fix(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 #14028.

Author: crisbeto

src/material/menu/menu.spec.ts

@@ -231,6 +231,26 @@ describe('MatMenu', () => {
     expect(document.activeElement).toBe(triggerEl);
   });
 
+  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]);
 
@@ -288,6 +308,7 @@ 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');
@@ -2515,7 +2536,6 @@ class DynamicPanelMenu {
   @ViewChild('two') secondMenu: MatMenu;
 }
 
-
 @Component({
   template: `
     <button [matMenuTriggerFor]="menu">Toggle menu</button>
@@ -2590,3 +2610,18 @@ class LazyMenuWithOnPush {
   @ViewChild('triggerEl', {read: ElementRef}) rootTrigger: ElementRef;
   @ViewChild('menuItem', {read: ElementRef}) menuItemWithSubmenu: ElementRef;
 }
+
+@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

@@ -268,6 +268,24 @@ export class _MatMenuBase implements AfterContentInit, MatMenuPanel<MatMenuItem>
       startWith(this._directDescendantItems),
       switchMap(items => merge<MatMenuItem>(...items.map((item: MatMenuItem) => item._focused)))
     ).subscribe(focusedItem => this._keyManager.updateActiveItem(focusedItem));
+
+    // 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.
+    this._directDescendantItems.changes.subscribe(itemsList => {
+      const manager = this._keyManager;
+      const items = itemsList.toArray();
+
+      if (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() {