gh-159440: Pass --work-tree to the git commands used for the version tag

[sendaoYan]

Summary

The GITTAG build stamp uses git --git-dir $(srcdir)/.git describe --all --always --dirty. --git-dir does not imply a work tree, so git falls back to the current directory. In an out-of-tree build make runs in the build tree, where none of the tracked files exist, so the internal diff-index HEAD of --dirty reports every tracked file as deleted and the tag always comes out as heads/<branch>-dirty — even for a pristine checkout. In-tree builds never hit this, and GITVERSION/GITBRANCH don't touch the work tree, so only the dirty check was wrong.

Pass --work-tree $(srcdir) for all three commands. The semantics of -dirty are preserved (a genuinely modified source tree still reports -dirty), and in-tree builds are unchanged because $(srcdir) is ..

Reproduce

sys.version reports a spurious -dirty git tag for out-of-tree builds, even when the checkout is pristine:

$ mkdir -p ~/build/cpython && cd ~/build/cpython
$ bash ~/git/cpython/configure --prefix=$HOME/opt/cpython > /dev/null
$ make -j && make install -j
$ ~/opt/cpython/bin/python3 -VV
Python 3.16.0a1+dev (heads/main-dirty:25883627946, Oct 14 2026, 22:17:06) [GCC 11.4.0]

Root cause

GITTAG uses git --git-dir $(srcdir)/.git describe --all --always --dirty. --git-dir does not imply a work tree, so git falls back to the current directory. In an out-of-tree build make runs in the build directory, where none of the tracked files exist, and the internal diff-index HEAD behind --dirty reports every tracked file as deleted. GITVERSION and GITBRANCH never touch the work tree, so only the dirty check was wrong.

Change

All three git commands now get --work-tree $(srcdir):

-    GITTAG="git --git-dir \$(srcdir)/.git describe --all --always --dirty"
+    GITTAG="git --git-dir \$(srcdir)/.git --work-tree \$(srcdir) describe --all --always --dirty"

The semantics of -dirty are preserved: a genuinely modified source tree still reports -dirty, and in-tree builds are unchanged because $(srcdir) is ..

Testing

• Out-of-tree build from a clean checkout: ./python -VV reports heads/main: instead of heads/main-dirty:.
• With an uncommitted change to a tracked file in the source tree, the rebuild correctly reports heads/main-dirty: again.
• In-tree build: the git commands resolve to the same values as before ($(srcdir) is .).
• git state checks / make regen-configure produce no further diff in configure, pyconfig.h.in or aclocal.m4.

Issue

• Issue: Out-of-tree builds always report a "-dirty" git tag in sys.version #159440

[itamaro]

looks good to me, thank you for the fix!

[miss-islington-app]

Thanks @sendaoYan for the PR, and @itamaro for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14, 3.15.
🐍🍒⛏🤖

[bedevere-app]

GH-159443 is a backport of this pull request to the 3.15 branch.

[bedevere-app]

GH-159444 is a backport of this pull request to the 3.14 branch.