fix(differ): clean up stale identity change refs

Closes #7193

modules/angular2/src/core/change_detection/differs/default_iterable_differ.ts

@@ -325,6 +325,9 @@ export class DefaultIterableDiffer implements IterableDiffer {
     if (this._removalsTail !== null) {
       this._removalsTail._nextRemoved = null;
     }
+    if (this._identityChangesTail !== null) {
+      this._identityChangesTail._nextIdentityChange = null;
+    }
   }
 
   /** @internal */

modules/angular2/test/common/directives/ng_for_spec.ts

@@ -365,7 +365,7 @@ export function main() {
       it('should not replace tracked items',
          inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
            var template =
-               `<template ngFor #item [ngForOf]="items" [ngForTrackBy]="customTrackBy" #i="index">
+               `<template ngFor #item [ngForOf]="items" [ngForTrackBy]="trackById" #i="index">
                <p>{{items[i]}}</p>
               </template>`;
            tcb.overrideTemplate(TestComponent, template)
@@ -387,7 +387,7 @@ export function main() {
       it('should update implicit local variable on view',
          inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
            var template =
-               `<div><template ngFor #item [ngForOf]="items" [ngForTrackBy]="customTrackBy">{{item['color']}}</template></div>`;
+               `<div><template ngFor #item [ngForOf]="items" [ngForTrackBy]="trackById">{{item['color']}}</template></div>`;
            tcb.overrideTemplate(TestComponent, template)
                .createAsync(TestComponent)
                .then((fixture) => {
@@ -403,7 +403,7 @@ export function main() {
       it('should move items around and keep them updated ',
          inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
            var template =
-               `<div><template ngFor #item [ngForOf]="items" [ngForTrackBy]="customTrackBy">{{item['color']}}</template></div>`;
+               `<div><template ngFor #item [ngForOf]="items" [ngForTrackBy]="trackById">{{item['color']}}</template></div>`;
            tcb.overrideTemplate(TestComponent, template)
                .createAsync(TestComponent)
                .then((fixture) => {
@@ -418,6 +418,24 @@ export function main() {
                  async.done();
                });
          }));
+
+      it('should handle added and removed items properly when tracking by index',
+         inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
+           var template =
+               `<div><template ngFor #item [ngForOf]="items" [ngForTrackBy]="trackByIndex">{{item}}</template></div>`;
+           tcb.overrideTemplate(TestComponent, template)
+               .createAsync(TestComponent)
+               .then((fixture) => {
+                 fixture.debugElement.componentInstance.items = ['a', 'b', 'c', 'd'];
+                 fixture.detectChanges();
+                 fixture.debugElement.componentInstance.items = ['e', 'f', 'g', 'h'];
+                 fixture.detectChanges();
+                 fixture.debugElement.componentInstance.items = ['e', 'f', 'h'];
+                 fixture.detectChanges();
+                 expect(fixture.debugElement.nativeElement).toHaveText('efh');
+                 async.done();
+               });
+         }));
     });
   });
 }
@@ -432,7 +450,8 @@ class TestComponent {
   @ContentChild(TemplateRef) contentTpl: TemplateRef;
   items: any;
   constructor() { this.items = [1, 2]; }
-  customTrackBy(index: number, item: any): string { return item['id']; }
+  trackById(index: number, item: any): string { return item['id']; }
+  trackByIndex(index: number, item: any): number { return index; }
 }
 
 @Component({selector: 'outer-cmp'})

modules/angular2/test/core/change_detection/differs/default_iterable_differ_spec.ts

@@ -338,7 +338,7 @@ export function main() {
       });
     });
 
-    describe('trackBy function', function() {
+    describe('trackBy function by id', function() {
       var differ;
 
       var trackByItemId = (index: number, item: any): any => item.id;
@@ -433,5 +433,29 @@ export function main() {
             }));
       });
     });
+    describe('trackBy function by index', function() {
+      var differ;
+
+      var trackByIndex = (index: number, item: any): number => index;
+
+      beforeEach(() => { differ = new DefaultIterableDiffer(trackByIndex); });
+
+      it('should track removals normally', () => {
+        differ.check(['a', 'b', 'c', 'd']);
+        differ.check(['e', 'f', 'g', 'h']);
+        differ.check(['e', 'f', 'h']);
+
+        expect(differ.toString())
+            .toEqual(iterableChangesAsString({
+              collection: ['e', 'f', 'h'],
+              previous: ['e', 'f', 'h', 'h[3->null]'],
+              removals: ['h[3->null]'],
+              identityChanges: ['h']
+            }));
+      });
+
+    });
+
+
   });
 }