fix(cdk-experimental/dialog): focus restoration not working inside shadow dom

src/cdk-experimental/dialog/BUILD.bazel

@@ -15,6 +15,7 @@ ng_module(
         "//src/cdk/bidi",
         "//src/cdk/keycodes",
         "//src/cdk/overlay",
+        "//src/cdk/platform",
         "//src/cdk/portal",
         "@npm//@angular/animations",
         "@npm//@angular/core",
@@ -38,6 +39,7 @@ ng_test_library(
         "//src/cdk/bidi",
         "//src/cdk/keycodes",
         "//src/cdk/overlay",
+        "//src/cdk/platform",
         "//src/cdk/testing/private",
         "@npm//@angular/common",
         "@npm//@angular/platform-browser",

src/cdk-experimental/dialog/dialog-container.ts

@@ -8,6 +8,7 @@
 
 import {animate, AnimationEvent, state, style, transition, trigger} from '@angular/animations';
 import {FocusTrapFactory} from '@angular/cdk/a11y';
+import {_getFocusedElementPierceShadowDom} from '@angular/cdk/platform';
 import {
   BasePortalOutlet,
   CdkPortalOutlet,
@@ -228,7 +229,7 @@ export class CdkDialogContainer extends BasePortalOutlet implements OnDestroy {
   /** Saves a reference to the element that was focused before the dialog was opened. */
   private _savePreviouslyFocusedElement() {
     if (this._document) {
-      this._elementFocusedBeforeDialogWasOpened = this._document.activeElement as HTMLElement;
+      this._elementFocusedBeforeDialogWasOpened = _getFocusedElementPierceShadowDom();
     }
   }
 
@@ -259,7 +260,7 @@ export class CdkDialogContainer extends BasePortalOutlet implements OnDestroy {
         }
       });
     } else {
-      const activeElement = this._document.activeElement;
+      const activeElement = _getFocusedElementPierceShadowDom();
 
       // Otherwise ensure that focus is on the dialog container. It's possible that a different
       // component tried to move focus while the open animation was running. See:

src/cdk-experimental/dialog/dialog.spec.ts

@@ -16,7 +16,8 @@ import {
   NgModule,
   TemplateRef,
   ViewChild,
-  ViewContainerRef
+  ViewContainerRef,
+  ViewEncapsulation
 } from '@angular/core';
 import {By} from '@angular/platform-browser';
 import {NoopAnimationsModule} from '@angular/platform-browser/animations';
@@ -26,11 +27,12 @@ import {Directionality} from '@angular/cdk/bidi';
 import {CdkDialogContainer} from './dialog-container';
 import {OverlayContainer} from '@angular/cdk/overlay';
 import {A, ESCAPE} from '@angular/cdk/keycodes';
+import {_supportsShadowDom} from '@angular/cdk/platform';
 import {
   dispatchKeyboardEvent,
   createKeyboardEvent,
   dispatchEvent,
-} from '../../cdk/testing/private';
+} from '@angular/cdk/testing/private';
 import {DIALOG_DATA, Dialog, DialogModule, DialogRef} from './index';
 
 describe('Dialog', () => {
@@ -935,6 +937,32 @@ describe('Dialog', () => {
       document.body.removeChild(button);
     }));
 
+    it('should re-focus trigger element inside the shadow DOM when dialog closes', fakeAsync(() => {
+      if (!_supportsShadowDom()) {
+        return;
+      }
+
+      viewContainerFixture.destroy();
+      const fixture = TestBed.createComponent(ShadowDomComponent);
+      fixture.detectChanges();
+      const button = fixture.debugElement.query(By.css('button'))!.nativeElement;
+
+      button.focus();
+
+      const dialogRef = dialog.openFromComponent(PizzaMsg);
+      flushMicrotasks();
+      fixture.detectChanges();
+      flushMicrotasks();
+
+      const spy = spyOn(button, 'focus').and.callThrough();
+      dialogRef.close();
+      flushMicrotasks();
+      fixture.detectChanges();
+      tick(500);
+
+      expect(spy).toHaveBeenCalled();
+    }));
+
     it('should not move focus if it was moved outside the dialog while animating', fakeAsync(() => {
       // Create a element that has focus before the dialog is opened.
       const button = document.createElement('button');
@@ -1220,6 +1248,12 @@ class DialogWithInjectedData {
 @Component({template: '<p>Pasta</p>'})
 class DialogWithoutFocusableElements {}
 
+@Component({
+  template: `<button>I'm a button</button>`,
+  encapsulation: ViewEncapsulation.ShadowDom
+})
+class ShadowDomComponent {}
+
 // Create a real (non-test) NgModule as a workaround for
 // https://github.com/angular/angular/issues/10760
 const TEST_DIRECTIVES = [
@@ -1230,7 +1264,8 @@ const TEST_DIRECTIVES = [
   ComponentWithOnPushViewContainer,
   ContentElementDialog,
   DialogWithInjectedData,
-  DialogWithoutFocusableElements
+  DialogWithoutFocusableElements,
+  ShadowDomComponent,
 ];
 
 @NgModule({