fix(core): Multiple subscribers to ApplicationRef.isStable should all…

… see values (#53541)

The behavior of `ApplicationRef.isStable` changed in 16.1 due to
28c68f7.
This change added a `share` to the `isStable` observable, which prevents
additional subscribers from getting a value until a new one emits. One
solution to the problem would be `shareReplay(1)`. However, that would
increase the bundle size since we do not use `shareReplay` elsewhere.
Instead, we don't even really need to share the observable.

The `Observable` available in `ApplicationRef.isStable` before the above commit
was the zone stable observable, without a `share`. The new behavior adds
only an additional observable to the stream, `hasPendingTasks` (a `BehaviorSubject`).
The observables in this stream are not expensive to subscribe to. The
only one with side effects is the `isStable` (because it subscribes to
onStable), but that one already has the `share` operator on it.
Omitting the `share` in `ApplicationRef` also means that applications on `zoneless` will not
have to pay the cost of the operator when we make zones optional because
the zone stable observable is the only place we use it.

PR Close #53541

packages/core/src/application/application_ref.ts

@@ -10,7 +10,7 @@ import '../util/ng_jit_mode';
 
 import {setThrowInvalidWriteToSignalError} from '@angular/core/primitives/signals';
 import {Observable, of} from 'rxjs';
-import {distinctUntilChanged, first, share, switchMap} from 'rxjs/operators';
+import {distinctUntilChanged, first, switchMap} from 'rxjs/operators';
 
 import {getCompilerFacade, JitCompilerUsage} from '../compiler/compiler_facade';
 import {Console} from '../console';
@@ -351,7 +351,6 @@ export class ApplicationRef {
           .hasPendingTasks.pipe(
               switchMap(hasPendingTasks => hasPendingTasks ? of(false) : this.zoneIsStable),
               distinctUntilChanged(),
-              share(),
           );
 
   private readonly _injector = inject(EnvironmentInjector);

packages/core/test/application_ref_spec.ts

@@ -21,6 +21,7 @@ import type {ServerModule} from '@angular/platform-server';
 import {ApplicationRef} from '../src/application/application_ref';
 import {NoopNgZone} from '../src/zone/ng_zone';
 import {ComponentFixtureNoNgZone, inject, TestBed, waitForAsync, withModule} from '../testing';
+import {take} from 'rxjs/operators';
 
 let serverPlatformModule: Promise<Type<ServerModule>>|null = null;
 if (isNode) {
@@ -795,6 +796,14 @@ describe('AppRef', () => {
        expectStableTexts(MacroMicroTaskComp, ['111']);
      }));
 
+  it('isStable can be subscribed to many times', async () => {
+    const appRef: ApplicationRef = TestBed.inject(ApplicationRef);
+    // Create stable subscription but do not unsubscribe before the second subscription is made
+    appRef.isStable.subscribe();
+    await expectAsync(appRef.isStable.pipe(take(1)).toPromise()).toBeResolved();
+    stableCalled = true;
+  });
+
   describe('unstable', () => {
     let unstableCalled = false;
 

packages/core/test/bundling/animations-standalone/bundle.golden_symbols.json

@@ -1406,9 +1406,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

packages/core/test/bundling/animations/bundle.golden_symbols.json

@@ -1478,9 +1478,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

packages/core/test/bundling/cyclic_import/bundle.golden_symbols.json

@@ -1178,9 +1178,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

packages/core/test/bundling/defer/bundle.golden_symbols.json

@@ -2336,9 +2336,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

packages/core/test/bundling/forms_reactive/bundle.golden_symbols.json

@@ -1649,9 +1649,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

packages/core/test/bundling/forms_template_driven/bundle.golden_symbols.json

@@ -1625,9 +1625,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

packages/core/test/bundling/hello_world/bundle.golden_symbols.json

@@ -932,9 +932,6 @@
   {
     "name": "setUpAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

packages/core/test/bundling/hydration/bundle.golden_symbols.json

@@ -1274,9 +1274,6 @@
   {
     "name": "setUpAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

packages/core/test/bundling/router/bundle.golden_symbols.json

@@ -1961,9 +1961,6 @@
   {
     "name": "shallowEqual"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

packages/core/test/bundling/standalone_bootstrap/bundle.golden_symbols.json

@@ -1031,9 +1031,6 @@
   {
     "name": "setUpAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },

packages/core/test/bundling/todo/bundle.golden_symbols.json

@@ -1418,9 +1418,6 @@
   {
     "name": "setupStaticAttributes"
   },
-  {
-    "name": "share"
-  },
   {
     "name": "shareSubjectFactory"
   },