Skip commits with a Drift: ignore trailer

[dave-shawley]

Summary

analyze() now excludes commits from the drift report when their message carries a Drift: ignore trailer, letting an author explicitly vouch for a change instead of it showing up as unexplained drift.

Problem

Some commits (e.g. a reformat, a deliberate one-off tweak) touch paths that drift would otherwise report, even though the author already knows about them and doesn't want them flagged. There was no way to mark a commit as intentionally exempt.

Solution

• A non-merge commit whose message has a Drift: ignore trailer is traversed but never classified, the same treatment merges already get.
• The trailer's token and value are matched ASCII case-insensitively, since gix only trims whitespace on trailers and doesn't fold case.
• Added ignored_commits_skipped to the JSON report, counted separately from commits_scanned and merge_commits_skipped.
• Documented the new field and trailer semantics in README's "Defined behavior" section, per the project's contract that semantic changes update that section in the same commit.

Testing

• cargo test, cargo clippy --all-targets -- -D warnings, and cargo fmt --check all pass.
• Added CLI tests: log-mode exclusion, tree-mode leaving an unattributed path, and case-insensitive trailer matching.

Summary by CodeRabbit

• New Features
  • Commits marked with a Drift: ignore trailer are now excluded from drift analysis.
  • Ignored commits are counted separately in reports.
  • Trailer matching is case-insensitive.
  • Tree reports identify paths changed only by ignored commits as unattributed.
• Documentation
  • Added report field details and clarified how ignored commits affect scanning and attribution.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: b44a2dc4-227d-47e8-8391-701113a23253

📥 Commits

Reviewing files that changed from the base of the PR and between 3dd503e and 4f5de55.

📒 Files selected for processing (4)

• README.md
• src/report.rs
• src/scan.rs
• tests/cli.rs

Included review availability: Your plan provides up to 1 included review per hour; 0 remain after this review.

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📝 Walkthrough

Walkthrough

The scanner now detects case-insensitive Drift: ignore trailers, skips those commits from classification, counts them separately, and reports their tree-mode paths as unattributed. The report schema, tests, and README document this behavior.

Changes

Ignored commit handling

Layer / File(s)	Summary
Report contract src/report.rs	Summary and Report now include ignored_commits_skipped. Report construction and fixtures propagate the value.
Scan ignore-trailer handling src/scan.rs	The scanner detects matching trailers, skips affected non-merge commits, and includes the count in the report.
Behavior validation and documentation tests/cli.rs, README.md	Tests cover exclusion, case-insensitive matching, and tree-mode unattributed paths. The README documents the field and behavior.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 4f5de

The change adds an explicit trailer-based way to exclude intentional drift from reports and records those exclusions separately; no actionable merge-blocking risk remains beyond normal checks and review.

Sequence Diagram(s)

sequenceDiagram
  participant CLI
  participant scan
  participant Commit
  participant Report
  CLI->>scan: start scan
  scan->>Commit: load non-merge commit
  scan->>Commit: read trailers
  Commit-->>scan: return Drift: ignore match
  scan->>Report: count skipped commit
  scan-->>CLI: return report without classified ignored commit

Loading

Possibly related PRs

• gmr/drift#1: Introduced the scan and report logic extended by this change.

Suggested reviewers: gmr

Poem

I hop through commits in the morning light,
Mark ignored changes and keep counts right.
Paths left unseen stay gently declared,
Reports carry every detail prepared.
— A careful rabbit 🐇

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: skipping commits with a Drift: ignore trailer.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[dave-shawley]

🤖 This comment was posted by Claude on behalf of @dave-shawley

Status check for this cycle:

• CodeRabbit has reviewed HEAD (4f5de551) and reported no actionable comments ("No actionable comments were generated in the recent review."). No review threads are open.
• The Testing and Docker GitHub Actions workflow runs for this PR are stuck in action_required — GitHub is holding them for maintainer approval since this PR comes from a fork (dave-shawley/drift). I attempted to approve the runs via the API and was correctly denied (403, requires admin rights on gmr/drift), so this needs a maintainer to approve.

@gmr — could you approve the pending workflow runs for this PR (Actions tab, or "Approve and run") so CI can execute? Nothing else is blocking merge once CI runs green.