bug symfony#24531 [HttpFoundation] Fix forward-compat of NativeSessionStorage with PHP 7.2 (sroze)

This PR was merged into the 2.7 branch.

Discussion
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[HttpFoundation] Fix forward-compat of NativeSessionStorage with PHP 7.2

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#24524
| License       | MIT
| Doc PR        | ø

PHP 7.2 disallow setting session options when the session was already started. This PR will not set any option if the session is already started and throw an exception if trying to do so with custom options.

Commits
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00a1357 [HttpFoundation] Fix forward-compat of NativeSessionStorage with PHP 7.2

Author: nicolas-grekas

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

@@ -102,6 +102,12 @@ class NativeSessionStorage implements SessionStorageInterface
      */
     public function __construct(array $options = array(), $handler = null, MetadataBag $metaBag = null)
     {
+        $this->setMetadataBag($metaBag);
+
+        if (\PHP_VERSION_ID >= 50400 && \PHP_SESSION_ACTIVE === session_status()) {
+            return;
+        }
+
         $options += array(
             // disable by default because it's managed by HeaderBag (if used)
             'cache_limiter' => '',
@@ -114,7 +120,6 @@ public function __construct(array $options = array(), $handler = null, MetadataB
             register_shutdown_function('session_write_close');
         }
 
-        $this->setMetadataBag($metaBag);
         $this->setOptions($options);
         $this->setSaveHandler($handler);
     }

src/Symfony/Component/HttpFoundation/Tests/Session/Storage/NativeSessionStorageTest.php

@@ -270,4 +270,30 @@ public function testRestart()
         $this->assertSame($id, $storage->getId(), 'Same session ID after restarting');
         $this->assertSame(7, $storage->getBag('attributes')->get('lucky'), 'Data still available');
     }
+
+    /**
+     * @requires PHP 5.4
+     */
+    public function testCanCreateNativeSessionStorageWhenSessionAlreadyStarted()
+    {
+        session_start();
+        $this->getStorage();
+
+        // Assert no exception has been thrown by `getStorage()`
+        $this->addToAssertionCount(1);
+    }
+
+    /**
+     * @requires PHP 5.4
+     */
+    public function testSetSessionOptionsOnceSessionStartedIsIgnored()
+    {
+        session_start();
+        $this->getStorage(array(
+            'name' => 'something-else',
+        ));
+
+        // Assert no exception has been thrown by `getStorage()`
+        $this->addToAssertionCount(1);
+    }
 }