fix: disable automatic Git maintenance in gix-testtools

[Sebastian Thiel (Byron)]

Tasks

• refackiew

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Created by Codex on behalf of Byron. Byron will review before this is ready to merge.

Reported issue

Make sure that `gix-testtools` doesn't allow git gc to run automatically, in anything that it executes. See here for details.

Root cause: the fixture used a tick() function that set GIT_COMMITTER_DATE
to a fixed timestamp in January 2023. On git 2.54, git maintenance runs
automatically in the background after commits (triggered by git commit via
--auto). It packs loose objects and creates cruft packs, assigning each
object an mtime derived from its referencing commit's committer date. With
a 2023 timestamp, all objects appeared over two years old — exceeding
gc.cruftPackExpire=2.weeks.ago — and were pruned immediately, corrupting
the repository mid-fixture.

Summary

• Added command-scope Git config helpers in gix-testtools to set maintenance.auto=false and gc.auto=0 for processes the crate executes.
• Applied the guard to fixture script execution, git(), run_git(), invoke_bash(), git-daemon wrappers, Git version discovery, metadata generation, cargo example builds, and shell helpers.
• Added regression coverage for direct Git, bash-launched Git, and the high-level git() helper.

Git reference

Git's prepare_auto_maintenance() skips automatic maintenance when maintenance.auto=false; Git's maintenance documentation also states that git maintenance register disables foreground maintenance by setting maintenance.auto=false. The fix also sets gc.auto=0 to cover older git gc --auto paths.

Validation

• cargo test -p gix-testtools auto_maintenance
• cargo test -p gix-testtools
• cargo clippy -p gix-testtools --all-targets
• cargo test -p gix-testtools auto_maintenance --no-default-features

Review

• codex review --commit de7be303f3f6b9edc5d759f3ae7b39e89ed162e1 found no actionable issues.

[Eliah Kagan (EliahKagan)]

It looks like this fixes the problem that causes all CI runs to fail, as seen in all recent PRs and feature branches--and as would be seen on main, but it's been a couple weeks since the last push. Rerunning the tests does not cause them to pass, but the change here does.

I'm not sure what's causing that problem. I haven't managed to look into it much, and I unfortunately I don't have time to look into it for most of today. I suspect it may relate to changes how Git does geometric repacking, making it so that when unanticipated garbage collection occurs, the result does not match what we've tested. I don't know to what extent, if any, it overlaps with the problem described in this PR as the motivating issue for it.

I only advocate merging this if it is already known to be correct. Because this remains a draft, I don't want to assume that it is ready. However, I mention this now just in case it turns out this is ready and in case it's considered valuable to get CI working in advance of the forthcoming monthly release (#2618).

[Copilot]

Pull request overview

This PR hardens gix-testtools (and its companion test binary) against Git 2.54+ auto-maintenance by forcing command-scope config that disables automatic maintenance/auto-gc for Git processes launched by test helpers, and adds regression tests to ensure this remains in effect.

Changes:

• Introduce and apply command-scope Git config injection (maintenance.auto=false, gc.auto=0) across multiple process-spawning helpers.
• Extend the “isolated git config” used for fixture/script Git invocations to include the maintenance/auto-gc disables.
• Add regression tests covering direct Git execution, bash-launched Git, and the high-level git() helper.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
tests/tools/src/lib.rs	Adds command-scope config helper and applies it broadly to Git-related process spawning (git discovery, run helpers, daemon, meta generation, etc.).
tests/tools/src/main.rs	Applies the same command-scope config to the git-daemon wrapper used by journey tests.
tests/tools/src/tests.rs	Adds regression tests asserting maintenance.auto and gc.auto are disabled through key helpers.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

[Sebastian Thiel (Byron)]

Eliah Kagan (@EliahKagan) Thanks for the heads-up, I wasn't aware. In these PR it's probably the same issue (and I didn't even notice yet), and I agree this should be part of the next release.
Now I should be able to release gix-testtools at will as well as it was decoupled from the workspace crates, solving another unpleasantness that plagued gitoxide for long enough.

Now I just shouldn't forget to rebase the report PR because I plan to release from there directly.

[Eliah Kagan (EliahKagan)]

Thanks!

I should refine my description of the situation I believe this fixed, by saying that it was occasionally possible for the test suite to pass after the problem started yet before this fix, but I have only managed to produce one known example of it passing. So in a sense it was a flake, but it was more of an anti-flake--the test job passing was the rare thing. I expect that the fix here will much reduce or eliminate the problems, other than those that are due to problems with GHA's own infrastructure (which have been going on for a bit longer than the ones that appear correlated with the new Git version).

[Eliah Kagan (EliahKagan)]

Now I just shouldn't forget to rebase the report PR because I plan to release from there directly.

If feasible, I think it would be helpful to Windows users if #2607 can also come in before the monthly gitoxide release. I think everything there is in good shape, I've rebased it, and due to the fix in this PR, I expect all tests to pass. I've enabled auto-merge in #2607.

Edit: #2607 has merged.