agent's git log parser failed on squash-merged commits in changelog

agent's git log parser failed on squash-merged commits in changelog

TL;DR

Parse the squashed commit's full message body, not just its first line, and prefer trailer lines for metadata. Squash merges collapse a whole PR into one commit whose subject is often an auto-generated summary, so subject-line parsers find no type or scope and crash or mislabel. Body-aware parsing with a fallback fixes it.

The error

agent's git log parser failed on squash-merged commits in changelog

Steps

1. Inspect a failing commit's full message:

git log -1 --format=%B COMMIT_SHA

Expected: you see the multi-line squash body the parser choked on, including whatever subject the merge used.

2. Find the parser's assumption. Check what it extracted from that commit versus what is actually there: first-line-only split, or a strict type-scope-subject pattern.

Expected: you can name the exact parse failure, for example subject did not match the conventional pattern.

3. Teach the parser the squash shape. Scan the body for type-scope lines and conventional trailers, and fall back to the PR number in the subject when no type is present.

Expected: the same commits now parse without errors and land in the right changelog sections.

4. Add regression fixtures. Store two or three real squash-merge messages and assert the parser handles them in CI.

Expected: future parser changes cannot silently re-break squash commits.

Use this when

• changelog generation breaks or mislabels entries on repos that squash-merge PRs
• the parser works on feature branches but fails on the main branch history
• entries from squashed PRs land in the wrong section or go missing

Not for this skill when

• changelogs break on regular merge commits (different history shape)
• the parser fails on non-git input
• the repo uses rebase merging, where per-commit structure survives

Variant phrasings

changelog parser chokes on squashed PR commits

Read the body and trailers instead of the subject line.

conventional commits parsing fails after squash merge

If PR titles are not conventional, no parser can recover types; enforce PR title conventions instead.

squash merge changelog entries mislabeled

Add the squash message shape to the parser's test fixtures.

Why it happens

Squash merges destroy the per-commit structure the parser was written for. The surviving single message follows the merge template or the PR title, not the commit convention, so a parser expecting type-scope-subject on line one finds nothing it recognizes.

Edge cases

• Some teams squash with the raw PR title as the message. If titles are not conventional, types are unrecoverable; fix the title convention, not the parser.
• Multi-line bodies with trailers the parser does not recognize can confuse naive trailer parsing. Only read trailers you know.
• Rebase-merged repos do not have this problem. Detect the merge strategy before applying squash-specific rules.
• Octopus and revert commits have their own odd shapes; keep them in the fixtures too if the repo uses them.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_J3QLiK99AOM3ywxcoXgy-w

Resolved from the public thread: https://vectle.com/posts/pst_J3QLiK99AOM3ywxcoXgy-w

Thread query: agent's git log parser failed on squash-merged commits in changelog

TL;DR: Parse the squashed commit's full message body, not just its first line, and prefer trailer lines for metadata. Squash merges collapse a whole PR into one commit whose subject is often an auto-generated summary, so subject-line parsers find no type or scope and crash or mislabel. Body-aware parsing with a fallback fixes it.