fix(input,select): equality comparison is used to detect changes

When model changes are detected, a equality comparison with a local copy
of the value ($modelValue).

ngModelController provides the method $setCompareByEquality to change between
equality and reference comparisons.

Closes angular#1751

Author: Gonzalo Ruiz de Villa

src/ng/directive/input.js

@@ -911,6 +911,7 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
   this.$valid = true;
   this.$invalid = false;
   this.$name = $attr.name;
+  this.$objectEquality = true;
 
   var ngModelGet = $parse($attr.ngModel),
       ngModelSet = ngModelGet.assign;
@@ -948,6 +949,10 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
       addClass((isValid ? VALID_CLASS : INVALID_CLASS) + validationErrorKey);
   }
 
+  this.$setCompareByEquality = function (value) {
+    this.$objectEquality = value;
+  }
+
   /**
    * @ngdoc function
    * @name ng.directive:ngModel.NgModelController#$setValidity
@@ -1038,8 +1043,8 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
       value = fn(value);
     });
 
-    if (this.$modelValue !== value) {
-      this.$modelValue = value;
+    if (this.$objectEquality ? !equals(this.$modelValue, value) : this.$modelValue !== value ) {
+      this.$modelValue = ctrl.$objectEquality ? copy(value) : value;
       ngModelSet($scope, value);
       forEach(this.$viewChangeListeners, function(listener) {
         try {
@@ -1058,12 +1063,12 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
     var value = ngModelGet($scope);
 
     // if scope model value and ngModel value are out of sync
-    if (ctrl.$modelValue !== value) {
+    if (ctrl.$objectEquality ? !equals(ctrl.$modelValue, value) : ctrl.$modelValue !== value) {
 
       var formatters = ctrl.$formatters,
           idx = formatters.length;
 
-      ctrl.$modelValue = value;
+      ctrl.$modelValue = ctrl.$objectEquality ? copy(value) : value;
       while(idx--) {
         value = formatters[idx](value);
       }

src/ng/directive/select.js

@@ -213,6 +213,9 @@ var selectDirective = ['$compile', '$parse', function($compile,   $parse) {
 
       selectCtrl.init(ngModelCtrl, nullOption, unknownOption);
 
+      //select must compare objects by reference, not by equality
+      ngModelCtrl.$setCompareByEquality(false);
+
       // required validator
       if (multiple && (attr.required || attr.ngRequired)) {
         var requiredValidator = function(value) {

test/ng/directive/inputSpec.js

@@ -990,6 +990,20 @@ describe('input', function() {
     });
 
 
+    it("should detect changes in the values of an array", function () {
+      var list = ['x', 'y', 'z'];
+      compileInput('<input type="text" ng-model="list" ng-list />');
+      scope.$apply(function() {
+        scope.list = list;
+      });
+      expect(inputElm.val()).toBe('x, y, z');
+      scope.$apply(function() {
+        list.unshift('w');
+      });
+      expect(inputElm.val()).toBe('w, x, y, z');
+    });
+
+
     xit('should require at least one item', function() {
       compileInput('<input type="text" ng-model="list" ng-list required />');