fix(@angular/build): inject source-map-support for Vitest browser tests

packages/angular/build/src/builders/unit-test/options.ts

@@ -8,6 +8,7 @@
 
 import { type BuilderContext, targetFromTargetString } from '@angular-devkit/architect';
 import { constants, promises as fs } from 'node:fs';
+import { createRequire } from 'node:module';
 import path from 'node:path';
 import { normalizeCacheOptions } from '../../utils/normalize-cache';
 import { getProjectRootPaths } from '../../utils/project-metadata';
@@ -135,6 +136,22 @@ export async function normalizeOptions(
   };
 }
 
-export function injectTestingPolyfills(polyfills: string[] = []): string[] {
-  return polyfills.includes('zone.js') ? [...polyfills, 'zone.js/testing'] : polyfills;
+export function injectTestingPolyfills(
+  configuredPolyfills: string[] = [],
+  sourcemapSupport: boolean = false,
+): string[] {
+  const updatedPolyfills = [...configuredPolyfills];
+
+  // Resolve and add sourcemap support (mainly for browsers)
+  if (sourcemapSupport) {
+    const packageResolve = createRequire(__filename).resolve;
+    updatedPolyfills.unshift(packageResolve('source-map-support/browser-source-map-support.js'));
+  }
+
+  // Add zone.js testing if zone.js is present
+  if (configuredPolyfills.includes('zone.js')) {
+    updatedPolyfills.push('zone.js/testing');
+  }
+
+  return updatedPolyfills;
 }

packages/angular/build/src/builders/unit-test/runners/vitest/build-options.ts

@@ -128,7 +128,10 @@ export async function getVitestBuildOptions(
     externalDependencies,
   };
 
-  buildOptions.polyfills = injectTestingPolyfills(buildOptions.polyfills);
+  buildOptions.polyfills = injectTestingPolyfills(
+    buildOptions.polyfills,
+    !!options.browsers?.length,
+  );
 
   const testBedInitContents = createTestBedInitVirtualFile(
     providersFile,

tests/legacy-cli/e2e/tests/vitest/browser-sourcemaps.ts

@@ -0,0 +1,39 @@
+import assert from 'node:assert/strict';
+import { applyVitestBuilder } from '../../utils/vitest';
+import { ng } from '../../utils/process';
+import { installPackage } from '../../utils/packages';
+import { writeFile } from '../../utils/fs';
+
+export default async function (): Promise<void> {
+  await applyVitestBuilder();
+  await installPackage('playwright@1');
+  await installPackage('@vitest/browser-playwright@4');
+  await ng('generate', 'component', 'my-comp');
+
+  // Add a failing test to verify source map support
+  await writeFile(
+    'src/app/failing.spec.ts',
+    `
+      describe('Failing Test', () => {
+        it('should fail', () => {
+          throw new Error('This is a failing test');
+        });
+      });
+    `,
+  );
+
+  try {
+    await ng('test', '--no-watch', '--browsers', 'chromiumHeadless');
+    throw new Error('Expected "ng test" to fail.');
+  } catch (error: any) {
+    const stdout = error.stdout || error.message;
+    // We expect the failure from failing.spec.ts
+    assert.match(stdout, /1 failed/, 'Expected 1 test to fail.');
+    // Check that the stack trace points to the correct file
+    assert.match(
+      stdout,
+      /src\/app\/failing\.spec\.ts:\d+:\d+/,
+      'Expected stack trace to point to the source file.',
+    );
+  }
+}