feat(core): add runtime support for outputs in signal components

Runtime implementation is very simple - it adds the output function that
acts as an alias to the existing EventEmitter class constructor.

Author: pkozlowski-opensource

goldens/public-api/core/index.md

@@ -1194,6 +1194,9 @@ export interface Output {
 // @public (undocumented)
 export const Output: OutputDecorator;
 
+// @public (undocumented)
+export function output<T>(isAsync?: boolean): EventEmitter<T>;
+
 // @public
 export interface OutputDecorator {
     (alias?: string): any;

packages/core/src/core_reactivity_export_internal.ts

@@ -40,4 +40,5 @@ export {input} from './render3/reactivity/input';
 export {InputSignal, ɵɵGetInputSignalWriteType} from './render3/reactivity/input_signal';
 export {ModelSignal} from './render3/reactivity/model_signal';
 export {contentChild, contentChildren, viewChild, viewChildren} from './render3/reactivity/queries';
+export {output} from './render3/reactivity/output';
 // clang-format on

packages/core/src/render3/reactivity/output.ts

@@ -0,0 +1,13 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {EventEmitter} from '../../event_emitter';
+
+export function output<T>(isAsync?: boolean): EventEmitter<T> {
+  return new EventEmitter(isAsync);
+}

packages/core/test/acceptance/signal-components/output.spec.ts

@@ -0,0 +1,42 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {Component, Output, output, signal} from '@angular/core';
+import {TestBed} from '@angular/core/testing';
+
+describe('outputs', () => {
+  xit('should subscribe to signal directive outputs', () => {
+    @Component({
+      selector: 'with-output-cmp',
+      standalone: true,
+      signals: true,
+      template: `<button (click)="increment.emit()"></button>`,
+    })
+    class WithOutputCmp {
+      counter = signal(0);
+      @Output() increment = output<void>();
+    }
+
+    @Component({
+      signals: true,
+      standalone: true,
+      imports: [WithOutputCmp],
+      template: `<with-output-cmp (increment)="bumpUp()" />{{inc()}}`,
+    })
+    class App {
+      inc = signal(0);
+      onIncrement() {
+        this.inc.update(c => c + 1);
+      }
+    }
+
+    const fixture = TestBed.createComponent(App);
+    fixture.detectChanges();
+    expect(fixture.nativeElement.textContent).toBe('0');
+  });
+});