perf(@angular/build): default chunk optimization to use Rolldown

Now that Rolldown is stable, swap the default chunk optimizer from Rollup to Rolldown to utilize native compilation benefits and optimize heap memory usage.

Rollup remains an optional peer dependency of @angular/build, allowing users to opt back into Rollup by setting the environment variable `NG_BUILD_CHUNKS_ROLLDOWN=false` if it is also installed in the project.

Author: clydin

packages/angular/build/package.json

@@ -36,7 +36,7 @@
     "parse5-html-rewriting-stream": "8.0.1",
     "picomatch": "4.0.4",
     "piscina": "5.2.0",
-    "rollup": "4.62.0",
+    "rolldown": "1.1.1",
     "sass": "1.101.0",
     "semver": "7.8.4",
     "source-map-support": "0.5.21",
@@ -55,7 +55,7 @@
     "less": "4.6.6",
     "ng-packagr": "22.1.0-next.2",
     "postcss": "8.5.15",
-    "rolldown": "1.1.1",
+    "rollup": "4.62.0",
     "rxjs": "7.8.2",
     "vitest": "4.1.9"
   },
@@ -73,6 +73,7 @@
     "less": "^4.2.0",
     "ng-packagr": "0.0.0-NG-PACKAGR-PEER-DEP",
     "postcss": "^8.4.0",
+    "rollup": "^4.0.0",
     "tailwindcss": "^2.0.0 || ^3.0.0 || ^4.0.0",
     "tslib": "^2.3.0",
     "typescript": ">=6.0 <6.1",
@@ -112,6 +113,9 @@
     "postcss": {
       "optional": true
     },
+    "rollup": {
+      "optional": true
+    },
     "tailwindcss": {
       "optional": true
     },

packages/angular/build/src/builders/application/chunk-optimizer.ts

@@ -19,7 +19,7 @@
 
 import type { Message, Metafile } from 'esbuild';
 import assert from 'node:assert';
-import { type Plugin, rollup } from 'rollup';
+import type { Plugin } from 'rollup';
 import { BundleContextResult } from '../../tools/esbuild/bundler-context';
 import {
   type BuildOutputFile,
@@ -306,6 +306,15 @@ export async function optimizeChunks(
       });
       optimizedOutput = result.output;
     } else {
+      let rollup;
+      try {
+        rollup = (await import('rollup')).rollup;
+      } catch {
+        throw new Error(
+          `Rollup is required when 'NG_BUILD_CHUNKS_ROLLDOWN' is set to false. ` +
+            `Please install 'rollup' manually (e.g. 'npm install rollup --save-dev') to use this fallback.`,
+        );
+      }
       bundle = await rollup({
         input: mainFile,
         plugins: plugins as Plugin[],

packages/angular/build/src/utils/environment-options.ts

@@ -106,7 +106,7 @@ export const allowMinify = debugOptimize.minify;
  * Allows using Rolldown for chunk optimization instead of Rollup.
  * This is useful for debugging and testing scenarios.
  */
-export const useRolldownChunks = parseTristate(process.env['NG_BUILD_CHUNKS_ROLLDOWN']) ?? false;
+export const useRolldownChunks = parseTristate(process.env['NG_BUILD_CHUNKS_ROLLDOWN']) ?? true;
 
 /**
  * Some environments, like CircleCI which use Docker report a number of CPUs by the host and not the count of available.

pnpm-lock.yaml

@@ -86,20 +86,30 @@ export default async function () {
     `Expected build with threshold 4 and 3 chunks to NOT be optimized. Thresh 4: ${jsFiles3Thresh4.length}, Unoptimized: ${jsFiles3Unopt.length}`,
   );
 
-  // Case 4: Opt into Rolldown
-  await installPackage('rolldown@1.0.0-rc.12');
+  // Case 4: Opt back into Rollup (requires manual install since it's an optional peer dependency)
+  await installPackage('rollup@4.62.0');
   try {
     await execWithEnv('ng', ['build', '--output-hashing=none'], {
       ...process.env,
-      NG_BUILD_CHUNKS_ROLLDOWN: '1',
+      NG_BUILD_CHUNKS_ROLLDOWN: 'false',
       NG_BUILD_OPTIMIZE_CHUNKS: 'true',
     });
-    const filesRolldown = await readdir('dist/test-project/browser');
-    const jsFilesRolldown = filesRolldown.filter((f) => f.endsWith('.js'));
+    const filesRollup = await readdir('dist/test-project/browser');
+    const jsFilesRollup = filesRollup.filter((f) => f.endsWith('.js'));
 
-    assert.ok(jsFilesRolldown.length > 0, 'Expected Rolldown build to produce output files.');
+    assert.ok(jsFilesRollup.length > 0, 'Expected Rollup build to produce output files.');
   } finally {
     // Clean up
-    await uninstallPackage('rolldown');
+    await uninstallPackage('rollup');
   }
+
+  // Case 5: Opt back into Rollup without installing it (should throw a helpful error)
+  await assert.rejects(
+    execWithEnv('ng', ['build', '--output-hashing=none'], {
+      ...process.env,
+      NG_BUILD_CHUNKS_ROLLDOWN: 'false',
+      NG_BUILD_OPTIMIZE_CHUNKS: 'true',
+    }),
+    /Rollup is required when 'NG_BUILD_CHUNKS_ROLLDOWN' is set to false/,
+  );
 }