Update to drupal 8.0.0-rc1. For more information, see https://www.drupal.org/node/2582663

vendor/symfony/http-foundation/Session/Attribute/AttributeBagInterface.php

@@ -0,0 +1,72 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\HttpFoundation\Session\Attribute;
+
+use Symfony\Component\HttpFoundation\Session\SessionBagInterface;
+
+/**
+ * Attributes store.
+ *
+ * @author Drak <drak@zikula.org>
+ */
+interface AttributeBagInterface extends SessionBagInterface
+{
+    /**
+     * Checks if an attribute is defined.
+     *
+     * @param string $name The attribute name
+     *
+     * @return bool true if the attribute is defined, false otherwise
+     */
+    public function has($name);
+
+    /**
+     * Returns an attribute.
+     *
+     * @param string $name    The attribute name
+     * @param mixed  $default The default value if not found
+     *
+     * @return mixed
+     */
+    public function get($name, $default = null);
+
+    /**
+     * Sets an attribute.
+     *
+     * @param string $name
+     * @param mixed  $value
+     */
+    public function set($name, $value);
+
+    /**
+     * Returns attributes.
+     *
+     * @return array Attributes
+     */
+    public function all();
+
+    /**
+     * Sets attributes.
+     *
+     * @param array $attributes Attributes
+     */
+    public function replace(array $attributes);
+
+    /**
+     * Removes an attribute.
+     *
+     * @param string $name
+     *
+     * @return mixed The removed value or null when it does not exist
+     */
+    public function remove($name);
+}