feat(cdk-experimental/menu): add roving tab index to menu items

The element under focus has a tab index of 0 while all others are set to -1. As other elements come
into focus, the previous elements tab index is reset to -1 and the newly focused element has a tab
index set to 0.

Author: andy9775

src/cdk-experimental/menu/menu-bar.spec.ts

@@ -228,6 +228,32 @@ describe('MenuBar', () => {
           }
         );
 
+        it('should toggle tabindex of menu bar items with left/right arrow keys', () => {
+          focusMenuBar();
+
+          dispatchKeyboardEvent(nativeMenuBar, 'keydown', RIGHT_ARROW);
+          detectChanges();
+          expect(menuBarNativeItems[0].tabIndex).toEqual(-1);
+          expect(menuBarNativeItems[1].tabIndex).toEqual(0);
+
+          dispatchKeyboardEvent(nativeMenuBar, 'keydown', RIGHT_ARROW);
+          detectChanges();
+          expect(menuBarNativeItems[0].tabIndex).toEqual(0);
+          expect(menuBarNativeItems[1].tabIndex).toEqual(-1);
+
+          dispatchKeyboardEvent(nativeMenuBar, 'keydown', LEFT_ARROW);
+          detectChanges();
+          expect(menuBarNativeItems[0].tabIndex).toEqual(-1);
+          expect(menuBarNativeItems[1].tabIndex).toEqual(0);
+
+          dispatchKeyboardEvent(nativeMenuBar, 'keydown', LEFT_ARROW);
+          detectChanges();
+          expect(menuBarNativeItems[0].tabIndex).toEqual(0);
+          expect(menuBarNativeItems[1].tabIndex).toEqual(-1);
+
+          expect(nativeMenus.length).toBe(0);
+        });
+
         it(
           "should open the focused menu item's menu and focus the first submenu" +
             ' item on the down key',
@@ -264,6 +290,28 @@ describe('MenuBar', () => {
 
           expect(document.activeElement).toEqual(fileMenuNativeItems[0]);
         });
+
+        it(
+          'should set the tabindex to 0 on the active item and reset the previous active items ' +
+            'to -1 when navigating down to a submenu and within it using the arrow keys',
+          () => {
+            focusMenuBar();
+
+            expect(menuBarNativeItems[0].tabIndex).toEqual(0);
+
+            dispatchKeyboardEvent(menuBarNativeItems[0], 'keydown', SPACE);
+            detectChanges();
+
+            expect(menuBarNativeItems[0].tabIndex).toEqual(-1);
+            expect(fileMenuNativeItems[0].tabIndex).toEqual(0);
+
+            dispatchKeyboardEvent(fileMenuNativeItems[0], 'keydown', DOWN_ARROW);
+            detectChanges();
+
+            expect(fileMenuNativeItems[0].tabIndex).toEqual(-1);
+            expect(fileMenuNativeItems[1].tabIndex).toEqual(0);
+          }
+        );
       });
 
       describe('for Menu', () => {
@@ -1041,6 +1089,60 @@ describe('MenuBar', () => {
         expect(nativeMenus.length).toBe(0);
       }
     );
+
+    it(
+      'should not set the tabindex when hovering over menubar item and there is no open' +
+        ' sibling menu',
+      () => {
+        dispatchMouseEvent(menuBarNativeItems[0], 'mouseenter');
+        detectChanges();
+
+        expect(menuBarNativeItems[0].tabIndex).toBe(-1);
+      }
+    );
+
+    it(
+      'should set the tabindex of the opened trigger to 0 and toggle sibling tabindex' +
+        ' on hover',
+      () => {
+        openFileMenu();
+
+        expect(menuBarNativeItems[0].tabIndex).toBe(0);
+
+        dispatchMouseEvent(menuBarNativeItems[1], 'mouseenter');
+        detectChanges();
+
+        expect(menuBarNativeItems[0].tabIndex).toBe(-1);
+        expect(menuBarNativeItems[1].tabIndex).toBe(0);
+
+        dispatchMouseEvent(menuBarNativeItems[0], 'mouseenter');
+        detectChanges();
+
+        expect(menuBarNativeItems[0].tabIndex).toBe(0);
+        expect(menuBarNativeItems[1].tabIndex).toBe(-1);
+      }
+    );
+
+    it(
+      'should set the tabindex to 0 on the active item and reset the previous active items ' +
+        'to -1 when navigating down to a submenu and within it using a mouse',
+      () => {
+        openFileMenu();
+        expect(menuBarNativeItems[0].tabIndex).toBe(0);
+
+        dispatchMouseEvent(fileMenuNativeItems[0], 'mouseenter');
+        detectChanges();
+
+        expect(menuBarNativeItems[0].tabIndex).toBe(-1);
+        expect(fileMenuNativeItems[0].tabIndex).toBe(0);
+
+        dispatchMouseEvent(fileMenuNativeItems[1], 'mouseenter');
+        detectChanges();
+
+        expect(fileMenuNativeItems[0].tabIndex).toBe(-1);
+        expect(fileMenuNativeItems[1].tabIndex).toBe(0);
+      }
+    );
   });
 });
 

src/cdk-experimental/menu/menu-item-checkbox.ts

@@ -18,6 +18,7 @@ import {CdkMenuItem} from './menu-item';
   selector: '[cdkMenuItemCheckbox]',
   exportAs: 'cdkMenuItemCheckbox',
   host: {
+    '[tabindex]': '_tabindex',
     'type': 'button',
     'role': 'menuitemcheckbox',
     '[attr.aria-checked]': 'checked || null',

src/cdk-experimental/menu/menu-item-radio.ts

@@ -31,6 +31,7 @@ import {CDK_MENU, Menu} from './menu-interface';
   selector: '[cdkMenuItemRadio]',
   exportAs: 'cdkMenuItemRadio',
   host: {
+    '[tabindex]': '_tabindex',
     'type': 'button',
     'role': 'menuitemradio',
     '[attr.aria-checked]': 'checked || null',

src/cdk-experimental/menu/menu-item.ts

@@ -47,7 +47,7 @@ function removeIcons(element: Element) {
   selector: '[cdkMenuItem]',
   exportAs: 'cdkMenuItem',
   host: {
-    'tabindex': '-1',
+    '[tabindex]': '_tabindex',
     'type': 'button',
     'role': 'menuitem',
     'class': 'cdk-menu-item',
@@ -71,6 +71,12 @@ export class CdkMenuItem implements FocusableOption, FocusableElement, OnDestroy
    */
   @Output('cdkMenuItemTriggered') triggered: EventEmitter<void> = new EventEmitter();
 
+  /**
+   * The tabindex for this menu item managed internally and used for implementing roving a
+   * tab index.
+   */
+  _tabindex: 0 | -1 = -1;
+
   /** Emits when the menu item is destroyed. */
   private readonly _destroyed: Subject<void> = new Subject();
 
@@ -89,9 +95,20 @@ export class CdkMenuItem implements FocusableOption, FocusableElement, OnDestroy
 
   /** Place focus on the element. */
   focus() {
+    this._tabindex = 0;
     this._elementRef.nativeElement.focus();
   }
 
+  // In Ivy the `host` metadata will be merged, whereas in ViewEngine it is overridden. In order
+  // to avoid double event listeners, we need to use `HostListener`. Once Ivy is the default, we
+  // can move this back into `host`.
+  // tslint:disable:no-host-decorator-in-concrete
+  @HostListener('blur')
+  /** Reset the _tabindex to -1. */
+  _blur() {
+    this._tabindex = -1;
+  }
+
   // In Ivy the `host` metadata will be merged, whereas in ViewEngine it is overridden. In order
   // to avoid double event listeners, we need to use `HostListener`. Once Ivy is the default, we
   // can move this back into `host`.
@@ -102,9 +119,12 @@ export class CdkMenuItem implements FocusableOption, FocusableElement, OnDestroy
    * on the cdkMenuItemTriggered emitter and close all open menus.
    */
   trigger() {
-    if (!this.disabled && !this.hasMenu()) {
-      this.triggered.next();
-      this._getMenuStack().closeAll();
+    if (!this.disabled) {
+      if (!this.hasMenu()) {
+        this.triggered.next();
+        this._getMenuStack().closeAll();
+      }
+      this.focus();
     }
   }