[BUGFIX] Fix text input cursor behavior

packages/morph-attr/lib/main.js

@@ -9,8 +9,16 @@ function getProperty() {
 
 function updateProperty(value) {
   if (this._renderedInitially === true || !isAttrRemovalValue(value)) {
-    // do not render if initial value is undefined or null
-    this.domHelper.setPropertyStrict(this.element, this.attrName, value);
+    let element = this.element;
+    let attrName = this.attrName;
+
+    if (attrName === 'value' && element.tagName === 'INPUT' && element.value === value) {
+      // Do nothing. Attempts to avoid accidently changing the input cursor location.
+      // See https://github.com/tildeio/htmlbars/pull/447 for more details.
+    } else {
+      // do not render if initial value is undefined or null
+      this.domHelper.setPropertyStrict(element, attrName, value);
+    }
   }
 
   this._renderedInitially = true;

packages/morph-attr/tests/attr-morph-test.js

@@ -2,6 +2,7 @@
 
 import DOMHelper from "../dom-helper";
 import SafeString from "htmlbars-util/safe-string";
+import AttrMorph from "morph-attr";
 
 var svgNamespace = "http://www.w3.org/2000/svg",
     xlinkNamespace = "http://www.w3.org/1999/xlink";
@@ -249,3 +250,27 @@ test("embed src as data uri is sanitized", function() {
         'unsafe:data:image/svg+xml;base64,PH',
         'attribute is escaped');
 });
+
+// Regression test for https://github.com/tildeio/htmlbars/pull/447.
+test("the value property of an input element is not set if the value hasn't changed", function() {
+  let calls = 0;
+
+  let domHelperStub = {
+    setPropertyStrict() {
+      calls++;
+    }
+  };
+
+  let input = document.createElement('input');
+  let morph = AttrMorph.create(input, 'value', domHelperStub);
+
+  equal(calls, 0);
+  morph.setContent('one');
+  equal(calls, 1);
+  morph.setContent('one');
+  equal(calls, 1);
+  morph.setContent('two');
+  equal(calls, 2);
+  morph.setContent('two');
+  equal(calls, 2);
+});