fix($compile): support transcluding multi-element directives

Previously, transcluding multi-element directives (e.g. `foo-start`/`foo-end`)
was not supported on elements with multi-slot transclusion (a `uterdir` error
was thrown).
This commit fixes it by putting the transcluded nodes into a DocumentFragment,
where they can be traversed via `.nextSibling`.

Fixes #15554

Author: gkalpak

src/ng/compile.js

@@ -2480,7 +2480,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
               // We have transclusion slots,
               // collect them up, compile them and store their transclusion functions
-              $template = [];
+              $template = window.document.createDocumentFragment();
 
               var slotMap = createMap();
               var filledSlots = createMap();
@@ -2508,10 +2508,10 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
                 var slotName = slotMap[directiveNormalize(nodeName_(node))];
                 if (slotName) {
                   filledSlots[slotName] = true;
-                  slots[slotName] = slots[slotName] || [];
-                  slots[slotName].push(node);
+                  slots[slotName] = slots[slotName] || window.document.createDocumentFragment();
+                  slots[slotName].appendChild(node);
                 } else {
-                  $template.push(node);
+                  $template.appendChild(node);
                 }
               });
 
@@ -2525,9 +2525,11 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
               for (var slotName in slots) {
                 if (slots[slotName]) {
                   // Only define a transclusion function if the slot was filled
-                  slots[slotName] = compilationGenerator(mightHaveMultipleTransclusionError, slots[slotName], transcludeFn);
+                  slots[slotName] = compilationGenerator(mightHaveMultipleTransclusionError, slots[slotName].childNodes, transcludeFn);
                 }
               }
+
+              $template = $template.childNodes;
             }
 
             $compileNode.empty(); // clear contents

test/ng/compileSpec.js

@@ -8349,6 +8349,50 @@ describe('$compile', function() {
             });
           });
 
+
+          it('should correctly handle multi-element directives', function() {
+            module(function() {
+              directive('foo', valueFn({
+                template: '[<div ng-transclude></div>]',
+                transclude: true
+              }));
+              directive('bar', valueFn({
+                template: '[<div ng-transclude="header"></div>|<div ng-transclude="footer"></div>]',
+                transclude: {
+                  header: 'header',
+                  footer: 'footer'
+                }
+              }));
+            });
+
+            inject(function($compile, $rootScope) {
+              var tmplWithFoo =
+                  '<foo>' +
+                    '<div ng-if-start="true">Hello, </div>' +
+                    '<div ng-if-end>world!</div>' +
+                  '</foo>';
+              var tmplWithBar =
+                  '<bar>' +
+                    '<header ng-if-start="true">This is a </header>' +
+                    '<header ng-if-end>header!</header>' +
+                    '<footer ng-if-start="true">This is a </footer>' +
+                    '<footer ng-if-end>footer!</footer>' +
+                  '</bar>';
+
+              var elem1 = $compile(tmplWithFoo)($rootScope);
+              var elem2 = $compile(tmplWithBar)($rootScope);
+
+              $rootScope.$digest();
+
+              expect(elem1.text()).toBe('[Hello, world!]');
+              expect(elem2.text()).toBe('[This is a header!|This is a footer!]');
+
+              dealoc(elem1);
+              dealoc(elem2);
+            });
+          });
+
+
           //see issue https://github.com/angular/angular.js/issues/12936
           it('should use the proper scope when it is on the root element of a replaced directive template', function() {
             module(function() {