=Exception):
+        with self.assertRaises(Exception):
+          self.wrapper.check_repo_rev(self.GIT_DIR, 'stable')
+
+  def test_verify_ignore(self):
+    """Should pass when verification is disabled."""
+    with mock.patch.object(self.wrapper, 'verify_rev', side_effect=Exception):
+      rrev, lrev = self.wrapper.check_repo_rev(self.GIT_DIR, 'stable', repo_verify=False)
+    self.assertEqual('refs/heads/stable', rrev)
+    self.assertEqual(self.REV_LIST[1], lrev)
+
+
 if __name__ == '__main__':
   unittest.main()
diff --git a/tox.ini b/tox.ini
index 02c5647d..aa4e2979 100644
--- a/tox.ini
+++ b/tox.ini
@@ -15,8 +15,19 @@
 # https://tox.readthedocs.io/
 
 [tox]
-envlist = py27, py36, py37, py38
+envlist = py36, py37, py38, py39
+
+[gh-actions]
+python =
+    3.6: py36
+    3.7: py37
+    3.8: py38
+    3.9: py39
 
 [testenv]
 deps = pytest
-commands = {toxinidir}/run_tests
+commands = {envpython} run_tests
+setenv =
+    GIT_AUTHOR_NAME = Repo test author
+    GIT_COMMITTER_NAME = Repo test committer
+    EMAIL = repo@gerrit.nodomain
diff --git a/wrapper.py b/wrapper.py
index 0ce32508..b1aa4c50 100644
--- a/wrapper.py
+++ b/wrapper.py
@@ -1,5 +1,3 @@
-# -*- coding:utf-8 -*-
-#
 # Copyright (C) 2014 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -14,7 +12,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from __future__ import print_function
 try:
   from importlib.machinery import SourceFileLoader
   _loader = lambda *args: SourceFileLoader(*args).load_module()
@@ -27,7 +24,10 @@ import os
 def WrapperPath():
   return os.path.join(os.path.dirname(__file__), 'repo')
 
+
 _wrapper_module = None
+
+
 def Wrapper():
   global _wrapper_module
   if not _wrapper_module: