How to var_dump variables in twig templates?

Question

As of Twig 1.5, the correct answer is to use the dump function. It is fully documented in the Twig documentation. Here is the documentation to enable this inside Symfony2.

{{ dump(user) }}

You can use the debug tag, which is documented here.

{% debug expression.varname %}

Edit: As of Twig 1.5, this has been deprecated and replaced with the new dump function (note, it's now a function and no longer a tag). See also: The accepted answer above.

If you are in an environment where you can't use the dump function (ex: opencart), you can try:

{{ my_variable | json_encode(constant('JSON_PRETTY_PRINT')) }}

So I got it working, partly a bit hackish:

1. Set twig: debug: 1 in app/config/config.yml

2. Add this to config_dev.yml

   services:
       debug.twig.extension:
           class: Twig_Extensions_Extension_Debug
           tags: [{ name: 'twig.extension' }]
   

3. sudo rm -fr app/cache/dev

4. To use my own debug function instead of print_r(), I opened vendor/twig-extensions/lib/Twig/Extensions/Node/Debug.php and changed print_r( to d(

PS. I would still like to know how/where to grab the $twig environment to add filters and extensions.