Don't substitute self/parent with anonymous class

Fixes phpGH-18373
Closes phpGH-19537

Author: iluuu1994

NEWS

@@ -25,6 +25,8 @@ PHP                                                                        NEWS
     operators" RFC, meaning that incrementing non-numeric strings is now
     deprecated. (Girgias).
   . Various closure binding issues are now deprecated. (alexandre-daubois)
+  . Fixed bug GH-18373 (Don't substitute self/parent with anonymous class).
+    (ilutov)
 
 - Filter:
   . Added support for configuring the URI parser for FILTER_VALIDATE_URL

Zend/tests/gh19304.phpt

@@ -15,4 +15,4 @@ try {
 
 ?>
 --EXPECT--
-Cannot assign int to property class@anonymous::$v of type class@anonymous
+Cannot assign int to property class@anonymous::$v of type self

Zend/zend_compile.c

@@ -7091,16 +7091,20 @@ static zend_type zend_compile_single_typename(zend_ast *ast)
 				ZEND_ASSERT(fetch_type == ZEND_FETCH_CLASS_SELF || fetch_type == ZEND_FETCH_CLASS_PARENT);
 
 				zend_ensure_valid_class_fetch_type(fetch_type);
+
+				bool substitute_self_parent = zend_is_scope_known()
+					&& !(CG(active_class_entry)->ce_flags & ZEND_ACC_ANON_CLASS);
+
 				if (fetch_type == ZEND_FETCH_CLASS_SELF) {
 					/* Scope might be unknown for unbound closures and traits */
-					if (zend_is_scope_known()) {
+					if (substitute_self_parent) {
 						class_name = CG(active_class_entry)->name;
 						ZEND_ASSERT(class_name && "must know class name when resolving self type at compile time");
 					}
 				} else {
 					ZEND_ASSERT(fetch_type == ZEND_FETCH_CLASS_PARENT);
 					/* Scope might be unknown for unbound closures and traits */
-					if (zend_is_scope_known()) {
+					if (substitute_self_parent) {
 						class_name = CG(active_class_entry)->parent_name;
 						ZEND_ASSERT(class_name && "must know class name when resolving parent type at compile time");
 					}

ext/reflection/tests/gh18373.phpt

@@ -0,0 +1,14 @@
+--TEST--
+GH-18373: Don't substitute self/parent with anonymous class
+--FILE--
+<?php
+
+$o = new class() {
+    public function test(): self {}
+};
+
+echo (new ReflectionClass($o))->getMethod('test')->getReturnType()->getName(), "\n";
+
+?>
+--EXPECT--
+self