--- /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\Yield_;
+use PhpParser\Node\FunctionLike;
+use Psy\Exception\FatalErrorException;
+
+class FunctionContextPass extends CodeCleanerPass
+{
+ /** @var int */
+ private $functionDepth;
+
+ /**
+ * @param array $nodes
+ */
+ public function beforeTraverse(array $nodes)
+ {
+ $this->functionDepth = 0;
+ }
+
+ public function enterNode(Node $node)
+ {
+ if ($node instanceof FunctionLike) {
+ $this->functionDepth++;
+
+ return;
+ }
+
+ // node is inside function context
+ if ($this->functionDepth !== 0) {
+ return;
+ }
+
+ // It causes fatal error.
+ if ($node instanceof Yield_) {
+ $msg = 'The "yield" expression can only be used inside a function';
+ throw new FatalErrorException($msg, 0, E_ERROR, null, $node->getLine());
+ }
+ }
+
+ /**
+ * @param \PhpParser\Node $node
+ */
+ public function leaveNode(Node $node)
+ {
+ if ($node instanceof FunctionLike) {
+ $this->functionDepth--;
+ }
+ }
+}