fix($compile): connect transclude scopes to their containing scope to…

… prevent memory leaks

Transcluded scopes are now connected to the scope in which they are created via their `$parent`
property. This means that they will be automatically destroyed when their "containing" scope is
destroyed, without having to resort to listening for a `$destroy` event on various DOM elements
or other scopes.

Previously, transclude scope not only inherited prototypically from the scope from which they were
transcluded but they were also still owned by that "outer" scope. This meant that there were
scenarios where the "real" container scope/element was destroyed but the transclude scope was not,
leading to memory leaks.

The original strategy for dealing with this was to attach a `$destroy` event handler to the DOM
elements in the transcluded content, so that if the elements were removed from the DOM then their
associated transcluded scope would be destroyed.

This didn't work for transclude contents that didn't contain any elements - most importantly in
the case of the transclude content containing an element transclude directive at its root, since
the compiler swaps out this element for a comment before a destroy handler could be attached.

BREAKING CHANGE:

`$transclude` functions no longer attach `$destroy` event handlers to the transcluded content,
and so the associated transclude scope will not automatically be destroyed if you remove a
transcluded element from the DOM using direct DOM manipulation such as the jquery `remove()`
method.

If you want to explicitly remove DOM elements inside your directive that have been compiled, and so
potentially contain child (and transcluded) scopes, then it is your responsibility to get hold of
the scope and destroy it at the same time.

The suggested approach is to create a new child scope of your own around any DOM elements that you
wish to manipulate in this way and destroy those scopes if you remove their contents - any child
scopes will then be destroyed and cleaned up automatically.

Note that all the built-in directives that manipulate the DOM (ngIf, ngRepeat, ngSwitch, etc)
already follow this best practice, so if you only use these for manipulating the DOM then you
do not have to worry about this change.

Closes angular#9095

src/ng/compile.js

@@ -294,13 +294,20 @@
  * compile the content of the element and make it available to the directive.
  * Typically used with {@link ng.directive:ngTransclude
  * ngTransclude}. The advantage of transclusion is that the linking function receives a
- * transclusion function which is pre-bound to the correct scope. In a typical setup the widget
- * creates an `isolate` scope, but the transclusion is not a child, but a sibling of the `isolate`
- * scope. This makes it possible for the widget to have private state, and the transclusion to
- * be bound to the parent (pre-`isolate`) scope.
+ * transclusion function which is pre-bound to the scope of the position in the DOM from where
+ * it was taken.
  *
- * * `true` - transclude the content of the directive.
- * * `'element'` - transclude the whole element including any directives defined at lower priority.
+ * In a typical setup the widget creates an `isolate` scope, but the transcluded
+ * content has its own **transclusion scope**. While the **transclusion scope** is owned as a child,
+ * by the **isolate scope**, it prototypically inherits from the original scope from where the
+ * transcluded content was taken.
+ *
+ * This makes it possible for the widget to have private state, and the transclusion to
+ * be bound to the original (pre-`isolate`) scope.
+ *
+ * * `true` - transclude the content (i.e. the child nodes) of the directive's element.
+ * * `'element'` - transclude the whole of the directive's element including any directives on this
+ *   element that defined at a lower priority than this directive.
  *
  * <div class="alert alert-warning">
  * **Note:** When testing an element transclude directive you must not place the directive at the root of the
@@ -1166,20 +1173,15 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
     function createBoundTranscludeFn(scope, transcludeFn, previousBoundTranscludeFn, elementTransclusion) {
 
-      var boundTranscludeFn = function(transcludedScope, cloneFn, controllers, futureParentElement) {
+      var boundTranscludeFn = function(transcludedScope, cloneFn, controllers, futureParentElement, containingScope) {
         var scopeCreated = false;
 
         if (!transcludedScope) {
-          transcludedScope = scope.$new();
+          transcludedScope = scope.$new(false, containingScope);
           transcludedScope.$$transcluded = true;
-          scopeCreated = true;
         }
 
-        var clone = transcludeFn(transcludedScope, cloneFn, controllers, previousBoundTranscludeFn, futureParentElement);
-        if (scopeCreated && !elementTransclusion) {
-          clone.on('$destroy', function() { transcludedScope.$destroy(); });
-        }
-        return clone;
+        return transcludeFn(transcludedScope, cloneFn, controllers, previousBoundTranscludeFn, futureParentElement);
       };
 
       return boundTranscludeFn;
@@ -1810,7 +1812,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
           if (!futureParentElement) {
             futureParentElement = hasElementTranscludeDirective ? $element.parent() : $element;
           }
-          return boundTranscludeFn(scope, cloneAttachFn, transcludeControllers, futureParentElement);
+          return boundTranscludeFn(scope, cloneAttachFn, transcludeControllers, futureParentElement, scopeToChild);
         }
       }
     }

test/ng/compileSpec.js

@@ -4331,17 +4331,21 @@ describe('$compile', function() {
             return {
               transclude: 'content',
               replace: true,
-              scope: true,
-              template: '<ul><li>W:{{$parent.$id}}-{{$id}};</li><li ng-transclude></li></ul>'
+              scope: {},
+              link: function(scope) {
+                scope.x='iso';
+              },
+              template: '<ul><li>W:{{x}}-{{$parent.$id}}-{{$id}};</li><li ng-transclude></li></ul>'
             };
           });
         });
         inject(function(log, $rootScope, $compile) {
-          element = $compile('<div><div trans>T:{{$parent.$id}}-{{$id}}<span>;</span></div></div>')
+          element = $compile('<div><div trans>T:{{x}}-{{$parent.$id}}-{{$id}}<span>;</span></div></div>')
               ($rootScope);
+          $rootScope.x = 'root';
           $rootScope.$apply();
-          expect(element.text()).toEqual('W:1-2;T:1-3;');
-          expect(jqLite(element.find('span')[0]).text()).toEqual('T:1-3');
+          expect(element.text()).toEqual('W:iso-1-2;T:root-2-3;');
+          expect(jqLite(element.find('span')[0]).text()).toEqual('T:root-2-3');
           expect(jqLite(element.find('span')[1]).text()).toEqual(';');
         });
       });
@@ -4551,47 +4555,6 @@ describe('$compile', function() {
       }
 
 
-      it('should remove transclusion scope, when the DOM is destroyed', function() {
-        module(function() {
-          directive('box', valueFn({
-            transclude: true,
-            scope: { name: '=', show: '=' },
-            template: '<div><h1>Hello: {{name}}!</h1><div ng-transclude></div></div>',
-            link: function(scope, element) {
-              scope.$watch(
-                  'show',
-                  function(show) {
-                    if (!show) {
-                      element.find('div').find('div').remove();
-                    }
-                  }
-              );
-            }
-          }));
-        });
-        inject(function($compile, $rootScope) {
-          $rootScope.username = 'Misko';
-          $rootScope.select = true;
-          element = $compile(
-              '<div><div box name="username" show="select">user: {{username}}</div></div>')
-              ($rootScope);
-          $rootScope.$apply();
-          expect(element.text()).toEqual('Hello: Misko!user: Misko');
-
-          var widgetScope = $rootScope.$$childHead;
-          var transcludeScope = widgetScope.$$nextSibling;
-          expect(widgetScope.name).toEqual('Misko');
-          expect(widgetScope.$parent).toEqual($rootScope);
-          expect(transcludeScope.$parent).toEqual($rootScope);
-
-          $rootScope.select = false;
-          $rootScope.$apply();
-          expect(element.text()).toEqual('Hello: Misko!');
-          expect(widgetScope.$$nextSibling).toEqual(null);
-        });
-      });
-
-
       it('should add a $$transcluded property onto the transcluded scope', function() {
         module(function() {
           directive('trans', function() {
@@ -4964,6 +4927,118 @@ describe('$compile', function() {
       });
 
 
+      // see issue https://github.com/angular/angular.js/issues/9095
+      describe('removing a transcluded element', function() {
+
+        function countScopes($rootScope) {
+          return [$rootScope].concat(
+            getChildScopes($rootScope)
+          ).length;
+
+          function getChildScopes(scope) {
+            var children = [];
+            if (!scope.$$childHead) { return children; }
+            var childScope = scope.$$childHead;
+            do {
+              children.push(childScope);
+              children = children.concat(getChildScopes(childScope));
+            } while ((childScope = childScope.$$nextSibling));
+            return children;
+          }
+        }
+
+        beforeEach(module(function() {
+          directive('toggle', function() {
+            return {
+              transclude: true,
+              template: '<div ng:if="t"><div ng:transclude></div></div>'
+            };
+          });
+        }));
+
+
+        it('should not leak the transclude scope when the transcluded content is an element transclusion directive',
+              inject(function($compile, $rootScope) {
+
+          element = $compile(
+            '<div toggle>' +
+              '<div ng:repeat="msg in [\'msg-1\']">{{ msg }}</div>' +
+            '</div>'
+          )($rootScope);
+
+          $rootScope.$apply('t = true');
+          expect(element.text()).toContain('msg-1');
+          expect(countScopes($rootScope)).toEqual(4);
+
+          $rootScope.$apply('t = false');
+          expect(element.text()).not.toContain('msg-1');
+          expect(countScopes($rootScope)).toEqual(1);
+
+          $rootScope.$apply('t = true');
+          expect(element.text()).toContain('msg-1');
+          expect(countScopes($rootScope)).toEqual(4);
+
+          $rootScope.$apply('t = false');
+          expect(element.text()).not.toContain('msg-1');
+          expect(countScopes($rootScope)).toEqual(1);
+        }));
+
+
+        it('should not leak the transclude scope if the transcluded contains only comments',
+              inject(function($compile, $rootScope) {
+
+          element = $compile(
+            '<div toggle>' +
+              '<!-- some comment -->' +
+            '</div>'
+          )($rootScope);
+
+          $rootScope.$apply('t = true');
+          expect(element.html()).toContain('some comment');
+          expect(countScopes($rootScope)).toEqual(3);
+
+          $rootScope.$apply('t = false');
+          expect(element.html()).not.toContain('some comment');
+          expect(countScopes($rootScope)).toEqual(1);
+
+          $rootScope.$apply('t = true');
+          expect(element.html()).toContain('some comment');
+          expect(countScopes($rootScope)).toEqual(3);
+
+          $rootScope.$apply('t = false');
+          expect(element.html()).not.toContain('some comment');
+          expect(countScopes($rootScope)).toEqual(1);
+        }));
+
+        it('should not leak the transclude scope if the transcluded contains only text nodes',
+              inject(function($compile, $rootScope) {
+
+          element = $compile(
+            '<div toggle>' +
+              'some text' +
+            '</div>'
+          )($rootScope);
+
+          $rootScope.$apply('t = true');
+          expect(element.html()).toContain('some text');
+          expect(countScopes($rootScope)).toEqual(3);
+
+          $rootScope.$apply('t = false');
+          expect(element.html()).not.toContain('some text');
+          expect(countScopes($rootScope)).toEqual(1);
+
+          $rootScope.$apply('t = true');
+          expect(element.html()).toContain('some text');
+          expect(countScopes($rootScope)).toEqual(3);
+
+          $rootScope.$apply('t = false');
+          expect(element.html()).not.toContain('some text');
+          expect(countScopes($rootScope)).toEqual(1);
+        }));
+
+      });
+
+
       describe('nested transcludes', function() {
 
         beforeEach(module(function($compileProvider) {