fix(@angular-devkit/build-angular): display actionable error when a style does not exist in Karma builder

Prior to this change the the error was not displayed correctly due to compilation being undefined.

Closes #24416

Author: alan-agius4

packages/angular_devkit/build_angular/src/builders/karma/tests/options/styles_spec.ts

@@ -16,7 +16,7 @@ describeBuilder(execute, KARMA_BUILDER_INFO, (harness) => {
         'src/styles.css': 'p {display: none}',
         'src/app/app.component.ts': `
           import { Component } from '@angular/core';
-  
+
           @Component({
             selector: 'app-root',
             template: '<p>Hello World</p>'
@@ -27,7 +27,7 @@ describeBuilder(execute, KARMA_BUILDER_INFO, (harness) => {
         'src/app/app.component.spec.ts': `
           import { TestBed } from '@angular/core/testing';
           import { AppComponent } from './app.component';
-  
+
           describe('AppComponent', () => {
             beforeEach(async () => {
               await TestBed.configureTestingModule({
@@ -38,7 +38,7 @@ describeBuilder(execute, KARMA_BUILDER_INFO, (harness) => {
                 ]
               }).compileComponents();
             });
-  
+
             it('should not contain text that is hidden via css', () => {
               const fixture = TestBed.createComponent(AppComponent);
               expect(fixture.nativeElement.innerText).not.toContain('Hello World');
@@ -129,5 +129,22 @@ describeBuilder(execute, KARMA_BUILDER_INFO, (harness) => {
       const { result } = await harness.executeOnce();
       expect(result?.success).toBeTrue();
     });
+
+    it('fails and shows an error if style does not exist', async () => {
+      harness.useTarget('test', {
+        ...BASE_OPTIONS,
+        styles: ['src/test-style-a.css'],
+      });
+
+      const { result, logs } = await harness.executeOnce({ outputLogsOnFailure: false });
+
+      expect(result?.success).toBeFalse();
+      expect(logs).toContain(
+        jasmine.objectContaining({
+          level: 'error',
+          message: jasmine.stringMatching(`Can't resolve 'src/test-style-a.css'`),
+        }),
+      );
+    });
   });
 });

packages/angular_devkit/build_angular/src/webpack/plugins/styles-webpack-plugin.ts

@@ -7,7 +7,6 @@
  */
 
 import assert from 'assert';
-import { pluginName } from 'mini-css-extract-plugin';
 import type { Compilation, Compiler } from 'webpack';
 import { assertIsError } from '../../utils/error';
 import { addError } from '../../utils/webpack-diagnostics';
@@ -30,10 +29,6 @@ export class StylesWebpackPlugin {
 
   apply(compiler: Compiler): void {
     const { entryPoints, preserveSymlinks, root } = this.options;
-    const webpackOptions = compiler.options;
-    const entry =
-      typeof webpackOptions.entry === 'function' ? webpackOptions.entry() : webpackOptions.entry;
-
     const resolver = compiler.resolverFactory.get('global-styles', {
       conditionNames: ['sass', 'less', 'style'],
       mainFields: ['sass', 'less', 'style', 'main', '...'],
@@ -45,32 +40,38 @@ export class StylesWebpackPlugin {
       fileSystem: compiler.inputFileSystem,
     });
 
-    webpackOptions.entry = async () => {
-      const entrypoints = await entry;
+    const webpackOptions = compiler.options;
+    compiler.hooks.environment.tap(PLUGIN_NAME, () => {
+      const entry =
+        typeof webpackOptions.entry === 'function' ? webpackOptions.entry() : webpackOptions.entry;
 
-      for (const [bundleName, paths] of Object.entries(entryPoints)) {
-        entrypoints[bundleName] ??= {};
-        const entryImport = (entrypoints[bundleName].import ??= []);
+      webpackOptions.entry = async () => {
+        const entrypoints = await entry;
 
-        for (const path of paths) {
-          try {
-            const resolvedPath = resolver.resolveSync({}, root, path);
-            if (resolvedPath) {
-              entryImport.push(`${resolvedPath}?ngGlobalStyle`);
-            } else {
+        for (const [bundleName, paths] of Object.entries(entryPoints)) {
+          entrypoints[bundleName] ??= {};
+          const entryImport = (entrypoints[bundleName].import ??= []);
+
+          for (const path of paths) {
+            try {
+              const resolvedPath = resolver.resolveSync({}, root, path);
+              if (resolvedPath) {
+                entryImport.push(`${resolvedPath}?ngGlobalStyle`);
+              } else {
+                assert(this.compilation, 'Compilation cannot be undefined.');
+                addError(this.compilation, `Cannot resolve '${path}'.`);
+              }
+            } catch (error) {
               assert(this.compilation, 'Compilation cannot be undefined.');
-              addError(this.compilation, `Cannot resolve '${path}'.`);
+              assertIsError(error);
+              addError(this.compilation, error.message);
             }
-          } catch (error) {
-            assert(this.compilation, 'Compilation cannot be undefined.');
-            assertIsError(error);
-            addError(this.compilation, error.message);
           }
         }
-      }
 
-      return entrypoints;
-    };
+        return entrypoints;
+      };
+    });
 
     compiler.hooks.thisCompilation.tap(PLUGIN_NAME, (compilation) => {
       this.compilation = compilation;