Fix

Author: nicolas-grekas

Compiler/FactoryReturnTypePass.php

@@ -93,7 +93,7 @@ private function updateDefinition(ContainerBuilder $container, $id, Definition $
 
         $returnType = $m->getReturnType();
         if (null !== $returnType && !$returnType->isBuiltin()) {
-            $returnType = $returnType instanceof \ReflectionNamedType ? $returnType->getName() : $returnType->__toString();
+            $returnType = $returnType instanceof \ReflectionNamedType ? $returnType->getName() : (string) $returnType;
             if (null !== $class) {
                 $declaringClass = $m->getDeclaringClass()->getName();
                 if ('self' === strtolower($returnType)) {