fix(legacy): use prebuilt-chunk for polyfill chunks (#21498)

Author: sapphi-red

docs/guide/migration.md

@@ -342,7 +342,6 @@ The following options are deprecated and will be removed in the future:
 These breaking changes are expected to only affect a minority of use cases:
 
 - **[TODO: this will be fixed before stable release]** https://github.com/rolldown/rolldown/issues/5726 (affects nuxt, qwik)
-- **[TODO: this will be fixed before stable release]** Legacy chunks are emitted as an asset file instead of a chunk file due to the lack of prebuilt chunk emit feature ([rolldown#4304](https://github.com/rolldown/rolldown/issues/4034)). This means the chunk related options does not apply to legacy chunks and the manifest file will not include legacy chunks as a chunk file.
 - **[TODO: this will be fixed before stable release]** `@vite-ignore` comment edge case ([rolldown-vite#426](https://github.com/vitejs/rolldown-vite/issues/426))
 - [Extglobs](https://github.com/micromatch/picomatch/blob/master/README.md#extglobs) are not supported yet ([rolldown-vite#365](https://github.com/vitejs/rolldown-vite/issues/365))
 - `define` does not share reference for objects: When you pass an object as a value to `define`, each variable will have a separate copy of the object. See [Oxc Transformer document](https://oxc.rs/docs/guide/usage/transformer/global-variable-replacement#define) for more details.

packages/plugin-legacy/src/index.ts

@@ -900,9 +900,16 @@ async function buildPolyfillChunk(
 
   // add the chunk to the bundle
   ctx.emitFile({
-    type: 'asset',
+    type: 'prebuilt-chunk',
+    name: polyfillChunk.name,
     fileName: polyfillChunk.fileName,
-    source: polyfillChunk.code,
+    code: polyfillChunk.code,
+    facadeModuleId: polyfillChunk.facadeModuleId ?? undefined,
+    isEntry: polyfillChunk.isEntry,
+    isDynamicEntry: polyfillChunk.isDynamicEntry,
+    exports: [],
+    map: polyfillChunk.map ?? undefined,
+    sourcemapFileName: polyfillChunk.sourcemapFileName ?? undefined,
   })
   if (polyfillChunk.sourcemapFileName) {
     const polyfillChunkMapAsset = _polyfillChunk.output.find(

playground/legacy/__tests__/legacy.spec.ts

@@ -86,11 +86,10 @@ describe.runIf(isBuild)('build', () => {
   test('should generate correct manifest', async () => {
     const manifest = readManifest()
     // legacy polyfill
-    // FIXME: needs https://github.com/rolldown/rolldown/issues/4034
-    // expect(manifest['../../vite/legacy-polyfills-legacy']).toBeDefined()
-    // expect(manifest['../../vite/legacy-polyfills-legacy'].src).toBe(
-    //   '../../vite/legacy-polyfills-legacy',
-    // )
+    expect(manifest['../../vite/legacy-polyfills-legacy']).toBeDefined()
+    expect(manifest['../../vite/legacy-polyfills-legacy'].src).toBe(
+      '../../vite/legacy-polyfills-legacy',
+    )
     expect(manifest['custom0-legacy.js'].file).toMatch(
       /chunk-X-legacy\.[-\w]{8}.js/,
     )
@@ -101,11 +100,10 @@ describe.runIf(isBuild)('build', () => {
       /chunk-X-legacy[-\w]{8}.js/,
     )
     // modern polyfill
-    // FIXME: needs https://github.com/rolldown/rolldown/issues/4034
-    // expect(manifest['../../vite/legacy-polyfills']).toBeDefined()
-    // expect(manifest['../../vite/legacy-polyfills'].src).toBe(
-    //   '../../vite/legacy-polyfills',
-    // )
+    expect(manifest['../../vite/legacy-polyfills']).toBeDefined()
+    expect(manifest['../../vite/legacy-polyfills'].src).toBe(
+      '../../vite/legacy-polyfills',
+    )
   })
 
   test('should minify legacy chunks with terser', async () => {

playground/legacy/__tests__/watch/legacy-styles-only-entry-watch.spec.ts

@@ -17,7 +17,7 @@ test.runIf(isBuild)('rebuilds styles only entry on change', async () => {
   )
   expect(findAssetFile(/polyfills-legacy-.+\.js/, 'watch')).toBeTruthy()
   const numberOfManifestEntries = Object.keys(readManifest('watch')).length
-  expect(numberOfManifestEntries).toBe(2) // FIXME: needs https://github.com/rolldown/rolldown/issues/4034
+  expect(numberOfManifestEntries).toBe(3)
 
   editFile('style-only-entry.css', (originalContents) =>
     originalContents.replace('#ff69b4', '#ffb6c1'),