add experimental git worktree support

This provides initial support for using git worktrees internally
instead of our own ad-hoc symlink tree.  It's been lightly tested
which is why it's not currently exposed via --help.

When people opt-in to worktrees in an existing repo client checkout,
no projects are migrated.  Instead, only new projects will use the
worktree method.  This allows for limited testing/opting in without
having to completely blow things away or get a second checkout.

Bug: https://crbug.com/gerrit/11486
Change-Id: Ic3ff891b30940a6ba497b406b2a387e0a8517ed8
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/254075
Tested-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/subcmds/init.py b/subcmds/init.py
index 3c68c2c3..8a29321e 100644
--- a/subcmds/init.py
+++ b/subcmds/init.py
@@ -15,6 +15,8 @@
 # limitations under the License.
 
 from __future__ import print_function
+
+import optparse
 import os
 import platform
 import re
@@ -128,6 +130,10 @@ to update the working directory files.
     g.add_option('--clone-filter', action='store', default='blob:none',
                  dest='clone_filter',
                  help='filter for use with --partial-clone [default: %default]')
+    # TODO(vapier): Expose option with real help text once this has been in the
+    # wild for a while w/out significant bug reports.  Goal is by ~Sep 2020.
+    g.add_option('--worktree', action='store_true',
+                 help=optparse.SUPPRESS_HELP)
     g.add_option('--archive',
                  dest='archive', action='store_true',
                  help='checkout an archive instead of a git repository for '
@@ -246,6 +252,20 @@ to update the working directory files.
     if opt.dissociate:
       m.config.SetString('repo.dissociate', 'true')
 
+    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.SetString('repo.worktree', 'true')
+      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')
@@ -459,6 +479,10 @@ to update the working directory files.
             % ('.'.join(str(x) for x in MIN_GIT_VERSION_SOFT),),
             file=sys.stderr)
 
+    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)