Commit Diff Analyzer

Usage Pattern

When user provides two commit IDs (in any order or format), analyze the changes between them:

1. Validate commits exist: Run git cat-file -t <commit> for each commit ID
2. Get commit info: Run git log -1 --format=fuller <commit> for both commits
3. Show diff: Run git diff <older-commit>..<newer-commit> (chronological order)
4. Show stats: Run git diff --stat <older-commit>..<newer-commit>

Output Organization

Present the analysis with:

1. Commit metadata - Author, date, commit message for both commits
2. Change summary - Files changed, insertions, deletions
3. Detailed diff - Line-by-line changes with context
4. File breakdown - Group by: Modified, Added, Deleted files

Key Commands

# Validate commits exist
git cat-file -t <commit-id>

# Get full commit info
git log -1 --format="Hash: %H%nAuthor: %an%nDate: %ad%nMessage: %s%n" <commit-id>

# Chronological diff (older..newer)
git diff <older-commit>..<newer-commit>

# Diff stat
git diff --stat <older-commit>..<newer-commit>

# Show files changed
git diff --name-only <older-commit>..<newer-commit>

Handling Edge Cases

• Invalid commit IDs: Report error and suggest running git log to see recent commits
• Same commit: Notify user both IDs point to the same commit
• Non-git directory: Error - skill only works in git repositories
• Reverse order: Detect which commit is older and adjust command accordingly

Commit ID Formats

Accept various formats:

• Full SHA: abc123def456...
• Short SHA: abc123d (at least 7 chars)
• Branch names (if they point to commits)
• HEAD references like HEAD~5

Example Output Structure

=== Commit A ===
Hash: abc123...
Author: John Doe
Date: 2024-01-15 10:30:00
Message: feat: add user login

=== Commit B ===
Hash: def456...
Author: Jane Smith
Date: 2024-01-20 14:45:00
Message: fix: resolve auth bug

=== Changes Summary ===
5 files changed, 120 insertions(+), 35 deletions(-)

=== File Breakdown ===
Modified: src/auth.js, src/login.html
Added: src/auth-utils.ts
Deleted: src/old-auth.php

=== Diff ===
... (detailed diff output)