I was struggling to debug why I got a circular reference error trying to add my controller to a new application. The controller below with the config in routing.yml should be able to reproduce this. I found out that the error is triggered by a missing use statement: use Sensio\Bundle\FrameworkExtraBundle\Configuration\Template; as I used @Template(). I get the same error if the @Route use statement is missing.

This error is very unclear and should be able to get a better message.

FileLoaderImportCircularReferenceException in FileLoader.php line 97:
Circular reference detected in "/home/ivanderberg/projects/login/www/app/config/routing.yml" ("/home/ivanderberg/projects/login/www/app/config/routing.yml" > "/home/ivanderberg/projects/login/www/src/App/Controller" > "/home/ivanderberg/projects/login/www/app/config/routing.yml").

// routing.yml
app:
    resource: "@App/Controller"
    type:     annotation
    prefix:   /

<?php
namespace App\Controller\Auth;

use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;

/**
 * @Route(service="app.controller.auth.login")
 */
class LoginController
{
    /**
     * @Route("/", name="app.auth.login")
     * @Template()
     */
    public function loginAction()
    {
        return [];
    }
}