refactor(upgrade): remove redundant call to `appRef.detach()`

Once  a `ViewRef` is attached to the `ApplicationRef`, destroying the corresponding `ComponentRef` will automatically detach the `ViewRef`.

packages/upgrade/src/common/downgrade_component.ts

@@ -115,7 +115,7 @@ export function downgradeComponent(info: {
           facade.createComponent(projectableNodes);
           facade.setupInputs(needsNgZone, info.propagateDigest);
           facade.setupOutputs();
-          facade.registerCleanup(needsNgZone);
+          facade.registerCleanup();
 
           injectorPromise.resolve(facade.getInjector());
 

packages/upgrade/src/common/downgrade_component_adapter.ts

@@ -25,7 +25,6 @@ export class DowngradeComponentAdapter {
   private componentRef: ComponentRef<any>;
   private component: any;
   private changeDetector: ChangeDetectorRef;
-  private appRef: ApplicationRef;
 
   constructor(
       private element: angular.IAugmentedJQuery, private attrs: angular.IAttributes,
@@ -35,7 +34,6 @@ export class DowngradeComponentAdapter {
       private componentFactory: ComponentFactory<any>,
       private wrapCallback: <T>(cb: () => T) => () => T) {
     this.componentScope = scope.$new();
-    this.appRef = parentInjector.get(ApplicationRef);
   }
 
   compileContents(): Node[][] {
@@ -154,7 +152,8 @@ export class DowngradeComponentAdapter {
 
     // Attach the view so that it will be dirty-checked.
     if (needsNgZone) {
-      this.appRef.attachView(this.componentRef.hostView);
+      const appRef = this.parentInjector.get<ApplicationRef>(ApplicationRef);
+      appRef.attachView(this.componentRef.hostView);
     }
   }
 
@@ -202,7 +201,7 @@ export class DowngradeComponentAdapter {
     }
   }
 
-  registerCleanup(needsNgZone: boolean) {
+  registerCleanup() {
     const destroyComponentRef = this.wrapCallback(() => this.componentRef.destroy());
 
     this.element.on !('$destroy', () => {
@@ -210,9 +209,6 @@ export class DowngradeComponentAdapter {
       this.componentRef.injector.get(TestabilityRegistry)
           .unregisterApplication(this.componentRef.location.nativeElement);
       destroyComponentRef();
-      if (needsNgZone) {
-        this.appRef.detachView(this.componentRef.hostView);
-      }
     });
   }
 

packages/upgrade/test/static/integration/downgrade_module_spec.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Component, Inject, Injector, Input, NgModule, NgZone, OnChanges, OnDestroy, StaticProvider, destroyPlatform} from '@angular/core';
+import {ApplicationRef, Component, Inject, Injector, Input, NgModule, NgZone, OnChanges, OnDestroy, StaticProvider, ViewRef, destroyPlatform} from '@angular/core';
 import {async, fakeAsync, tick} from '@angular/core/testing';
 import {BrowserModule} from '@angular/platform-browser';
 import {platformBrowserDynamic} from '@angular/platform-browser-dynamic';
@@ -306,6 +306,53 @@ export function main() {
            });
          }));
 
+      it('should detach hostViews from the ApplicationRef once destroyed', async(() => {
+           let ng2Component: Ng2Component;
+
+           @Component({selector: 'ng2', template: ''})
+           class Ng2Component {
+             constructor(public appRef: ApplicationRef) {
+               ng2Component = this;
+               spyOn(appRef, 'attachView').and.callThrough();
+               spyOn(appRef, 'detachView').and.callThrough();
+             }
+           }
+
+           @NgModule({
+             declarations: [Ng2Component],
+             entryComponents: [Ng2Component],
+             imports: [BrowserModule],
+           })
+           class Ng2Module {
+             ngDoBootstrap() {}
+           }
+
+           const bootstrapFn = (extraProviders: StaticProvider[]) =>
+               platformBrowserDynamic(extraProviders).bootstrapModule(Ng2Module);
+           const lazyModuleName = downgradeModule<Ng2Module>(bootstrapFn);
+           const ng1Module =
+               angular.module('ng1', [lazyModuleName])
+                   .directive(
+                       'ng2', downgradeComponent({component: Ng2Component, propagateDigest}));
+
+           const element = html('<ng2 ng-if="!hideNg2"></ng2>');
+           const $injector = angular.bootstrap(element, [ng1Module.name]);
+           const $rootScope = $injector.get($ROOT_SCOPE) as angular.IRootScopeService;
+
+           // Wait for the module to be bootstrapped.
+           setTimeout(() => {
+             const hostView: ViewRef =
+                 (ng2Component.appRef.attachView as jasmine.Spy).calls.mostRecent().args[0];
+
+             expect(hostView.destroyed).toBe(false);
+
+             $rootScope.$apply('hideNg2 = true');
+
+             expect(hostView.destroyed).toBe(true);
+             expect(ng2Component.appRef.detachView).toHaveBeenCalledWith(hostView);
+           });
+         }));
+
       it('should only retrieve the Angular zone once (and cache it for later use)',
          fakeAsync(() => {
            let count = 0;