Symfony - Unable to register extension "AppBundle\Twig\Extension\FileExtension" as it is already registered

Question

When I try to implement custom Twig Extension in Symfony2-project, I get following error:

Unable to register extension "AppBundle\Twig\Extension\FileExtension" as it is already registered.

In my app/config/services.yml, I have following:

parameters:
    app.file.twig.extension.class: AppBundle\Twig\Extension\FileExtension

services:
    app.twig.file_extension:
        class: '%app.file.twig.extension.class%'
        tags:
            - { name: 'twig.extension' }

In AppBundle/Twig/Extensions/FileExtension, i have:

<?php

namespace AppBundle\Twig\Extension;

class FileExtension extends \Twig_Extension
{
    /**
     * Return the functions registered as twig extensions
     * 
     * @return array
     */
    public function getFunctions()
    {
        return array(
            new \Twig_SimpleFunction('file_exists', array($this, 'file_exists')),
        );
    }

    public function getName()
    {
        return 'app_file';
    }
}
?>

I tried to clear cache, but not working. Anybody ideas why Twig renders twice?

Answer 1

正如@Cerad所说，从 Symfony 3.3开始，twig扩展会自动加载，无需在默认services.yml.

根据官方文档：

如果你使用默认的 services.yml 配置，你就大功告成了！Symfony 会自动知道你的新服务并添加标签。