fix(select): add basic track by and select as support

Instead of throwing an error when using "track by" and "select as" expressions,
ngOptions will assume that the track by expression is valid, and will use it to
compare values.

Closes angular#6564

Author: jeffbcross

src/ng/directive/select.js

@@ -363,13 +363,6 @@ var selectDirective = ['$compile', '$parse', function($compile,   $parse) {
             //re-usable object to represent option's locals
             locals = {};
 
-        if (trackFn && selectAsFn) {
-          throw ngOptionsMinErr('trkslct',
-            "Comprehension expression cannot contain both selectAs '{0}' " +
-            "and trackBy '{1}' expressions.",
-            selectAs, track);
-        }
-
         if (nullOption) {
           // compile the element since there might be bindings in it
           $compile(nullOption)(scope);
@@ -470,15 +463,16 @@ var selectDirective = ['$compile', '$parse', function($compile,   $parse) {
             } else {
               selectedSet = new HashMap(viewValue);
             }
-          } else if (!selectAsFn && trackFn) {
+          } else if (trackFn) {
             viewValue = callExpression(trackFn, null, viewValue);
           }
+
           return function isSelected(key, value) {
             var compareValueFn;
-            if (selectAsFn) {
-              compareValueFn = selectAsFn;
-            } else if (trackFn) {
+            if (trackFn) {
               compareValueFn = trackFn;
+            } else if (selectAsFn) {
+              compareValueFn = selectAsFn;
             } else {
               compareValueFn = valueFn;
             }

test/ng/directive/selectSpec.js

@@ -819,20 +819,43 @@ describe('select', function() {
 
     describe('selectAs+trackBy expression', function() {
       beforeEach(function() {
-        scope.arr = [{id: 10, label: 'ten'}, {id:'20', label: 'twenty'}];
+        scope.arr = [{subItem: {label: 'ten', id: 10}}, {subItem: {label: 'twenty', id: 20}}];
         scope.obj = {'10': {score: 10, label: 'ten'}, '20': {score: 20, label: 'twenty'}};
       });
 
 
-      it('should throw a helpful minerr', function() {
-        expect(function() {
+      it('should bind to scope value through experession while tracking/identifying objects', function() {
+        createSelect({
+          'ng-model': 'selected',
+          'ng-options': 'item.subItem as item.name for item in arr track by (item.id || item.subItem.id)'
+        });
+
+        scope.$apply(function() {
+          scope.selected = scope.arr[0].subItem;
+        });
+        expect(element.val()).toEqual('0');
+
+        scope.$apply(function() {
+          scope.selected = scope.arr[1].subItem;
+        });
+        expect(element.val()).toEqual('1');
+
+        // Now test val() -> model
+
+        element.val('0');
+        browserTrigger(element, 'change');
+        expect(scope.selected).toBe(scope.arr[0].subItem);
 
-            createSelect({
-              'ng-model': 'selected',
-              'ng-options': 'item.id as item.name for item in values track by item.id'
-            });
 
-        }).toThrowMinErr('ngOptions', 'trkslct', "Comprehension expression cannot contain both selectAs 'item.id' and trackBy 'item.id' expressions.");
+        scope.$apply(function() {
+          scope.arr[1] = {subItem: {label: 'new item', id: 20}};
+          scope.selected = scope.arr[1];
+        });
+        expect(element.val()).toBe('1')
+
+        element.val('1');
+        browserTrigger(element, 'change');
+        expect(scope.selected).toBe(scope.arr[1].subItem);
       });
     });