Symfony form how to add class to form group - forms

Question

Using:
->add('name', TextType::class, [
'label' => 'Name',
'required' => true,
'attr' => [
'class' => 'myclass'
],
])
I'm adding the class "myclass" to the <input> element, getting:
<div class="form-group">
<label ...>Name</label>
<input type="text" required="required" class="myclass" ...>
</div>
What if I wanted to add the "myclass" class not to the input itself, but to its <div class="form-group"> container, in order to get:
<div class="form-group myclass">
<label ...>Name</label>
<input type="text" required="required" ...>
</div>
What's the best way to accomplish that?

Answer 1

I actually found a way of doing it in PHP (Symfony 4.4.2). Class has to go into 'row_attr' instead of 'attr'. For the given example it'd be:
->add('name', TextType::class, [
'label' => 'Name',
'required' => true,
'row_attr' => [
'class' => 'myclass'
],
])
related docs: https://symfony.com/doc/current/reference/forms/types/text.html#row-attr

Answer 2

In my case I needed to override the form_row block:
{% block form_row -%}
<div class="form-group myclass{% if (not compound or force_error|default(false)) and not valid %} has-error{% endif %}">
{{- form_label(form) -}}
{{- form_widget(form) -}}
{{- form_errors(form) -}}
</div>
{%- endblock form_row %}
as suggested, the docs helps to understand why.

Answer 3

As #Yoshi pointed out, in the form definition itself you cannot add classes to the container div.
The right way to customize form rendering is to override the base block via Twig as explained here: http://symfony.com/doc/current/cookbook/form/form_customization.html#how-to-customize-an-individual-field (BTW I suggest you to read carefully the whole article to know everything you need to know about customizations).
In the overridden block you have also the widget data if you want e.g. to add a class with the field id:
{% block _product_name_widget %}
<div class="text_widget {{ id }}">
{{ block('form_widget_simple') }}
</div>
{% endblock %}
in this example above, {{ id }} will be replaced with the widget (field) id.