Add Composer autoloading functions and PHPStan for testing

vendor/symfony/contracts/Cache/CallbackInterface.php

@@ -0,0 +1,30 @@
+<?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\Contracts\Cache;
+
+use Psr\Cache\CacheItemInterface;
+
+/**
+ * Computes and returns the cached value of an item.
+ *
+ * @author Nicolas Grekas <p@tchwork.com>
+ */
+interface CallbackInterface
+{
+    /**
+     * @param CacheItemInterface|ItemInterface $item  The item to compute the value for
+     * @param bool                             &$save Should be set to false when the value should not be saved in the pool
+     *
+     * @return mixed The computed value for the passed item
+     */
+    public function __invoke(CacheItemInterface $item, bool &$save);
+}