failing test to reproduce session problem

src/Symfony/Bundle/FrameworkBundle/Tests/Functional/Bundle/TestBundle/Controller/SessionController.php

@@ -43,6 +43,14 @@ class SessionController implements ContainerAwareInterface
         return new Response(sprintf('Welcome back %s, nice to meet you.', $name));
     }
 
+    public function cacheableAction()
+    {
+        $response = new Response('all good');
+        $response->setSharedMaxAge(100);
+
+        return $response;
+    }
+
     public function logoutAction(Request $request)
     {
         $request->getSession()->invalidate();

src/Symfony/Bundle/FrameworkBundle/Tests/Functional/Bundle/TestBundle/Resources/config/routing.yml

@@ -2,6 +2,10 @@ session_welcome:
     path:     /session
     defaults: { _controller: TestBundle:Session:welcome }
 
+session_cacheable:
+    path:     /cacheable
+    defaults: { _controller: Symfony\Bundle\FrameworkBundle\Tests\Functional\Bundle\TestBundle\Controller\SessionController::cacheableAction }
+
 session_welcome_name:
     path:     /session/{name}
     defaults: { _controller: TestBundle:Session:welcome }

src/Symfony/Bundle/FrameworkBundle/Tests/Functional/SessionTest.php

@@ -126,6 +126,22 @@ class SessionTest extends WebTestCase
         $this->assertContains('Welcome back client2, nice to meet you.', $crawler2->text());
     }
 
+    /**
+     * @dataProvider getConfigs
+     */
+    public function testCorrectCacheControlHeadersForCacheableAction($config, $insulate)
+    {
+        $client = $this->createClient(array('test_case' => 'Session', 'root_config' => $config));
+        if ($insulate) {
+            $client->insulate();
+        }
+
+        $client->request('GET', '/cacheable');
+
+        $response = $client->getResponse();
+        $this->assertSame('public, s-maxage=100', $response->headers->get('cache-control'));
+    }
+
     public function getConfigs()
     {
         return array(

src/Symfony/Component/HttpFoundation/Session/Session.php

@@ -54,8 +54,6 @@ class Session implements SessionInterface, \IteratorAggregate, \Countable
      */
     public function start()
     {
-        ++$this->usageIndex;
-
         return $this->storage->start();
     }
 

src/Symfony/Component/HttpFoundation/Session/SessionBagProxy.php

@@ -44,6 +44,11 @@ final class SessionBagProxy implements SessionBagInterface
      */
     public function isEmpty()
     {
+        if (!isset($this->data[$this->bag->getStorageKey()])) {
+            return true;
+        }
+        ++$this->usageIndex;
+
         return empty($this->data[$this->bag->getStorageKey()]);
     }