adding test

Author: devnexen

Zend/tests/gh18519.phpt

@@ -0,0 +1,34 @@
+--TEST--
+GH-18519: Nested object comparison leading to stack overflow
+--FILE--
+<?php
+
+class Node {
+    public $next;
+    // forcing dynamic property creation is key
+}
+
+$first = new Node();
+$first->previous = $first;
+$first->next = $first;
+
+$cur = $first;
+
+for ($i = 0; $i < 50000; $i++) {
+    $new = new Node();
+    $new->previous = $cur;
+    $cur->next = $new;
+    $new->next = $first;
+    $first->previous = $new;
+    $cur = $new;
+}
+
+try {
+	// Force comparison manually to trigger zend_hash_compare
+	$first == $cur;
+} catch(Error $e) {
+	echo $e->getMessage(). PHP_EOL;
+}
+?>
+--EXPECT--
+Object compare - stack limit reached