bug symfony#24774 [HttpKernel] Let the storage manage the session starts (sroze)

This PR was squashed before being merged into the 3.4 branch (closes symfony#24774).

Discussion
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[HttpKernel] Let the storage manage the session starts

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#24730
| License       | MIT
| Doc PR        | ø

HttpKernel's request collector should not really care if the session has started or not, be let the storage decide. Without the session, it is not possible to track the redirected pages.

I don't think the consideration of "we should not start the session if not needed by the user's code" applies here as if this is running, that is very likely that the user is running the dev environment anyway.

Commits
-------

95d0b72 [HttpKernel] Let the storage manage the session starts

Author: fabpot

src/Symfony/Component/HttpKernel/DataCollector/RequestDataCollector.php

@@ -131,7 +131,7 @@ public function collect(Request $request, Response $response, \Exception $except
             unset($this->controllers[$request]);
         }
 
-        if (null !== $session && $session->isStarted()) {
+        if (null !== $session) {
             if ($request->attributes->has('_redirected')) {
                 $this->data['redirect'] = $session->remove('sf_redirect');
             }
@@ -315,7 +315,7 @@ public function onKernelController(FilterControllerEvent $event)
 
     public function onKernelResponse(FilterResponseEvent $event)
     {
-        if (!$event->isMasterRequest() || !$event->getRequest()->hasSession() || !$event->getRequest()->getSession()->isStarted()) {
+        if (!$event->isMasterRequest() || !$event->getRequest()->hasSession()) {
             return;
         }
 

src/Symfony/Component/HttpKernel/Tests/DataCollector/RequestDataCollectorTest.php

@@ -17,7 +17,6 @@
 use Symfony\Component\HttpFoundation\Session\Session;
 use Symfony\Component\HttpFoundation\Session\Storage\MockArraySessionStorage;
 use Symfony\Component\HttpKernel\Controller\ArgumentResolverInterface;
-use Symfony\Component\HttpKernel\Event\FilterResponseEvent;
 use Symfony\Component\HttpKernel\HttpKernel;
 use Symfony\Component\HttpKernel\HttpKernelInterface;
 use Symfony\Component\HttpKernel\DataCollector\RequestDataCollector;
@@ -71,20 +70,6 @@ public function testCollectWithoutRouteParams()
         $this->assertEquals(array(), $c->getRouteParams());
     }
 
-    public function testKernelResponseDoesNotStartSession()
-    {
-        $kernel = $this->getMockBuilder(HttpKernelInterface::class)->getMock();
-        $request = new Request();
-        $session = new Session(new MockArraySessionStorage());
-        $request->setSession($session);
-        $response = new Response();
-
-        $c = new RequestDataCollector();
-        $c->onKernelResponse(new FilterResponseEvent($kernel, $request, HttpKernelInterface::MASTER_REQUEST, $response));
-
-        $this->assertFalse($session->isStarted());
-    }
-
     /**
      * @dataProvider provideControllerCallables
      */