feat(autocomplete): add screenreader support

src/lib/autocomplete/autocomplete-trigger.ts

@@ -12,7 +12,15 @@ export const MD_AUTOCOMPLETE_PANEL_OFFSET = 6;
 @Directive({
   selector: 'input[mdAutocomplete], input[matAutocomplete]',
   host: {
-    '(focus)': 'openPanel()'
+    'role': 'combobox',
+    'autocomplete': 'off',
+    '(focus)': 'openPanel()',
+    '(keydown)': '_handleKeydown($event)',
+    'aria-autocomplete': 'list',
+    'aria-multiline': 'false',
+    '[attr.aria-activedescendant]': 'activeOption?.id',
+    '[attr.aria-expanded]': 'panelOpen.toString()',
+    '[attr.aria-owns]': 'autocomplete?.id'
   }
 })
 export class MdAutocompleteTrigger implements OnDestroy {

src/lib/autocomplete/autocomplete.html

@@ -1,5 +1,5 @@
 <template>
-  <div class="md-autocomplete-panel">
+  <div class="md-autocomplete-panel" role="listbox" [id]="id">
     <ng-content></ng-content>
   </div>
 </template>

src/lib/autocomplete/autocomplete.spec.ts

@@ -135,6 +135,84 @@ describe('MdAutocomplete', () => {
 
   });
 
+  describe('aria', () => {
+
+    it('should set role of input to combobox', () => {
+      expect(input.getAttribute('role'))
+          .toEqual('combobox', 'Expected role of input to be combobox.');
+    });
+
+    it('should set role of autocomplete panel to listbox', () => {
+      const panel = fixture.debugElement.query(By.css('.md-autocomplete-panel')).nativeElement;
+
+      expect(panel.getAttribute('role'))
+          .toEqual('listbox', 'Expected role of the panel to be listbox.');
+    });
+
+    it('should set aria-autocomplete to list', () => {
+      expect(input.getAttribute('aria-autocomplete'))
+          .toEqual('list', 'Expected aria-autocomplete attribute to equal list.');
+    });
+
+    it('should set aria-multiline to false', () => {
+      expect(input.getAttribute('aria-multiline'))
+          .toEqual('false', 'Expected aria-multiline attribute to equal false.');
+    });
+
+    it('should set aria-activedescendant based on the active option', () => {
+      fixture.componentInstance.trigger.openPanel();
+      fixture.detectChanges();
+
+      expect(input.hasAttribute('aria-activedescendant'))
+          .toBe(false, 'Expected aria-activedescendant to be absent if no active item.');
+
+      const DOWN_ARROW_EVENT = new FakeKeyboardEvent(DOWN_ARROW) as KeyboardEvent;
+      fixture.componentInstance.trigger._handleKeydown(DOWN_ARROW_EVENT);
+      fixture.detectChanges();
+
+      expect(input.getAttribute('aria-activedescendant'))
+          .toEqual(fixture.componentInstance.options.first.id,
+              'Expected aria-activedescendant to match the active item after 1 down arrow.');
+
+      fixture.componentInstance.trigger._handleKeydown(DOWN_ARROW_EVENT);
+      fixture.detectChanges();
+
+      expect(input.getAttribute('aria-activedescendant'))
+          .toEqual(fixture.componentInstance.options.toArray()[1].id,
+              'Expected aria-activedescendant to match the active item after 2 down arrows.');
+    });
+
+    it('should set aria-expanded based on whether the panel is open', async(() => {
+      expect(input.getAttribute('aria-expanded'))
+          .toBe('false', 'Expected aria-expanded to be false while panel is closed.');
+
+      fixture.componentInstance.trigger.openPanel();
+      fixture.detectChanges();
+
+      expect(input.getAttribute('aria-expanded'))
+          .toBe('true', 'Expected aria-expanded to be true while panel is open.');
+
+      fixture.componentInstance.trigger.closePanel();
+      fixture.detectChanges();
+
+      fixture.whenStable().then(() => {
+        expect(input.getAttribute('aria-expanded'))
+            .toBe('false', 'Expected aria-expanded to be false when panel closes again.');
+      });
+    }));
+
+    it('should set aria-owns based on the attached autocomplete', () => {
+      fixture.componentInstance.trigger.openPanel();
+      fixture.detectChanges();
+
+      const panel = fixture.debugElement.query(By.css('.md-autocomplete-panel')).nativeElement;
+
+      expect(input.getAttribute('aria-owns'))
+          .toEqual(panel.getAttribute('id'), 'Expected aria-owns to match attached autocomplete.');
+    });
+
+  });
+
 });
 
 @Component({

src/lib/autocomplete/autocomplete.ts

@@ -8,6 +8,12 @@ import {
 } from '@angular/core';
 import {MdOption} from '../core';
 
+/**
+ * Autocomplete IDs need to be unique across components, so this counter exists outside of
+ * the component definition.
+ */
+let _uniqueAutocompleteIdCounter = 0;
+
 @Component({
   moduleId: module.id,
   selector: 'md-autocomplete, mat-autocomplete',
@@ -20,5 +26,8 @@ export class MdAutocomplete {
 
   @ViewChild(TemplateRef) template: TemplateRef<any>;
   @ContentChildren(MdOption) options: QueryList<MdOption>;
+
+  /** Unique ID to be used by autocomplete trigger's "aria-owns" property. */
+  id: string = `md-autocomplete-${_uniqueAutocompleteIdCounter++}`;
 }