feat(menu): add nested menu functionality

src/demo-app/menu/menu-demo.html

@@ -15,7 +15,61 @@
     </md-menu>
   </div>
   <div class="menu-section">
-    <p> Clicking these will navigate:</p>
+    <p>Nested menu</p>
+
+    <md-toolbar>
+      <button md-icon-button [mdMenuTriggerFor]="animals">
+        <md-icon>more_vert</md-icon>
+      </button>
+    </md-toolbar>
+
+    <md-menu #animals="mdMenu">
+      <button md-menu-item [mdMenuTriggerFor]="vertebrates">Vertebrates</button>
+      <button md-menu-item [mdMenuTriggerFor]="invertebrates">Invertebrates</button>
+    </md-menu>
+
+    <md-menu #vertebrates="mdMenu">
+      <button md-menu-item [mdMenuTriggerFor]="fish">Fishes</button>
+      <button md-menu-item [mdMenuTriggerFor]="amphibians">Amphibians</button>
+      <button md-menu-item [mdMenuTriggerFor]="reptiles">Reptiles</button>
+      <button md-menu-item>Birds</button>
+      <button md-menu-item>Mammals</button>
+    </md-menu>
+
+    <md-menu #invertebrates="mdMenu">
+      <button md-menu-item>Insects</button>
+      <button md-menu-item>Molluscs</button>
+      <button md-menu-item>Crustaceans</button>
+      <button md-menu-item>Corals</button>
+      <button md-menu-item>Arachnids</button>
+      <button md-menu-item>Velvet worms</button>
+      <button md-menu-item>Horseshoe crabs</button>
+    </md-menu>
+
+    <md-menu #fish="mdMenu">
+      <button md-menu-item>Baikal oilfish</button>
+      <button md-menu-item>Bala shark</button>
+      <button md-menu-item>Ballan wrasse</button>
+      <button md-menu-item>Bamboo shark</button>
+      <button md-menu-item>Banded killifish</button>
+    </md-menu>
+
+    <md-menu #amphibians="mdMenu">
+      <button md-menu-item>Sonoran desert toad</button>
+      <button md-menu-item>Western toad</button>
+      <button md-menu-item>Arroyo toad</button>
+      <button md-menu-item>Yosemite toad</button>
+    </md-menu>
+
+    <md-menu #reptiles="mdMenu">
+      <button md-menu-item>Banded Day Gecko</button>
+      <button md-menu-item>Banded Gila Monster</button>
+      <button md-menu-item>Black Tree Monitor</button>
+      <button md-menu-item>Blue Spiny Lizard</button>
+    </md-menu>
+  </div>
+  <div class="menu-section">
+    <p>Clicking these will navigate:</p>
     <md-toolbar>
       <button md-icon-button [mdMenuTriggerFor]="anchorMenu" aria-label="Open anchor menu">
         <md-icon>more_vert</md-icon>

src/lib/menu/_menu-theme.scss

@@ -24,7 +24,12 @@
       vertical-align: middle;
     }
 
-    &:hover:not([disabled]), &:focus:not([disabled]) {
+  }
+
+  .mat-menu-item:hover,
+  .mat-menu-item:focus,
+  .mat-menu-item-highlighted {
+    &:not([disabled]) {
       background: mat-color($background, 'hover');
     }
   }

src/lib/menu/menu-directive.ts

@@ -29,7 +29,10 @@ import {FocusKeyManager} from '../core/a11y/focus-key-manager';
 import {MdMenuPanel} from './menu-panel';
 import {Subscription} from 'rxjs/Subscription';
 import {transformMenu, fadeInItems} from './menu-animations';
-import {ESCAPE} from '../core/keyboard/keycodes';
+import {ESCAPE, LEFT_ARROW, RIGHT_ARROW} from '../core/keyboard/keycodes';
+import {merge} from 'rxjs/observable/merge';
+import {Observable} from 'rxjs/Observable';
+import {Direction} from '../core';
 
 
 @Component({
@@ -59,6 +62,12 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
   /** Current state of the panel animation. */
   _panelAnimationState: 'void' | 'enter-start' | 'enter' = 'void';
 
+  /** Whether the menu is a sub-menu or a top-level menu. */
+  isSubmenu: boolean = false;
+
+  /** Layout direction of the menu. */
+  direction: Direction;
+
   /** Position of the menu in the X axis. */
   @Input()
   get xPosition() { return this._xPosition; }
@@ -115,24 +124,39 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
 
   ngAfterContentInit() {
     this._keyManager = new FocusKeyManager(this.items).withWrap();
-    this._tabSubscription = this._keyManager.tabOut.subscribe(() => this._emitCloseEvent());
+    this._tabSubscription = this._keyManager.tabOut.subscribe(() => this.close.emit());
   }
 
   ngOnDestroy() {
     if (this._tabSubscription) {
       this._tabSubscription.unsubscribe();
     }
 
-    this._emitCloseEvent();
+    this.close.emit();
     this.close.complete();
   }
 
+  /** Stream that emits whenever the hovered menu item changes. */
+  hover(): Observable<MdMenuItem> {
+    return merge(...this.items.map(item => item.hover));
+  }
+
   /** Handle a keyboard event from the menu, delegating to the appropriate action. */
   _handleKeydown(event: KeyboardEvent) {
     switch (event.keyCode) {
       case ESCAPE:
-        this._emitCloseEvent();
-        return;
+        this.close.emit();
+      break;
+      case LEFT_ARROW:
+        if (this.isSubmenu && this.direction === 'ltr') {
+          this.close.emit();
+        }
+      break;
+      case RIGHT_ARROW:
+        if (this.isSubmenu && this.direction === 'rtl') {
+          this.close.emit();
+        }
+      break;
       default:
         this._keyManager.onKeydown(event);
     }
@@ -146,14 +170,6 @@ export class MdMenu implements AfterContentInit, MdMenuPanel, OnDestroy {
     this._keyManager.setFirstItemActive();
   }
 
-  /**
-   * This emits a close event to which the trigger is subscribed. When emitted, the
-   * trigger will close the menu.
-   */
-  _emitCloseEvent(): void {
-    this.close.emit();
-  }
-
   /**
    * It's necessary to set position-based classes to ensure the menu panel animation
    * folds out from the correct direction.

src/lib/menu/menu-item.ts

@@ -6,9 +6,10 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {Component, ElementRef, ChangeDetectionStrategy} from '@angular/core';
+import {Component, ElementRef, OnDestroy, ChangeDetectionStrategy} from '@angular/core';
 import {Focusable} from '../core/a11y/focus-key-manager';
 import {CanDisable, mixinDisabled} from '../core/common-behaviors/disabled';
+import {Subject} from 'rxjs/Subject';
 
 // Boilerplate for applying mixins to MdMenuItem.
 /** @docs-private */
@@ -26,16 +27,23 @@ export const _MdMenuItemMixinBase = mixinDisabled(MdMenuItemBase);
   host: {
     'role': 'menuitem',
     'class': 'mat-menu-item',
+    '[class.mat-menu-item-highlighted]': '_highlighted',
     '[attr.tabindex]': '_getTabIndex()',
     '[attr.aria-disabled]': 'disabled.toString()',
     '[attr.disabled]': 'disabled || null',
     '(click)': '_checkDisabled($event)',
+    '(mouseenter)': '_emitHoverEvent()',
   },
   changeDetection: ChangeDetectionStrategy.OnPush,
   templateUrl: 'menu-item.html',
   exportAs: 'mdMenuItem',
 })
-export class MdMenuItem extends _MdMenuItemMixinBase implements Focusable, CanDisable {
+export class MdMenuItem extends _MdMenuItemMixinBase implements Focusable, CanDisable, OnDestroy {
+  /** Stream that emits when the menu item is hovered. */
+  hover: Subject<MdMenuItem> = new Subject();
+
+  /** Whether the menu item is highlighted. */
+  _highlighted: boolean = false;
 
   constructor(private _elementRef: ElementRef) {
     super();
@@ -46,6 +54,10 @@ export class MdMenuItem extends _MdMenuItemMixinBase implements Focusable, CanDi
     this._getHostElement().focus();
   }
 
+  ngOnDestroy() {
+    this.hover.complete();
+  }
+
   /** Used to set the `tabindex`. */
   _getTabIndex(): string {
     return this.disabled ? '-1' : '0';
@@ -63,5 +75,13 @@ export class MdMenuItem extends _MdMenuItemMixinBase implements Focusable, CanDi
       event.stopPropagation();
     }
   }
+
+  /** Emits to the hover stream. */
+  _emitHoverEvent() {
+    if (!this.disabled) {
+      this.hover.next(this);
+    }
+  }
+
 }
 

src/lib/menu/menu-panel.ts

@@ -8,14 +8,16 @@
 
 import {EventEmitter, TemplateRef} from '@angular/core';
 import {MenuPositionX, MenuPositionY} from './menu-positions';
+import {Direction} from '../core';
 
 export interface MdMenuPanel {
   xPosition: MenuPositionX;
   yPosition: MenuPositionY;
   overlapTrigger: boolean;
   templateRef: TemplateRef<any>;
   close: EventEmitter<void>;
+  isSubmenu: boolean;
+  direction: Direction;
   focusFirstItem: () => void;
   setPositionClasses: (x: MenuPositionX, y: MenuPositionY) => void;
-  _emitCloseEvent: () => void;
 }