feat(input): support dynamic element validation

Interpolates the form controll attribute name, so that dynamic form controls (such as those rendered
in an ngRepeat) will always have their expected interpolated name.

Closes angular#4791

Author: caitp

src/ng/directive/input.js

@@ -1657,8 +1657,8 @@ var VALID_CLASS = 'ng-valid',
  *
  *
  */
-var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$parse', '$animate', '$timeout', '$rootScope', '$q',
-    function($scope, $exceptionHandler, $attr, $element, $parse, $animate, $timeout, $rootScope, $q) {
+var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$parse', '$animate', '$timeout', '$rootScope', '$q', '$interpolate',
+    function($scope, $exceptionHandler, $attr, $element, $parse, $animate, $timeout, $rootScope, $q, $interpolate) {
   this.$viewValue = Number.NaN;
   this.$modelValue = Number.NaN;
   this.$validators = {};
@@ -1675,7 +1675,7 @@ var NgModelController = ['$scope', '$exceptionHandler', '$attrs', '$element', '$
   this.$error = {}; // keep invalid keys here
   this.$$success = {}; // keep valid keys here
   this.$pending = undefined; // keep pending keys here
-  this.$name = $attr.name;
+  this.$name = $interpolate($attr.name || '', false)($scope);
 
 
   var parsedNgModel = $parse($attr.ngModel),

test/ng/directive/inputSpec.js

@@ -1289,6 +1289,34 @@ describe('input', function() {
     }
   }));
 
+
+  it('should interpolate input names (string)', function() {
+    scope.nameID = '47';
+    compileInput('<input type="text" ng-model="name" name="name{{nameID}}" />');
+    expect(scope.form.name47.$pristine).toBeTruthy();
+    changeInputValueTo('caitp');
+    expect(scope.form.name47.$dirty).toBeTruthy();
+  });
+
+
+  it('should interpolate input names (number)', function() {
+    scope.nameID = 47;
+    compileInput('<input type="text" ng-model="name" name="name{{nameID}}" />');
+    expect(scope.form.name47.$pristine).toBeTruthy();
+    changeInputValueTo('caitp');
+    expect(scope.form.name47.$dirty).toBeTruthy();
+  });
+
+
+  it('should interpolate input names (undefined)', function() {
+    scope.nameID = undefined;
+    compileInput('<input type="text" ng-model="name" name="name{{nameID}}" />');
+    expect(scope.form.name.$pristine).toBeTruthy();
+    changeInputValueTo('caitp');
+    expect(scope.form.name.$dirty).toBeTruthy();
+  });
+
+
   describe('"change" event', function() {
     function assertBrowserSupportsChangeEvent(inputEventSupported) {
       // Force browser to report a lack of an 'input' event