--- /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\Empty_ as ExprEmpty;
+use PhpParser\Node\Expr\Variable;
+use Psy\Exception\ParseErrorException;
+
+/**
+ * Validate that the user did not call the language construct `empty()` on a
+ * statement in PHP < 5.5.
+ */
+class LegacyEmptyPass extends CodeCleanerPass
+{
+ /**
+ * Validate use of empty in PHP < 5.5.
+ *
+ * @throws ParseErrorException if the user used empty with anything but a variable
+ *
+ * @param Node $node
+ */
+ public function enterNode(Node $node)
+ {
+ if (version_compare(PHP_VERSION, '5.5', '>=')) {
+ return;
+ }
+
+ if (!$node instanceof ExprEmpty) {
+ return;
+ }
+
+ if (!$node->expr instanceof Variable) {
+ $msg = sprintf('syntax error, unexpected %s', $this->getUnexpectedThing($node->expr));
+
+ throw new ParseErrorException($msg, $node->expr->getLine());
+ }
+ }
+
+ private function getUnexpectedThing(Node $node)
+ {
+ switch ($node->getType()) {
+ case 'Scalar_String':
+ case 'Scalar_LNumber':
+ case 'Scalar_DNumber':
+ return json_encode($node->value);
+
+ case 'Expr_ConstFetch':
+ return (string) $node->name;
+
+ default:
+ return $node->getType();
+ }
+ }
+}