1 files changed, 75 insertions, 29 deletions

diff --git a/docs/python-support.md b/docs/python-support.md
index 3eaaba33..e4ee96c4 100644
--- a/docs/python-support.md
+++ b/docs/python-support.md
@@ -1,47 +1,93 @@
 # Supported Python Versions
 
-With Python 2.7 officially going EOL on [01 Jan 2020](https://pythonclock.org/),
-we need a support plan for the repo project itself.
-Inevitably, there will be a long tail of users who still want to use Python 2 on
-their old LTS/corp systems and have little power to change the system.
+This documents the current supported Python versions, and tries to provide
+guidance for when we decide to drop support for older versions.
 
 ## Summary
 
-* Python 3.6 (released Dec 2016) is required by default starting with repo-2.x.
-* Older versions of Python (e.g. v2.7) may use the legacy feature-frozen branch
-  based on repo-1.x.
+*   Python 3.6 (released Dec 2016) is required starting with repo-2.0.
+*   Older versions of Python (e.g. v2.7) may use old releases via the repo-1.x
+    branch, but no support is provided.
 
-## Overview
+## repo hooks
 
-We provide a branch for Python 2 users that is feature-frozen.
-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.
+Projects that use [repo hooks] run on independent schedules.
+Since it's not possible to detect what version of Python the hooks were written
+or tested against, we always import & exec them with the active Python version.
 
-Users can select this during `repo init` time via the [repo launcher].
-Otherwise the default branches (e.g. stable & main) will be used which will
-require Python 3.
+If the user's Python is too new for the [repo hooks], then it is up to the hooks
+maintainer to update.
 
-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.
+## Repo launcher
 
-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.
+The [repo launcher] is an independent script that can support older versions of
+Python without holding back the rest of the codebase.
+If it detects the current version of Python is too old, it will try to reexec
+via a newer version of Python via standard `pythonX.Y` interpreter names.
 
-### repo hooks
+However, this is provided as a nicety when it is not onerous, and there is no
+official support for older versions of Python than the rest of the codebase.
 
-Projects that use [repo hooks] run on independent schedules.
-They might migrate to Python 3 earlier or later than us.
-To support them, we'll probe the shebang of the hook script and if we find an
-interpreter in there that indicates a different version than repo is currently
-running under, we'll attempt to reexec ourselves under that.
+If your default python interpreters are too old to run the launcher even though
+you have newer versions installed, your choices are:
+
+*   Modify the [repo launcher]'s shebang to suite your environment.
+*   Download an older version of the [repo launcher] and don't upgrade it.
+    Be aware that there is no guarantee old repo launchers are WILL work with
+    current versions of repo.  Bug reports using old launchers will not be
+    accepted.
+
+## When to drop support
+
+So far, Python 3.6 has provided most of the interesting features that we want
+(e.g. typing & f-strings), and there haven't been features in newer versions
+that are critical to us.
+
+That said, let's assume we need functionality that only exists in Python 3.7.
+How do we decide when it's acceptable to drop Python 3.6?
+
+1.  Review the [Project References](./release-process.md#project-references) to
+    see what major distros are using the previous version of Python, and when
+    they go EOL.  Generally we care about Ubuntu LTS & current/previous Debian
+    stable versions.
+    *   If they're all EOL already, then go for it, drop support.
+    *   If they aren't EOL, start a thread on [repo-discuss] to see how the user
+        base feels about the proposal.
+1.  Update the "soft" versions in the codebase.  This will start warning users
+    that the older version is deprecated.
+    *   Update [repo](/repo) if the launcher needs updating.
+        This only helps with people who download newer launchers.
+    *   Update [main.py](/main.py) for the main codebase.
+        This warns for everyone regardless of [repo launcher] version.
+    *   Update [requirements.json](/requirements.json).
+        This allows [repo launcher] to display warnings/errors without having
+        to execute the new codebase.  This helps in case of syntax or module
+        changes where older versions won't even be able to import the new code.
+1.  After some grace period (ideally at least 2 quarters after the first release
+    with the updated soft requirements), update the "hard" versions, and then
+    start using the new functionality.
+
+## Python 2.7 & 3.0-3.5
+
+> **There is no support for these versions.**
+> **Do not file bugs if you are using old Python versions.**
+> **Any such reports will be marked invalid and ignored.**
+> **Upgrade your distro and/or runtime instead.**
+
+Fetch an old version of the [repo launcher]:
+
+```sh
+$ curl https://storage.googleapis.com/git-repo-downloads/repo-2.32 > ~/.bin/repo-2.32
+$ chmod a+rx ~/.bin/repo-2.32
+```
 
-For example, a hook with a header like `#!/usr/bin/python2` will have repo
-execute `/usr/bin/python2` to execute the hook code specifically if repo is
-currently running Python 3.
+Then initialize an old version of repo:
 
-For more details, consult the [repo hooks] documentation.
+```sh
+$ repo-2.32 init --repo-rev=repo-1 ...
+```
 
 
+[repo-discuss]: https://groups.google.com/forum/#!forum/repo-discuss
 [repo hooks]: ./repo-hooks.md
 [repo launcher]: ../repo