Fix resolution of "parent" during inheritance check

We can't assume that the method we're checking against is part of
the parent class...

Author: nikic

Zend/tests/type_declarations/parent_is_not_proto.phpt

@@ -0,0 +1,17 @@
+--TEST--
+The parent class is not necessarily the class of the prototype
+--FILE--
+<?php
+
+class A {
+    function test(): B {}
+}
+class B extends A {}
+class C extends B {
+    function test(): parent {}
+}
+
+?>
+===DONE===
+--EXPECT--
+===DONE===

Zend/zend_inheritance.c

@@ -193,8 +193,8 @@ static int zend_do_perform_type_hint_check(const zend_function *fe, zend_arg_inf
 		fe_class_name = ZEND_TYPE_NAME(fe_arg_info->type);
 		class_name = ZSTR_VAL(fe_class_name);
 		class_name_len = ZSTR_LEN(fe_class_name);
-		if (class_name_len == sizeof("parent")-1 && !strcasecmp(class_name, "parent") && proto->common.scope) {
-			fe_class_name = zend_string_copy(proto->common.scope->name);
+		if (class_name_len == sizeof("parent")-1 && !strcasecmp(class_name, "parent") && fe->common.scope && fe->common.scope->parent) {
+			fe_class_name = zend_string_copy(fe->common.scope->parent->name);
 		} else if (class_name_len == sizeof("self")-1 && !strcasecmp(class_name, "self") && fe->common.scope) {
 			fe_class_name = zend_string_copy(fe->common.scope->name);
 		} else {