Custom Symfony2 filter not triggering with custom twig tag

I suggest you to have a look to vendor/symfony/assetic-bundle/ files as it contains the {% javascripts %} implementation.

From that bundle's Resources/config/templating_twig.yml, they inject a service named @templating.name_parser, it looks like that's just what you are looking for.

You can have a try in a controller to do:

var_dump(  $this    ->get('templating.name_parser')    ->parse('@AcmeBundle/Resources/dart/AcmeMain/web/main.dart')    ->getPath());

About the tag itself, you can heavily copy/paste from the assetic bundle. And get some explanations about custom tags over one of my previous answers, here.

I think there is a very simple solution for your problem, that removes the need for a new {% darts %} tag.

In Assetic tags, you can specify an output argument, that allows you to override the default output path (which is js/*.js in case of the {% javascripts %} tag). By setting output to dart/*.dart, you not only change the directory where the files will be stored, but also the file extension.

Example:

{% javascripts '@AcmeBundle/Resources/dart/AcmeMain/web/main.dart' filter="MyCustomFilter" output='dart/*.dart' %}    <script type="application/dart" src="{{ asset_url }}"></script>{% endjavascripts %}

Will (in production environment) result in:

<script type="application/dart" src="/dart/0b13818.dart"></script>

This feature is described here in the Symfony documentation, although it does not mention the fact that you can change the extension.

I just ran a quick test in my Symfony application and it seems to be working perfectly.