Skill: Review Diff

Purpose

Use Cases

• Pre-commit: Quick diff-only check before commit.
• Orchestrated review: Used as the scope step when review-code runs scope → language → framework → library → cognitive.
• Focused change review: When the user explicitly wants only "what changed" analyzed.

Behavior

Scope

• Analyze: Only files in the change set — diff (staged + unstaged) and untracked files that are part of the same change (included by default). Do not analyze unchanged or out-of-scope files.
• Untracked files: Included by default. When the invoker passes paths and full content of untracked files (e.g. new files to be committed), treat each as a full-file addition and apply the same review checklist; reference file path and line ranges as for added lines.
• Do not: Review whole repo, or cover architecture/security/language-specific rules; defer to review-codebase, review-security, review-dotnet, etc.

Review checklist (diff dimension only)

1. Intent and impact: What changed and why (if inferable); impact on callers, data, config, deployment.
2. Regression and correctness: Does this change introduce bugs or miss edge cases? If it is a fix, is the fix complete?
3. Breaking changes and compatibility: Does it break API/data/config contracts? Backward compatibility or versioning/deprecation?
4. Side effects and idempotency: Unintended side effects, data corruption, duplication, or idempotency issues?
5. Observability and debugging: Does the change add or fix logs, metrics, or error messages for production debugging?
6. Concrete suggestions: Actionable fix or improvement with file:line or @@ block references.

Tone and references

• Professional and engineering-focused: Review as if this will run in production.
• Precise: Reference specific locations (file:line or @@ block in the diff).

Special cases

• Bug fix: Verify the fix is correct and note any remaining or partial issues.
• Format/comments only: State briefly "format/comments only, no behavior change"; if comments contradict or mislead, still emit a finding with suggestion.

Input & Output

Input

• git diff: Changes on the current branch vs HEAD (staged + unstaged), provided when invoking this skill.
• Untracked files (in scope by default): Paths and full content of untracked files that belong to the same change set. The invoker should include them so they are reviewed as full-file additions.

Output

• Emit zero or more findings in the format defined in Appendix: Output contract.
• Each finding MUST include Location, Category, Severity, Title, Description, and optionally Suggestion.
• Category for this skill is always scope.

Restrictions

• Do not review files outside the diff or the whole repo.
• Do not give conclusions without specific locations or actionable suggestions.
• Do not use vague language (e.g. "might be wrong" without type and fix direction).
• Do not perform security, architecture, or language/framework-specific checks; stay within the diff scope dimension.

Self-Check

• Was only the diff (and untracked files in the change set, when included) reviewed?
• Were intent, impact, regression, correctness, compatibility, side effects, and observability covered?
• Is each finding emitted with Location, Category=scope, Severity, Title, Description, and optional Suggestion?
• Are issues referenced with file:line or @@?
• For bug fixes, was fix logic verified and any remaining issues noted?

Examples

Example 1: API change

• Input: Diff adds a query param and changes response shape.
• Expected: Emit findings for intent/impact on callers, backward compatibility risk, breaking-change risk with suggestion (e.g. versioning or deprecation); reference specific lines or @@ blocks. Do not emit security or architecture findings in this skill.

Example 2: Bug fix

• Input: Diff fixes a null pointer and one error code.
• Expected: Emit finding(s) confirming the fix and any regression (e.g. similar null-pointer or error-code issues); note observability (logs/errors); reference changed lines. Category = scope for all.

Edge case: Format/comments only

• Input: Diff only has indentation, spaces, or comment changes.
• Expected: Either no findings or a single minor/suggestion finding: "format/comments only, no behavior change"; if comments contradict code, emit a finding with Title and Suggestion.

Edge case: New (untracked) file in change set

• Input: Diff plus one untracked file (path + full content) as part of the change set (included by default).
• Expected: Review the new file as a full-file addition; apply the same checklist (intent, impact, regression, compatibility, side effects, observability); emit findings with Location = path and line references. Category = scope for all.

Appendix: Output contract

path/to/file.ext

src/api.go:42

scope

critical

major

minor

suggestion

- **Location**: `pkg/handler.go:31`
- **Category**: scope
- **Severity**: major
- **Title**: New query param may break existing clients
- **Description**: Response shape changed without versioning. Old clients may fail.
- **Suggestion**: Add API version or deprecation header; document in CHANGELOG.