bench.yml

name: Bench

on:
  pull_request:
    branches: [main]

# Skip on docs-only PRs to avoid slowing them down.
permissions:
  contents: read
  pull-requests: write

jobs:
  bench:
    runs-on: ubuntu-latest
    timeout-minutes: 15
    steps:
      - name: Checkout PR
        uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Set up Bun
        uses: oven-sh/setup-bun@v2
        with:
          bun-version: 1.3.14
      
      - name: Cache Bun dependencies
        uses: actions/cache@v4
        with:
          path: |
            ~/.bun/install/cache
            **/node_modules
          key: ${{ runner.os }}-bun-${{ hashFiles('bun.lock') }}
          restore-keys: |
            ${{ runner.os }}-bun-
      
      - name: Install dependencies
        run: bun install --frozen-lockfile
      
      - name: Bench HEAD
        run: |
          bun run bench | tee bench-head.txt
          grep '^BENCH_RESULT_JSON: ' bench-head.txt | sed 's/^BENCH_RESULT_JSON: //' > bench-head.json

      - name: Checkout main into worktree
        run: git worktree add ../main-worktree origin/main

      - name: Install dependencies (main)
        working-directory: ../main-worktree
        run: bun install --frozen-lockfile

      - name: Bench main
        working-directory: ../main-worktree
        run: |
          if [ -f packages/core/src/benchmark/run-all.ts ]; then
            bun run bench | tee ../bench-main.txt
            grep '^BENCH_RESULT_JSON: ' ../bench-main.txt | sed 's/^BENCH_RESULT_JSON: //' > $GITHUB_WORKSPACE/bench-main.json
          elif [ -f packages/core/src/benchmark/render-loop.ts ]; then
            bun packages/core/src/benchmark/render-loop.ts | tee ../bench-main.txt
            grep '^BENCH_RESULT_JSON: ' ../bench-main.txt | sed 's/^BENCH_RESULT_JSON: //' > $GITHUB_WORKSPACE/bench-main.json
          else
            echo "No benchmark on main yet — using HEAD as baseline (no regression possible)."
            cp $GITHUB_WORKSPACE/bench-head.json $GITHUB_WORKSPACE/bench-main.json
          fi

      - name: Check if this is benchmark system upgrade
        id: check-upgrade
        run: |
          # Check if run-all.ts exists in PR but not in main, or if they differ
          if [ -f packages/core/src/benchmark/run-all.ts ] && [ ! -f ../main-worktree/packages/core/src/benchmark/run-all.ts ]; then
            echo "is_upgrade=true" >> $GITHUB_OUTPUT
            echo "This PR adds the benchmark system - skipping regression checks"
          elif [ -f packages/core/src/benchmark/run-all.ts ] && [ -f ../main-worktree/packages/core/src/benchmark/run-all.ts ]; then
            # Compare the files directly
            if ! diff -q packages/core/src/benchmark/run-all.ts ../main-worktree/packages/core/src/benchmark/run-all.ts > /dev/null 2>&1; then
              echo "is_upgrade=true" >> $GITHUB_OUTPUT
              echo "This PR upgrades the benchmark system - skipping regression checks"
            else
              echo "is_upgrade=false" >> $GITHUB_OUTPUT
            fi
          else
            echo "is_upgrade=false" >> $GITHUB_OUTPUT
          fi

      - name: Compare results
        id: compare
        continue-on-error: true
        if: steps.check-upgrade.outputs.is_upgrade != 'true'
        run: |
          node scripts/compare-bench.mjs bench-head.json bench-main.json --threshold 0.20
          echo "Compare exit code: $?"

      - name: Skip comparison for upgrade
        if: steps.check-upgrade.outputs.is_upgrade == 'true'
        run: |
          echo '<!-- termui-bench-comment -->' > bench-comment.md
          echo '## Performance benchmarks' >> bench-comment.md
          echo '' >> bench-comment.md
          echo 'ℹ️ **Benchmark system upgrade** - This PR adds or upgrades the benchmark infrastructure.' >> bench-comment.md
          echo '' >> bench-comment.md
          echo 'Regression checks are skipped for this upgrade PR. Future PRs will compare against the new baseline.' >> bench-comment.md
          echo '' >> bench-comment.md
          echo 'Benchmark results:' >> bench-comment.md
          cat bench-head.json >> bench-comment.md

      - name: Post or update PR comment
        continue-on-error: true
        uses: peter-evans/create-or-update-comment@v4
        with:
          issue-number: ${{ github.event.pull_request.number }}
          body-path: bench-comment.md
          edit-mode: replace

      - name: Fail on regression
        if: steps.compare.outcome == 'failure'
        run: |
          echo "::error::Performance benchmark regressed by ≥20% on at least one metric."
          exit 1