Twig: Selecting certain blocks and rendering them

I am intergrating the twig templating engine into a PHP application. In particular, I would like to use the twig engine to render forms.

Having had a look at how symfony2 uses twig to render form widgets, they have a huge template file which contains all the widgets like so:

(...)
{% block password_widget %}
{% spaceless %}
    {% set type = type|default('password') %}
    {{ block('field_widget') }}
{% endspaceless %}
{% endblock password_widget %}

{% block hidden_widget %}
    {% set type = type|default('hidden') %}
    {{ block('field_widget') }}
{% endblock hidden_widget %}

{% block email_widget %}
{% spaceless %}
    {% set type = type|default('email') %}
    {{ block('field_widget') }}
{% endspaceless %}
{% endblock email_widget %}

{% block test_widget %}
{% spaceless %}
   <div>
     {{test}}
   <div>
{% endspaceless %}
{% endblock test_widget %}

(...)

The question I have is how can I “grab” blocks out of this template and render them?

So far, I am able to load the template, and call get blocks to get all the blocks:

twig = new Twig_Environment($loader, array('cache' => 'cache'));
$template = $twig->loadTemplate('viewform_div_layout.html.twig');
//var_dump($template->getBlocks()); //try getting all blocks
$template->displayBlock('test_widget', array('test' => 'test'));
echo $template->render();

Unfortunately, I am not able to render just the ‘test_widget’ block in this case. What should I do to retrieve the ‘test_widget’ block from the template and then insert it into a different template to render the whole form?

Answer

Turns out that one should use $template->renderBlock('blockname', array('test' => 'test')); instead. This will make twig render that block and then return a string containing the markup for that block. One can then use echo to display it or insert it into other templates.

Full example:

$loader = new Twig_Loader_Filesystem(array('/my-template-root'));
$twig = new Twig_Environment($loader, array('debug' => true));
$template = $twig->loadTemplate('viewform_div_layout.html.twig');
$result = $template->renderBlock('blockname', array('test' => 'test'));
echo $result;