fix(@angular-devkit/build-angular): ensure vitest code coverage handles virtual files correctly

Vitest's default coverage provider checks for the physical existence of files to determine inclusion in the coverage report. This behavior excludes in-memory files generated by the build process from the final report. This change patches the `isIncluded` method of Vitest's `BaseCoverageProvider` to correctly account for these virtual files, ensuring they are included in the coverage analysis.

Additionally, bundler-generated helper code chunks without any original source code can have empty sourcemaps. Vitest includes files with such sourcemaps in the coverage report, which is incorrect. This change adds a virtual source to these sourcemaps to prevent them from being included in the final coverage output.

(cherry picked from commit 2c846fb)

Author: clydin

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

@@ -9,6 +9,7 @@
 import type { BuilderOutput } from '@angular-devkit/architect';
 import assert from 'node:assert';
 import path from 'node:path';
+import { isMatch } from 'picomatch';
 import type { InlineConfig, Vitest } from 'vitest/node';
 import { assertIsError } from '../../../../utils/error';
 import { toPosixPath } from '../../../../utils/path';
@@ -141,7 +142,9 @@ export class VitestExecutor implements TestExecutor {
     } = this.options;
 
     let vitestNodeModule;
+    let vitestCoverageModule;
     try {
+      vitestCoverageModule = await import('vitest/coverage');
       vitestNodeModule = await import('vitest/node');
     } catch (error: unknown) {
       assertIsError(error);
@@ -154,6 +157,21 @@ export class VitestExecutor implements TestExecutor {
     }
     const { startVitest } = vitestNodeModule;
 
+    // Augment BaseCoverageProvider to include logic to support the built virtual files.
+    // Temporary workaround to avoid the direct filesystem checks in the base provider that
+    // were introduced in v4. Also ensures that all built virtual files are available.
+    const builtVirtualFiles = this.buildResultFiles;
+    vitestCoverageModule.BaseCoverageProvider.prototype.isIncluded = function (filename) {
+      const relativeFilename = path.relative(workspaceRoot, filename);
+      if (!this.options.include || builtVirtualFiles.has(relativeFilename)) {
+        return !isMatch(relativeFilename, this.options.exclude);
+      } else {
+        return isMatch(relativeFilename, this.options.include, {
+          ignore: this.options.exclude,
+        });
+      }
+    };
+
     // Setup vitest browser options if configured
     const browserOptions = await setupBrowserConfiguration(
       browsers,

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

@@ -117,15 +117,26 @@ export function createVitestPlugins(
                     outputFile.origin === 'memory'
                       ? Buffer.from(outputFile.contents).toString('utf-8')
                       : await readFile(outputFile.inputPath, 'utf-8');
-                  const map = sourceMapFile
+                  const sourceMapText = sourceMapFile
                     ? sourceMapFile.origin === 'memory'
                       ? Buffer.from(sourceMapFile.contents).toString('utf-8')
                       : await readFile(sourceMapFile.inputPath, 'utf-8')
                     : undefined;
 
+                  // Vitest will include files in the coverage report if the sourcemap contains no sources.
+                  // For builder-internal generated code chunks, which are typically helper functions,
+                  // a virtual source is added to the sourcemap to prevent them from being incorrectly
+                  // included in the final coverage report.
+                  const map = sourceMapText ? JSON.parse(sourceMapText) : undefined;
+                  if (map) {
+                    if (!map.sources?.length && !map.sourcesContent?.length && !map.mappings) {
+                      map.sources = ['virtual:builder'];
+                    }
+                  }
+
                   return {
                     code,
-                    map: map ? JSON.parse(map) : undefined,
+                    map,
                   };
                 }
               },

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

@@ -28,7 +28,7 @@ describeBuilder(execute, UNIT_TEST_BUILDER_INFO, (harness) => {
 
       const { result } = await harness.executeOnce();
       expect(result?.success).toBeTrue();
-      expect(harness.hasFile('coverage/test/index.html')).toBeFalse();
+      harness.expectFile('coverage/test/index.html').toNotExist();
     });
 
     it('should generate a code coverage report when coverage is true', async () => {
@@ -39,7 +39,19 @@ describeBuilder(execute, UNIT_TEST_BUILDER_INFO, (harness) => {
 
       const { result } = await harness.executeOnce();
       expect(result?.success).toBeTrue();
-      expect(harness.hasFile('coverage/test/index.html')).toBeTrue();
+      harness.expectFile('coverage/test/index.html').toExist();
+    });
+
+    it('should generate a code coverage report when coverage is true', async () => {
+      harness.useTarget('test', {
+        ...BASE_OPTIONS,
+        coverage: true,
+        coverageReporters: ['json'] as any,
+      });
+
+      const { result } = await harness.executeOnce();
+      expect(result?.success).toBeTrue();
+      harness.expectFile('coverage/test/coverage-final.json').content.toContain('app.component.ts');
     });
   });
 });