How to customize the data-prototype attribute in Symfony 2 forms

A bit old, but here is a deadly simple solution.

The idea is simply to render the collection items through a Twig template, so you have full ability to customize the prototype that will be placed in your data-prototype="..." tag. Just as if it was a normal, usual form.

In yourMainForm.html.twig:

<div id="collectionContainer"
     data-prototype="
         {% filter escape %}
             {{ include('MyBundle:MyViewsDirectory:prototype.html.twig', { 'form': form.myForm.vars.prototype }) }}
         {% endfilter %}">
</div>

And in MyBundle:MyViewsDirectory:prototype.html.twig:

<div>
    <!-- customize as you wish -->
    {{ form_label(form.field1) }}
    {{ form_widget(form.field1) }}
    {{ form_label(form.field2) }}
    {{ form_widget(form.field2) }}
</div>

Credit: adapted from https://gist.github.com/tobalgists/4032213