--- /dev/null
+<?php
+
+/*
+ * This file is part of Psy Shell.
+ *
+ * (c) 2012-2017 Justin Hileman
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Psy\CodeCleaner;
+
+use PhpParser\Node;
+use PhpParser\Node\Expr\Variable;
+use Psy\Exception\RuntimeException;
+
+/**
+ * Validate that the user input does not reference the `$__psysh__` variable.
+ */
+class LeavePsyshAlonePass extends CodeCleanerPass
+{
+ /**
+ * Validate that the user input does not reference the `$__psysh__` variable.
+ *
+ * @throws RuntimeException if the user is messing with $__psysh__
+ *
+ * @param Node $node
+ */
+ public function enterNode(Node $node)
+ {
+ if ($node instanceof Variable && $node->name === '__psysh__') {
+ throw new RuntimeException('Don\'t mess with $__psysh__. Bad things will happen.');
+ }
+ }
+}