Commit 88cfc54552 ("nix-prefetch-git: disable maintenance mode via
environment variables") disabled maintenance.auto (git's new
auto-maintenance) via GIT_CONFIG_*, which propagates to submodules. But
the legacy auto-gc path (gc.auto plus detached gc.autoDetach) is still
enabled, and it keeps repacking .git/modules/<sub>/objects after a nested
submodule reports "checked out", racing the later `rm -rf .git`:
- rm empties objects/pack, the detached gc drops a fresh pack in, and
rmdir fails with "Directory not empty" (exit 123); or
- removal partially completes, leaving varying .git remnants, yielding a
non-deterministic NAR hash.
Disable gc.auto/gc.autoDetach alongside maintenance.auto, using the same
GIT_CONFIG_* mechanism so the settings reach every git invocation and its
children (including nested submodule fetches). Fold the repeated
boilerplate into a small git_config_env helper.
The successful output is unchanged (.git is removed either way), so
pinned fetchgit hashes stay valid; this only makes removal deterministic.
Fixes#524215.
Assisted-by: Claude Code (claude-opus-4-8)
Philip Taron
5b5c421f52