bisect

# bisect — Find the First Bad Commit Use `git bisect` to binary-search through commit history and find the first commit that introduced a failure. ## Step 1: Ensure clean working tree Check that there are no staged or unstaged changes. If there are, **stop and tell the user** they need a clean working tree before bisecting, since git bisect checks out older commits. ```bash git status --porcelain ``` If the output is non-empty, stop and ask the user to commit or stash their changes first. ## Step 2: Determine the test command Use `$ARGUMENTS` to understand what the user wants to test. This should describe a command or check that fails on the current commit. Determine the exact shell command to run. ## Step 3: Verify the current commit is bad Run the test command on the current commit (HEAD). If it **passes** (exits 0), stop and tell the user — the current commit doesn't exhibit the failure, so there's nothing to bisect. ## Step 4: Find a good commit Start searching backwards from HEAD in steps of 10 commits to find a commit where the test passes. ```bash git stash --include-untracked -q 2>/dev/null; true git checkout HEAD~10 --quiet ``` Run the test command. If it still fails, go back another 10 commits (`HEAD~10` from the current position). Repeat until either: - A passing commit is found, or - You've gone back 100+ commits without finding a passing one — stop and ask the user for guidance (maybe a known-good commit SHA). Once a good commit is found, note its SHA. ## Step 5: Run git bisect Return to the original branch first, then start bisecting: ```bash git checkout - --quiet git bisect start git bisect bad git bisect good <good-commit-sha> ``` Git will check out a middle commit. Run the test command on it: - If the test **fails** → `git bisect bad` - If the test **passes** → `git bisect good` Repeat until git reports the first bad commit. ## Step 6: Record the result and clean up Save the first bad commit SHA and message. Then reset: ```bash git bisect reset ``` ## Step 7: Report Tell the user the first bad commit, including: - The commit SHA - The commit message - The commit author and date - A brief `git show --stat` of the commit so they can see which files changed