refactor(core): deprecate allowing full context object to be replaced…

… in `EmbeddedViewRef` (#51887)

This partially reverts commit a3e1719
and deprecates behavior added.

The context of an embedded view ref at some point was switched from a
getter to an actual assignable property. This is something we revert
as it introduces additional complexity for our generated code
(in terms of closures capturing the `ctx`), creates technical
limitations for Angular's internals and the usage pattern is rarely
used (and can be addressed via simple assignments, `Object.assign` or
the use of a proxy if replacing the full context object is still
desirable)

DEPRECATED: Swapping out the context object for `EmbeddedViewRef`
is no longer supported. Support for this was introduced with v12.0.0, but
this pattern is rarely used. There is no replacement, but you can use
simple assignments in most cases, or `Object.assign , or alternatively
still replace the full object by using a `Proxy` (see `NgTemplateOutlet`
as an example).

Also adds a warning if the deprecated

PR Close #51887

packages/core/src/render3/view_ref.ts

@@ -63,7 +63,19 @@ export class ViewRef<T> implements EmbeddedViewRef<T>, InternalViewRef, ChangeDe
     return this._lView[CONTEXT] as unknown as T;
   }
 
+  /**
+   * @deprecated Replacing the full context object is not supported. Modify the context
+   *   directly, or consider using a `Proxy` if you need to replace the full object.
+   * // TODO(devversion): Remove this.
+   */
   set context(value: T) {
+    if (ngDevMode) {
+      // Note: We have a warning message here because the `@deprecated` JSDoc will not be picked
+      // up for assignments on the setter. We want to let users know about the deprecated usage.
+      console.warn(
+          'Angular: Replacing the `context` object of an `EmbeddedViewRef` is deprecated.');
+    }
+
     this._lView[CONTEXT] = value as unknown as {};
   }
 

packages/core/test/acceptance/template_ref_spec.ts

@@ -317,5 +317,26 @@ describe('TemplateRef', () => {
       button.click();
       expect(events).toEqual(['Frodo', 'Bilbo']);
     });
+
+    it('should warn if the context of an embedded view ref is replaced', () => {
+      TestBed.configureTestingModule({declarations: [App]});
+      const fixture = TestBed.createComponent(App);
+      fixture.detectChanges();
+      const viewRef = fixture.componentInstance.templateRef.createEmbeddedView({name: 'Frodo'});
+      fixture.componentInstance.containerRef.insert(viewRef);
+      fixture.detectChanges();
+
+      expect(fixture.nativeElement.textContent).toBe('Frodo');
+      spyOn(console, 'warn');
+
+      viewRef.context = {name: 'Bilbo'};
+      fixture.detectChanges();
+
+      expect(console.warn).toHaveBeenCalledTimes(1);
+      expect(console.warn)
+          .toHaveBeenCalledWith(jasmine.stringContaining(
+              'Replacing the `context` object of an `EmbeddedViewRef` is deprecated'));
+      expect(fixture.nativeElement.textContent).toBe('Bilbo');
+    });
   });
 });