{{ form_start(form, {
    'attr': {
        'id': 'form_show_utilisateur',
        'class': 'bg-white px-2 py-2 mb-3 form-ajax',
        'data-no-reset' :'no-reset',
        'data-js' : "$('.help-block').remove();$('.input-group.has-error').removeClass('has-error');",
    }
}) }}
<div class="my-custom-class-for-errors">
    {{ form_errors(form) }}
</div>
<div class="row mb-4">
    <div class="col-3">
        {{ form_row(form.prenom) }}
    </div>
    <div class="col-3">
        {{ form_row(form.nom,{'attr': {'class': ' text-uppercase'} }) }}
    </div>
    <div class="col-1">
        {{ form_row(form.initiales) }}
    </div>
    <div class="col-2">
        {{ form_row(form.login) }}
    </div>
    <div class="col-3">
        {{ form_row(form.type_utilisateur) }}
    </div>
</div>
<div class="row mb-4">
    <div class="col-2">
        {{ form_row(form.role) }}
    </div>
    <div class="col-2">
        {{ form_row(form.url_homepage) }}
    </div>
    <div class="col-auto js-site-target">
        {{ form_row(form.sites) }}
    </div>
</div>
<input type="hidden" name="id" value="{{ user.id }}">
{{ form_end(form) }}