[HttpKernel] Dont implement ServiceSubscriberInterface on *SessionListener

src/Symfony/Bundle/FrameworkBundle/Resources/config/session.xml

@@ -53,8 +53,14 @@
 
         <service id="session_listener" class="Symfony\Component\HttpKernel\EventListener\SessionListener">
             <tag name="kernel.event_subscriber" />
-            <tag name="container.service_subscriber" id="session" />
+            <argument type="service">
-            <argument type="service" id="container" />
+                <service class="Symfony\Component\DependencyInjection\ServiceLocator">
+                    <tag name="container.service_locator" />
+                    <argument type="collection">
+                        <argument key="session" type="service" id="session" on-invalid="ignore" />
+                    </argument>
+                </service>
+            </argument>
         </service>
 
         <service id="session.save_listener" class="Symfony\Component\HttpKernel\EventListener\SaveSessionListener">

src/Symfony/Bundle/FrameworkBundle/Resources/config/test.xml

@@ -22,8 +22,14 @@
 
         <service id="test.session.listener" class="Symfony\Component\HttpKernel\EventListener\TestSessionListener">
             <tag name="kernel.event_subscriber" />
-            <tag name="container.service_subscriber" id="session" />
+            <argument type="service">
-            <argument type="service" id="container" />
+                <service class="Symfony\Component\DependencyInjection\ServiceLocator">
+                    <tag name="container.service_locator" />
+                    <argument type="collection">
+                        <argument key="session" type="service" id="session" on-invalid="ignore" />
+                    </argument>
+                </service>
+            </argument>
         </service>
     </services>
 </container>

src/Symfony/Component/HttpKernel/EventListener/SessionListener.php

@@ -12,8 +12,6 @@
 namespace Symfony\Component\HttpKernel\EventListener;
 
 use Psr\Container\ContainerInterface;
-use Symfony\Component\DependencyInjection\ServiceSubscriberInterface;
-use Symfony\Component\HttpFoundation\Session\SessionInterface;
 
 /**
  * Sets the session in the request.
@@ -22,7 +20,7 @@ use Symfony\Component\HttpFoundation\Session\SessionInterface;
  *
  * @final since version 3.3
  */
-class SessionListener extends AbstractSessionListener implements ServiceSubscriberInterface
+class SessionListener extends AbstractSessionListener
 {
     private $container;
 
@@ -39,14 +37,4 @@ class SessionListener extends AbstractSessionListener implements ServiceSubscrib
 
         return $this->container->get('session');
     }
-
-    /**
-     * {@inheritdoc}
-     */
-    public static function getSubscribedServices()
-    {
-        return array(
-            'session' => '?'.SessionInterface::class,
-        );
-    }
 }

src/Symfony/Component/HttpKernel/EventListener/TestSessionListener.php

@@ -12,8 +12,6 @@
 namespace Symfony\Component\HttpKernel\EventListener;
 
 use Psr\Container\ContainerInterface;
-use Symfony\Component\DependencyInjection\ServiceSubscriberInterface;
-use Symfony\Component\HttpFoundation\Session\SessionInterface;
 
 /**
  * Sets the session in the request.
@@ -22,7 +20,7 @@ use Symfony\Component\HttpFoundation\Session\SessionInterface;
  *
  * @final since version 3.3
  */
-class TestSessionListener extends AbstractTestSessionListener implements ServiceSubscriberInterface
+class TestSessionListener extends AbstractTestSessionListener
 {
     private $container;
 
@@ -39,14 +37,4 @@ class TestSessionListener extends AbstractTestSessionListener implements Service
 
         return $this->container->get('session');
     }
-
-    /**
-     * {@inheritdoc}
-     */
-    public static function getSubscribedServices()
-    {
-        return array(
-            'session' => '?'.SessionInterface::class,
-        );
-    }
 }

src/Symfony/Component/HttpKernel/Tests/EventListener/TestSessionListenerTest.php

@@ -12,10 +12,13 @@
 namespace Symfony\Component\HttpKernel\Tests\EventListener;
 
 use PHPUnit\Framework\TestCase;
+use Symfony\Component\DependencyInjection\ServiceSubscriberInterface;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\HttpKernel\HttpKernelInterface;
 use Symfony\Component\HttpKernel\Event\FilterResponseEvent;
+use Symfony\Component\HttpKernel\EventListener\SessionListener;
+use Symfony\Component\HttpKernel\EventListener\TestSessionListener;
 use Symfony\Component\HttpFoundation\Session\SessionInterface;
 
 /**
@@ -79,6 +82,15 @@ class TestSessionListenerTest extends TestCase
         $this->filterResponse(new Request());
     }
 
+    public function testDoesNotImplementServiceSubscriberInterface()
+    {
+        $this->assertTrue(interface_exists(ServiceSubscriberInterface::class));
+        $this->assertTrue(class_exists(SessionListener::class));
+        $this->assertTrue(class_exists(TestSessionListener::class));
+        $this->assertFalse(is_subclass_of(SessionListener::class, ServiceSubscriberInterface::class), 'Implementing ServiceSubscriberInterface would create a dep on the DI component, which eg Silex cannot afford');
+        $this->assertFalse(is_subclass_of(TestSessionListener::class, ServiceSubscriberInterface::class, 'Implementing ServiceSubscriberInterface would create a dep on the DI component, which eg Silex cannot afford'));
+    }
+
     private function filterResponse(Request $request, $type = HttpKernelInterface::MASTER_REQUEST)
     {
         $request->setSession($this->session);