Extension.php

<?php
namespace Pvr\PheelitBundle\Twig;

use Symfony\Component\DependencyInjection\ContainerInterface;
use eZ\Publish\Core\Repository\UserServiceInterface;

class PvrPheelitExtension extends \Twig_Extension
{
    private $container;
    private $service_user;

    public function __construct( ContainerInterface $container, UserServiceInterface $service_user )
    {
        $this->container = $container;
        $this->service_user = $service_user;
    }
    
    public function getFilters()
    {
        return array(
            'user_name' => new \Twig_Filter_Method($this, 'userNameFilter'),
            'displayImage' => new \Twig_Filter_Method($this, 'displayImage'),
        );
    }

    // pas de filter...
    public function userNameFilter($userId)
    {
        //$userService = $this->container->get('ezpublish.api.repository')->getUserService();
        $user = $service_user->loadUser( $userId );
        
        return $user->content->contentInfo->name;
    }

services.yml

services:
    Pheelit.twig_extension:
        class: %pheelit.twig_extension.class%
        arguments: [@service_container, @ezpublish.api.service.user]
        tags:
            - { name: twig.extension }