What's the "right" way to override a symfony extension from another bundle

Question

I need to override the file /vendor/symfony/symfony/src/Symfony/Bundle/TwigBundle/Extension/AssetsExtension.php

It loads the twig getAssetUrl from the bundle using the twig function 'asset'

/**
 * Returns a list of functions to add to the existing list.
 *
 * @return array An array of functions
 */
public function getFunctions()
{
    return array(
        new \Twig_SimpleFunction('asset', array($this, 'getAssetUrl')),
        new \Twig_SimpleFunction('assets_version', array($this, 'getAssetsVersion')),
    );
}

I want to override the asset() twig function without touching the core files, which otherwise would be overridden by the next symfony update

Answer 1

Consider that your code live in AppBundle namespace. First create service configuration in app/config.yml or src/AppBundle/Resources/config/something.yml (you have to load this configuration file in bundle extension). Don't forget place it under services key.

twig.extension.assets:
    class:     AppBundle\Twig\AssetsExtension
    arguments: ["@service_container", "@?router.request_context"]
    public: false
    tags:
        - { name: twig.extension }

Now let's create extension src/AppBundle/Twig/AssetsExtension.php. This class inherits from original extension and I will override just one method (in template asset()).

<?php

namespace AppBundle\Twig;

class AssetsExtension extends \Symfony\Bundle\TwigBundle\Extension\AssetsExtension
{
    public function getAssetUrl($path, $packageName = null, $absolute = false, $version = null)
    {
        return parent::getAssetUrl('/something/' . $path, $packageName, $absolute, $version);
    }
}

Now, after reload, all your assets should be incorrect and prefixed with /something/ by default. You can try to delete Symfony cache in case of problems. I tested this scenario on Symfony 2.5.5.

Another way how to work with built-in services is compiler pass. In compiler pass you can modified whole Symfony service container (delete, replace, modify services). Symfony is all about DIC. I hope it is good enough solution.