Rule source on GitHub

DowngradeRecursiveDirectoryIteratorHasChildrenRector

Remove bool type hint on child of RecursiveDirectoryIterator hasChildren allowLinks parameter

 class RecursiveDirectoryIteratorChild extends \RecursiveDirectoryIterator
 {
-    public function hasChildren(bool $allowLinks = false): bool
+    public function hasChildren($allowLinks = false): bool
     {
         return true;
     }
 }

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp80\Rector\ClassMethod\DowngradeRecursiveDirectoryIteratorHasChildrenRector;

return RectorConfig::configure()
    ->withRules([
        DowngradeRecursiveDirectoryIteratorHasChildrenRector::class,
    ]);