fix(@angular/build): correct Vitest builder watch mode execution

The experimental Vitest-based unit test builder did not always correctly re-run tests in watch mode. This commit refactors the Vitest executor to provide more accurate watch mode behavior by: - Disabling Vitest's internal file watcher (`watch: null`) to make the Angular builder's watcher the single source of truth. - Triggering a test run via `vitest.rerunTestSpecifications()` within the `execute` method after each incremental build is complete.

Author: clydin

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

@@ -15,7 +15,7 @@ import type { InlineConfig, Vitest } from 'vitest/node';
 import { assertIsError } from '../../../../utils/error';
 import { loadEsmModule } from '../../../../utils/load-esm';
 import { toPosixPath } from '../../../../utils/path';
-import type { FullResult, IncrementalResult } from '../../../application/results';
+import { type FullResult, type IncrementalResult, ResultKind } from '../../../application/results';
 import { writeTestFiles } from '../../../karma/application_builder';
 import { NormalizedUnitTestBuilderOptions } from '../../options';
 import type { TestExecutor } from '../api';
@@ -40,20 +40,49 @@ export class VitestExecutor implements TestExecutor {
  await writeTestFiles(buildResult.files, this.outputPath);
 
  this.latestBuildResult = buildResult;
+
+ // Initialize Vitest if not already present.
  this.vitest ??= await this.initializeVitest();
+ const vitest = this.vitest;
+
+ let testResults;
+ if (buildResult.kind === ResultKind.Incremental) {
+ const addedFiles = buildResult.added.map((file) => path.join(this.outputPath, file));
+ const modifiedFiles = buildResult.modified.map((file) => path.join(this.outputPath, file));
+
+ if (addedFiles.length === 0 && modifiedFiles.length === 0) {
+ yield { success: true };
+
+ return;
+ }
+
+ // If new files are added, use `start` to trigger test discovery.
+ // Also pass modified files to `start` to ensure they are re-run.
+ if (addedFiles.length > 0) {
+ await vitest.start([...addedFiles, ...modifiedFiles]);
+ } else {
+ // For modified files only, use the more efficient `rerunTestSpecifications`
+ const specsToRerun = modifiedFiles.flatMap((file) => vitest.getModuleSpecifications(file));
+
+ if (specsToRerun.length > 0) {
+ modifiedFiles.forEach((file) => vitest.invalidateFile(file));
+ testResults = await vitest.rerunTestSpecifications(specsToRerun);
+ }
+ }
+ }
 
  // Check if all the tests pass to calculate the result
- const testModules = this.vitest.state.getTestModules();
+ const testModules = testResults?.testModules;
 
- yield { success: testModules.every((testModule) => testModule.ok()) };
+ yield { success: testModules?.every((testModule) => testModule.ok()) ?? true };
  }
 
  async [Symbol.asyncDispose](): Promise<void> {
  await this.vitest?.close();
  }
 
  private async initializeVitest(): Promise<Vitest> {
- const { codeCoverage, reporters, watch, workspaceRoot, setupFiles, browsers, debug } =
+ const { codeCoverage, reporters, workspaceRoot, setupFiles, browsers, debug, watch } =
  this.options;
  const { outputPath, projectName, latestBuildResult } = this;
 
@@ -101,7 +130,7 @@ export class VitestExecutor implements TestExecutor {
 
  return startVitest(
  'test',
- undefined /* cliFilters */,
+ undefined,
  {
  // Disable configuration file resolution/loading
  config: false,
@@ -115,6 +144,11 @@ export class VitestExecutor implements TestExecutor {
  ...debugOptions,
  },
  {
+ server: {
+ // Disable the actual file watcher. The boolean watch option above should still
+ // be enabled as it controls other internal behavior related to rerunning tests.
+ watch: null,
+ },
  plugins: [
  {
  name: 'angular:project-init',