fix(common): cleanup URL change listeners when the root view is removed (#44901)

The `Location` creates the `_urlChangeSubscription` when the `onUrlChange` is called for the first time.
The subscription `next` function captures `this` and prevents the `Location` from being garbage collected
when the root view is removed.

PR Close #44901

packages/common/src/location/location.ts

@@ -6,8 +6,9 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {EventEmitter, Injectable, ɵɵinject} from '@angular/core';
+import {EventEmitter, Injectable, OnDestroy, ɵɵinject} from '@angular/core';
 import {SubscriptionLike} from 'rxjs';
+
 import {LocationStrategy} from './location_strategy';
 import {PlatformLocation} from './platform_location';
 import {joinWithSlash, normalizeQueryParams, stripTrailingSlash} from './util';
@@ -53,7 +54,7 @@ export interface PopStateEvent {
   // See #23917
   useFactory: createLocation,
 })
-export class Location {
+export class Location implements OnDestroy {
   /** @internal */
   _subject: EventEmitter<any> = new EventEmitter();
   /** @internal */
@@ -65,7 +66,7 @@ export class Location {
   /** @internal */
   _urlChangeListeners: ((url: string, state: unknown) => void)[] = [];
   /** @internal */
-  _urlChangeSubscription?: SubscriptionLike;
+  _urlChangeSubscription: SubscriptionLike|null = null;
 
   constructor(platformStrategy: LocationStrategy, platformLocation: PlatformLocation) {
     this._platformStrategy = platformStrategy;
@@ -82,6 +83,12 @@ export class Location {
     });
   }
 
+  /** @nodoc */
+  ngOnDestroy(): void {
+    this._urlChangeSubscription?.unsubscribe();
+    this._urlChangeListeners = [];
+  }
+
   /**
    * Normalizes the URL path for this location.
    *
@@ -209,8 +216,9 @@ export class Location {
    * framework that are not detectible through "popstate" or "hashchange" events.
    *
    * @param fn The change handler function, which take a URL and a location history state.
+   * @returns A function that, when executed, unregisters a URL change listener.
    */
-  onUrlChange(fn: (url: string, state: unknown) => void) {
+  onUrlChange(fn: (url: string, state: unknown) => void): VoidFunction {
     this._urlChangeListeners.push(fn);
 
     if (!this._urlChangeSubscription) {
@@ -218,6 +226,16 @@ export class Location {
         this._notifyUrlChangeListeners(v.url, v.state);
       });
     }
+
+    return () => {
+      const fnIndex = this._urlChangeListeners.indexOf(fn);
+      this._urlChangeListeners.splice(fnIndex, 1);
+
+      if (this._urlChangeListeners.length === 0) {
+        this._urlChangeSubscription?.unsubscribe();
+        this._urlChangeSubscription = null;
+      }
+    };
   }
 
   /** @internal */

packages/common/testing/src/location_mock.ts

@@ -33,7 +33,12 @@ export class SpyLocation implements Location {
   /** @internal */
   _urlChangeListeners: ((url: string, state: unknown) => void)[] = [];
   /** @internal */
-  _urlChangeSubscription?: SubscriptionLike;
+  _urlChangeSubscription: SubscriptionLike|null = null;
+
+  ngOnDestroy(): void {
+    this._urlChangeSubscription?.unsubscribe();
+    this._urlChangeListeners = [];
+  }
 
   setInitialPath(url: string) {
     this._history[this._historyIndex].path = url;
@@ -138,7 +143,7 @@ export class SpyLocation implements Location {
     }
   }
 
-  onUrlChange(fn: (url: string, state: unknown) => void) {
+  onUrlChange(fn: (url: string, state: unknown) => void): VoidFunction {
     this._urlChangeListeners.push(fn);
 
     if (!this._urlChangeSubscription) {
@@ -146,6 +151,16 @@ export class SpyLocation implements Location {
         this._notifyUrlChangeListeners(v.url, v.state);
       });
     }
+
+    return () => {
+      const fnIndex = this._urlChangeListeners.indexOf(fn);
+      this._urlChangeListeners.splice(fnIndex, 1);
+
+      if (this._urlChangeListeners.length === 0) {
+        this._urlChangeSubscription?.unsubscribe();
+        this._urlChangeSubscription = null;
+      }
+    };
   }
 
   /** @internal */

packages/router/test/bootstrap.spec.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {APP_BASE_HREF, DOCUMENT, ɵgetDOM as getDOM} from '@angular/common';
+import {APP_BASE_HREF, DOCUMENT, Location, ɵgetDOM as getDOM} from '@angular/common';
 import {ApplicationRef, Component, CUSTOM_ELEMENTS_SCHEMA, destroyPlatform, NgModule} from '@angular/core';
 import {inject} from '@angular/core/testing';
 import {BrowserModule} from '@angular/platform-browser';
@@ -407,6 +407,51 @@ describe('bootstrap', () => {
     expect(window.removeEventListener).toHaveBeenCalledWith('hashchange', jasmine.any(Function));
   });
 
+  it('should unregister a URL change listener and unsubscribe from URL changes when the root view is removed',
+     async () => {
+       const changeListener = jasmine.createSpy('changeListener');
+
+       @Component({template: 'second simple'})
+       class SecondSimpleCmp {
+       }
+
+       @NgModule({
+         imports: [
+           BrowserModule,
+           RouterModule.forRoot(
+               [{path: 'a', component: SimpleCmp}, {path: 'b', component: SecondSimpleCmp}],
+               {initialNavigation: 'enabled'})
+         ],
+         declarations: [RootCmp, SimpleCmp, SecondSimpleCmp],
+         bootstrap: [RootCmp],
+         providers: testProviders
+       })
+       class TestModule {
+       }
+
+       const ngModuleRef = await platformBrowserDynamic().bootstrapModule(TestModule);
+       const router = ngModuleRef.injector.get(Router);
+       const location = ngModuleRef.injector.get(Location);
+
+       const removeUrlChangeFn = location.onUrlChange(changeListener);
+
+       await router.navigateByUrl('/a');
+       expect(changeListener).toHaveBeenCalledTimes(1);
+
+       removeUrlChangeFn();
+       await router.navigateByUrl('/b');
+       expect(changeListener).toHaveBeenCalledTimes(1);
+
+       location.onUrlChange((url: string, state: unknown) => {});
+
+       ngModuleRef.destroy();
+
+       // Let's ensure that URL change listeners are unregistered when the root view is removed,
+       // tho the last returned `onUrlChange` function hasn't been invoked.
+       expect((location as any)._urlChangeListeners.length).toEqual(0);
+       expect((location as any)._urlChangeSubscription.closed).toEqual(true);
+     });
+
   it('can schedule a navigation from the NavigationEnd event #37460', async (done) => {
     @NgModule({
       imports: [