fix(router): Ensure that new RouterOutlet instances work after old ones are destroyed (#46554)

There can be timing issues with removing an old outlet and creating a
new one to replace it. Before calling `onChildOutletDestroyed`, the
`RouterOutlet` will first check to ensure that it is still the one
registered for that outlet name.

Fixes #36711
Fixes #32453

PR Close #46554

packages/router/src/directives/router_outlet.ts

@@ -183,7 +183,10 @@ export class RouterOutlet implements OnDestroy, OnInit, RouterOutletContract {
 
   /** @nodoc */
   ngOnDestroy(): void {
-    this.parentContexts.onChildOutletDestroyed(this.name);
+    // Ensure that the registered outlet is this one before removing it on the context.
+    if (this.parentContexts.getContext(this.name)?.outlet === this) {
+      this.parentContexts.onChildOutletDestroyed(this.name);
+    }
   }
 
   /** @nodoc */

packages/router/test/regression_integration.spec.ts

@@ -10,7 +10,7 @@ import {CommonModule, Location} from '@angular/common';
 import {SpyLocation} from '@angular/common/testing';
 import {ChangeDetectionStrategy, ChangeDetectorRef, Component, Injectable, NgModule, TemplateRef, Type, ViewChild, ViewContainerRef} from '@angular/core';
 import {ComponentFixture, fakeAsync, TestBed, tick} from '@angular/core/testing';
-import {Resolve, Router} from '@angular/router';
+import {ChildrenOutletContexts, Resolve, Router} from '@angular/router';
 import {RouterTestingModule} from '@angular/router/testing';
 import {of} from 'rxjs';
 import {delay, mapTo} from 'rxjs/operators';
@@ -339,6 +339,49 @@ describe('Integration', () => {
          expect(fixture.nativeElement.innerHTML).toContain('one');
        }));
   });
+
+  it('should not unregister outlet if a different one already exists #36711, 32453', async () => {
+    @Component({
+      template: `
+      <router-outlet *ngIf="outlet1"></router-outlet>
+      <router-outlet *ngIf="outlet2"></router-outlet>
+      `,
+    })
+    class TestCmp {
+      outlet1 = true;
+      outlet2 = false;
+    }
+
+    @Component({template: ''})
+    class EmptyCmp {
+    }
+
+    TestBed.configureTestingModule({
+      imports: [CommonModule, RouterTestingModule.withRoutes([{path: '**', component: EmptyCmp}])],
+      declarations: [TestCmp, EmptyCmp]
+    });
+    const fixture = TestBed.createComponent(TestCmp);
+    const contexts = TestBed.inject(ChildrenOutletContexts);
+    await TestBed.inject(Router).navigateByUrl('/');
+    fixture.detectChanges();
+
+    expect(contexts.getContext('primary')).toBeDefined();
+    expect(contexts.getContext('primary')?.outlet).not.toBeNull();
+
+    // Show the second outlet. Applications shouldn't really have more than one outlet but there can
+    // be timing issues between destroying and recreating a second one in some cases:
+    // https://github.com/angular/angular/issues/36711,
+    // https://github.com/angular/angular/issues/32453
+    fixture.componentInstance.outlet2 = true;
+    fixture.detectChanges();
+    expect(contexts.getContext('primary')?.outlet).not.toBeNull();
+
+    fixture.componentInstance.outlet1 = false;
+    fixture.detectChanges();
+    // Destroying the first one show not clear the outlet context because the second one takes over
+    // as the registered outlet.
+    expect(contexts.getContext('primary')?.outlet).not.toBeNull();
+  });
 });
 
 function advance<T>(fixture: ComponentFixture<T>): void {