benchmark.yml

name: Benchmark PR

on:
  pull_request:
    types: [opened, synchronize, reopened]

permissions:
  contents: read
  pull-requests: write

jobs:
  benchmark:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v6
        with:
          fetch-depth: 0

      - uses: dtolnay/rust-toolchain@stable

      - uses: actions/cache@v5
        with:
          path: |
            ~/.cargo/registry
            ~/.cargo/git
            target
          key: ${{ runner.os }}-bench-${{ hashFiles('**/Cargo.lock') }}

      - name: Benchmark main branch
        run: |
          git fetch origin ${{ github.base_ref }}
          git checkout origin/${{ github.base_ref }}
          cargo bench --bench flatten --color never -- --save-baseline main

      - name: Benchmark PR branch
        run: |
          git checkout ${{ github.event.pull_request.head.sha }}
          cargo bench --bench flatten --color never -- --baseline main > bench_output.txt 2>&1

      - name: Extract comparison summary
        run: |
          grep -E "(^flatten_|^\s+(time:|thrpt:|change:)|Performance has)" bench_output.txt > bench_summary.txt || echo "No comparison data" > bench_summary.txt
          cat bench_summary.txt

      - name: Comment PR
        uses: actions/github-script@v9
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const fs = require('fs');
            const output = fs.readFileSync('bench_summary.txt', 'utf8');

            const body = `## Benchmark Results

            \`\`\`
            ${output}
            \`\`\`

            ---
            Benchmarked on commit \`${{ github.event.pull_request.head.sha }}\``;

            const { data: comments } = await github.rest.issues.listComments({
              owner: context.repo.owner,
              repo: context.repo.repo,
              issue_number: context.issue.number,
            });

            const botComment = comments.find(c =>
              c.user.login === 'github-actions[bot]' &&
              c.body.includes('Benchmark Results')
            );

            if (botComment) {
              await github.rest.issues.updateComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                comment_id: botComment.id,
                body: body
              });
            } else {
              await github.rest.issues.createComment({
                owner: context.repo.owner,
                repo: context.repo.repo,
                issue_number: context.issue.number,
                body: body
              });
            }