fix(material/menu): focus lost if active item is removed

Fixes the user's focus being lost if the active item is destroyed while a menu is open.

Fixes angular#14028.

src/material-experimental/mdc-menu/menu.spec.ts

@@ -259,6 +259,28 @@ describe('MDC-based MatMenu', () => {
     tick(500);
   }));
 
+  it('should move focus to another item if the active item is destroyed', fakeAsync(() => {
+    const fixture = createComponent(MenuWithRepeatedItems, [], [FakeIcon]);
+    fixture.detectChanges();
+    const triggerEl = fixture.componentInstance.triggerEl.nativeElement;
+
+    triggerEl.click();
+    fixture.detectChanges();
+    tick(500);
+
+    const items = overlayContainerElement.querySelectorAll(
+      '.mat-mdc-menu-panel .mat-mdc-menu-item',
+    );
+
+    expect(document.activeElement).toBe(items[0]);
+
+    fixture.componentInstance.items.shift();
+    fixture.detectChanges();
+    tick(500);
+
+    expect(document.activeElement).toBe(items[1]);
+  }));
+
   it('should be able to set a custom class on the backdrop', fakeAsync(() => {
     const fixture = createComponent(SimpleMenu, [], [FakeIcon]);
 
@@ -3071,3 +3093,18 @@ class StaticAriaLabelledByMenu {}
   template: '<mat-menu aria-describedby="some-element"></mat-menu>',
 })
 class StaticAriaDescribedbyMenu {}
+
+@Component({
+  template: `
+    <button [matMenuTriggerFor]="menu" #triggerEl>Toggle menu</button>
+    <mat-menu #menu="matMenu">
+      <button *ngFor="let item of items" mat-menu-item>{{item}}</button>
+    </mat-menu>
+  `,
+})
+class MenuWithRepeatedItems {
+  @ViewChild(MatMenuTrigger, {static: false}) trigger: MatMenuTrigger;
+  @ViewChild('triggerEl', {static: false}) triggerEl: ElementRef<HTMLElement>;
+  @ViewChild(MatMenu, {static: false}) menu: MatMenu;
+  items = ['One', 'Two', 'Three'];
+}

src/material/menu/menu.spec.ts

@@ -259,6 +259,26 @@ describe('MatMenu', () => {
     tick(500);
   }));
 
+  it('should move focus to another item if the active item is destroyed', fakeAsync(() => {
+    const fixture = createComponent(MenuWithRepeatedItems, [], [FakeIcon]);
+    fixture.detectChanges();
+    const triggerEl = fixture.componentInstance.triggerEl.nativeElement;
+
+    triggerEl.click();
+    fixture.detectChanges();
+    tick(500);
+
+    const items = overlayContainerElement.querySelectorAll('.mat-menu-panel .mat-menu-item');
+
+    expect(document.activeElement).toBe(items[0]);
+
+    fixture.componentInstance.items.shift();
+    fixture.detectChanges();
+    tick(500);
+
+    expect(document.activeElement).toBe(items[1]);
+  }));
+
   it('should be able to set a custom class on the backdrop', fakeAsync(() => {
     const fixture = createComponent(SimpleMenu, [], [FakeIcon]);
 
@@ -351,6 +371,7 @@ describe('MatMenu', () => {
     // Add 50 items to make the menu scrollable
     fixture.componentInstance.extraItems = new Array(50).fill('Hello there');
     fixture.detectChanges();
+    tick(50);
 
     const triggerEl = fixture.componentInstance.triggerEl.nativeElement;
     dispatchFakeEvent(triggerEl, 'mousedown');
@@ -3053,3 +3074,18 @@ class StaticAriaLabelledByMenu {}
   template: '<mat-menu aria-describedby="some-element"></mat-menu>',
 })
 class StaticAriaDescribedbyMenu {}
+
+@Component({
+  template: `
+    <button [matMenuTriggerFor]="menu" #triggerEl>Toggle menu</button>
+    <mat-menu #menu="matMenu">
+      <button *ngFor="let item of items" mat-menu-item>{{item}}</button>
+    </mat-menu>
+  `,
+})
+class MenuWithRepeatedItems {
+  @ViewChild(MatMenuTrigger, {static: false}) trigger: MatMenuTrigger;
+  @ViewChild('triggerEl', {static: false}) triggerEl: ElementRef<HTMLElement>;
+  @ViewChild(MatMenu, {static: false}) menu: MatMenu;
+  items = ['One', 'Two', 'Three'];
+}

src/material/menu/menu.ts

@@ -40,7 +40,7 @@ import {
   ChangeDetectorRef,
 } from '@angular/core';
 import {merge, Observable, Subject, Subscription} from 'rxjs';
-import {startWith, switchMap, take} from 'rxjs/operators';
+import {startWith, switchMap, take, tap} from 'rxjs/operators';
 import {matMenuAnimations} from './menu-animations';
 import {MAT_MENU_CONTENT, MatMenuContent} from './menu-content';
 import {MenuPositionX, MenuPositionY} from './menu-positions';
@@ -298,6 +298,28 @@ export class _MatMenuBase
         switchMap(items => merge(...items.map((item: MatMenuItem) => item._focused))),
       )
       .subscribe(focusedItem => this._keyManager.updateActiveItem(focusedItem as MatMenuItem));
+
+    this._directDescendantItems.changes.subscribe((itemsList: QueryList<MatMenuItem>) => {
+      // Move focus to another item, if the active item is removed from the list.
+      // We need to debounce the callback, because multiple items might be removed
+      // in quick succession.
+      const manager = this._keyManager;
+      const items = itemsList.toArray();
+
+      if (
+        this._panelAnimationState === 'enter' &&
+        manager.activeItem &&
+        items.indexOf(manager.activeItem) === -1
+      ) {
+        const index = Math.max(0, Math.min(items.length - 1, manager.activeItemIndex || 0));
+
+        if (items[index] && !items[index].disabled) {
+          manager.setActiveItem(index);
+        } else {
+          manager.setNextItemActive();
+        }
+      }
+    });
   }
 
   ngOnDestroy() {