| name | why-this-change |
| description | Use when the user asks "why was this cop added/removed", "find upstream PR for a cop", "trace cop change in Rails", "what's the reason for this cop", or wants to find the rails/rails PR or commit that introduced or removed a specific RuboCop cop. |
| allowed-tools | Bash, WebSearch, WebFetch |
| args | copName |
Why This Change
Research the upstream rails/rails repository to find the PR or commit that introduced or removed the given RuboCop cop, and summarize why the change was made.
Steps
1. Search rails/rails with gh CLI
Search for PRs and commits mentioning the cop name:
gh search prs "{copName}" --repo rails/rails --limit 5
gh search commits "{copName}" --repo rails/rails --limit 5
2. Verify the match
For the most relevant result, check the .rubocop.yml diff to confirm it actually adds or removes the cop:
gh pr diff <PR_NUMBER> --repo rails/rails -- .rubocop.yml
gh api repos/rails/rails/commits/<SHA> --jq '.files[] | select(.filename == ".rubocop.yml") | .patch'
3. Fallback: Web search
If gh CLI doesn't return useful results, use WebSearch:
- Query:
site:github.com/rails/rails "{copName}" .rubocop.yml
4. Report findings
Present:
- PR/Commit URL: The link to the upstream change
- Summary: A brief explanation of why the cop was added or removed
- Relevant quote (if available): Key excerpt from the PR description or commit message
