fix(ivy): allow TestBed to recompile AOT-compiled components in case of template overrides (#29555)

Prior to this change, recompilation of AOT-compiled components in TestBed may fail when template override is requested. That was happening due to the `styleUrls` field defined for a Component, thus switching its state to "requires resolution" (i.e. having external resources) at compile time. This change avoids this issue by storing styles and resetting `styleUrls` field before recompilation. Once compilation is done, saved styles are patched back onto Component def.

PR Close #29555

packages/core/test/test_bed_spec.ts

@@ -6,8 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {ResourceLoader} from '@angular/compiler';
-import {Component, Directive, ErrorHandler, Inject, InjectionToken, NgModule, Optional, Pipe, ɵNG_COMPONENT_DEF as NG_COMPONENT_DEF} from '@angular/core';
+import {Component, Directive, ErrorHandler, Inject, InjectionToken, NgModule, Optional, Pipe, ɵdefineComponent as defineComponent, ɵsetClassMetadata as setClassMetadata, ɵtext as text} from '@angular/core';
 import {TestBed, getTestBed} from '@angular/core/testing/src/test_bed';
 import {By} from '@angular/platform-browser';
 import {expect} from '@angular/platform-browser/testing/src/matchers';
@@ -270,6 +269,60 @@ describe('TestBed', () => {
     expect(TestBed.get(ErrorHandler)).toEqual(jasmine.any(CustomErrorHandler));
   });
 
+  onlyInIvy('TestBed should handle AOT pre-compiled Components')
+      .describe('AOT pre-compiled components', () => {
+        /**
+         * Function returns a class that represents AOT-compiled version of the following Component:
+         *
+         * @Component({
+         *  selector: 'comp',
+         *  templateUrl: './template.ng.html',
+         *  styleUrls: ['./style.css']
+         * })
+         * class ComponentClass {}
+         *
+         * This is needed to closer match the behavior of AOT pre-compiled components (compiled
+         * outside of TestBed) without changing TestBed state and/or Component metadata to compile
+         * them via TestBed with external resources.
+         */
+        const getAOTCompiledComponent = () => {
+          class ComponentClass {
+            static ngComponentDef = defineComponent({
+              type: ComponentClass,
+              selectors: [['comp']],
+              factory: () => new ComponentClass(),
+              consts: 1,
+              vars: 0,
+              template: (rf: any, ctx: any) => {
+                if (rf & 1) {
+                  text(0, 'Some template');
+                }
+              },
+              styles: ['body { margin: 0; }']
+            });
+          }
+          setClassMetadata(
+              ComponentClass, [{
+                type: Component,
+                args: [{
+                  selector: 'comp',
+                  templateUrl: './template.ng.html',
+                  styleUrls: ['./style.css'],
+                }]
+              }],
+              null, null);
+          return ComponentClass;
+        };
+
+        it('should have an ability to override template', () => {
+          const SomeComponent = getAOTCompiledComponent();
+          TestBed.configureTestingModule({declarations: [SomeComponent]});
+          TestBed.overrideTemplateUsingTestingModule(SomeComponent, 'Template override');
+          const fixture = TestBed.createComponent(SomeComponent);
+          expect(fixture.nativeElement.innerHTML).toBe('Template override');
+        });
+      });
+
   onlyInIvy('patched ng defs should be removed after resetting TestingModule')
       .describe('resetting ng defs', () => {
         it('should restore ng defs to their initial states', () => {

packages/core/testing/src/r3_test_bed_compiler.ts

@@ -87,6 +87,10 @@ export class R3TestBedCompiler {
   private seenComponents = new Set<Type<any>>();
   private seenDirectives = new Set<Type<any>>();
 
+  // Store resolved styles for Components that have template overrides present and `styleUrls`
+  // defined at the same time.
+  private existingComponentStyles = new Map<Type<any>, string[]>();
+
   private resolvers: Resolvers = initResolvers();
 
   private componentToModuleScope = new Map<Type<any>, Type<any>|TESTING_MODULE>();
@@ -194,9 +198,26 @@ export class R3TestBedCompiler {
   }
 
   overrideTemplateUsingTestingModule(type: Type<any>, template: string): void {
-    // In Ivy, compiling a component does not require knowing the module providing the component's
-    // scope, so overrideTemplateUsingTestingModule can be implemented purely via overrideComponent.
-    this.overrideComponent(type, {set: {template}});
+    const def = (type as any)[NG_COMPONENT_DEF];
+    const hasStyleUrls = (): boolean => {
+      const metadata = this.resolvers.component.resolve(type) !as Component;
+      return !!metadata.styleUrls && metadata.styleUrls.length > 0;
+    };
+    const overrideStyleUrls = !!def && !isComponentDefPendingResolution(type) && hasStyleUrls();
+
+    // In Ivy, compiling a component does not require knowing the module providing the
+    // component's scope, so overrideTemplateUsingTestingModule can be implemented purely via
+    // overrideComponent. Important: overriding template requires full Component re-compilation,
+    // which may fail in case styleUrls are also present (thus Component is considered as required
+    // resolution). In order to avoid this, we preemptively set styleUrls to an empty array,
+    // preserve current styles available on Component def and restore styles back once compilation
+    // is complete.
+    const override = overrideStyleUrls ? {template, styles: [], styleUrls: []} : {template};
+    this.overrideComponent(type, {set: override});
+
+    if (overrideStyleUrls && def.styles && def.styles.length > 0) {
+      this.existingComponentStyles.set(type, def.styles);
+    }
 
     // Set the component's scope to be the testing module.
     this.componentToModuleScope.set(type, TESTING_MODULE);
@@ -231,6 +252,10 @@ export class R3TestBedCompiler {
 
     this.applyProviderOverrides();
 
+    // Patch previously stored `styles` Component values (taken from ngComponentDef), in case these
+    // Components have `styleUrls` fields defined and template override was requested.
+    this.patchComponentsWithExistingStyles();
+
     // Clear the componentToModuleScope map, so that future compilations don't reset the scope of
     // every component.
     this.componentToModuleScope.clear();
@@ -347,7 +372,7 @@ export class R3TestBedCompiler {
     this.seenComponents.clear();
     this.seenDirectives.clear();
   }
-  // ...
+
   private applyProviderOverridesToModule(moduleType: Type<any>): void {
     const injectorDef: any = (moduleType as any)[NG_INJECTOR_DEF];
     if (this.providerOverridesByToken.size > 0) {
@@ -369,6 +394,12 @@ export class R3TestBedCompiler {
     }
   }
 
+  private patchComponentsWithExistingStyles(): void {
+    this.existingComponentStyles.forEach(
+        (styles, type) => (type as any)[NG_COMPONENT_DEF].styles = styles);
+    this.existingComponentStyles.clear();
+  }
+
   private queueTypeArray(arr: any[], moduleType: Type<any>|TESTING_MODULE): void {
     for (const value of arr) {
       if (Array.isArray(value)) {