fix(@angular/build): adjust sourcemap sources when Vitest wrapper is bypassed

When code coverage is disabled, the Vitest builder bypasses the secondary import wrapper
and serves the compiled output directly as the test file. This caused sourcemaps to be
incorrect because the `sources` field in the map (relative to the build root) was being
resolved relative to the test file's location.

This commit adjusts the `sources` in the sourcemap to be relative to the test file's
directory, ensuring correct source mapping in debuggers.

Author: clydin

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

@@ -113,8 +113,11 @@ export async function createVitestConfigPlugin(
         delete config.plugins;
       }
 
-      // Add browser source map support
-      if (browser || testConfig?.browser?.enabled) {
+      // Add browser source map support if coverage is enabled
+      if (
+        (browser || testConfig?.browser?.enabled) &&
+        (options.coverage.enabled || testConfig?.coverage?.enabled)
+      ) {
         projectPlugins.unshift(createSourcemapSupportPlugin());
         setupFiles.unshift('virtual:source-map-support');
       }
@@ -291,6 +294,17 @@ export function createVitestPlugins(pluginOptions: PluginOptions): VitestPlugins
           if (map) {
             if (!map.sources?.length && !map.sourcesContent?.length && !map.mappings) {
               map.sources = ['virtual:builder'];
+            } else if (!vitestConfig.coverage.enabled && Array.isArray(map.sources)) {
+              map.sources = (map.sources as string[]).map((source) => {
+                if (source.startsWith('angular:')) {
+                  return source;
+                }
+
+                // source is relative to the workspace root because the output file is at the root of the output.
+                const absoluteSource = path.join(workspaceRoot, source);
+
+                return toPosixPath(path.relative(path.dirname(id), absoluteSource));
+              });
             }
           }
 

tests/e2e/tests/vitest/node-sourcemaps.ts

@@ -0,0 +1,37 @@
+import assert from 'node:assert/strict';
+import { applyVitestBuilder } from '../../utils/vitest';
+import { ng, noSilentNg } from '../../utils/process';
+import { writeFile } from '../../utils/fs';
+import { stripVTControlCharacters } from 'node:util';
+
+export default async function (): Promise<void> {
+  await applyVitestBuilder();
+  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', () => {
+          expect(true).toBe(false);
+        });
+      });
+    `,
+  );
+
+  try {
+    await noSilentNg('test', '--no-watch');
+    throw new Error('Expected "ng test" to fail.');
+  } catch (error: any) {
+    const stdout = stripVTControlCharacters(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,
+      /\bsrc[\/\\]app[\/\\]failing\.spec\.ts:4:\d+/,
+      'Expected stack trace to point to the source file.',
+    );
+  }
+}