fix(menu): keyboard controls not working if all items are disabled

Currently we depend on `focusFirstItem` to bring focus into the menu, however if all the items are disabled, focus will stay on the trigger and the user won't get feedback that something has happened. Furthermore, the keyboard shortcuts that are implemented in the menu won't work either, because the keyboard event listener is on the menu.

These changes work around the issue by setting focus on the `role="menu"` if none of the items were focusable.

Fixes #16565.

Author: crisbeto

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

@@ -762,6 +762,44 @@ describe('MatMenu', () => {
     flush();
   }));
 
+  it('should respect the DOM order, rather than insertion order, when moving focus using ' +
+    'the arrow keys', fakeAsync(() => {
+      let fixture = createComponent(SimpleMenuWithRepeater);
+
+      fixture.detectChanges();
+      fixture.componentInstance.trigger.openMenu();
+      fixture.detectChanges();
+      tick(500);
+
+      let menuPanel = document.querySelector('.mat-mdc-menu-panel')!;
+      let items = menuPanel.querySelectorAll('.mat-mdc-menu-panel [mat-menu-item]');
+
+      expect(document.activeElement).toBe(items[0], 'Expected first item to be focused on open');
+
+      // Add a new item after the first one.
+      fixture.componentInstance.items.splice(1, 0, {label: 'Calzone', disabled: false});
+      fixture.detectChanges();
+
+      items = menuPanel.querySelectorAll('.mat-mdc-menu-panel [mat-menu-item]');
+      dispatchKeyboardEvent(menuPanel, 'keydown', DOWN_ARROW);
+      fixture.detectChanges();
+      tick();
+
+      expect(document.activeElement).toBe(items[1], 'Expected second item to be focused');
+      flush();
+    }));
+
+  it('should focus the menu panel if all items are disabled', fakeAsync(() => {
+    const fixture = createComponent(SimpleMenuWithRepeater, [], [FakeIcon]);
+    fixture.componentInstance.items.forEach(item => item.disabled = true);
+    fixture.detectChanges();
+    fixture.componentInstance.trigger.openMenu();
+    fixture.detectChanges();
+
+    expect(document.activeElement)
+        .toBe(overlayContainerElement.querySelector('.mat-mdc-menu-panel'));
+  }));
+
   describe('lazy rendering', () => {
     it('should be able to render the menu content lazily', fakeAsync(() => {
       const fixture = createComponent(SimpleLazyMenu);
@@ -2361,3 +2399,21 @@ class DynamicPanelMenu {
 class MenuWithCheckboxItems {
   @ViewChild(MatMenuTrigger, {static: false}) trigger: MatMenuTrigger;
 }
+
+
+@Component({
+  template: `
+    <button [matMenuTriggerFor]="menu">Toggle menu</button>
+    <mat-menu #menu="matMenu">
+      <button
+        *ngFor="let item of items"
+        [disabled]="item.disabled"
+        mat-menu-item>{{item.label}}</button>
+    </mat-menu>
+  `
+})
+class SimpleMenuWithRepeater {
+  @ViewChild(MatMenuTrigger, {static: false}) trigger: MatMenuTrigger;
+  @ViewChild(MatMenu, {static: false}) menu: MatMenu;
+  items = [{label: 'Pizza', disabled: false}, {label: 'Pasta', disabled: false}];
+}

src/material/menu/menu.spec.ts

@@ -762,6 +762,16 @@ describe('MatMenu', () => {
     flush();
   }));
 
+  it('should focus the menu panel if all items are disabled', fakeAsync(() => {
+    const fixture = createComponent(SimpleMenuWithRepeater, [], [FakeIcon]);
+    fixture.componentInstance.items.forEach(item => item.disabled = true);
+    fixture.detectChanges();
+    fixture.componentInstance.trigger.openMenu();
+    fixture.detectChanges();
+
+    expect(document.activeElement).toBe(overlayContainerElement.querySelector('.mat-menu-panel'));
+  }));
+
   describe('lazy rendering', () => {
     it('should be able to render the menu content lazily', fakeAsync(() => {
       const fixture = createComponent(SimpleLazyMenu);
@@ -882,7 +892,7 @@ describe('MatMenu', () => {
         expect(document.activeElement).toBe(items[0], 'Expected first item to be focused on open');
 
         // Add a new item after the first one.
-        fixture.componentInstance.items.splice(1, 0, 'Calzone');
+        fixture.componentInstance.items.splice(1, 0, {label: 'Calzone', disabled: false});
         fixture.detectChanges();
 
         items = menuPanel.querySelectorAll('.mat-menu-panel [mat-menu-item]');
@@ -2383,14 +2393,17 @@ class MenuWithCheckboxItems {
   template: `
     <button [matMenuTriggerFor]="menu">Toggle menu</button>
     <mat-menu #menu="matMenu">
-      <button *ngFor="let item of items" mat-menu-item>{{item}}</button>
+      <button
+        *ngFor="let item of items"
+        [disabled]="item.disabled"
+        mat-menu-item>{{item.label}}</button>
     </mat-menu>
   `
 })
 class SimpleMenuWithRepeater {
   @ViewChild(MatMenuTrigger, {static: false}) trigger: MatMenuTrigger;
   @ViewChild(MatMenu, {static: false}) menu: MatMenu;
-  items = ['Pizza', 'Pasta'];
+  items = [{label: 'Pizza', disabled: false}, {label: 'Pasta', disabled: false}];
 }
 
 @Component({

src/material/menu/menu.ts

@@ -320,13 +320,35 @@ export class _MatMenuBase implements AfterContentInit, MatMenuPanel<MatMenuItem>
    * @param origin Action from which the focus originated. Used to set the correct styling.
    */
   focusFirstItem(origin: FocusOrigin = 'program'): void {
+    const manager = this._keyManager;
+
     // When the content is rendered lazily, it takes a bit before the items are inside the DOM.
     if (this.lazyContent) {
       this._ngZone.onStable.asObservable()
         .pipe(take(1))
-        .subscribe(() => this._keyManager.setFocusOrigin(origin).setFirstItemActive());
+        .subscribe(() => manager.setFocusOrigin(origin).setFirstItemActive());
     } else {
-      this._keyManager.setFocusOrigin(origin).setFirstItemActive();
+      manager.setFocusOrigin(origin).setFirstItemActive();
+    }
+
+    // If there's no active item at this point, it means that all the items are disabled.
+    // Move focus to the menu panel so keyboard events like Escape still work. Also this will
+    // give _some_ feedback to screen readers.
+    if (!manager.activeItem && this._directDescendantItems.length) {
+      let element = this._directDescendantItems.first._getHostElement().parentElement;
+
+      // Because the `mat-menu` is at the DOM insertion point, not inside the overlay, we don't
+      // have a nice way of getting a hold of the menu panel. We can't use a `ViewChild` either
+      // because the panel is inside an `ng-template`. We work around it by starting from one of
+      // the items and walking up the DOM.
+      while (element) {
+        if (element.getAttribute('role') === 'menu') {
+          element.focus();
+          break;
+        } else {
+          element = element.parentElement;
+        }
+      }
     }
   }