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@@ -2,7 +2,10 @@
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name: git-history
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description: >
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Inspect git history: query logs with pickaxe, line-range, or custom formats; find bug origins via bisect; locate problematic commits for cherry-picking or reverting. Use when investigating history, tracing when a change happened, or finding the commit that broke something. Return structured results for downstream agents. Do not use for authoring or formatting commit messages, or executing rebase/squash/fixup operations — use git-commits for that.
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Use when investigating git history — querying logs, tracing when a change
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landed, bisecting the commit that broke something, or locating one to
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revert or backport. Not authoring or rebasing commits -> `git-commits`.
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Not history on a Gitea server -> `gitea-branches`.
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metadata:
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category: git
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@@ -16,81 +19,47 @@ allowed-tools: Bash
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## Gotchas
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- **Pickaxe searches (`-S` vs `-G`)**: `-S"string"` finds commits where string count changed; `-G"regex"` finds any line matching regex in diffs. They're not equivalent: a line replaced (one removal + one addition) matches `-G` but not `-S` if count is unchanged.
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- **`--follow` only works for single files**: it traces renames but fails with multiple paths or directory globs. Use `git log -- <single-file>` or query without `--follow`.
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- **Bisect with skips**: if bisect cannot pinpoint a commit because the culprit is adjacent to skipped commits, it reports "cannot find exact culprit" and lists candidates. This is not a failure — it's as precise as the skip range allows.
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- **Interactive rebase is non-recoverable on mistake**: there's no undo once `rebase -i` starts. Suggest `git reflog` to recover if the user realizes mid-way they selected the wrong commits.
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- **`-L` (line-range history) requires exact line numbers or regex patterns**: off-by-one errors omit the target range. Test the range with `git log -L` before offering it to users.
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- `-S"string"` matches only where the string's *count* changed, so a line edited in place matches `-G"regex"` and not `-S`. Reach for `-G` whenever the string may have moved rather than appeared.
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- `--follow` traces renames for exactly one path. Given several paths or a glob it fails instead of degrading, so run it once per file.
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- Under `git bisect run`, exit `128` or above **aborts the session** rather than marking the commit bad, so a crashing test script ends the search silently.
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- Bisect answering "cannot find exact culprit" beside skipped commits is a complete result: it is as precise as the skip range allows.
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## Query Logs and Locate Commits
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## Step 1 — Pick the entry procedure
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Default to `git log --oneline` for quick inspection. For deeper queries:
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| What is known | Procedure |
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|---|---|
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| Content, a file, or a line range to search for | Query the log — Step 2 |
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| Nothing to search for — only that the behaviour changed between two points | Bisect — read `references/bisect.md` |
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| The commit itself, already identified | Step 3 |
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- **Find when a string appeared or disappeared**: Use `git log -S"string"` (count-sensitive, finds adds/removes). If you need any mention of the string in diffs, use `git log -G"regex"` instead. Add `--pickaxe-regex` to treat the `-S` string as a POSIX ERE, and `--pickaxe-all` to show every changed file in a matching changeset, not just the matching ones. Binary files are searched by `-S`; `-G` ignores them unless `--text` is also supplied.
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- **Trace changes to a specific line or function**: Use `git log -L <start>,<end>:<file>` or `git log -L :<function>:<file>` (requires function name heuristic). This shows the evolution of that range across all commits.
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- **Filter by change type**: Use `git log --diff-filter=<type>` (A=added, M=modified, D=deleted, R=renamed) to narrow to specific file operations.
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- **Mainline-only history through merges**: Use `--first-parent` to follow only the integration branch and skip merged-in side-branch commits; combine with `--merges`/`--no-merges` or `--ancestry-path`/`--min-parents`/`--max-parents` for other ancestry-graph filtering — see `references/git-log-format.md` for the full set.
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- **Custom format for structured output**: Construct format string with `%h` (hash), `%s` (subject), `%an` (author), `%ar` (relative date), `%b` (body). Example: `git log --format="%h | %s | %an (%ar)"`.
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- **File-specific history with renames**: Use `git log --follow -- <file>` (single file only). Without `--follow`, log stops at the rename boundary.
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## Step 2 — Query the log
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## Bisect to Find Blame Commit
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Default to `git log --oneline`, then narrow by whatever is known:
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Use bisect when hunting for the commit that introduced a bug or behaviour change. Binary search reduces iterations from O(N) to O(log N).
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- **Content**: `git log -S"string"`, or `-G"regex"` to match any diff line. `--pickaxe-regex` makes the `-S` argument a POSIX ERE; `--pickaxe-all` shows every file in a matching changeset.
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- **A line or function**: `git log -L <start>,<end>:<file>` or `git log -L :<function>:<file>`. Confirm the range resolves before reporting on it — an off-by-one silently omits the target.
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- **A file across renames**: `git log --follow -- <file>`. Without `--follow` the history stops at the rename boundary.
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- **Mainline only**: `--first-parent` follows the integration branch and skips commits merged in from side branches.
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- **Structured output**: `git log --format="%h | %s | %an (%ar)"`.
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**Basic manual flow:**
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```bash
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git bisect start
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git bisect bad [HEAD] # mark current (or specified) as broken
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git bisect good <commit> # mark known-good baseline
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# Git checks out midpoint; test it manually
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git bisect good # if test passes
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git bisect bad # if test fails
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# Repeat until git reports "X is the first bad commit"
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git bisect reset # return to original HEAD
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If you need the placeholder catalogue, format presets, `--diff-filter` letters, full `-L` syntax, ancestry filters, pickaxe binary-file behaviour, or `git diff` output-control flags such as `--stat`, `--word-diff` and the whitespace options, read `references/git-log-format.md`.
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## Step 3 — Act on a located commit
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Offer the operation and its consequence; run it only once the user has chosen.
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- `git cherry-pick <commit>` copies the commit's changes onto the current HEAD — for backporting a fix to another branch.
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- `git revert <commit>` adds a new commit undoing it — for un-applying merged work without rewriting history.
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- `git blame <file>` attributes each line to the commit that last touched it, when the question is which commit introduced one specific line.
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For diff output control on the located commit, read `references/git-log-format.md`.
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## Step 4 — Return the result
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Report each located commit in this shape, so a calling agent can act on it without reparsing raw log output:
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```text
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<sha> — <subject>
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<author> (<relative date>)
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Recommendation: <action or "none">
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```
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**Automated with `git bisect run`:** if a test command exists, use `git bisect run <cmd>`. Git interprets the exit code: `0`=good, `1-124`=bad, `125`=skip (build broken), `126-127`=POSIX shell errors treated as bad, `128+`=**aborts the bisect session entirely** (not treated as bad — a crashed test script can silently end the search).
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**With skip:** if a commit is untestable (broken build), use `git bisect skip` to exclude it without manually deciding good/bad. If the first-bad is adjacent to skips, bisect reports it cannot pinpoint but lists candidates.
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**Undoing a wrong good/bad call:** `git bisect log` prints the session's decision history; save it (`git bisect log > bisect.log`), edit out the mistaken entry, then `git bisect reset && git bisect replay bisect.log` to resume from the corrected log instead of restarting the whole search.
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**Narrowing and speeding up the search:** `git bisect start HEAD v1.2 -- src/` limits bisection to a path, cutting the number of trials. `--no-checkout` updates the `BISECT_HEAD` ref instead of checking out a working tree (useful for tests that don't need one; automatic in bare repos). `--first-parent` follows only first parents at merges, finding the integration commit that introduced a regression while ignoring broken side branches.
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**Inspecting remaining candidates visually:** `git bisect visualize` (alias `view`) opens the suspects in gitk; add `--stat` or `-p` to show diffstat or full patches instead. Falls back to `git log` when no graphical display is detected.
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**For non-regression hunts:** use `git bisect start --term-new <new> --term-old <old>` to search for a property change instead of a bug (e.g., performance regression). Then use the custom terms instead of `good`/`bad`.
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For rebase execution (interactive rebase, squash/fixup/reword, conflict handling) see git-commits — it owns history-rewriting operations. This skill only locates commits and reports on history; it does not execute rebases.
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## Find and Manipulate Problematic Commits
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Once a commit is identified (via log query or bisect), offer cherry-pick or revert. This section is general git knowledge, not sourced from `history-inspection.md` — `git-branches`'s SKILL.md explicitly delegates cherry-pick/revert here (see its Merging section), which is why this skill carries them rather than treating them as out of scope:
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- **Cherry-pick**: `git cherry-pick <commit>` copies a commit's changes onto current HEAD. Use when backporting fixes to other branches.
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- **Revert**: `git revert <commit>` creates a new commit that undoes the changes. Use when un-applying a merged commit without rewriting history.
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- **Blame for context**: `git blame <file>` shows which commit last changed each line. Use to trace a specific line back to its introducing commit.
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## Inspect Diffs
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Diff-output tuning is in scope too: `--stat` for a diffstat summary, `--word-diff` for word-level (not line-level) changes, and whitespace flags (`-w`, `--ignore-blank-lines`) to suppress noise from reformatting. See `references/git-log-format.md` for the full flag set.
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## Return Results Structured
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For agent consumption, return:
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- **Commit SHA** (full or abbreviated as appropriate)
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- **Subject line** (from `%s`)
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- **Author and date** (from `%an` and `%ar`)
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- **Action taken or recommended** (e.g., "Found via bisect", "Offer cherry-pick to main", "Rebase conflicts detected")
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Example for agent:
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```
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Found first bad commit: abc1234
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Subject: fix null pointer in parser
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Author: Alice (2 weeks ago)
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Recommendation: Backport to release branch via cherry-pick
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```
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## Reference
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For the full log format placeholder catalogue, named format presets, `--diff-filter` letters, `-L` range syntax, ancestry filters, and `git diff` output-control flags, read `references/git-log-format.md`.
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