fix(menu): nested menu error when items are rendered in a repeater

Fixes an error that was being thrown when the menu items that trigger a sub-menu are rendered in a repeater.

Fixes #6765.

src/lib/menu/menu-directive.ts

@@ -35,6 +35,8 @@ import {ESCAPE, LEFT_ARROW, RIGHT_ARROW} from '../core/keyboard/keycodes';
 import {merge} from 'rxjs/observable/merge';
 import {Observable} from 'rxjs/Observable';
 import {Direction} from '@angular/cdk/bidi';
+import {Subject} from 'rxjs/Subject';
+import {RxChain, switchMap, first} from '@angular/cdk/rxjs';
 
 /** Default `md-menu` options that can be overridden. */
 export interface MdMenuDefaultOptions {
@@ -76,8 +78,11 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
   /** Subscription to tab events on the menu panel */
   private _tabSubscription: Subscription;
 
+  /** Stream that emits whenever the component is intialized. */
+  private _initialized = new Subject<void>();
+
   /** Config object to be passed into the menu's ngClass */
-  _classList: any = {};
+  _classList: {[key: string]: boolean} = {};
 
   /** Current state of the panel animation. */
   _panelAnimationState: 'void' | 'enter-start' | 'enter' = 'void';
@@ -147,6 +152,8 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
   ngAfterContentInit() {
     this._keyManager = new FocusKeyManager<MdMenuItem>(this.items).withWrap();
     this._tabSubscription = this._keyManager.tabOut.subscribe(() => this.close.emit('keydown'));
+    this._initialized.next();
+    this._initialized.complete();
   }
 
   ngOnDestroy() {
@@ -160,7 +167,9 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
 
   /** Stream that emits whenever the hovered menu item changes. */
   hover(): Observable<MdMenuItem> {
-    return merge(...this.items.map(item => item.hover));
+    return this.items ?
+      merge(...this.items.map(item => item.hover)) :
+      RxChain.from(this._initialized).call(first).call(switchMap, () => this.hover()).result();
   }
 
   /** Handle a keyboard event from the menu, delegating to the appropriate action. */

src/lib/menu/menu-trigger.ts

@@ -7,7 +7,7 @@
  */
 
 import {
-  AfterViewInit,
+  AfterContentInit,
   Directive,
   ElementRef,
   EventEmitter,
@@ -85,7 +85,7 @@ export const MENU_PANEL_TOP_PADDING = 8;
   },
   exportAs: 'mdMenuTrigger'
 })
-export class MdMenuTrigger implements AfterViewInit, OnDestroy {
+export class MdMenuTrigger implements AfterContentInit, OnDestroy {
   private _portal: TemplatePortal<any>;
   private _overlayRef: OverlayRef | null = null;
   private _menuOpen: boolean = false;
@@ -149,7 +149,7 @@ export class MdMenuTrigger implements AfterViewInit, OnDestroy {
     }
   }
 
-  ngAfterViewInit() {
+  ngAfterContentInit() {
     this._checkMenu();
 
     this.menu.close.subscribe(reason => {

src/lib/menu/menu.spec.ts

@@ -47,7 +47,8 @@ describe('MdMenu', () => {
         CustomMenuPanel,
         CustomMenu,
         NestedMenu,
-        NestedMenuCustomElevation
+        NestedMenuCustomElevation,
+        NestedMenuRepeater
       ],
       providers: [
         {provide: OverlayContainer, useFactory: () => {
@@ -996,6 +997,23 @@ describe('MdMenu', () => {
       expect(overlay.querySelectorAll('.mat-menu-panel').length).toBe(0, 'Expected no open menus');
     }));
 
+    it('should handle the items being rendered in a repeater', fakeAsync(() => {
+      const repeaterFixture = TestBed.createComponent(NestedMenuRepeater);
+      overlay = overlayContainerElement;
+
+      expect(() => repeaterFixture.detectChanges()).not.toThrow();
+
+      repeaterFixture.componentInstance.rootTriggerEl.nativeElement.click();
+      repeaterFixture.detectChanges();
+      expect(overlay.querySelectorAll('.mat-menu-panel').length).toBe(1, 'Expected one open menu');
+
+      const items = Array.from(overlay.querySelectorAll('.mat-menu-panel [md-menu-item]'));
+      const levelOneTrigger = overlay.querySelector('.level-one-trigger')!;
+
+      dispatchMouseEvent(levelOneTrigger, 'mouseenter');
+      repeaterFixture.detectChanges();
+      expect(overlay.querySelectorAll('.mat-menu-panel').length).toBe(2, 'Expected two open menus');
+    }));
 
   });
 
@@ -1177,3 +1195,28 @@ class NestedMenuCustomElevation {
   @ViewChild('rootTrigger') rootTrigger: MdMenuTrigger;
   @ViewChild('levelOneTrigger') levelOneTrigger: MdMenuTrigger;
 }
+
+
+@Component({
+  template: `
+    <button [mdMenuTriggerFor]="root" #rootTriggerEl>Toggle menu</button>
+    <md-menu #root="mdMenu">
+      <button
+        md-menu-item
+        class="level-one-trigger"
+        *ngFor="let item of items"
+        [mdMenuTriggerFor]="levelOne">{{item}}</button>
+    </md-menu>
+
+    <md-menu #levelOne="mdMenu">
+      <button md-menu-item>Four</button>
+      <button md-menu-item>Five</button>
+    </md-menu>
+  `
+})
+class NestedMenuRepeater {
+  @ViewChild('rootTriggerEl') rootTriggerEl: ElementRef;
+  @ViewChild('levelOneTrigger') levelOneTrigger: MdMenuTrigger;
+
+  items = ['one', 'two', 'three'];
+}