fix(@angular/build): resolve library bundle sourcemap sources relative to output directory

Use `sourcemapPathTransform` when generating FESM and declaration bundles in the library builder so that emitted sourcemap `sources` entries are computed relative to the actual output directory rather than the relative bundle directory.

Author: alan-agius4

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

@@ -295,7 +295,7 @@ function processRolldownOutput(output: RolldownOutput['output'], dir: string): M
  * @param preserveSymlinks Whether to preserve symlinks during module resolution.
  * @param extension Output file extension ('mjs' or 'd.ts').
  * @param sourcemap Whether to emit sourcemaps.
- * @param findEntryPoint Lookup function to resolve chunk entry point ownership.
+ * @param outputPath The absolute base output directory path.
  * @returns A promise resolving to the multi-bundle output.
  */
 async function executeMultiBundle(
@@ -304,9 +304,11 @@ async function executeMultiBundle(
   preserveSymlinks: boolean,
   extension: 'mjs' | 'd.ts',
   sourcemap: boolean,
+  outputPath: string,
 ): Promise<MultiBundleOutput> {
   const isDts = extension === 'd.ts';
   const dir = isDts ? TYPES_OUTPUT_DIR : FESM_OUTPUT_DIR;
+  const outputDir = path.join(outputPath, dir);
   const bundle = await rolldown({
     context: 'this',
     input,
@@ -326,6 +328,12 @@ async function executeMultiBundle(
       entryFileNames: `[name].${extension}`,
       chunkFileNames: `[name]-[hash].${extension}`,
       sourcemap,
+      sourcemapPathTransform: (sourcePath, sourcemapPath) => {
+        const absoluteSourcePath = path.resolve(path.dirname(sourcemapPath), sourcePath);
+        const relativeSourcePath = path.relative(outputDir, absoluteSourcePath);
+
+        return toPosixPath(relativeSourcePath);
+      },
       hoistTransitiveImports: false,
       comments: { jsdoc: isDts, legal: true, annotation: true },
     });
@@ -359,6 +367,7 @@ async function bundleAllEsm(
     options.preserveSymlinks,
     'mjs',
     true,
+    options.outputPath,
   );
 }
 
@@ -389,10 +398,13 @@ async function bundleAllDts(
     dtsInput: true,
     tsconfig: false,
     sourcemap: dtsSourcemap,
+    generator: 'oxc',
   });
+
   const dtsPlugins = rawDtsPlugins.filter(
     (plugin) => plugin.name !== 'rolldown-plugin-dts:resolver',
   );
+
   assert(
     dtsPlugins.length < rawDtsPlugins.length,
     'Expected "rolldown-plugin-dts:resolver" plugin to be present in rolldown-plugin-dts.',
@@ -404,5 +416,6 @@ async function bundleAllDts(
     options.preserveSymlinks,
     'd.ts',
     dtsSourcemap,
+    options.outputPath,
   );
 }

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

@@ -26,6 +26,10 @@ describeLibraryBuilder(executeLibraryBuilder, LIBRARY_BUILDER_INFO, (harness) =>
       expect(fesmContent).toContain('LibComponent');
       expect(fesmContent).toContain('ɵcmp');
 
+      harness.expectFile('dist/lib/fesm2022/lib.mjs.map').toExist();
+      const fesmMap = JSON.parse(harness.readFile('dist/lib/fesm2022/lib.mjs.map'));
+      expect(fesmMap.sources).toContain('../../../projects/lib/src/lib/lib.ts');
+
       harness.expectFile('dist/lib/types/lib.d.ts').toExist();
       const dtsContent = harness.readFile('dist/lib/types/lib.d.ts');
       expect(dtsContent).toContain('LibComponent');

packages/angular/build/src/builders/library/tests/options/declaration-map_spec.ts

@@ -38,6 +38,8 @@ describeLibraryBuilder(executeLibraryBuilder, LIBRARY_BUILDER_INFO, (harness) =>
       expect(harness.hasFile('dist/lib/fesm2022/lib.mjs.map')).toBeTrue();
       // DTS sourcemaps should be generated
       expect(harness.hasFile('dist/lib/types/lib.d.ts.map')).toBeTrue();
+      const dtsMap = JSON.parse(harness.readFile('dist/lib/types/lib.d.ts.map'));
+      expect(dtsMap.sources).toContain('../../../projects/lib/src/lib/lib.ts');
     });
   });
 });