Test Failures in `rust:slim-bookworm` (Debian 12) Due to Git Version Incompatibility

[AtnesNess]

Environment

• Docker Image: rust:slim-bookworm
• OS: Debian 12 (Bookworm)
• Git Version: 2.39.5
• Rust Version: 1.90.0

Issue Description

Four tests fail when running cargo test in the rust:slim-bookworm Docker image due to Git version incompatibility. The tests attempt to use the --merge-base option with git merge-tree --write-tree, which is not supported in Git 2.39.5.

Failed Tests

1. authorship::rebase_authorship::tests::test_prepare_working_log_simple_squash
2. authorship::rebase_authorship::tests::test_prepare_working_log_squash_multiple_files
3. authorship::rebase_authorship::tests::test_prepare_working_log_squash_multiple_sessions
4. authorship::rebase_authorship::tests::test_prepare_working_log_squash_with_main_changes

Error Message

error: unknown option `merge-base=<sha>'
usage: git merge-tree [--write-tree] [<options>] <branch1> <branch2>
   or: git merge-tree [--trivial-merge] <base-tree> <branch1> <branch2>

Command Being Executed

git merge-tree --write-tree --merge-base=<commit-sha> -X ours <branch1> <branch2>

Root Cause

The --merge-base option for git merge-tree --write-tree was introduced in Git 2.46.0 (or a version between 2.39.5 and 2.47.0). Debian 12 (Bookworm) ships with Git 2.39.5, which doesn't support this option.

Test Results

Docker Image	Debian Version	Git Version	Test Result
rust:latest	Trixie (13)	2.47.3	✅ All tests pass
rust:slim-bookworm	Bookworm (12)	2.39.5	❌ 4 tests fail

Reproduction Steps

docker run --rm -v $(pwd):/workspace -w /workspace rust:slim-bookworm bash -c "
  apt-get update && apt-get install -y libssl-dev pkg-config git &&
  cargo test -- --test-threads=1
"

Possible Solutions

1. Update minimum Git version requirement to 2.46.0+ in documentation
2. Add fallback logic for older Git versions that don't support --merge-base
3. Use alternative Git commands that are compatible with Git 2.39.5
4. Update CI/CD to use a Docker image with Git 2.46.0+

Related Code

The failures occur in src/authorship/rebase_authorship.rs where git merge-tree is invoked with the --merge-base option for handling squash merge scenarios.

Impact

• Users running on Debian 12 (Bookworm) stable will experience test failures
• CI/CD pipelines using rust:slim-bookworm will fail
• Affects production environments using Debian 12 if these code paths are executed