Use esbuild for bundle-size measurements

.github/workflows/pr-bundle-size-comment.yml

@@ -35,6 +35,9 @@ jobs:
           repository: ${{ github.repository }}
           run-id: ${{ github.event.workflow_run.id }}
 
+      - name: Validate downloaded bundle size report
+        run: node apps/bundle-size/scripts/validate-report.mjs bundle-size-analysis/report.md
+
       - name: Publish bundle size PR comment
         env:
           EXPECTED_HEAD_REPOSITORY: ${{ github.event.workflow_run.head_repository.full_name }}

.github/workflows/pr.yml

@@ -75,6 +75,9 @@ jobs:
       - name: Measure bundle sizes
         run: yarn bundle-size --baseline "$env:RUNNER_TEMP\bundle-size-baseline.json"
 
+      - name: Validate bundle size report
+        run: yarn workspace @fluentui-react-native/bundle-size validate-report
+
       - name: Publish bundle size summary
         run: Get-Content apps\bundle-size\dist\bundle-size\report.md -Raw | Out-File -FilePath $env:GITHUB_STEP_SUMMARY -Append
 

apps/bundle-size/README.md

@@ -1,10 +1,8 @@
 # Bundle-size fixture
 
-This private app measures minified, tree-shaken Metro consumer bundles without including a test
-app or Storybook catalog. It uses `@rnx-kit/metro-config`,
-`@rnx-kit/metro-resolver-symlinks` with `oxc-resolver`, and
-`@rnx-kit/metro-serializer-esbuild`. Each target scenario is compared with the same React Native
-shell on macOS, Win32, and Windows.
+This private app measures minified, tree-shaken esbuild consumer bundles without including a test
+app or Storybook catalog. React, React Native, React Native SVG, desktop React Native forks, and
+`@svgo` imports are external so measurements contain only the package code under test.
 
 Run every configured scenario from the repository root:
 
@@ -20,16 +18,12 @@ yarn bundle-size --platform macos --platform win32
 ```
 
 Results, source maps, and esbuild metafiles are written to the ignored `dist/bundle-size`
-directory. The runner passes `--tree-shake true` and `--metafile <scenario>.meta.json` to
-`rnx-cli bundle`. The JSON report contains raw bytes, gzip bytes, contributing esbuild input
-counts, Metro source-map counts, workspace package contribution bytes, and shell deltas. Raw
-bytes are the primary comparison; gzip and module attribution are diagnostic signals. The
-terminal summary shows the shell's absolute cost and each package scenario's incremental module
-and byte cost above its platform shell, plus signed deltas from the baseline.
-
-The Babel configuration preserves ESM for the serializer while explicitly lowering JSX. The
-explicit JSX transform is required because the desktop React Native packages publish JSX in
-`.js` files, which esbuild otherwise parses with its plain JavaScript loader.
+directory. Platform-specific module resolution prefers `.<platform>`, then `.native`, then
+generic TypeScript and JavaScript extensions. Package exports use the `react-native` condition.
+The JSON report contains raw bytes, gzip bytes, contributing esbuild input counts, and workspace
+package contribution bytes. Raw bytes are the primary comparison; gzip and module attribution
+are diagnostic signals. The terminal summary shows each scenario's absolute module and byte cost
+plus signed deltas from the baseline.
 
 ## Baselines and pull requests
 
@@ -42,18 +36,19 @@ yarn bundle-size:update
 ```
 
 Review the baseline diff together with the implementation that caused it. The PR workflow adds
-the Markdown comparison to its job summary, updates one persistent PR comment, and uploads the
-complete `dist/bundle-size` directory, including the esbuild metafiles, for investigation.
-Same-repository PRs publish directly; fork and Dependabot reports are strictly validated and
-published by a separate trusted completion workflow.
+the Markdown comparison to its job summary only after validating the trusted report format,
+updates one persistent PR comment, and uploads the complete `dist/bundle-size` directory,
+including the esbuild metafiles, for investigation. Same-repository PRs publish directly; fork
+and Dependabot reports are validated again and published by a separate trusted completion
+workflow.
 
 ## Adding a package or submodule
 
-1. Add the package to this fixture's dependencies so the pnpm linker exposes it to Metro.
+1. Add the package to this fixture's dependencies so the pnpm linker exposes it to esbuild.
 2. Add a scenario to `scenarios.json` with a stable name, module specifier, and either `exports`
    or `namespace: true`.
-3. Run `yarn bundle-size` and inspect the shell delta and generated esbuild metafile. The
-   metafile can also be loaded into the esbuild bundle analyzer.
+3. Run `yarn bundle-size` and inspect the generated esbuild metafile. The metafile can also be
+   loaded into the esbuild bundle analyzer.
 
 Use a supported public package or subpath export when measuring consumer cost. A source-relative
 module path is useful for diagnostics, but it does not prove the cost of the published API.