analyze-pr

Analyze Pull Request

Given a PR URL, fetch the code changes and web description, then generate a comprehensive analysis document. The PR is guaranteed to belong to the current local repository.

Workflow

Step 1: Parse the PR URL

Extract from the URL:

• Platform: GitHub or GitLab
• Owner/Org, Repo, PR Number

Supported formats:

https://github.com/{owner}/{repo}/pull/{number}
https://gitlab.com/{owner}/{repo}/-/merge_requests/{number}

Step 2: Fetch PR Metadata

Use the WebFetch tool to read the PR page and extract:

• PR title, description, author, labels, linked issues
• Review comments and discussion highlights

For GitHub PRs, also fetch the API endpoint for structured data:

https://api.github.com/repos/{owner}/{repo}/pulls/{number}

This gives you base.ref (base branch name), head.ref, additions, deletions, changed_files, etc.

Step 3: Fetch the PR Branch Locally

# Record current branch for later restore
ORIGINAL_BRANCH=$(git rev-parse --abbrev-ref HEAD)

# GitHub
git fetch origin pull/{number}/head:pr-{number}

# GitLab
git fetch origin merge-requests/{number}/head:mr-{number}

Do NOT checkout the PR branch — use it as a ref for diff only, to avoid disrupting the working tree.

Step 4: Generate the Diff

Use base.ref from Step 2 as the base branch (do NOT hardcode main):

BASE_BRANCH={base.ref from step 2}

# Changed file list
git diff --name-only origin/$BASE_BRANCH...pr-{number}

# Stats summary
git diff --stat origin/$BASE_BRANCH...pr-{number}

# Full diff
git diff origin/$BASE_BRANCH...pr-{number}

# Commit history
git log --oneline origin/$BASE_BRANCH..pr-{number}

Step 5: Analyze the Changes

For each changed file, understand:

1. What changed: additions, deletions, modifications
2. Why it changed: infer from commit messages, PR description, and code context
3. Impact: which components/modules are affected

Group changes by category:

• New Features: new files, new functions, new APIs
• Bug Fixes: error handling, logic corrections
• Refactoring: code reorganization, naming changes
• Configuration: build, CI/CD, dependency changes
• Documentation: README, comments, docs
• Tests: new or modified tests