[PHP 8.0] Skip void type in union (#4835)

packages/phpstan-static-type-mapper/src/TypeMapper/UnionTypeMapper.php

@@ -230,6 +230,11 @@ final class UnionTypeMapper implements TypeMapperInterface
         $phpParserUnionedTypes = [];
 
         foreach ($unionType->getTypes() as $unionedType) {
+            // void type is not allowed in union
+            if ($unionedType instanceof VoidType) {
+                return null;
+            }
+
             /** @var Identifier|Name|null $phpParserNode */
             $phpParserNode = $this->phpStanStaticTypeMapper->mapToPhpParserNode($unionedType);
             if ($phpParserNode === null) {

rules/php80/tests/Rector/FunctionLike/UnionTypesRector/Fixture/skip_void.php.inc

@@ -0,0 +1,13 @@
+<?php
+
+namespace Rector\Php80\Tests\Rector\FunctionLike\UnionTypesRector\Fixture;
+
+class SkipVoid
+{
+    /**
+     * @return int|void
+     */
+    public function go()
+    {
+    }
+}