Git bisect forensics

Skill narenaryan/agent-skills/skills/git/git-bisect-forensics

Use when hunting a regression across many commits or tracing the origin of a line/function/string — covers automated bisect, skip, replay, blame -L/-C/-w, and pickaxe search (-S/-G)From its SKILL.md

Install

npx -y skills add narenaryan/agent-skills --skill git-bisect-forensics

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

One thing to look at

0 stars0 stars. Stars are a popularity signal and not a quality one, but at this level it is likely that nobody has read this closely except its author, and you would be relying on your own review.

SKILL.md

2.2 KB, 560 tokens by cl100k_base, as published. Nobody here has run it

Git Bisect & Forensics

Bisect: Binary Search

git bisect start <bad> <good>     # or: start; bad; good <tag>
# git checks out midpoint; you test, then:
git bisect good | bad | skip
git bisect reset                  # finish, back to original HEAD

Automated

Exit codes: 0 good, 1–124,126,127 bad, 125 skip, ≥128 abort.

git bisect start HEAD v1.4.0
git bisect run ./reproduce.sh
git bisect run sh -c 'cargo build && cargo test --test regression'

1000 commits → ~10 test runs.

Save / Resume

git bisect log > bisect.log
git bisect reset
# later:
git bisect replay bisect.log

Blame

git blame -L 40,80 file.py                 # line range
git blame -L :funcName:file.py             # by function
git blame -w file.py                       # ignore whitespace-only
git blame -C file.py                       # detect moves within same-commit diffs
git blame -C -C -C file.py                 # across files in any commit (thorough)
git blame --ignore-rev <sha> file.py       # skip a mass-format commit
git config blame.ignoreRevsFile .git-blame-ignore-revs

-C bypasses "moved file → blame points at the move commit."

Pickaxe

git log -S"token"                  # when token count in file changed
git log -S"pat" --pickaxe-regex
git log -G"regex"                  # any line matching was touched
git log -L :ClassName:src/p.ts     # full evolution of a symbol
git log --follow -p -- path        # history across renames

-S: added/removed detection (precise).
-G: any touch of matching lines (broader).

Combo: Narrow then Bisect

git log -S"oldLogic" -- src/       # last clean commit
git bisect start HEAD <that-sha>
git bisect run pytest tests/test_regression.py

Pitfalls

On commits that don't build, return 125 (skip), not 1, from the bisect script.
-S is literal by default; use --pickaxe-regex.
Bisect leaves detached HEAD — always git bisect reset before committing.

What ships with it

Read from the repository

Just SKILL.md. No reference files, no scripts.