[debugging] How to var_dump variables in twig templates?

View layer pattern where you only present what you have been given is fine and all, but how do you know what is available? Is there a "list all defined variables" functionality in TWIG? Is there a way to dump a variable?

The solution I found by searching for it was to define a function where I can use my existing php debug tools by injecting a function, but all references I have found to that includes these nice two lines of code, but nowhere is it specified where to place them. Going by the fact that they need a $loader variable defined, I tried /app/config/autoload.php but the $loader there was the wrong kind. Where do I place the php code for adding a twig function?

you can use dump function and print it like this

{{ dump(MyVar) }}

but there is one nice thing too, if you don't set any argument to dump function, it will print all variables are available, like

{{ dump() }}

As most good PHP programmers like to use XDebug to actually step through running code and watch variables change in real-time, using dump() feels like a step back to the bad old days.

That's why I made a Twig Debug extension and put it on Github.

https://github.com/delboy1978uk/twig-debug

composer require delboy1978uk/twig-debug

Then add the extension. If you aren't using Symfony, like this:

<?php

use Del\Twig\DebugExtension;

/** @var $twig Twig_Environment */
$twig->addExtension(new DebugExtension());

If you are, like this in your services YAML config:

twig_debugger:
    class: Del\Twig\DebugExtension
    tags:
        - { name: twig.extension }

Once registered, you can now do this anywhere in a twig template:

{{ breakpoint() }}

Now, you can use XDebug, execution will pause, and you can see all the properties of both the Context and the Environment.

Have fun! :-D

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.

Since Symfony >= 2.6, there is a nice VarDumper component, but it is not used by Twig's dump() function.

To overwrite it, we can create an extension:

In the following implementation, do not forget to replace namespaces.

Fuz/AppBundle/Resources/config/services.yml

parameters:
   # ...
   app.twig.debug_extension.class: Fuz\AppBundle\Twig\Extension\DebugExtension

services:
   # ...
   app.twig.debug_extension:
       class: %app.twig.debug_extension.class%
       arguments: []
       tags:
           - { name: twig.extension }

Fuz/AppBundle/Twig/Extension/DebugExtension.php

<?php

namespace Fuz\AppBundle\Twig\Extension;

class DebugExtension extends \Twig_Extension
{

    public function getFunctions()
    {
        return array (
              new \Twig_SimpleFunction('dump', array('Symfony\Component\VarDumper\VarDumper', 'dump')),
        );
    }

    public function getName()
    {
        return 'FuzAppBundle:Debug';
    }

}

The complete recipe here for quicker reference (note that all the steps are mandatory):

1) when instantiating Twig, pass the debug option

$twig = new Twig_Environment(
$loader, ['debug'=>true, 'cache'=>false, /*other options */]
);

2) add the debug extension

$twig->addExtension(new \Twig_Extension_Debug());

3) Use it like @Hazarapet Tunanyan pointed out

{{ dump(MyVar) }}

or

{{ dump() }}

or

{{ dump(MyObject.MyPropertyName) }}

You can edit

/vendor/twig/twig/lib/Twig/Extension/Debug.php

and change the var_dump() functions to \Doctrine\Common\Util\Debug::dump()

If you are using Twig in your application as a component you can do this:

$twig = new Twig_Environment($loader, array(
    'autoescape' => false
));

$twig->addFilter('var_dump', new Twig_Filter_Function('var_dump'));

Then in your templates:

{{ my_variable | var_dump }}

For debugging Twig templates you can use the debug statement.

There you can set the debug setting explicitely.

If you are using Twig as a standalone component here's some example of how to enable debugging as it's unlikely the dump(variable) function will work straight out of the box

Standalone

This was found on the link provided by icode4food

$twig = new Twig_Environment($loader, array(
    'debug' => true,
    // ...
));
$twig->addExtension(new Twig_Extension_Debug());

Silex

$app->register(new \Silex\Provider\TwigServiceProvider(), array(
    'debug' => true,
    'twig.path' => __DIR__.'/views'
));

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')) }}

Dump all custom variables:

<h1>Variables passed to the view:</h1>
{% for key, value in _context %}
    {% if key starts with '_' %}
    {% else %}
        <pre style="background: #eee">{{ key }}</pre>
        {{ dump(value) }}
    {% endif %}
{% endfor %}

You can use my plugin which will do that for you (an will nicely format the output):

Twig Dump Bar

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.

{{ dump() }} doesn't work for me. PHP chokes. Nesting level too deep I guess.

All you really need to debug Twig templates if you're using a debugger is an extension like this.

Then it's just a matter of setting a breakpoint and calling {{ inspect() }} wherever you need it. You get the same info as with {{ dump() }} but in your debugger.