fix(@ngtools/webpack): retain child compilation warnings and errors

At the moment child compilation warnings and errors are being lost as they are not passed to the root compilation.  This means that any errors that are being set by clean-css for component styles are being lost.

Author: alan-agius4

packages/angular_devkit/build_angular/test/browser/aot_spec_large.ts

@@ -7,7 +7,7 @@
  */
 
 import { Architect } from '@angular-devkit/architect';
-import { join, normalize, virtualFs } from '@angular-devkit/core';
+import { join, logging, normalize, virtualFs } from '@angular-devkit/core';
 import { BrowserBuilderOutput } from '../../src/browser';
 import { createArchitect, host, ivyEnabled } from '../utils';
 
@@ -39,4 +39,28 @@ describe('Browser Builder AOT', () => {
 
     await run.stop();
   });
+
+  it('shows warnings for component styles', async () => {
+    const overrides = {
+      aot: true,
+      optimization: true,
+    };
+
+    host.writeMultipleFiles({
+      'src/app/app.component.css': `
+        .foo { color: white; padding: 1px; };
+        .buz { color: white; padding: 2px; };
+      `,
+    });
+
+    const logger = new logging.Logger('');
+    const logs: string[] = [];
+    logger.subscribe(e => logs.push(e.message));
+
+    const run = await architect.scheduleTarget(targetSpec, overrides, { logger });
+    const output = await run.result;
+    expect(output.success).toBe(true);
+    expect(logs.join()).toContain('WARNING in Invalid selector');
+    await run.stop();
+  });
 });

packages/ngtools/webpack/src/resource_loader.ts

@@ -100,10 +100,19 @@ export class WebpackResourceLoader {
     return new Promise((resolve, reject) => {
       childCompiler.compile((err: Error, childCompilation: any) => {
         // Resolve / reject the promise
-        if (childCompilation && childCompilation.errors && childCompilation.errors.length) {
-          const errorDetails = childCompilation.errors.map(function (error: any) {
-            return error.message + (error.error ? ':\n' + error.error : '');
-          }).join('\n');
+        const { warnings, errors } = childCompilation;
+
+        if (warnings && warnings.length) {
+          this._parentCompilation.warnings.push(...warnings);
+        }
+
+        if (errors && errors.length) {
+          this._parentCompilation.errors.push(...errors);
+
+          const errorDetails = errors
+            .map((error: any) => error.message + (error.error ? ':\n' + error.error : ''))
+            .join('\n');
+
           reject(new Error('Child compilation failed:\n' + errorDetails));
         } else if (err) {
           reject(err);