EventSubscriberMethodReturnVoidRector

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Event subscriber methods hooked in getSubscribedEvents() must return void, as the event is passed by reference and returning it has no effect

 use Symfony\Component\EventDispatcher\EventSubscriberInterface;
 use Symfony\Contracts\EventDispatcher\Event;

 final class SomeEventSubscriber implements EventSubscriberInterface
 {
     public static function getSubscribedEvents(): array
     {
         return ['some_event' => 'onEvent'];
     }

-    public function onEvent(Event $event): Event
+    public function onEvent(Event $event): void
     {
-        return $event->setSomething('value');
+        $event->setSomething('value');
     }
 }

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\Symfony\CodeQuality\Rector\Class_\EventSubscriberMethodReturnVoidRector;

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

SETS: Code Quality