fix(core): untrack various core operations (#54614)

One downside of implicit dependency tracking in `effect()`s is that it's easy
to for downstream code to end up running inside the effect context by accident.
For example, if an effect raises an event (e.g. by `next()`ing a `Subject`), the
subscribers to that `Observable` will run inside the effect's reactive context,
and any signals read within the subscriber will end up as dependencies of the
effect. This is why the `untracked` function is useful, to run certain
operations without incidental signal reads ending up tracked.

However, knowing when this is necessary is non-trivial. For example, injecting
a dependency might cause it to be instantiated, which would run the constructor
in the effect context unless the injection operation is untracked.

Therefore, Angular will automatically drop the reactive context within a number
of framework APIs. This commit addresses these use cases:

* creating and destroying views
* creating and destroying DI injectors
* injecting dependencies
* emitting outputs

Fixes #54548

There are likely other APIs which would benefit from this approach, but this
is a start.

PR Close #54614

packages/core/src/application/application_ref.ts

@@ -8,7 +8,7 @@
 
 import '../util/ng_jit_mode';
 
-import {setThrowInvalidWriteToSignalError} from '@angular/core/primitives/signals';
+import {setActiveConsumer, setThrowInvalidWriteToSignalError} from '@angular/core/primitives/signals';
 import {Observable} from 'rxjs';
 import {first, map} from 'rxjs/operators';
 
@@ -492,6 +492,7 @@ export class ApplicationRef {
           ngDevMode && 'ApplicationRef.tick is called recursively');
     }
 
+    const prevConsumer = setActiveConsumer(null);
     try {
       this._runningTick = true;
 
@@ -507,6 +508,7 @@ export class ApplicationRef {
       this.internalErrorHandler(e);
     } finally {
       this._runningTick = false;
+      setActiveConsumer(prevConsumer);
     }
   }
 

packages/core/src/di/r3_injector.ts

@@ -34,6 +34,7 @@ import {NullInjector} from './null_injector';
 import {isExistingProvider, isFactoryProvider, isTypeProvider, isValueProvider, SingleProvider} from './provider_collection';
 import {ProviderToken} from './provider_token';
 import {INJECTOR_SCOPE, InjectorScope} from './scope';
+import {setActiveConsumer} from '@angular/core/primitives/signals';
 
 /**
  * Marker which indicates that a value has not yet been created from the factory function.
@@ -194,6 +195,7 @@ export class R3Injector extends EnvironmentInjector {
 
     // Set destroyed = true first, in case lifecycle hooks re-enter destroy().
     this._destroyed = true;
+    const prevConsumer = setActiveConsumer(null);
     try {
       // Call all the lifecycle hooks.
       for (const service of this._ngOnDestroyHooks) {
@@ -211,6 +213,7 @@ export class R3Injector extends EnvironmentInjector {
       this.records.clear();
       this._ngOnDestroyHooks.clear();
       this.injectorDefTypes.clear();
+      setActiveConsumer(prevConsumer);
     }
   }
 
@@ -322,6 +325,7 @@ export class R3Injector extends EnvironmentInjector {
 
   /** @internal */
   resolveInjectorInitializers() {
+    const prevConsumer = setActiveConsumer(null);
     const previousInjector = setCurrentInjector(this);
     const previousInjectImplementation = setInjectImplementation(undefined);
     let prevInjectContext: InjectorProfilerContext|undefined;
@@ -346,6 +350,7 @@ export class R3Injector extends EnvironmentInjector {
       setCurrentInjector(previousInjector);
       setInjectImplementation(previousInjectImplementation);
       ngDevMode && setInjectorProfilerContext(prevInjectContext!);
+      setActiveConsumer(prevConsumer);
     }
   }
 
@@ -419,24 +424,29 @@ export class R3Injector extends EnvironmentInjector {
   }
 
   private hydrate<T>(token: ProviderToken<T>, record: Record<T>): T {
-    if (ngDevMode && record.value === CIRCULAR) {
-      throwCyclicDependencyError(stringify(token));
-    } else if (record.value === NOT_YET) {
-      record.value = CIRCULAR;
-
-      if (ngDevMode) {
-        runInInjectorProfilerContext(this, token as Type<T>, () => {
+    const prevConsumer = setActiveConsumer(null);
+    try {
+      if (ngDevMode && record.value === CIRCULAR) {
+        throwCyclicDependencyError(stringify(token));
+      } else if (record.value === NOT_YET) {
+        record.value = CIRCULAR;
+
+        if (ngDevMode) {
+          runInInjectorProfilerContext(this, token as Type<T>, () => {
+            record.value = record.factory!();
+            emitInstanceCreatedByInjectorEvent(record.value);
+          });
+        } else {
           record.value = record.factory!();
-          emitInstanceCreatedByInjectorEvent(record.value);
-        });
-      } else {
-        record.value = record.factory!();
+        }
       }
+      if (typeof record.value === 'object' && record.value && hasOnDestroy(record.value)) {
+        this._ngOnDestroyHooks.add(record.value);
+      }
+      return record.value as T;
+    } finally {
+      setActiveConsumer(prevConsumer);
     }
-    if (typeof record.value === 'object' && record.value && hasOnDestroy(record.value)) {
-      this._ngOnDestroyHooks.add(record.value);
-    }
-    return record.value as T;
   }
 
   private injectableDefInScope(def: ɵɵInjectableDeclaration<any>): boolean {

packages/core/src/event_emitter.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {setActiveConsumer} from '@angular/core/primitives/signals';
 import {PartialObserver, Subject, Subscription} from 'rxjs';
 
 /**
@@ -109,7 +110,12 @@ class EventEmitter_ extends Subject<any> {
   }
 
   emit(value?: any) {
-    super.next(value);
+    const prevConsumer = setActiveConsumer(null);
+    try {
+      super.next(value);
+    } finally {
+      setActiveConsumer(prevConsumer);
+    }
   }
 
   override subscribe(observerOrNext?: any, error?: any, complete?: any): Subscription {