bug symfony#18388 [EventDispatcher] check for method to exist (xabbuh)

This PR was merged into the 2.8 branch.

Discussion
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[EventDispatcher] check for method to exist

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#16301 (comment)
| License       | MIT
| Doc PR        |

This change must be reverted after being merged into the `3.0` branch (the `getListenerPriority()` method was added to the interface in Symfony 3.0).

Commits
-------

78ae2ad [EventDispatcher] check for method to exist

Author: fabpot

src/Symfony/Component/EventDispatcher/Debug/TraceableEventDispatcher.php

@@ -104,6 +104,10 @@ public function getListeners($eventName = null)
      */
     public function getListenerPriority($eventName, $listener)
     {
+        if (!method_exists($this->dispatcher, 'getListenerPriority')) {
+            return 0;
+        }
+
         return $this->dispatcher->getListenerPriority($eventName, $listener);
     }
 

src/Symfony/Component/EventDispatcher/Tests/Debug/TraceableEventDispatcherTest.php

@@ -73,6 +73,16 @@ public function testGetListenerPriority()
         $this->assertSame(123, $tdispatcher->getListenerPriority('foo', $listeners[0]));
     }
 
+    public function testGetListenerPriorityReturnsZeroWhenWrappedMethodDoesNotExist()
+    {
+        $dispatcher = $this->getMock('Symfony\Component\EventDispatcher\EventDispatcherInterface');
+        $traceableEventDispatcher = new TraceableEventDispatcher($dispatcher, new Stopwatch());
+        $traceableEventDispatcher->addListener('foo', function () {}, 123);
+        $listeners = $traceableEventDispatcher->getListeners('foo');
+
+        $this->assertSame(0, $traceableEventDispatcher->getListenerPriority('foo', $listeners[0]));
+    }
+
     public function testAddRemoveSubscriber()
     {
         $dispatcher = new EventDispatcher();