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

vendor/symfony/validator/Constraints/Callback.php

@@ -0,0 +1,81 @@
+<?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\Validator\Constraints;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * @Annotation
+ * @Target({"CLASS", "PROPERTY", "METHOD", "ANNOTATION"})
+ *
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ *
+ * @api
+ */
+class Callback extends Constraint
+{
+    /**
+     * @var string|callable
+     *
+     * @since 2.4
+     */
+    public $callback;
+
+    /**
+     * @var array
+     *
+     * @deprecated since version 2.4, to be removed in 3.0.
+     */
+    public $methods;
+
+    /**
+     * {@inheritdoc}
+     */
+    public function __construct($options = null)
+    {
+        // Invocation through annotations with an array parameter only
+        if (is_array($options) && 1 === count($options) && isset($options['value'])) {
+            $options = $options['value'];
+        }
+
+        if (is_array($options) && isset($options['methods'])) {
+            @trigger_error('The "methods" option of the '.__CLASS__.' class is deprecated since version 2.4 and will be removed in 3.0. Use the "callback" option instead.', E_USER_DEPRECATED);
+        }
+
+        if (is_array($options) && !isset($options['callback']) && !isset($options['methods']) && !isset($options['groups'])) {
+            if (is_callable($options) || !$options) {
+                $options = array('callback' => $options);
+            } else {
+                // @deprecated, to be removed in 3.0
+                $options = array('methods' => $options);
+            }
+        }
+
+        parent::__construct($options);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getDefaultOption()
+    {
+        return 'callback';
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getTargets()
+    {
+        return array(self::CLASS_CONSTRAINT, self::PROPERTY_CONSTRAINT);
+    }
+}