Fix GH-16317: DOM classes do not allow __debugInfo() overrides to work

ext/dom/php_dom.c

@@ -401,6 +401,7 @@ static int dom_property_exists(zend_object *object, zend_string *name, int check
 }
 /* }}} */
 
+/* This custom handler is necessary to avoid a recursive construction of the entire subtree. */
 static HashTable* dom_get_debug_info_helper(zend_object *object, int *is_temp) /* {{{ */
 {
 	dom_object			*obj = php_dom_obj_from_obj(object);
@@ -411,6 +412,11 @@ static HashTable* dom_get_debug_info_helper(zend_object *object, int *is_temp) /
 	dom_prop_handler	*entry;
 	zend_string         *object_str;
 
+	/* As we have a custom implementation, we must manually check for overrides. */
+	if (object->ce->__debugInfo) {
+		return zend_std_get_debug_info(object, is_temp);
+	}
+
 	*is_temp = 1;
 
 	std_props = zend_std_get_properties(object);

ext/dom/tests/gh16317.phpt

@@ -0,0 +1,20 @@
+--TEST--
+GH-16317 (DOM classes do not allow __debugInfo() overrides to work)
+--FILE--
+<?php
+
+class Demo extends DOMNode {
+    public function __construct() {}
+    public function __debugInfo(): array {
+        return ['x' => 'y'];
+    }
+}
+
+var_dump(new Demo());
+
+?>
+--EXPECT--
+object(Demo)#1 (1) {
+  ["x"]=>
+  string(1) "y"
+}