Fix unbound closure

Author: Girgias

Zend/tests/return_types/025_2.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Return type of self is allowed in closure but $this return value must be checked as closure might not be bound to a class
+--FILE--
+<?php
+
+$c = function(): self { return $this; };
+try {
+	var_dump($c());
+} catch (Throwable $e) {
+	echo $e::class, ': ', $e->getMessage(), PHP_EOL;
+}
+?>
+--EXPECT--
+Error: Using $this when not in object context

Zend/zend_compile.c

@@ -2672,6 +2672,11 @@ static bool zend_is_this_instance_of_name(const zend_string *type_name)
 
 static bool zend_is_this_valid_for_return_type(zend_type type)
 {
+	/* Closures can be bound to a class scope, however it might not and this must type error */
+	if (CG(active_op_array)->fn_flags & ZEND_ACC_CLOSURE) {
+		return false;
+	}
+
 	if (ZEND_TYPE_FULL_MASK(type) & (MAY_BE_OBJECT|MAY_BE_STATIC)) {
 		return true;
 	}