Render all flash messages in Twig

symfony_flash.md

{% for label, flashes in app.session.flashbag.all %}
    {% for flash in flashes %}
        <div class="alert alert-{{ label }}">
            {{ flash }}
        </div>
    {% endfor %}
{% endfor %}

source: http://www.lucas.courot.com/render-all-flash-messages-in-twig.html