Merge branch '4.2' into 4.3

* 4.2:
  [Lock] fix missing inherit docs in RedisStore
  fix accessing session bags
  Add missing rendering of form help block.

src/Symfony/Bridge/Twig/Resources/views/Form/bootstrap_3_layout.html.twig

@@ -114,6 +114,7 @@
     <div class="form-group{% if (not compound or force_error|default(false)) and not valid %} has-error{% endif %}">
         {{- form_label(form) }} {# -#}
         {{ form_widget(form, widget_attr) }} {# -#}
+        {{- form_help(form) -}}
         {{ form_errors(form) }} {# -#}
     </div> {# -#}
 {%- endblock form_row %}

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

@@ -253,7 +253,9 @@ class Session implements SessionInterface, \IteratorAggregate, \Countable
      */
     public function getBag($name)
     {
-        return $this->storage->getBag($name)->getBag();
+        $bag = $this->storage->getBag($name);
+
+        return method_exists($bag, 'getBag') ? $bag->getBag() : $bag;
     }
 
     /**

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

@@ -15,6 +15,7 @@ use PHPUnit\Framework\TestCase;
 use Symfony\Component\HttpFoundation\Session\Attribute\AttributeBag;
 use Symfony\Component\HttpFoundation\Session\Flash\FlashBag;
 use Symfony\Component\HttpFoundation\Session\Session;
+use Symfony\Component\HttpFoundation\Session\SessionBagProxy;
 use Symfony\Component\HttpFoundation\Session\Storage\MockArraySessionStorage;
 
 /**
@@ -260,4 +261,28 @@ class SessionTest extends TestCase
         $flash->get('hello');
         $this->assertTrue($this->session->isEmpty());
     }
+
+    public function testGetBagWithBagImplementingGetBag()
+    {
+        $bag = new AttributeBag();
+        $bag->setName('foo');
+
+        $storage = new MockArraySessionStorage();
+        $storage->registerBag($bag);
+
+        $this->assertSame($bag, (new Session($storage))->getBag('foo'));
+    }
+
+    public function testGetBagWithBagNotImplementingGetBag()
+    {
+        $data = [];
+
+        $bag = new AttributeBag();
+        $bag->setName('foo');
+
+        $storage = new MockArraySessionStorage();
+        $storage->registerBag(new SessionBagProxy($bag, $data, $usageIndex));
+
+        $this->assertSame($bag, (new Session($storage))->getBag('foo'));
+    }
 }

src/Symfony/Component/Lock/Store/RedisStore.php

@@ -71,6 +71,9 @@ class RedisStore implements StoreInterface
         $this->checkNotExpired($key);
     }
 
+    /**
+     * {@inheritdoc}
+     */
     public function waitAndSave(Key $key)
     {
         throw new InvalidArgumentException(sprintf('The store "%s" does not supports blocking locks.', \get_class($this)));