[SymfonyCache] Prevent event class from being cached by Symfony's class cache

Resources/doc/features/symfony-http-cache.rst

@@ -83,4 +83,22 @@ Each feature has its subscriber. Subscribers are provided by the FOSHttpCache_
 library. You can find the documentation for the subscribers in the
 :ref:`FOSHttpCache Symfony Cache documentation section <foshttpcache:symfony httpcache configuration>`.
 
+Prevent redeclaration error for Event class
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Under some circumstances this bundle loads a class which inherits from
+class ``Symfony\Component\EventDispatcher\Event`` in early cache lookup phase. This
+results in the following error message::
+
+    Fatal error: Cannot redeclare class Symfony\Component\EventDispatcher\Event in app/cache/dev/classes.php on line ...
+
+This error may occur if you have told the kernel to load class cache in your
+``app/console`` script, by adding something like ``$kernel->loadClassCache()``.
+To get around the error you can either stop using the class cache or adding this
+line to your ``app/console``::
+
+    class_exists('FOS\\HttpCache\\SymfonyCache\\CacheEvent');
+
+directly below the inclusion of ``bootstrap.php.cache``.
+
 .. _Symfony HttpCache documentation: http://symfony.com/doc/current/book/http_cache.html#symfony-reverse-proxy

SymfonyCache/EventDispatchingHttpCache.php

@@ -119,6 +119,12 @@ public function handle(Request $request, $type = HttpKernelInterface::MASTER_REQ
             }
         }
 
+        // load `CacheEvent` class and its parent classes to prevent Symfony
+        // from adding them to its class cache, what results in redeclaration
+        // error. For more background information consult
+        // https://github.com/FriendsOfSymfony/FOSHttpCacheBundle/issues/242
+        class_exists('FOS\\HttpCache\\SymfonyCache\\CacheEvent');
+
         return parent::handle($request, $type, $catch);
     }