fix(tabs): fix infinite tab loop (#6663)

Fixes #4639

src/lib/tabs/tab-group.spec.ts

@@ -70,6 +70,25 @@ describe('MdTabGroup', () => {
       });
     }));
 
+    it('should set to correct tab on fast change', async(() => {
+      let component = fixture.componentInstance;
+      component.selectedIndex = 0;
+      fixture.detectChanges();
+
+      setTimeout(() => {
+        component.selectedIndex = 1;
+        fixture.detectChanges();
+
+        setTimeout(() => {
+          component.selectedIndex = 0;
+          fixture.detectChanges();
+          fixture.whenStable().then(() => {
+            expect(component.selectedIndex).toBe(0);
+          });
+        }, 1);
+      }, 1);
+    }));
+
     it('should change tabs based on selectedIndex', fakeAsync(() => {
       let component = fixture.componentInstance;
       let tabComponent = fixture.debugElement.query(By.css('md-tab-group')).componentInstance;

src/lib/tabs/tab-group.ts

@@ -25,8 +25,6 @@ import {
   ViewEncapsulation,
 } from '@angular/core';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
-import {map} from '@angular/cdk/rxjs';
-import {Observable} from 'rxjs/Observable';
 import {Subscription} from 'rxjs/Subscription';
 import {MdTab} from './tab';
 import {merge} from 'rxjs/observable/merge';
@@ -131,9 +129,7 @@ export class MdTabGroup extends _MdTabGroupMixinBase implements AfterContentInit
   private _backgroundColor: ThemePalette;
 
   /** Output to enable support for two-way binding on `[(selectedIndex)]` */
-  @Output() get selectedIndexChange(): Observable<number> {
-    return map.call(this.selectChange, event => event.index);
-  }
+  @Output() selectedIndexChange: EventEmitter<number> = new EventEmitter();
 
   /** Event emitted when focus has changed within a tab group. */
   @Output() focusChange: EventEmitter<MdTabChangeEvent> = new EventEmitter<MdTabChangeEvent>();
@@ -157,16 +153,20 @@ export class MdTabGroup extends _MdTabGroupMixinBase implements AfterContentInit
    * a new selected tab should transition in (from the left or right).
    */
   ngAfterContentChecked(): void {
-    // Clamp the next selected index to the bounds of 0 and the tabs length. Note the `|| 0`, which
-    // ensures that values like NaN can't get through and which would otherwise throw the
-    // component into an infinite loop (since Math.max(NaN, 0) === NaN).
+    // Clamp the next selected index to the boundsof 0 and the tabs length.
+    // Note the `|| 0`, which ensures that values like NaN can't get through
+    // and which would otherwise throw the component into an infinite loop
+    // (since Math.max(NaN, 0) === NaN).
     let indexToSelect = this._indexToSelect =
         Math.min(this._tabs.length - 1, Math.max(this._indexToSelect || 0, 0));
 
     // If there is a change in selected index, emit a change event. Should not trigger if
     // the selected index has not yet been initialized.
     if (this._selectedIndex != indexToSelect && this._selectedIndex != null) {
       this.selectChange.emit(this._createChangeEvent(indexToSelect));
+      // Emitting this value after change detection has run
+      // since the checked content may contain this variable'
+      Promise.resolve().then(() => this.selectedIndexChange.emit(indexToSelect));
     }
 
     // Setup the position for each tab and optionally setup an origin on the next selected tab.