benchmark.yml

name: Benchmark

on:
  pull_request:
    branches: [master]

permissions:
  contents: read
  pull-requests: write

# Cancel a previous in-flight benchmark run when the PR gets a new push.
concurrency:
  group: benchmark-${{ github.event.pull_request.number || github.ref }}
  cancel-in-progress: true

jobs:
  benchmark:
    name: Benchmark Comparison
    runs-on: ubuntu-latest
    timeout-minutes: 20
    steps:
      - name: Checkout PR
        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v6

      - uses: actions/setup-go@b7ad1dad31e06c5925ef5d2fc7ad053ef454303e # v7.0.0
        with:
          go-version: stable

      # -run='^$' matches no tests, so this runs ONLY benchmarks. Without it,
      # `go test -bench` also runs the full unit-test suite (in both checkouts),
      # which is what made this job time out at 10m. -benchtime/-count are kept
      # modest to keep the PR signal fast; benchstat still flags real regressions.
      #
      # Results are written to $RUNNER_TEMP, not the workspace: the "Checkout base"
      # step below runs actions/checkout again, which cleans the working tree
      # (git clean -ffdx) and would otherwise delete pr.bench before benchstat runs.
      - name: Run benchmarks on PR
        run: go test -bench=. -benchmem -run='^$' -benchtime=100ms -count=6 -timeout=15m ./... | tee "$RUNNER_TEMP/pr.bench"

      - name: Checkout base
        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v6
        with:
          ref: ${{ github.event.pull_request.base.sha }}

      - name: Run benchmarks on base
        run: go test -bench=. -benchmem -run='^$' -benchtime=100ms -count=6 -timeout=15m ./... | tee "$RUNNER_TEMP/base.bench"

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

      - name: Compare benchmarks
        run: |
          echo '## Benchmark Comparison' > bench-report.md
          echo '' >> bench-report.md
          echo '```' >> bench-report.md
          benchstat "$RUNNER_TEMP/base.bench" "$RUNNER_TEMP/pr.bench" >> bench-report.md 2>&1 || true
          echo '```' >> bench-report.md

      - name: Post benchmark results
        uses: marocchino/sticky-pull-request-comment@5770ad5eb8f42dd2c4f34da00c94c5381e49af88 # v3.0.5
        with:
          header: benchmark
          path: bench-report.md