feat(ngModelOptions): add getterSetterContext to specify context for getter/setter bindings

Along with getterSetter, allow users to provide an expression via the getterSetterContext option.
This expression is evaluated to determine the context that should be used when invoking the ngModel
as a getter/setter function.

For example, <input ng-model="someObject.value" ng-model-options="{ getterSetter: true }"> would
previously invoke 'someObject.value()' from the global context. Now, users can specify context, like
ng-model-options="{ getterSetter: true, getterSetterContext: 'someObject'}", which would invoke
'someObject.value()' using 'someObject' as the calling context.

If getterSetterContext is not provided, fallback to using the current scope as the context.

Closes #9394

BREAKING CHANGE: previously, getter/setter functions would always be called from the global context.
This behaviour was unexpected by some users, as described in #9394, and is not particularly nice
anyways.  Applications that relied on this behaviour can use `$window` instead of `this` to access
the global object... but they probably shouldn't be storing global state anyways!

Author: NevilleS

src/ng/directive/input.js

@@ -1716,13 +1716,14 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
 
 
   var parsedNgModel = $parse($attr.ngModel),
+      parsedNgModelContext = null,
       pendingDebounce = null,
       ctrl = this;
 
   var ngModelGet = function ngModelGet() {
     var modelValue = parsedNgModel($scope);
     if (ctrl.$options && ctrl.$options.getterSetter && isFunction(modelValue)) {
-      modelValue = modelValue();
+      modelValue = modelValue.call(parsedNgModelContext ? parsedNgModelContext($scope) : $scope);
     }
     return modelValue;
   };
@@ -1732,7 +1733,7 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
     if (ctrl.$options && ctrl.$options.getterSetter &&
         isFunction(getterSetter = parsedNgModel($scope))) {
 
-      getterSetter(ctrl.$modelValue);
+      getterSetter.call(parsedNgModelContext ? parsedNgModelContext($scope) : $scope, ctrl.$modelValue);
     } else {
       parsedNgModel.assign($scope, ctrl.$modelValue);
     }
@@ -1741,6 +1742,11 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
   this.$$setOptions = function(options) {
     ctrl.$options = options;
 
+    if (ctrl.$options && ctrl.$options.getterSetter && ctrl.$options.getterSetterContext) {
+      // Use the provided context expression to specify the context used when invoking the
+      // getter/setter function
+      parsedNgModelContext = $parse(ctrl.$options.getterSetterContext);
+    }
     if (!parsedNgModel.assign && (!options || !options.getterSetter)) {
       throw $ngModelMinErr('nonassign', "Expression '{0}' is non-assignable. Element: {1}",
           $attr.ngModel, startingTag($element));

test/ng/directive/inputSpec.js

@@ -1975,6 +1975,83 @@ describe('input', function() {
           'ng-model-options="{ getterSetter: true }" />');
     });
 
+    it('should try to invoke a model with default context if getterSetter is true and getterSetterContext is not provided', function() {
+      scope.value = 'scopeContext';
+      compileInput(
+        '<input type="text" ng-model="someService.getterSetter" '+
+          'ng-model-options="{ getterSetter: true }" />');
+
+      scope.someService = {
+        value: 'b',
+        getterSetter: function(newValue) {
+          this.value = newValue || this.value;
+          return this.value;
+        }
+      };
+      spyOn(scope.someService, 'getterSetter').andCallThrough();
+      scope.$apply();
+      expect(inputElm.val()).toBe('scopeContext');
+      expect(scope.someService.getterSetter).toHaveBeenCalledWith();
+      expect(scope.someService.value).toBe('b'); // 'this' is not bound to the service w/o ngModelContext
+      expect(scope.value).toBe('scopeContext');
+
+      changeInputValueTo('a');
+      expect(scope.someService.getterSetter).toHaveBeenCalledWith('a');
+      expect(scope.someService.value).toBe('b');
+      expect(scope.value).toBe('a');
+
+      scope.someService.value = 'c';
+      scope.$apply();
+      expect(inputElm.val()).toBe('a');
+      expect(scope.someService.getterSetter).toHaveBeenCalledWith();
+      expect(scope.someService.value).toBe('c');
+      expect(scope.value).toBe('a');
+
+      scope.value = 'd';
+      scope.$apply();
+      expect(inputElm.val()).toBe('d');
+      expect(scope.someService.getterSetter).toHaveBeenCalledWith();
+      expect(scope.someService.value).toBe('c');
+      expect(scope.value).toBe('d');
+    });
+
+    it('should try to invoke a model with the provided context if getterSetter is true and getterSetterContext is an expression', function() {
+      compileInput(
+        '<input type="text" ng-model="someService.getterSetter" '+
+          'ng-model-options="{ getterSetter: true, getterSetterContext: \'someService\' }" />');
+
+      scope.someService = {
+        value: 'b',
+        getterSetter: function(newValue) {
+          this.value = newValue || this.value;
+          return this.value;
+        }
+      };
+      spyOn(scope.someService, 'getterSetter').andCallThrough();
+      scope.$apply();
+      expect(inputElm.val()).toBe('b');
+      expect(scope.someService.getterSetter).toHaveBeenCalledWith();
+      expect(scope.someService.value).toBe('b');
+
+      changeInputValueTo('a');
+      expect(scope.someService.getterSetter).toHaveBeenCalledWith('a');
+      expect(scope.someService.value).toBe('a');
+
+      scope.someService.value = 'c';
+      scope.$apply();
+      expect(inputElm.val()).toBe('c');
+      expect(scope.someService.getterSetter).toHaveBeenCalledWith();
+      expect(scope.someService.value).toBe('c');
+    });
+
+    it('should fail to parse if getterSetterContext is an invalid expression', function() {
+      expect(function() {
+        compileInput(
+          '<input type="text" ng-model="someService.getterSetter" '+
+            'ng-model-options="{ getterSetter: true, getterSetterContext: \'throw error\' }" />');
+      }).toThrowMinErr("$parse", "syntax", "Syntax Error: Token 'error' is an unexpected token at column 7 of the expression [throw error] starting at [error].");
+    });
+
     it('should assign invalid values to the scope if allowInvalid is true', function() {
       compileInput('<input type="text" name="input" ng-model="value" maxlength="1" ' +
                    'ng-model-options="{allowInvalid: true}" />');