feat(common): add an 'outlet' injector option for ngTemplateOutlet

mmalerba · AndrewKushnir · commit 18003a33bb0d · 2026-02-10T09:42:50.000-08:00
Adds an option (`ngTemplateOutletInjector="outlet"`) that instructs the ngTemplateOutlet to inherit its injector from the outlet's place in the instantiated DOM.
diff --git a/goldens/public-api/common/index.api.md b/goldens/public-api/common/index.api.md
@@ -729,10 +729,12 @@ export class NgSwitchDefault {
 export class NgTemplateOutlet<C = unknown> implements OnChanges {
     constructor(_viewContainerRef: ViewContainerRef);
     // (undocumented)
+    protected injector: Injector;
+    // (undocumented)
     ngOnChanges(changes: SimpleChanges): void;
     ngTemplateOutlet: TemplateRef<C> | null | undefined;
     ngTemplateOutletContext: C | null | undefined;
-    ngTemplateOutletInjector: Injector | null | undefined;
+    ngTemplateOutletInjector: Injector | 'outlet' | null | undefined;
     // (undocumented)
     static ɵdir: i0.ɵɵDirectiveDeclaration<NgTemplateOutlet<any>, "[ngTemplateOutlet]", never, { "ngTemplateOutletContext": { "alias": "ngTemplateOutletContext"; "required": false; }; "ngTemplateOutlet": { "alias": "ngTemplateOutlet"; "required": false; }; "ngTemplateOutletInjector": { "alias": "ngTemplateOutletInjector"; "required": false; }; }, {}, never, never, true, never>;
     // (undocumented)
diff --git a/packages/common/src/directives/ng_template_outlet.ts b/packages/common/src/directives/ng_template_outlet.ts
@@ -9,6 +9,7 @@
 import {
   Directive,
   EmbeddedViewRef,
+  inject,
   Injector,
   Input,
   OnChanges,
@@ -60,8 +61,13 @@ export class NgTemplateOutlet<C = unknown> implements OnChanges {
    */
   @Input() public ngTemplateOutlet: TemplateRef<C> | null | undefined = null;
 
-  /** Injector to be used within the embedded view. */
-  @Input() public ngTemplateOutletInjector: Injector | null | undefined = null;
+  /**
+   * Injector to be used within the embedded view. A value of "outlet" can be used to indicate
+   * that the injector should be inherited from the template outlet's location in the instantiated DOM.
+   */
+  @Input() public ngTemplateOutletInjector: Injector | 'outlet' | null | undefined = null;
+
+  protected injector = inject(Injector);
 
   constructor(private _viewContainerRef: ViewContainerRef) {}
 
@@ -83,11 +89,21 @@ export class NgTemplateOutlet<C = unknown> implements OnChanges {
       // without having to destroy and re-create views whenever the context changes.
       const viewContext = this._createContextForwardProxy();
       this._viewRef = viewContainerRef.createEmbeddedView(this.ngTemplateOutlet, viewContext, {
-        injector: this.ngTemplateOutletInjector ?? undefined,
+        injector: this._getInjector(),
       });
     }
   }
 
+  /**
+   * Gets the injector to use for the template outlet based on ngTemplateOutletInjector.
+   */
+  private _getInjector(): Injector | undefined {
+    if (this.ngTemplateOutletInjector === 'outlet') {
+      return this.injector;
+    }
+    return this.ngTemplateOutletInjector ?? undefined;
+  }
+
   /**
    * We need to re-create existing embedded view if either is true:
    * - the outlet changed.
diff --git a/packages/common/test/directives/ng_template_outlet_spec.ts b/packages/common/test/directives/ng_template_outlet_spec.ts
@@ -6,7 +6,6 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
-import {CommonModule, NgTemplateOutlet} from '../../index';
 import {
   Component,
   ContentChildren,
@@ -17,12 +16,16 @@ import {
   Injector,
   NO_ERRORS_SCHEMA,
   OnDestroy,
+  Optional,
   Provider,
   QueryList,
+  SkipSelf,
   TemplateRef,
+  inject,
 } from '@angular/core';
 import {ComponentFixture, TestBed} from '@angular/core/testing';
 import {expect} from '@angular/private/testing/matchers';
+import {CommonModule, NgTemplateOutlet} from '../../index';
 
 describe('NgTemplateOutlet', () => {
   let fixture: ComponentFixture<any>;
@@ -49,6 +52,8 @@ describe('NgTemplateOutlet', () => {
         DestroyableCmpt,
         MultiContextComponent,
         InjectValueComponent,
+        ProvideValueComponent,
+        NestingCounter,
       ],
       imports: [CommonModule],
       providers: [DestroyedSpyService],
@@ -360,6 +365,43 @@ describe('NgTemplateOutlet', () => {
     detectChangesAndExpectText('Hello world');
   });
 
+  it('should be able to inherit outlet injector', () => {
+    const template = `
+      <ng-template #tpl><inject-value></inject-value></ng-template>
+      <provide-value>
+        <ng-container *ngTemplateOutlet="tpl; injector: 'outlet'"></ng-container>
+      </provide-value>
+    `;
+    fixture = createTestComponent(template, [{provide: templateToken, useValue: 'root'}]);
+    detectChangesAndExpectText('Hello provide-value');
+  });
+
+  it('should be able to inherit outlet injector in a deeply nested structure', () => {
+    // This template should create the following rendered structure
+    // (Spaces & newlines added for readability):
+    // <nesting-counter> 1
+    //   <nesting counter> 2
+    //     <nesting-counter> 3
+    //       <nesting-counter> 4 </nesting-counter>
+    //     </nesting-counter>
+    //   </nesting-counter>
+    //   <nesting-counter> 2 </nesting-counter>
+    // </nesting-counter>
+    const template = `
+      <ng-container *ngTemplateOutlet="node; context: {$implicit: [[[[]]], []]}" />
+
+      <ng-template #node let-data>
+        <nesting-counter>
+          @for (item of data; track $index) {
+            <ng-container *ngTemplateOutlet="node; context: {$implicit: item}; injector: 'outlet'" />
+          } 
+        </nesting-counter>
+      </ng-template>
+    `;
+    fixture = createTestComponent(template);
+    detectChangesAndExpectText('12342');
+  });
+
   it('should be available as a standalone directive', () => {
     @Component({
       selector: 'test-component',
@@ -443,6 +485,14 @@ class TestComponent {
   injector: Injector | null = null;
 }
 
+@Component({
+  selector: 'provide-value',
+  template: '<ng-content />',
+  providers: [{provide: templateToken, useValue: 'provide-value'}],
+  standalone: false,
+})
+class ProvideValueComponent {}
+
 @Component({
   selector: 'inject-value',
   template: 'Hello {{tokenValue}}',
@@ -466,6 +516,24 @@ class MultiContextComponent {
   context2: {name: string} | undefined;
 }
 
+const NESTING_DEPTH = new InjectionToken<number>('NESTING_DEPTH');
+
+@Component({
+  selector: 'nesting-counter',
+  template: '{{depth}}<ng-content />',
+  providers: [
+    {
+      provide: NESTING_DEPTH,
+      useFactory: (l: number) => (l ? l + 1 : 1),
+      deps: [[new Optional(), new SkipSelf(), NESTING_DEPTH]],
+    },
+  ],
+  standalone: false,
+})
+class NestingCounter {
+  depth = inject(NESTING_DEPTH);
+}
+
 function createTestComponent(
   template: string,
   providers: Provider[] = [],
