Symfony - Render bootstrap 4 input-group (append)

form_layout.html.twig

{% use "bootstrap_4_horizontal_layout.html.twig" %}

{# Override form_widget_simple block to render bootstrap input-groups #}
{% block form_widget_simple -%}
    {%- if input_addon is defined -%}
        {% set aria_describedby = 'addon-' ~ random() %}
        {%- set attr = attr|merge({'aria-describedby': aria_describedby}) -%}
        <div class="input-group">
    {%- endif -%}
            {{- parent() -}}
    {%- if input_addon is defined -%}
            <div class="input-group-append">
                <span class="input-group-text" id="{{ aria_describedby }}">{{ input_addon }}</span>
            </div>
        </div>
    {%- endif -%}
{%- endblock form_widget_simple %}

{# Example of using an input-group with «m²» addon for a specific form field #}
{% block _project_facadeArea_widget -%}
    {% set input_addon = 'm²' %}
    {{ block('form_widget_simple') }}
{%- endblock %}

Good point, thx!