Build Size workflow (playcanvas/engine)

name: Build Size
 
# Builds only the minified engine bundles (UMD + ESM) for the PR head and its base, measures their
# raw / gzip / brotli sizes, diffs the two and posts/updates a sticky PR comment. There is no stored
# baseline - the base commit is rebuilt fresh in the same run, so the comparison is always "this PR
# vs the main it targets". Informative only; never fails the build.
#
# Only the min bundles are built (not rel/dbg/prf/types) to keep the run fast.
#
# Note: comments directly, so on fork PRs (read-only token) the comment step can't post; it is
# marked continue-on-error so those runs stay green (just without a comment).
 
on:
  pull_request:
    branches: [main]
    types: [opened, synchronize, reopened]
 
permissions:
  contents: read
  pull-requests: write
 
concurrency:
  group: build-size-${{ github.event.pull_request.number }}
  cancel-in-progress: true
 
jobs:
  build-size:
    name: Build Size
    runs-on: latchkey-small
    timeout-minutes: 20
    # Pin the embedded git revision to a constant for both builds; otherwise the differing commit
    # hashes baked into each bundle show up as a phantom (compressed-)size diff even when no code
    # changed. Honoured by utils/rollup-version-revision.mjs.
    env:
      ENGINE_BUILD_REVISION: ci-build-size
    steps:
      - name: Check out base
        uses: actions/checkout@v7.0.0
        with:
          ref: ${{ github.event.pull_request.base.sha }}
          path: base
 
      - name: Check out PR
        uses: actions/checkout@v7.0.0
        with:
          path: pr
 
      - name: Setup Node.js 24.x
        uses: actions/setup-node@v6
        with:
          cache: 'npm'
          node-version: 24.x
 
      - name: Build base bundles
        run: |
          cp pr/utils/build-size.mjs base/utils/build-size.mjs
          cp pr/utils/rollup-version-revision.mjs base/utils/rollup-version-revision.mjs
          cd base
          npm clean-install --progress=false --no-fund
          npm run build:min:umd
          npm run build:min:esm
          node utils/build-size.mjs > sizes.json
 
      - name: Build PR bundles
        run: |
          cd pr
          npm clean-install --progress=false --no-fund
          npm run build:min:umd
          npm run build:min:esm
          node utils/build-size.mjs > sizes.json
 
      - name: Comment on PR
        continue-on-error: true # fork PRs get a read-only token; don't fail the run if commenting is denied
        uses: actions/github-script@v9
        with:
          script: |
            const fs = require('fs');
            const MARKER = '<!-- build-size-bot -->';
            const prNumber = context.payload.pull_request.number;
 
            const read = p => fs.existsSync(p) ? JSON.parse(fs.readFileSync(p, 'utf8')) : {};
            const base = read('base/sizes.json');
            const pr = read('pr/sizes.json');
 
            const kb = n => `${(n / 1024).toFixed(1)} KB`;
            const cell = (b, p) => {
              const d = p - b;
              if (!b) return `${kb(p)} (new)`;
              if (!d) return `${kb(p)} -`;
              const sign = d > 0 ? '+' : '−';
              const pct = (Math.abs(d) / b * 100).toFixed(2);
              return `${kb(p)} (${sign}${kb(Math.abs(d))}, ${sign}${pct}%)`;
            };
 
            const bundles = [...new Set([...Object.keys(base), ...Object.keys(pr)])].sort();
            const changed = bundles.some(name =>
              ['raw', 'gzip', 'brotli'].some(m => (base[name]?.[m] ?? 0) !== (pr[name]?.[m] ?? 0)));
 
            const rows = bundles.map((name) => {
              const b = base[name] || {}, p = pr[name] || {};
              return `| \`${name}\` | ${cell(b.raw, p.raw)} | ${cell(b.gzip, p.gzip)} | ${cell(b.brotli, p.brotli)} |`;
            });
 
            const headline = changed
              ? 'This PR changes the size of the minified bundles.'
              : 'This PR does not change the size of the minified bundles.';
            const body = `${MARKER}\n### Build size report\n\n`
              + `${headline}\n\n`
              + `| Bundle | Minified | Gzip | Brotli |\n`
              + `| --- | --- | --- | --- |\n`
              + `${rows.join('\n')}\n`;
 
            const { owner, repo } = context.repo;
            const comments = await github.paginate(github.rest.issues.listComments, { owner, repo, issue_number: prNumber });
            const existing = comments.find(c => c.body && c.body.includes(MARKER));
 
            if (existing) {
              await github.rest.issues.updateComment({ owner, repo, comment_id: existing.id, body });
            } else {
              await github.rest.issues.createComment({ owner, repo, issue_number: prNumber, body });
            }