benchmarks.yml

name: Benchmarks

on:
  pull_request:
    paths:
      # perf-sensitive code — the measurement target
      - 'packages/**'
      # bench workflow itself — changes here take effect on this PR's own
      # run (pull_request uses PR-head YAML), so self-test
      - '.github/workflows/benchmarks.yml'
      # Bench source (bench-*.js, tachometer-ci*.json, build-ci.js) and
      # reporter (tools/ci/bench/reporter/**) are deliberately NOT listed here.
      # The discover and benchmarks jobs overlay main's copy of both before
      # every run, so PR-side edits have no effect on the PR's own comment.
      # Harness changes land on main in a separate PR; test-taker cannot
      # author the test.
  # Bench every merge commit on main so bench-history.json accumulates
  # absolute CIs per commit. These runs aren't gated against anything —
  # the report workflow branches on event type and appends history instead
  # of posting a PR comment.
  push:
    branches: [main]
    paths:
      - 'packages/**'

concurrency:
  group: bench-${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

permissions:
  contents: read

jobs:
  # Discover which tachometer configs are in changed packages.
  # Emits one matrix entry per tachometer-ci*.json so each runs in its own
  # parallel job with its own PR check.
  discover:
    runs-on: ubuntu-latest
    outputs:
      matrix: ${{ steps.matrix.outputs.result }}
      has-benchmarks: ${{ steps.matrix.outputs.has-benchmarks }}
    steps:
      - uses: actions/checkout@v6
        with:
          fetch-depth: 0

      - uses: actions/setup-node@v6
        with:
          node-version-file: '.node-version'

      # Pin bench harness to main. Matrix composition (tools/ci/bench/matrix,
      # bench source, tachometer configs, reporter) is author-neutral —
      # test-taker can't widen or narrow its own scope, rewrite discover.js,
      # or add a rigged config. Harness changes land on main first.
      - name: Overlay bench harness from main
        run: |
          git fetch origin main --depth=1
          git checkout origin/main -- packages/*/bench/ tools/ci/bench/reporter/ tools/ci/bench/matrix/ 2>/dev/null || true

      # Collect the PR's changed-file set vs base; discover.js filters the
      # matrix to configs whose owning package's @semantic-ui/* dep closure
      # intersects the diff. Push to main writes an empty file — discover.js
      # falls through to "run everything" for bench-history continuity.
      - name: Collect changed files
        run: |
          if [ '${{ github.event_name }}' = 'pull_request' ]; then
            git fetch origin ${{ github.event.pull_request.base.ref }} --depth=1
            git diff --name-only FETCH_HEAD...HEAD > /tmp/changed-files.txt
          else
            : > /tmp/changed-files.txt
          fi
          echo 'Changed files:'
          cat /tmp/changed-files.txt

      - name: Build matrix
        id: matrix
        env:
          CHANGED_FILES_PATH: /tmp/changed-files.txt
        run: node tools/ci/bench/matrix/discover.js

  benchmarks:
    needs: discover
    if: needs.discover.outputs.has-benchmarks == 'true'
    strategy:
      fail-fast: false
      matrix:
        entry: ${{ fromJson(needs.discover.outputs.matrix) }}
    name: bench-${{ matrix.entry.name }}
    runs-on: ubuntu-latest
    # With amplified metrics (Bench: Amplify… commits), a typical run lands
    # at 12-14 min — initial sampling dominates, ~9 min at N=50 × 2 benches ×
    # N metrics, then auto-sample usually converges in 2-3 min. 20-min cap
    # gives a few minutes of margin over the observed ceiling.
    timeout-minutes: 20

    steps:
      - uses: actions/checkout@v6

      - uses: actions/setup-node@v6
        with:
          node-version-file: '.node-version'
          cache: 'npm'
          cache-dependency-path: package-lock.json

      - name: Install dependencies
        run: npm ci

      - name: Install matching chromedriver
        run: |
          CHROME_VERSION=$(google-chrome --version | grep -oP '\d+' | head -1)
          npm install chromedriver@${CHROME_VERSION} --no-save

      # Pin bench harness to main for both current and baseline builds.
      # The PR only contributes packages/*/src/; bench code, tachometer
      # configs, and build-ci.js always come from main so the measurement
      # is author-neutral.
      - name: Overlay bench harness from main
        run: |
          git fetch origin main --depth=1
          git checkout origin/main -- packages/*/bench/ tools/ci/bench/reporter/ 2>/dev/null || true

      # Build current branch benchmark bundles
      - name: Build current
        run: node packages/${{ matrix.entry.package }}/bench/tachometer/build-ci.js current

      # Swap source to the appropriate baseline and build baseline bundles.
      # PR: baseline = base branch tip.
      # Push to main: baseline = this commit's parent (so the delta captures
      #   the merged commit's effect; bench-history indexes the current
      #   commit's absolute CI alongside the within-session percent-delta).
      #
      # Resolve baseline SHA inline so it can be written to the artifact as
      # a sidecar (baseline-sha.txt). The reporter pins each metric's
      # percent_delta_ci to that SHA — required for cross-iteration drift
      # detection (see tools/ci/bench/reporter/reporter.js:computeBaselineDrift).
      - name: Build baseline
        run: |
          if [ '${{ github.event_name }}' = 'push' ]; then
            # Fetch enough history to reach the parent commit locally.
            git fetch origin main --depth=2
            BASELINE_SHA=$(git rev-parse HEAD~1)
            git checkout HEAD~1 -- packages/*/src/
          else
            git fetch origin ${{ github.event.pull_request.base.ref }} --depth=1
            BASELINE_SHA=$(git rev-parse FETCH_HEAD)
            git checkout FETCH_HEAD -- packages/*/src/
          fi
          node packages/${{ matrix.entry.package }}/bench/tachometer/build-ci.js baseline
          git checkout HEAD -- packages/*/src/
          mkdir -p results
          echo "$BASELINE_SHA" > results/baseline-sha.txt

      # Run just this matrix cell's single config.
      # Per-cell auto-sample tail is governed by the config's own `timeout`
      # (tachometer rejects --timeout alongside --config). Hard runaway
      # protection is `timeout-minutes: 10` at the job level above.
      - name: Run benchmark
        run: |
          mkdir -p results
          npx tachometer \
            --config "${{ matrix.entry.config }}" \
            --json-file "results/${{ matrix.entry.package }}-${{ matrix.entry.name }}.json"

      - name: Upload results
        uses: actions/upload-artifact@v7
        with:
          name: results-${{ matrix.entry.name }}
          # Include baseline-sha.txt sidecar — the reporter and history
          # archiver read it to pin percent_delta_ci entries to their
          # baseline SHA.
          path: |
            results/*.json
            results/baseline-sha.txt