Merge branch '3.3' into 3.4

* 3.3:
  [DI] Fix infinite loop in InlineServiceDefinitionsPass
  Do not cache cache attributes if `attributes` is in the context
  Test that it do not remove the new flashes when displaying the existing ones
  [HttpFoundation] AutExpireFlashBag should not clear new flashes
  [FrameworkBundle][Serializer] Remove YamlEncoder definition if Yaml component isn't installed
  [DI] Fix tracking of env vars in exceptions
  [Form] Don't rely on  if http-foundation isn't in FileType
  Fix merge
  substitute aliases in inline mappings
  added ability for substitute aliases when mapping in YAML is on single line
  [Console] Fix global console flag when used in chain

Author: xabbuh

Extension/Core/Type/FileType.php

@@ -92,9 +92,12 @@ public function finishView(FormView $view, FormInterface $form, array $options)
      */
     public function configureOptions(OptionsResolver $resolver)
     {
-        $dataClass = function (Options $options) {
-            return $options['multiple'] ? null : 'Symfony\Component\HttpFoundation\File\File';
-        };
+        $dataClass = null;
+        if (class_exists('Symfony\Component\HttpFoundation\File\File')) {
+            $dataClass = function (Options $options) {
+                return $options['multiple'] ? null : 'Symfony\Component\HttpFoundation\File\File';
+            };
+        }
 
         $emptyData = function (Options $options) {
             return $options['multiple'] ? array() : null;