fix(@angular/build): filter Rolldown warnings and disable .d.ts annotation comments in library builder

Suppress noisy Rolldown warnings (`EMPTY_BUNDLE`, `UNUSED_EXTERNAL_IMPORT`, and `THIS_IS_UNDEFINED`) and disable annotation comments in `.d.ts` output bundles to match `ng-packagr` behavior.

Author: alan-agius4

packages/angular/build/src/builders/library/pipeline/bundler.ts

@@ -300,6 +300,15 @@ function processRolldownOutput(
   return { filesToEmit, moduleIdsByBundle, tslibBundles };
 }
 
+/**
+ * Set of Rolldown warning codes that should be ignored.
+ */
+const IGNORED_ROLLDOWN_WARNING_CODES: ReadonlySet<string> = new Set([
+  'EMPTY_BUNDLE',
+  'UNUSED_EXTERNAL_IMPORT',
+  'THIS_IS_UNDEFINED',
+]);
+
 /**
  * Executes a Rolldown bundle build across all provided entry inputs.
  *
@@ -341,7 +350,12 @@ async function executeMultiBundle(
     resolve: { symlinks: !preserveSymlinks },
     checks: { circularDependency: false },
     onLog(level, log) {
+      // Ignore specified warning codes
       if (level === 'warn') {
+        if (log.code && IGNORED_ROLLDOWN_WARNING_CODES.has(log.code)) {
+          return;
+        }
+
         warnings.push(log.message);
       }
     },
@@ -358,7 +372,7 @@ async function executeMultiBundle(
       chunkFileNames: `[name]-[hash].${extension}`,
       sourcemap,
       hoistTransitiveImports: false,
-      comments: { jsdoc: isDts, legal: true, annotation: true },
+      comments: { jsdoc: isDts, legal: true, annotation: !isDts },
     });
 
     return {

packages/angular/build/src/builders/library/tests/behavior/build_spec.ts

@@ -74,6 +74,47 @@ describeLibraryBuilder(executeLibraryBuilder, LIBRARY_BUILDER_INFO, (harness) =>
       );
     });
 
+    it('should not log EMPTY_BUNDLE warnings for type-only entry points', async () => {
+      await harness.writeFile(
+        'projects/lib/src/public-api.ts',
+        `export interface OnlyType { id: string; }`,
+      );
+
+      harness.useTarget('build', {
+        ...BASE_OPTIONS,
+      });
+
+      const { result, logs } = await harness.executeOnce();
+      expect(result?.success).toBeTrue();
+      expect(logs.some((l) => l.level === 'warn')).toBeFalse();
+    });
+
+    it('should preserve JSDoc comments in .d.ts and annotation comments in .mjs bundles', async () => {
+      await harness.writeFile(
+        'projects/lib/src/public-api.ts',
+        `
+        function identity<T>(x: T): T { return x; }
+        /** Public API JSDoc comment */
+        export const VALUE = /* @__PURE__ */ identity('test');
+        `,
+      );
+
+      harness.useTarget('build', {
+        ...BASE_OPTIONS,
+      });
+
+      const { result } = await harness.executeOnce();
+      expect(result?.success).toBeTrue();
+
+      const fesmContent = harness.readFile('dist/lib/fesm2022/lib.mjs');
+      expect(fesmContent).toContain('@__PURE__');
+      expect(fesmContent).not.toContain('Public API JSDoc comment');
+
+      const dtsContent = harness.readFile('dist/lib/types/lib.d.ts');
+      expect(dtsContent).toContain('Public API JSDoc comment');
+      expect(dtsContent).not.toContain('@__PURE__');
+    });
+
     it('should automatically add tslib to dependencies when output chunks import tslib', async () => {
       await harness.writeFile(
         'projects/lib/src/public-api.ts',