Retrieve Diff from GitHub PR Skill

An input skill that retrieves code diff and PR metadata from GitHub via the API. This is the entry point for reviewing GitHub Pull Requests.

Role

• Fetch: Get PR details and diff via GitHub API
• Extract: Parse changed files and their diffs
• Context: Gather PR metadata (title, description, author, reviews)

Inputs

Outputs

Required MCP Tools

This skill uses the GitHub MCP server with the following tools:

Step 1: Parse PR Reference

Accept PR reference in various formats:

Regex for URL: github\.com/([^/]+)/([^/]+)/pull/(\d+)
Regex for short: ([^/]+)/([^#]+)#(\d+)

Step 2: Fetch PR Details

Use the GitHub MCP tool to get PR information:

{
  "tool": "get_pull_request",
  "server": "user-github",
  "arguments": {
    "owner": "<owner>",
    "repo": "<repo>",
    "pull_number": <number>
  }
}

This returns:

• PR title and description
• Author information
• Base and head branches
• State (open/closed/merged)
• Labels and reviewers
• Head commit SHA (needed for submitting review)

Step 3: Fetch Changed Files

Use the GitHub MCP tool to get file changes:

{
  "tool": "get_pull_request_files",
  "server": "user-github",
  "arguments": {
    "owner": "<owner>",
    "repo": "<repo>",
    "pull_number": <number>
  }
}

This returns for each file:

• filename: Path to the file
• status: added, removed, modified, renamed
• additions: Lines added
• deletions: Lines deleted
• patch: Unified diff patch for the file

Step 4: Format Output

Structure the output for the review pipeline:

## PR Retrieved

**Repository**: owner/repo
**PR #**: 123
**Title**: feat: add user authentication

### PR Info

| Field | Value |
|-------|-------|
| Author | @username |
| State | open |
| Base | main |
| Head | feature/auth |
| Commits | 3 |
| Changed Files | 5 |

### Description

<PR description content>

### Files Changed

| Status | File | +/- |
|--------|------|-----|
| modified | src/auth/login.ts | +50/-10 |
| added | src/utils/helper.ts | +30/-0 |
| deleted | src/deprecated.ts | +0/-25 |

### Diff Content

<unified diff for each file>

Output Format

{
  "source": "github-pr",
  "repository": {
    "owner": "owner",
    "repo": "repo"
  },
  "pull_request": {
    "number": 123,
    "title": "feat: add user authentication",
    "body": "PR description...",
    "author": "username",
    "state": "open",
    "base": {
      "ref": "main",
      "sha": "abc123"
    },
    "head": {
      "ref": "feature/auth",
      "sha": "def456"
    },
    "labels": ["enhancement"],
    "created_at": "2024-01-15T10:30:00Z",
    "updated_at": "2024-01-15T12:00:00Z"
  },
  "stats": {
    "files_changed": 5,
    "additions": 120,
    "deletions": 45,
    "commits": 3
  },
  "files": [
    {
      "path": "src/auth/login.ts",
      "status": "modified",
      "additions": 50,
      "deletions": 10,
      "patch": "@@ -1,10 +1,50 @@\n..."
    }
  ],
  "diff": "<combined unified diff>"
}

Integration with Review Pipeline

After retrieving the PR diff, pass the output to:

1. codereview-orchestrator - For triage and routing
2. Then to appropriate specialist skills based on the triage
3. Finally to submit-github-review to post the review

Quick Reference

□ Parse PR Reference
  □ Extract owner, repo, pull_number
  □ Handle URL or short format

□ Fetch PR Details
  □ Call get_pull_request MCP tool
  □ Extract metadata and head SHA

□ Fetch Changed Files
  □ Call get_pull_request_files MCP tool
  □ Get patches for all files

□ Format Output
  □ Structure for review pipeline
  □ Include commit SHA for review submission

Example Usage in Pipeline

1. retrieve-diff-from-github-pr (this skill)
   ↓
2. codereview-orchestrator (triage)
   ↓
3. Specialist skills (review)
   ↓
4. submit-github-review (post review)

Error Handling