fix(autosize): Re-size input when placeholder changes

Fix the autosize directive so it correctly re-sizes the input element
when it's empty and its placeholder changes due to interpolation.

Closes #110

src/autosize.js

@@ -44,6 +44,12 @@ tagsInput.directive('tiAutosize', function() {
 
             ctrl.$parsers.unshift(resize);
             ctrl.$formatters.unshift(resize);
+
+            attrs.$observe('placeholder', function(value) {
+                if (!ctrl.$modelValue) {
+                    resize(value);
+                }
+            });
         }
     };
 });

test/autosize.spec.js

@@ -83,6 +83,21 @@ describe('autosize directive', function() {
         expect(element.css('width')).toBe(getTextWidth('Some placeholder'));
     });
 
+    it('sets the input width as the placeholder width when the input is empty and the placeholder changes', function() {
+        // Arrange
+        $scope.placeholder = 'Some placeholder';
+        compile('placeholder="{{placeholder}}"');
+        $scope.model = '';
+        $scope.$digest();
+
+        // Act
+        $scope.placeholder = 'Some very lengthy placeholder';
+        $scope.$digest();
+
+        // Assert
+        expect(element.css('width')).toBe(getTextWidth('Some very lengthy placeholder'));
+    });
+
     it('clears the input width when it cannot be calculated', function() {
         // Arrange
         container.hide();