How to Dump Debug Information in Twig Templates

When using PHP, you can use the dump() function from the VarDumper component if you need to quickly find the value of a variable passed. This is useful, for example, inside your controller:

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// src/AppBundle/Controller/ArticleController.php
namespace AppBundle\Controller;

// ...

class ArticleController extends Controller
{
    public function recentListAction()
    {
        $articles = ...;
        dump($articles);

        // ...
    }
}

In a Twig template, you can use the dump utility as a function or a tag:

• {% dump foo.bar %} is the way to go when the original template output shall not be modified: variables are not dumped inline, but in the web debug toolbar;
• on the contrary, {{ dump(foo.bar) }} dumps inline and thus may or not be suited to your use case (e.g. you shouldn't use it in an HTML attribute or a <script> tag).

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{# app/Resources/views/article/recent_list.html.twig #}
{# the contents of this variable are sent to the Web Debug Toolbar #}
{% dump articles %}

{% for article in articles %}
    {# the contents of this variable are displayed on the web page #}
    {{ dump(article) }}

    <a href="/article/{{ article.slug }}">
        {{ article.title }}
    </a>
{% endfor %}

By design, the dump() function is only available in the dev and test environments, to avoid leaking sensitive information in production. In fact, trying to use the dump() function in the prod environment will result in a PHP error.