fix($rootScope): fix potential memory leak when removing scope listeners

Previously the array entry for listeners was set to null but the array size was not
trimmed until the event was broadcasted again (see e6966e0).

By keeping track of the listener iteration index globally it can be adjusted if a listener
removal effects the index.

Fixes angular#16135

BREAKING CHANGE:

`$emit`/`$broadcast` listeners of a specific event name on a scope can no
longer be recursivly invoked.

docs/content/error/$rootScope/inevt.ngdoc

@@ -0,0 +1,22 @@
+@ngdoc error
+@name $rootScope:inevt
+@fullName Recursive $emit/$broadcast event
+@description
+
+This error occurs when the an event is `$emit`ed or `$broadcast`ed recursively on a scope.
+
+For example, when an event listener fires the same event being listened to.
+
+```
+$scope.$on('foo', function() {
+    $scope.$emit('foo');
+});
+```
+
+Or when a parent element causes indirect recursion.
+
+```
+$scope.$on('foo', function() {
+    $rootScope.$broadcast('foo');
+});
+```

src/ng/rootScope.js

@@ -1167,7 +1167,7 @@ function $RootScopeProvider() {
       $on: function(name, listener) {
         var namedListeners = this.$$listeners[name];
         if (!namedListeners) {
-          this.$$listeners[name] = namedListeners = [];
+          this.$$listeners[name] = namedListeners = extend([], {$$index: -1});
         }
         namedListeners.push(listener);
 
@@ -1181,10 +1181,14 @@ function $RootScopeProvider() {
 
         var self = this;
         return function() {
-          var indexOfListener = namedListeners.indexOf(listener);
-          if (indexOfListener !== -1) {
-            namedListeners[indexOfListener] = null;
+          var index = arrayRemove(namedListeners, listener);
+          if (index >= 0) {
             decrementListenerCount(self, 1, name);
+            // We are removing a listener while iterating over the list of listeners.
+            // Update the current $$index if necessary to ensure no listener is skipped.
+            if (index <= namedListeners.$$index) {
+              namedListeners.$$index--;
+            }
           }
         };
       },
@@ -1213,9 +1217,7 @@ function $RootScopeProvider() {
        * @return {Object} Event object (see {@link ng.$rootScope.Scope#$on}).
        */
       $emit: function(name, args) {
-        var empty = [],
-            namedListeners,
-            scope = this,
+        var scope = this,
             stopPropagation = false,
             event = {
               name: name,
@@ -1226,28 +1228,11 @@ function $RootScopeProvider() {
               },
               defaultPrevented: false
             },
-            listenerArgs = concat([event], arguments, 1),
-            i, length;
+            listenerArgs = concat([event], arguments, 1);
 
         do {
-          namedListeners = scope.$$listeners[name] || empty;
-          event.currentScope = scope;
-          for (i = 0, length = namedListeners.length; i < length; i++) {
-
-            // if listeners were deregistered, defragment the array
-            if (!namedListeners[i]) {
-              namedListeners.splice(i, 1);
-              i--;
-              length--;
-              continue;
-            }
-            try {
-              //allow all listeners attached to the current scope to run
-              namedListeners[i].apply(null, listenerArgs);
-            } catch (e) {
-              $exceptionHandler(e);
-            }
-          }
+          invokeListeners(scope, event, listenerArgs, name);
+
           //if any listener on the current scope stops propagation, prevent bubbling
           if (stopPropagation) {
             event.currentScope = null;
@@ -1299,28 +1284,11 @@ function $RootScopeProvider() {
 
         if (!target.$$listenerCount[name]) return event;
 
-        var listenerArgs = concat([event], arguments, 1),
-            listeners, i, length;
+        var listenerArgs = concat([event], arguments, 1);
 
         //down while you can, then up and next sibling or up and next sibling until back at root
         while ((current = next)) {
-          event.currentScope = current;
-          listeners = current.$$listeners[name] || [];
-          for (i = 0, length = listeners.length; i < length; i++) {
-            // if listeners were deregistered, defragment the array
-            if (!listeners[i]) {
-              listeners.splice(i, 1);
-              i--;
-              length--;
-              continue;
-            }
-
-            try {
-              listeners[i].apply(null, listenerArgs);
-            } catch (e) {
-              $exceptionHandler(e);
-            }
-          }
+          invokeListeners(current, event, listenerArgs, name);
 
           // Insanity Warning: scope depth-first traversal
           // yes, this code is a bit crazy, but it works and we have tests to prove it!
@@ -1350,6 +1318,27 @@ function $RootScopeProvider() {
 
     return $rootScope;
 
+    function invokeListeners(scope, event, listenerArgs, name) {
+      var listeners = scope.$$listeners[name];
+      if (listeners) {
+        if (listeners.$$index !== -1) {
+          throw $rootScopeMinErr('inevt', '{0} already $emit/$broadcast-ing on scope ({1})', name, scope.$id);
+        }
+        event.currentScope = scope;
+        try {
+          for (listeners.$$index = 0; listeners.$$index < listeners.length; listeners.$$index++) {
+            try {
+              //allow all listeners attached to the current scope to run
+              listeners[listeners.$$index].apply(null, listenerArgs);
+            } catch (e) {
+              $exceptionHandler(e);
+            }
+          }
+        } finally {
+          listeners.$$index = -1;
+        }
+      }
+    }
 
     function beginPhase(phase) {
       if ($rootScope.$$phase) {

test/ng/rootScopeSpec.js

@@ -2316,6 +2316,19 @@ describe('Scope', function() {
         }));
 
 
+        // See issue https://github.com/angular/angular.js/issues/16135
+        it('should deallocate the listener array entry', inject(function($rootScope) {
+          var remove1 = $rootScope.$on('abc', noop);
+          $rootScope.$on('abc', noop);
+
+          expect($rootScope.$$listeners['abc'].length).toBe(2);
+
+          remove1();
+
+          expect($rootScope.$$listeners['abc'].length).toBe(1);
+        }));
+
+
         it('should call next listener after removing the current listener via its own handler', inject(function($rootScope) {
           var listener1 = jasmine.createSpy('listener1').and.callFake(function() { remove1(); });
           var remove1 = $rootScope.$on('abc', listener1);
@@ -2448,6 +2461,80 @@ describe('Scope', function() {
           expect($rootScope.$$listenerCount).toEqual({abc: 1});
           expect(child.$$listenerCount).toEqual({abc: 1});
         }));
+
+
+        it('should throw on recursive $broadcast', inject(function($rootScope) {
+          $rootScope.$on('e', function() { $rootScope.$broadcast('e'); });
+
+          expect(function() { $rootScope.$emit('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+          expect(function() { $rootScope.$broadcast('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+        }));
+
+
+        it('should throw on nested recursive $broadcast', inject(function($rootScope) {
+          $rootScope.$on('e2', function() { $rootScope.$broadcast('e'); });
+          $rootScope.$on('e', function() { $rootScope.$broadcast('e2'); });
+
+          expect(function() { $rootScope.$emit('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+          expect(function() { $rootScope.$broadcast('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+        }));
+
+
+        it('should throw on recursive $emit', inject(function($rootScope) {
+          $rootScope.$on('e', function() { $rootScope.$emit('e'); });
+
+          expect(function() { $rootScope.$emit('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+          expect(function() { $rootScope.$broadcast('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+        }));
+
+
+        it('should throw on nested recursive $emit', inject(function($rootScope) {
+          $rootScope.$on('e2', function() { $rootScope.$emit('e'); });
+          $rootScope.$on('e', function() { $rootScope.$emit('e2'); });
+
+          expect(function() { $rootScope.$emit('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+          expect(function() { $rootScope.$broadcast('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+        }));
+
+
+        it('should throw on recursive $broadcast on child listener', inject(function($rootScope) {
+          var child = $rootScope.$new();
+          child.$on('e', function() { $rootScope.$broadcast('e'); });
+
+          expect(function() { child.$emit('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (2)');
+          expect(function() { child.$broadcast('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (2)');
+        }));
+
+
+        it('should throw on nested recursive $broadcast on child listener', inject(function($rootScope) {
+          var child = $rootScope.$new();
+          child.$on('e2', function() { $rootScope.$broadcast('e'); });
+          child.$on('e', function() { $rootScope.$broadcast('e2'); });
+
+          expect(function() { child.$emit('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (2)');
+          expect(function() { child.$broadcast('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (2)');
+        }));
+
+
+        it('should throw on recursive $emit parent listener', inject(function($rootScope) {
+          var child = $rootScope.$new();
+          $rootScope.$on('e', function() { child.$emit('e'); });
+
+          expect(function() { child.$emit('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+          expect(function() { $rootScope.$emit('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+          expect(function() { $rootScope.$broadcast('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+        }));
+
+
+        it('should throw on nested recursive $emit parent listener', inject(function($rootScope) {
+          var child = $rootScope.$new();
+          $rootScope.$on('e2', function() { child.$emit('e'); });
+          $rootScope.$on('e', function() { child.$emit('e2'); });
+
+          expect(function() { child.$emit('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+          expect(function() { $rootScope.$emit('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+          expect(function() { $rootScope.$broadcast('e', 5); }).toThrowMinErr('$rootScope', 'inevt', 'e already $emit/$broadcast-ing on scope (1)');
+        }));
       });
     });
 
@@ -2537,7 +2624,7 @@ describe('Scope', function() {
         expect(spy1).toHaveBeenCalledOnce();
         expect(spy2).toHaveBeenCalledOnce();
         expect(spy3).toHaveBeenCalledOnce();
-        expect(child.$$listeners['evt'].length).toBe(3); // cleanup will happen on next $emit
+        expect(child.$$listeners['evt'].length).toBe(2);
 
         spy1.calls.reset();
         spy2.calls.reset();
@@ -2571,7 +2658,7 @@ describe('Scope', function() {
         expect(spy1).toHaveBeenCalledOnce();
         expect(spy2).toHaveBeenCalledOnce();
         expect(spy3).toHaveBeenCalledOnce();
-        expect(child.$$listeners['evt'].length).toBe(3); //cleanup will happen on next $broadcast
+        expect(child.$$listeners['evt'].length).toBe(2);
 
         spy1.calls.reset();
         spy2.calls.reset();