feat(ngMessagesInclude): don't break on empty (or whitespace-only) templates

Fixes angular#12941

Closes angular#14726

Author: gkalpak

src/ngMessages/messages.js

@@ -552,22 +552,32 @@ angular.module('ngMessages', [])
         $templateRequest(src).then(function(html) {
           if ($scope.$$destroyed) return;
 
-          $compile(html)($scope, function(contents) {
-            element.after(contents);
-
-            // the anchor is placed for debugging purposes
-            var comment = $compile.$$createComment ?
-                $compile.$$createComment('ngMessagesInclude', src) :
-                $document[0].createComment(' ngMessagesInclude: ' + src + ' ');
-            var anchor = jqLite(comment);
-            element.after(anchor);
-
-            // we don't want to pollute the DOM anymore by keeping an empty directive element
-            element.remove();
-          });
+          if (isString(html) && !html.trim()) {
+            // Empty template - nothing to compile
+            replaceElementWithMarker(element, src);
+          } else {
+            // Non-empty template - compile and link
+            $compile(html)($scope, function(contents) {
+              element.after(contents);
+              replaceElementWithMarker(element, src);
+            });
+          }
         });
       }
     };
+
+    // Helpers
+    function replaceElementWithMarker(element, src) {
+      // A comment marker is placed for debugging purposes
+      var comment = $compile.$$createComment ?
+          $compile.$$createComment('ngMessagesInclude', src) :
+          $document[0].createComment(' ngMessagesInclude: ' + src + ' ');
+      var marker = jqLite(comment);
+      element.after(marker);
+
+      // Don't pollute the DOM anymore by keeping an empty directive element
+      element.remove();
+    }
   }])
 
   /**

test/ngMessages/messagesSpec.js

@@ -815,7 +815,6 @@ describe('ngMessages', function() {
       expect(trim(element.text())).toEqual("C");
     }));
 
-
     it('should properly detect a previous message, even if it was registered later',
       inject(function($compile, $rootScope, $templateCache) {
         $templateCache.put('include.html', '<div ng-message="a">A</div>');
@@ -865,6 +864,25 @@ describe('ngMessages', function() {
           $httpBackend.flush();
         }).not.toThrow();
     }));
+
+    it('should not throw if the template is empty',
+      inject(function($compile, $rootScope, $templateCache) {
+        var html =
+            '<div ng-messages="items">' +
+              '<div ng-messages-include="messages1.html"></div>' +
+              '<div ng-messages-include="messages2.html"></div>' +
+            '</div>';
+
+        $templateCache.put('messages1.html', '');
+        $templateCache.put('messages2.html', '   ');
+        element = $compile(html)($rootScope);
+        $rootScope.$digest();
+
+        expect(element.text()).toBe('');
+        expect(element.children().length).toBe(0);
+        expect(element.contents().length).toBe(2);
+      })
+    );
   });
 
   describe('when multiple', function() {