fix(@angular/build): keep Vite server file watcher disabled in Vitest watch mode

In Vitest 5, the internal `vitest:config:append` plugin uses a post
`configResolved` hook that resets `server.watch` to `{}` when watch mode
is enabled (`server.watch ??= {}`), overriding the `server: { watch: null }`
setting passed in `vitestServerConfig`. This caused Vite to start a
duplicate Chokidar file watcher alongside the Angular CLI build watcher
and trigger redundant, racing test reruns on file changes.

Enforce `post` ordering on `angular:vitest-configuration` and reset
`config.server.watch = null` in a post `configResolved` hook so Vite
uses its no-op watcher.

Author: clydin

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

@@ -398,11 +398,6 @@ export class VitestExecutor implements TestExecutor {
     const vitestServerConfig = {
       // Note `.vitest` is auto appended to the path.
       cacheDir: cacheOptions.path,
-      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: [
         await createVitestConfigPlugin({
           browser: browserOptions.browser,

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

@@ -164,6 +164,16 @@ export async function createVitestConfigPlugin(
 
   return {
     name: 'angular:vitest-configuration',
+    enforce: 'post',
+    configResolved: {
+      order: 'post',
+      handler(config: Vite.ResolvedConfig) {
+        // Vitest's internal post-configResolved hook resets `server.watch` to `{}` when
+        // `watch` is enabled (`server.watch ??= {}`). Force it back to `null` so Vite uses
+        // a no-op watcher and relies solely on the Angular CLI build watcher.
+        config.server.watch = null;
+      },
+    },
     async config(config: UserWorkspaceConfig & Vite.UserConfig) {
       const testConfig = config.test;
 

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

@@ -55,5 +55,38 @@ describeBuilder(execute, UNIT_TEST_BUILDER_INFO, (harness) => {
         },
       ]);
     });
+
+    it('should disable the Vite server file watcher when watch is true', async () => {
+      harness.useTarget('test', {
+        ...BASE_OPTIONS,
+        watch: true,
+        runnerConfig: 'vitest.config.mts',
+      });
+
+      await harness.writeFile(
+        'vitest.config.mts',
+        `
+          import { defineConfig } from 'vitest/config';
+          export default defineConfig({
+            plugins: [
+              {
+                name: 'assert-watch-disabled',
+                configureVitest({ vitest, project }) {
+                  if (vitest.vite.config.server.watch !== null || project.vite.config.server.watch !== null) {
+                    throw new Error('Expected Vite server.watch to be null');
+                  }
+                },
+              },
+            ],
+          });
+        `,
+      );
+
+      await harness.executeWithCases([
+        ({ result }) => {
+          expect(result?.success).toBeTrue();
+        },
+      ]);
+    });
   });
 });