bug #12848 [EventDispatcher] Fixed #12845 adding a listener to an event that is currently being dispatched (Pieter Jordaan)

This PR was merged into the 2.5 branch.

Discussion
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[EventDispatcher] Fixed #12845 adding a listener to an event that is currently being dispatched

[EventDispatcher] Fixed adding listener when event is currently being dispatched

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12845
| License       | MIT

Commits
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0cbc2b0 Fixed #12845 adding a listener to an event that is currently being dispatched will not result into a fatal error in TraceableEventDispatcher [EventDispatcher]

Author: fabpot

Tests/Debug/TraceableEventDispatcherTest.php

@@ -75,6 +75,24 @@ public function testStopwatchStopControllerOnRequestEvent()
         $kernel->handle($request);
     }
 
+    public function testAddListenerNested()
+    {
+        $called1 = false;
+        $called2 = false;
+        $dispatcher = new TraceableEventDispatcher(new EventDispatcher(), new Stopwatch());
+        $dispatcher->addListener('my-event', function () use ($dispatcher, &$called1, &$called2) {
+            $called1 = true;
+            $dispatcher->addListener('my-event', function () use (&$called2) {
+                $called2 = true;
+            });
+        });
+        $dispatcher->dispatch('my-event');
+        $this->assertTrue($called1);
+        $this->assertFalse($called2);
+        $dispatcher->dispatch('my-event');
+        $this->assertTrue($called2);
+    }
+
     protected function getHttpKernel($dispatcher, $controller)
     {
         $resolver = $this->getMock('Symfony\Component\HttpKernel\Controller\ControllerResolverInterface');