fix(radio): forward focus to native input (#6274)

* fix(radio): forward focus to native input

* add comment

src/lib/radio/radio.spec.ts

@@ -15,6 +15,7 @@ describe('MdRadio', () => {
     TestBed.configureTestingModule({
       imports: [MdRadioModule, FormsModule, ReactiveFormsModule],
       declarations: [
+        FocusableRadioButton,
         RadiosInsideRadioGroup,
         RadioGroupWithNgModel,
         RadioGroupWithFormControl,
@@ -640,6 +641,27 @@ describe('MdRadio', () => {
       }
     });
   });
+
+  describe('with tabindex', () => {
+    let fixture: ComponentFixture<FocusableRadioButton>;
+
+    beforeEach(() => {
+      fixture = TestBed.createComponent(FocusableRadioButton);
+      fixture.detectChanges();
+    });
+
+    it('should forward focus to native input', () => {
+      let radioButtonEl = fixture.debugElement.query(By.css('.mat-radio-button')).nativeElement;
+      let inputEl = fixture.debugElement.query(By.css('.mat-radio-input')).nativeElement;
+
+      radioButtonEl.focus();
+      // Focus events don't always fire in tests, so we needc to fake it.
+      dispatchFakeEvent(radioButtonEl, 'focus');
+      fixture.detectChanges();
+
+      expect(document.activeElement).toBe(inputEl);
+    });
+  });
 });
 
 
@@ -728,3 +750,8 @@ class RadioGroupWithNgModel {
 class RadioGroupWithFormControl {
   formControl = new FormControl();
 }
+
+@Component({
+  template: `<md-radio-button tabindex="-1"></md-radio-button>`
+})
+class FocusableRadioButton {}

src/lib/radio/radio.ts

@@ -332,6 +332,10 @@ export const _MdRadioButtonMixinBase = mixinColor(mixinDisableRipple(MdRadioButt
     '[class.mat-radio-checked]': 'checked',
     '[class.mat-radio-disabled]': 'disabled',
     '[attr.id]': 'id',
+    // Note: under normal conditions focus shouldn't land on this element, however it may be
+    // programmatically set, for example inside of a focus trap, in this case we want to forward
+    // the focus to the native element.
+    '(focus)': '_inputElement.nativeElement.focus()',
   },
   changeDetection: ChangeDetectionStrategy.OnPush,
 })