fix(@angular/build): ensure @angular/compiler is loaded for Vitest TestBed initialization

Provide a dedicated setup file to import '@angular/compiler' prior to TestBed initialization. This ensures the compiler facade is published before 'init-testbed.js' or any shared code-split chunks (such as those configured via 'providersFile') are evaluated, avoiding JIT compilation errors when injectable dependencies are resolved during test initialization.

Author: clydin

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

@@ -230,6 +230,10 @@ export async function getVitestBuildOptions(
     }
   }
 
+  // The Angular compiler facade must be loaded in a dedicated setup file before TestBed initialization.
+  // This ensures the compiler facade is published before 'init-testbed' or any shared code-split chunks
+  // (such as those from a configured 'providersFile') are evaluated.
+  entryPoints.set('init-compiler', 'angular:compiler-init');
   entryPoints.set('init-testbed', 'angular:test-bed-init');
   entryPoints.set('vitest-mock-patch', 'angular:vitest-mock-patch');
 
@@ -326,6 +330,7 @@ export async function getVitestBuildOptions(
   return {
     buildOptions,
     virtualFiles: {
+      'angular:compiler-init': "import '@angular/compiler';",
       'angular:test-bed-init': testBedInitContents,
       'angular:vitest-mock-patch': mockPatchContents,
     },

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

@@ -243,7 +243,12 @@ export class VitestExecutor implements TestExecutor {
   private prepareSetupFiles(): string[] {
     const { setupFiles } = this.options;
     // Add setup file entries for TestBed initialization and project polyfills
-    const testSetupFiles = ['init-testbed.js', 'vitest-mock-patch.js', ...setupFiles];
+    const testSetupFiles = [
+      'init-compiler.js',
+      'init-testbed.js',
+      'vitest-mock-patch.js',
+      ...setupFiles,
+    ];
 
     // TODO: Provide additional result metadata to avoid needing to extract based on filename
     if (this.buildResultFiles.has('polyfills.js')) {

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

@@ -60,5 +60,59 @@ describeBuilder(execute, UNIT_TEST_BUILDER_INFO, (harness) => {
       const { result } = await harness.executeOnce();
       expect(result?.success).toBeTrue();
     });
+
+    it('should work with providers that inject services requiring JIT compilation', async () => {
+      await harness.writeFiles({
+        'src/test.service.ts': `
+          import { Injectable, inject } from '@angular/core';
+          import { Router } from '@angular/router';
+
+          @Injectable({ providedIn: 'root' })
+          export class TestService {
+            router = inject(Router);
+          }
+        `,
+        'src/test.providers.ts': `
+          import { TestService } from './test.service';
+          export default [TestService];
+        `,
+        'src/app/app.component.spec.ts': `
+          import { TestBed } from '@angular/core/testing';
+          import { AppComponent } from './app.component';
+          import { TestService } from '../test.service';
+          import { describe, expect, it } from 'vitest';
+
+          describe('AppComponent', () => {
+            it('should create the app and inject TestService', () => {
+              TestBed.configureTestingModule({
+                declarations: [AppComponent],
+              });
+              const fixture = TestBed.createComponent(AppComponent);
+              const app = fixture.componentInstance;
+              const testService = TestBed.inject(TestService);
+              expect(app).toBeTruthy();
+              expect(testService).toBeTruthy();
+              expect(testService.router).toBeTruthy();
+            });
+          });
+        `,
+      });
+
+      await harness.modifyFile('src/tsconfig.spec.json', (content) => {
+        const tsConfig = JSON.parse(content);
+        tsConfig.files ??= [];
+        tsConfig.files.push('test.service.ts', 'test.providers.ts');
+
+        return JSON.stringify(tsConfig);
+      });
+
+      harness.useTarget('test', {
+        ...BASE_OPTIONS,
+        providersFile: 'src/test.providers.ts',
+      });
+
+      const { result } = await harness.executeOnce();
+      expect(result?.success).toBeTrue();
+    });
   });
 });