fix(input): don't dirty model when input event triggered due to placeholder change

Certain versions of IE inexplicably trigger an input event in response to a placeholder
being set.

It is not possible to sniff for this behaviour nicely as the event is not triggered if
the element is not attached to the document, and the event triggers asynchronously so
it is not possible to accomplish this without deferring DOM compilation and slowing down
load times.

Closes angular#2614
Closes angular#5960

Author: caitp

Diff for: src/ng/directive/input.js

@@ -435,6 +435,7 @@ function validate(ctrl, validatorName, validity, value){
 }
 
 function textInputType(scope, element, attr, ctrl, $sniffer, $browser) {
+  var placeholder = element[0].placeholder, noevent = {};
   // In composition mode, users are still inputing intermediate text buffer,
   // hold the listener until composition is done.
   // More about composition events: https://developer.mozilla.org/en-US/docs/Web/API/CompositionEvent
@@ -451,10 +452,18 @@ function textInputType(scope, element, attr, ctrl, $sniffer, $browser) {
     });
   }
 
-  var listener = function() {
+  var listener = function(event) {
     if (composing) return;
     var value = element.val();
 
+    // Some versions of MSIE emit an 'input' event when the placeholder attribute/property
+    // change. This hack prevents an otherwise pristine field from being dirtied on IE
+    // browsers.
+    if (msie && (event || noevent).type === 'input' && element[0].placeholder !== placeholder) {
+      placeholder = element[0].placeholder;
+      return;
+    }
+
     // By default we will trim the value
     // If the attribute ng-trim exists we will avoid trimming
     // e.g. <input ng-model="foo" ng-trim="false">

Diff for: test/ng/directive/inputSpec.js

@@ -520,6 +520,23 @@ describe('input', function() {
     }
   });
 
+  it('should not dirty the model on an input event in response to a placeholder change', inject(function($sniffer) {
+    if (msie && $sniffer.hasEvent('input')) {
+      compileInput('<input type="text" ng-model="name" name="name" />');
+      inputElm.attr('placeholder', 'Test');
+      browserTrigger(inputElm, 'input');
+
+      expect(inputElm.attr('placeholder')).toBe('Test');
+      expect(inputElm).toBePristine();
+
+      inputElm.attr('placeholder', 'Test Again');
+      browserTrigger(inputElm, 'input');
+
+      expect(inputElm.attr('placeholder')).toBe('Test Again');
+      expect(inputElm).toBePristine();
+    }
+  }));
+
   describe('"change" event', function() {
     function assertBrowserSupportsChangeEvent(inputEventSupported) {
       // Force browser to report a lack of an 'input' event