refactor(@angular-devkit/build-angular): use script target in custom babel loader

This change uses the project's TypeScript configuration script target to determine the required Babel processing.

Author: clydin

packages/angular_devkit/build_angular/src/babel/webpack-loader.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 import { custom } from 'babel-loader';
+import { ScriptTarget } from 'typescript';
 
 interface AngularCustomOptions {
   forceES5: boolean;
@@ -62,9 +63,11 @@ export default custom<AngularCustomOptions>(() => {
   });
 
   return {
-    async customOptions({ forceES5, ...loaderOptions }, { source }) {
-      let shouldProcess = forceES5;
+    async customOptions({ scriptTarget, ...loaderOptions }, { source }) {
+      // Must process file if plugins are added
+      let shouldProcess = Array.isArray(loaderOptions.plugins) && loaderOptions.plugins.length > 0;
 
+      // Analyze file for linking
       let shouldLink = false;
       const { hasLinkerSupport, requiresLinking } = await checkLinking(this.resourcePath, source);
       if (requiresLinking && !hasLinkerSupport) {
@@ -77,17 +80,27 @@ export default custom<AngularCustomOptions>(() => {
       }
       shouldProcess ||= shouldLink;
 
+      // Analyze for ES target processing
+      let forceES5 = false;
+      const esTarget = scriptTarget as ScriptTarget;
+      if (esTarget < ScriptTarget.ES2015) {
+        forceES5 = true;
+      }
+      shouldProcess ||= forceES5;
+
+      // Add provided loader options to default base options
       const options: Record<string, unknown> = {
         ...baseOptions,
         ...loaderOptions,
       };
 
+      // Skip babel processing if no actions are needed
       if (!shouldProcess) {
         // Force the current file to be ignored
         options.ignore = [() => true];
       }
 
-      return { custom: { forceES5: !!forceES5, shouldLink }, loader: options };
+      return { custom: { forceES5, shouldLink }, loader: options };
     },
     config(configuration, { customOptions }) {
       return {

packages/angular_devkit/build_angular/src/utils/build-options.ts

@@ -16,7 +16,6 @@ import {
   I18NMissingTranslation,
   IndexUnion,
   Localize,
-  OptimizationClass,
   SourceMapClass,
 } from '../browser/schema';
 import { Schema as DevServerSchema } from '../dev-server/schema';
@@ -98,5 +97,5 @@ export interface WebpackConfigOptions<T = BuildOptions> {
   buildOptions: T;
   tsConfig: ParsedConfiguration;
   tsConfigPath: string;
-  supportES2015: boolean;
+  scriptTarget: import('typescript').ScriptTarget;
 }

packages/angular_devkit/build_angular/src/utils/webpack-browser-config.ts

@@ -77,7 +77,7 @@ export async function generateWebpackConfig(
     buildOptions,
     tsConfig,
     tsConfigPath,
-    supportES2015,
+    scriptTarget,
   };
 
   wco.buildOptions.progress = defaultProgress(wco.buildOptions.progress);

packages/angular_devkit/build_angular/src/webpack/configs/common.ts

@@ -554,7 +554,7 @@ export function getCommonConfig(wco: WebpackConfigOptions): Configuration {
                 cacheIdentifier: JSON.stringify({
                   buildAngular: require('../../../package.json').version,
                 }),
-                forceES5: !wco.supportES2015,
+                scriptTarget: wco.scriptTarget,
               },
             },
             ...buildOptimizerUseRule,