fix(upgrade): avoid memory leak when removing downgraded components

Previously, due to the way the AngularJS and Angular clean-up processes
interfere with each other when removing an AngularJS element that
contains a downgraded Angular component, the data associated with the
host element of the downgraded component was not removed. This data was
kept in an internal AngularJS cache, which prevented the element and
component instance from being garbage-collected, leading to memory
leaks.

This commit fixes this by ensuring the element data is explicitly
removed when cleaning up a downgraded component.

NOTE:
This is essentially the equivalent of #26209 but for downgraded (instead
of upgraded) components.

Fixes #39911
Closes #39921

packages/upgrade/src/common/src/angular1.ts

@@ -126,6 +126,7 @@ export type IAugmentedJQuery = Node[]&{
   data?: (name: string, value?: any) => any;
   text?: () => string;
   inheritedData?: (name: string, value?: any) => any;
+  children?: () => IAugmentedJQuery;
   contents?: () => IAugmentedJQuery;
   parent?: () => IAugmentedJQuery;
   empty?: () => void;

packages/upgrade/src/common/src/downgrade_component_adapter.ts

@@ -8,7 +8,7 @@
 
 import {ApplicationRef, ChangeDetectorRef, ComponentFactory, ComponentRef, EventEmitter, Injector, OnChanges, SimpleChange, SimpleChanges, StaticProvider, Testability, TestabilityRegistry, Type} from '@angular/core';
 
-import {IAttributes, IAugmentedJQuery, ICompileService, INgModelController, IParseService, IScope} from './angular1';
+import {element as angularElement, IAttributes, IAugmentedJQuery, ICompileService, INgModelController, IParseService, IScope} from './angular1';
 import {PropertyBinding} from './component_info';
 import {$SCOPE} from './constants';
 import {getTypeName, hookupNgModel, strictEquals} from './util';
@@ -216,11 +216,38 @@ export class DowngradeComponentAdapter {
     const destroyComponentRef = this.wrapCallback(() => this.componentRef.destroy());
     let destroyed = false;
 
-    this.element.on!('$destroy', () => this.componentScope.$destroy());
+    this.element.on!('$destroy', () => {
+      // The `$destroy` event may have been triggered by the `cleanData()` call in the
+      // `componentScope` `$destroy` handler below. In that case, we don't want to call
+      // `componentScope.$destroy()` again.
+      if (!destroyed) this.componentScope.$destroy();
+    });
     this.componentScope.$on('$destroy', () => {
       if (!destroyed) {
         destroyed = true;
         testabilityRegistry.unregisterApplication(this.componentRef.location.nativeElement);
+
+        // The `componentScope` might be getting destroyed, because an ancestor element is being
+        // removed/destroyed. If that is the case, jqLite/jQuery would normally invoke `cleanData()`
+        // on the removed element and all descendants.
+        // - https://github.com/angular/angular.js/blob/2e72ea13fa98bebf6ed4b5e3c45eaf5f990ed16f/src/jqLite.js#L349-L355
+        // - https://github.com/jquery/jquery/blob/6984d1747623dbc5e87fd6c261a5b6b1628c107c/src/manipulation.js#L182
+        //
+        // Here, however, `destroyComponentRef()` may under some circumstances remove the element
+        // from the DOM and therefore it will no longer be a descendant of the removed element when
+        // `cleanData()` is called. This would result in a memory leak, because the element's data
+        // and event handlers (and all objects directly or indirectly referenced by them) would be
+        // retained.
+        //
+        // To ensure the element is always properly cleaned up, we manually call `cleanData()` on
+        // this element and its descendants before destroying the `ComponentRef`.
+        //
+        // NOTE:
+        // `cleanData()` also will invoke the AngularJS `$destroy` event on the element:
+        // - https://github.com/angular/angular.js/blob/2e72ea13fa98bebf6ed4b5e3c45eaf5f990ed16f/src/Angular.js#L1932-L1945
+        angularElement.cleanData(this.element);
+        angularElement.cleanData(this.element.children!());
+
         destroyComponentRef();
       }
     });

packages/upgrade/src/dynamic/test/upgrade_spec.ts

@@ -678,7 +678,7 @@ withEachNg1Version(() => {
              };
            });
 
-           @Component({selector: 'ng2', template: 'test'})
+           @Component({selector: 'ng2', template: '<span>test</span>'})
            class Ng2 {
              ngOnDestroy() {
                onDestroyed.emit('destroyed');
@@ -695,8 +695,32 @@ withEachNg1Version(() => {
            ng1Module.directive('ng2', adapter.downgradeNg2Component(Ng2));
            const element = html('<ng1></ng1>');
            adapter.bootstrap(element, ['ng1']).ready((ref) => {
+             const ng2Element = angular.element(element.querySelector('ng2') as Element);
+             const ng2Children = (ng2Element as any).children!();
+             let ng2ElementDestroyed = false;
+             let ng2ChildrenDestroyed = false;
+
+             ng2Element.data!('foo', 1);
+             ng2Children.data!('bar', 2);
+             ng2Element.on!('$destroy', () => ng2ElementDestroyed = true);
+             ng2Children.on!('$destroy', () => ng2ChildrenDestroyed = true);
+
+             expect(element.textContent).toContain('test');
+             expect(ng2Element.data!('foo')).toBe(1);
+             expect(ng2Children.data!('bar')).toBe(2);
+             expect(ng2ElementDestroyed).toBe(false);
+             expect(ng2ChildrenDestroyed).toBe(false);
+
              onDestroyed.subscribe(() => {
-               ref.dispose();
+               setTimeout(() => {
+                 expect(element.textContent).not.toContain('test');
+                 expect(ng2Element.data!('foo')).toBeUndefined();
+                 expect(ng2Children.data!('baz')).toBeUndefined();
+                 expect(ng2ElementDestroyed).toBe(true);
+                 expect(ng2ChildrenDestroyed).toBe(true);
+
+                 ref.dispose();
+               });
              });
            });
          }));

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

@@ -536,7 +536,7 @@ withEachNg1Version(() => {
 
     it('should properly run cleanup when ng1 directive is destroyed', waitForAsync(() => {
          let destroyed = false;
-         @Component({selector: 'ng2', template: 'test'})
+         @Component({selector: 'ng2', template: '<span>test</span>'})
          class Ng2Component implements OnDestroy {
            ngOnDestroy() {
              destroyed = true;
@@ -563,14 +563,33 @@ withEachNg1Version(() => {
          platformBrowserDynamic().bootstrapModule(Ng2Module).then((ref) => {
            const adapter = ref.injector.get(UpgradeModule) as UpgradeModule;
            adapter.bootstrap(element, [ng1Module.name]);
+
+           const ng2Element = angular.element(element.querySelector('ng2') as Element);
+           const ng2Children = (ng2Element as any).children!();
+           let ng2ElementDestroyed = false;
+           let ng2ChildrenDestroyed = false;
+
+           ng2Element.data!('foo', 1);
+           ng2Children.data!('bar', 2);
+           ng2Element.on!('$destroy', () => ng2ElementDestroyed = true);
+           ng2Children.on!('$destroy', () => ng2ChildrenDestroyed = true);
+
            expect(element.textContent).toContain('test');
            expect(destroyed).toBe(false);
+           expect(ng2Element.data!('foo')).toBe(1);
+           expect(ng2Children.data!('bar')).toBe(2);
+           expect(ng2ElementDestroyed).toBe(false);
+           expect(ng2ChildrenDestroyed).toBe(false);
 
            const $rootScope = adapter.$injector.get('$rootScope');
            $rootScope.$apply('destroyIt = true');
 
            expect(element.textContent).not.toContain('test');
            expect(destroyed).toBe(true);
+           expect(ng2Element.data!('foo')).toBeUndefined();
+           expect(ng2Children.data!('baz')).toBeUndefined();
+           expect(ng2ElementDestroyed).toBe(true);
+           expect(ng2ChildrenDestroyed).toBe(true);
          });
        }));
 

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

@@ -1187,6 +1187,68 @@ withEachNg1Version(() => {
            });
          }));
 
+      it('should properly run cleanup when a downgraded component is destroyed', waitForAsync(() => {
+           let destroyed = false;
+
+           @Component({selector: 'ng2', template: '<span>test</span>'})
+           class Ng2Component implements OnDestroy {
+             ngOnDestroy() {
+               destroyed = true;
+             }
+           }
+
+           @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('<div><div ng-if="!hideNg2"><ng2></ng2></div></div>');
+           const $injector = angular.bootstrap(element, [ng1Module.name]);
+           const $rootScope = $injector.get($ROOT_SCOPE) as angular.IRootScopeService;
+
+           setTimeout(() => {    // Wait for the module to be bootstrapped.
+             setTimeout(() => {  // Wait for the hostView to be attached (during the `$digest`).
+               const ng2Element = angular.element(element.querySelector('ng2') as Element);
+               const ng2Children = (ng2Element as any).children!();
+               let ng2ElementDestroyed = false;
+               let ng2ChildrenDestroyed = false;
+
+               ng2Element.data!('foo', 1);
+               ng2Children.data!('bar', 2);
+               ng2Element.on!('$destroy', () => ng2ElementDestroyed = true);
+               ng2Children.on!('$destroy', () => ng2ChildrenDestroyed = true);
+
+               expect(element.textContent).toContain('test');
+               expect(destroyed).toBe(false);
+               expect(ng2Element.data!('foo')).toBe(1);
+               expect(ng2Children.data!('bar')).toBe(2);
+               expect(ng2ElementDestroyed).toBe(false);
+               expect(ng2ChildrenDestroyed).toBe(false);
+
+               $rootScope.$apply('hideNg2 = true');
+
+               expect(element.textContent).not.toContain('test');
+               expect(destroyed).toBe(true);
+               expect(ng2Element.data!('foo')).toBeUndefined();
+               expect(ng2Children.data!('baz')).toBeUndefined();
+               expect(ng2ElementDestroyed).toBe(true);
+               expect(ng2ChildrenDestroyed).toBe(true);
+             });
+           });
+         }));
+
       it('should only retrieve the Angular zone once (and cache it for later use)',
          fakeAsync(() => {
            let count = 0;