Question

Is there a good way to indicate incorrect use of Twig macro from inside a macro?

For example:

{% macro _name_to_size(input) %}{% spaceless %}

    {% set size %}
        {% if input == 'small' %}20{% endif %}
        {% if input == 'medium' %}40{% endif %}
        {% if input == 'large' %}60{% endif %}
    {% endset %}

    {% if not size|trim|length %}
        {# tell user that something is wrong #}
    {% endif %}

    {{ size }}

{% endspaceless %}{% endmacro %}

Edit:

Thank you for your answers. I have ended up with something like this (there is a chance you will not miss something like this in the browser):

{% macro error(message) %}
    {% set notification %}
        <div style="
            background-color: {{ background }} !important;
            display: block !important;
            height: 100% !important;
            left: 0 !important;
            overflow: none !important;
            position: fixed !important;
            top: 0 !important;
            width: 100% !important;
            z-index: 1000 !important;
        ">
            <div style="
                background-color: {{ foreground }} !important;
                color: white !important;
                display: block !important;
                font-size: 4em !important;
                line-height: 1.6em !important;
                left: 0 !important;
                position: relative !important;
                text-align: center !important;
                top: 32% !important;
                z-index: 1100 !important;
            ">{{ message }}</div>
        </div>
    {% endset %}
    {{ notification }}
    <script>
        var messageDiv = document.createElement("div");
        messageDiv.innerHTML = "{{ notification|e('js') }}";
        document.body.appendChild(messageDiv);
    </script>
{% endmacro %}

Answer 1

You can print an error message, but that’s the best you can do from template.

If you want a better alternative, write a twig extension which creates a function that does what you want your macro to do. You can throw exceptions there.