Automate GitHub Pull Request Reviews with Antigravity: A Practical Guide

# Verify GitHub CLI installation
gh --version
# gh version 2.x.x
 
# Authenticate with GitHub (first time only)
gh auth login
# A browser window will open for GitHub authentication

// scripts/ai-pr-review.ts
// Antigravity × GitHub PR review automation script
import { execSync } from "child_process";
 
interface ReviewComment {
  file: string;
  line: number;
  severity: "error" | "warning" | "info";
  message: string;
}
 
function getPRDiff(prNumber: number): string {
  // Fetch the PR diff
  const diff = execSync(`gh pr diff ${prNumber}`, {
    encoding: "utf-8",
  });
  return diff;
}
 
function parseDiffFiles(diff: string): string[] {
  // Extract changed file names from the diff
  const files = diff
    .split("\n")
    .filter((line) => line.startsWith("diff --git"))
    .map((line) => {
      const match = line.match(/b\/(.+)$/);
      return match ? match[1] : "";
    })
    .filter(Boolean);
  return files;
}
 
function generateReviewPrompt(
  diff: string,
  files: string[]
): string {
  return `
Please review the following PR diff.
 
## Review Criteria
- Type safety (potential TypeScript type errors)
- Error handling (unhandled exceptions, edge cases)
- Security (injection vulnerabilities, auth gaps)
- Performance (unnecessary re-renders, N+1 queries)
- Code quality (naming conventions, separation of concerns)
 
## Changed Files
${files.map((f) => `- ${f}`).join("\n")}
 
## Diff
\`\`\`diff
${diff}
\`\`\`
 
For each file, provide specific line numbers and improvement suggestions.
If no issues are found, mark the file as "LGTM".
  `.trim();
}
 
// Main execution
const prNumber = parseInt(process.argv[2] || "0");
if (!prNumber) {
  console.error("Usage: npx tsx scripts/ai-pr-review.ts <PR_NUMBER>");
  process.exit(1);
}
 
const diff = getPRDiff(prNumber);
const files = parseDiffFiles(diff);
const prompt = generateReviewPrompt(diff, files);
 
console.log("📝 Files to review:");
files.forEach((f) => console.log(`  - ${f}`));
console.log("\n🤖 Pass this prompt to the Antigravity agent:\n");
console.log(prompt);
 
// Expected output:
// 📝 Files to review:
//   - src/components/UserProfile.tsx
//   - src/lib/api.ts
//
// 🤖 Pass this prompt to the Antigravity agent:
// (Review prompt is displayed)

# .github/workflows/ai-review.yml
name: AI Code Review
 
on:
  pull_request:
    types: [opened, synchronize]
 
permissions:
  contents: read
  pull-requests: write
 
jobs:
  ai-review:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 0
 
      - name: Get changed files
        id: changed
        run: |
          FILES=$(gh pr diff ${{ github.event.pull_request.number }} --name-only)
          echo "files<<EOF" >> $GITHUB_OUTPUT
          echo "$FILES" >> $GITHUB_OUTPUT
          echo "EOF" >> $GITHUB_OUTPUT
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
      - name: Run lint and type check
        run: |
          npm ci
          npm run lint -- --format json > lint-results.json || true
          npx tsc --noEmit 2> type-errors.txt || true
 
      - name: Post review summary
        if: always()
        run: |
          LINT_ERRORS=$(cat lint-results.json | jq '[.[] | .messages | length] | add // 0')
          TYPE_ERRORS=$(wc -l < type-errors.txt | tr -d ' ')
 
          BODY="## 🤖 AI Code Review Summary\n\n"
          BODY+="| Check | Result |\n"
          BODY+="| --- | --- |\n"
          BODY+="| Lint Errors | ${LINT_ERRORS} |\n"
          BODY+="| Type Errors | ${TYPE_ERRORS} |\n\n"
 
          if [ "$LINT_ERRORS" -gt 0 ] || [ "$TYPE_ERRORS" -gt 0 ]; then
            BODY+="⚠️ Issues detected by automated checks. See step logs for details."
          else
            BODY+="✅ All automated checks passed."
          fi
 
          gh pr comment ${{ github.event.pull_request.number }} --body "$(echo -e "$BODY")"
        env:
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}

# AGENTS.md — PR Review Policy
 
## Code Review Standards
 
### Must-Check Items (Blockers)
- Unhandled Promise / async-await errors
- Missing user input validation
- Hardcoded secrets (API keys, tokens)
- Inappropriate type assertions (as any)
 
### Recommendations (Suggestions)
- Suggest splitting functions longer than 50 lines
- Extract magic numbers into named constants
- Encourage comments that explain "why", not "what"
 
### Out of Scope
- Formatting (handled by Prettier)
- Import ordering (enforced by ESLint rules)

// scripts/post-review-comment.ts
// Post review results as a GitHub PR comment
import { execSync } from "child_process";
 
interface ReviewResult {
  summary: string;
  issues: Array<{
    file: string;
    line: number;
    message: string;
  }>;
  approved: boolean;
}
 
function postReviewComment(
  prNumber: number,
  review: ReviewResult
): void {
  const body = formatReviewBody(review);
 
  // Post PR comment using gh CLI
  execSync(
    `gh pr comment ${prNumber} --body '${body.replace(/'/g, "'\\''")}'`,
    { stdio: "inherit" }
  );
 
  console.log(`✅ Review comment posted to PR #${prNumber}`);
}
 
function formatReviewBody(review: ReviewResult): string {
  let body = "## 🤖 Antigravity AI Review\n\n";
  body += `**Verdict**: ${review.approved ? "✅ LGTM" : "⚠️ Changes Requested"}\n\n`;
  body += `### Summary\n${review.summary}\n\n`;
 
  if (review.issues.length > 0) {
    body += "### Issues Found\n\n";
    for (const issue of review.issues) {
      body += `- **${issue.file}:${issue.line}** — ${issue.message}\n`;
    }
  }
 
  return body;
}
 
// Usage example
const sampleReview: ReviewResult = {
  summary:
    "Overall code quality is good. One error handling improvement identified.",
  issues: [
    {
      file: "src/lib/api.ts",
      line: 45,
      message:
        "Missing error handling for fetch. Add a try-catch block to handle network errors gracefully.",
    },
  ],
  approved: false,
};
 
const prNumber = parseInt(process.argv[2] || "0");
if (prNumber) {
  postReviewComment(prNumber, sampleReview);
}
 
// Expected output:
// ✅ Review comment posted to PR #42