feat(@angular-devkit/build-angular): add experimentalImportFactories option

Author: filipesilva

packages/angular_devkit/build_angular/src/angular-cli-files/models/build-options.ts

@@ -59,6 +59,7 @@ export interface BuildOptions {
   forkTypeChecker: boolean;
   profile?: boolean;
   es5BrowserSupport?: boolean;
+  experimentalImportFactories?: boolean;
 
   main: string;
   index: string;

packages/angular_devkit/build_angular/src/angular-cli-files/models/webpack-configs/typescript.ts

@@ -75,6 +75,7 @@ function _createAotPlugin(
     contextElementDependencyConstructor: require('webpack/lib/dependencies/ContextElementDependency'),
     logger: wco.logger,
     directTemplateLoading: true,
+    importFactories: buildOptions.experimentalImportFactories,
     ...options,
   };
   return new AngularCompilerPlugin(pluginOptions);

packages/angular_devkit/build_angular/src/browser/schema.json

@@ -315,6 +315,11 @@
       "type": "boolean",
       "default": false,
       "x-deprecated": true
+    },
+    "experimentalImportFactories": {
+      "description": "**EXPERIMENTAL** Transform import statements for lazy routes to import factories when using View Engine. Should only be used when switching back and forth between View Engine and Ivy. See https://angular.io/guide/ivy for usage information.",
+      "type": "boolean",
+      "default": false
     }
   },
   "additionalProperties": false,

packages/ngtools/webpack/src/transformers/import_factory.ts

@@ -53,14 +53,18 @@ export function importFactory(
   warningCb: (warning: string) => void,
 ): ts.TransformerFactory<ts.SourceFile> {
   return (context: ts.TransformationContext) => {
+    // TODO(filipesilva): change the link to https://angular.io/guide/ivy once it is out.
     return (sourceFile: ts.SourceFile) => {
       const warning = `
 Found 'loadChildren' with a non-string syntax in ${sourceFile.fileName} but could not transform it.
 Make sure it matches the format below:
 
 loadChildren: () => import('IMPORT_STRING').then(m => m.EXPORT_NAME)
 
-Please note that only IMPORT_STRING and EXPORT_NAME can be replaced in this format.`;
+Please note that only IMPORT_STRING and EXPORT_NAME can be replaced in this format.
+
+Visit https://next.angular.io/guide/ivy for more information on using Ivy.
+`;
 
       const emitWarning = () => warningCb(warning);
       const visitVariableStatement: ts.Visitor = (node: ts.Node) => {