benchmark.yml

name: Benchmark

on:
  pull_request:
    branches: [main, develop]
  push:
    branches: [main, develop]

permissions:
  contents: read
  pull-requests: write
  packages: read

env:
  GOPRIVATE: github.com/GoCodeAlone/*
  GONOSUMCHECK: github.com/GoCodeAlone/*

jobs:
  benchmark:
    name: Performance Benchmarks
    runs-on: ubuntu-latest
    permissions:
      contents: read
      pull-requests: write
      packages: read

    steps:
    - name: Check out code
      uses: actions/checkout@v4

    - name: Set up Go
      uses: actions/setup-go@v5
      with:
        go-version: '1.26'
        cache: true

    - name: Set up Node.js
      uses: actions/setup-node@v4
      with:
        node-version: '20'
        registry-url: 'https://npm.pkg.github.com'
        cache: 'npm'
        cache-dependency-path: ui/package-lock.json

    - name: Build UI assets
      run: cd ui && npm ci && npm run build
      env:
        NODE_AUTH_TOKEN: ${{ secrets.GITHUB_TOKEN }}

    - name: Install benchstat
      run: go install golang.org/x/perf/cmd/benchstat@latest

    - name: Run benchmarks
      run: go test -bench=. -benchmem -count=6 -run=^$ -timeout=30m ./... | tee benchmark-results.txt

    - name: Restore baseline
      if: github.event_name == 'pull_request'
      id: restore-baseline
      uses: actions/cache/restore@v4
      with:
        path: baseline-bench.txt
        key: go-benchmark-${{ github.event.pull_request.base.ref }}-never
        restore-keys: |
          go-benchmark-${{ github.event.pull_request.base.ref }}-

    - name: Compare with baseline
      if: github.event_name == 'pull_request' && steps.restore-baseline.outputs.cache-matched-key != ''
      id: compare
      run: |
        echo "## benchstat: baseline → PR" > benchstat-output.txt
        benchstat baseline-bench.txt benchmark-results.txt >> benchstat-output.txt 2>&1 || true

        # Detect regressions: benchstat v2 output lines look like:
        #   BenchmarkName  1.00ns ± 1%  1.25ns ± 2%  +25.00% (p=0.002 n=6)
        # We look for lines containing a benchmark name (starts with Benchmark)
        # followed by a percentage increase >= 20%.
        regression=false
        while IFS= read -r line; do
          if echo "$line" | grep -qP '^\s*(│\s+)?Benchmark.*\+\d+\.\d+%'; then
            pct=$(echo "$line" | grep -oP '\+\K\d+\.\d+(?=%)' | tail -1)
            if [ -n "$pct" ] && echo "$pct" | awk '{ exit ($1 < 20.0) }'; then
              regression=true
              break
            fi
          fi
        done < benchstat-output.txt

        echo "regression=$regression" >> "$GITHUB_OUTPUT"
        if [ "$regression" = "true" ]; then
          echo "::warning::Potential performance regression detected (>= 20% slower)"
        fi

    - name: Comment PR with results
      if: github.event_name == 'pull_request' && steps.restore-baseline.outputs.cache-matched-key != ''
      uses: actions/github-script@v7
      with:
        script: |
          const fs = require('fs');
          const benchstat = fs.readFileSync('benchstat-output.txt', 'utf8');
          const regression = '${{ steps.compare.outputs.regression }}' === 'true';

          const body = [
            '## ⏱ Benchmark Results',
            '',
            regression
              ? '⚠️ **Potential performance regression detected** — one or more benchmarks regressed ≥ 20%.'
              : '✅ **No significant performance regressions detected.**',
            '',
            '<details>',
            '<summary>benchstat comparison (baseline → PR)</summary>',
            '',
            '```',
            benchstat,
            '```',
            '',
            '</details>',
            '',
            '> Benchmarks run with `go test -bench=. -benchmem -count=6`.',
            '> Regressions ≥ 20% are flagged. Results compared via [`benchstat`](https://pkg.go.dev/golang.org/x/perf/cmd/benchstat).',
          ].join('\n');

          // Upsert: update existing comment or create a new one.
          const { data: comments } = await github.rest.issues.listComments({
            owner: context.repo.owner,
            repo: context.repo.repo,
            issue_number: context.issue.number,
          });

          const marker = '## ⏱ Benchmark Results';
          const existing = comments.find(c => c.body.includes(marker));

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

    - name: No baseline available
      if: github.event_name == 'pull_request' && steps.restore-baseline.outputs.cache-matched-key == ''
      run: |
        echo "::notice::No benchmark baseline found for branch '${{ github.event.pull_request.base.ref }}'. Baseline will be created on next push to that branch."

    # On push to main/develop, save the results as the new baseline.
    - name: Prepare baseline for cache
      if: github.event_name == 'push'
      run: cp benchmark-results.txt baseline-bench.txt

    - name: Save baseline
      if: github.event_name == 'push'
      uses: actions/cache/save@v4
      with:
        path: baseline-bench.txt
        key: go-benchmark-${{ github.ref_name }}-${{ github.sha }}

    - name: Upload benchmark results
      if: always()
      uses: actions/upload-artifact@v4
      with:
        name: benchmark-results
        path: |
          benchmark-results.txt
          benchstat-output.txt
        retention-days: 30
        if-no-files-found: ignore

    - name: Fail on regression
      if: github.event_name == 'pull_request' && steps.compare.outputs.regression == 'true'
      run: |
        echo "::error::Performance regression detected. Review the benchmark results in the PR comment."
        exit 1