Macro for Google Fonts links for use Tera (a templating engine written in Rust)

tera_macro_google_fonts.html

{% macro google_fonts(families) %}
    <link rel="preconnect" href="https://fonts.googleapis.com">
    <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
    {% set prefix = "https://fonts.googleapis.com/css2?" -%}
    {% set s = "" -%}
    {% for family in families -%}
        {% if loop.index0 > 0 -%}
            {% set_global s = s ~ "&" -%}
        {% endif -%}
        {% set_global s = s ~ "family=" ~ family -%}
    {% endfor -%}
    {% set href = prefix ~ s ~ "&display=swap" -%}
    <link href="{{ href | safe }}" rel="stylesheet">
{% endmacro input %}

tera_templating_gotchas.md

Gotchas

Here are some gotchmes and hopefully not gotchyous:

• Don't write loop.index > 0 as it will always be true; loop.index is 1-indexed. Above, I needed the 0-indexed version: loop.index0. ¹

• "If you want to assign a value in the global context while in a for loop, you must use set_global" ²

• Don't forget to use | safe with trusted strings. ³

• Underscores are ok in Tera macro names but hyphens are not. ⁴

Footnotes

1. Explained in https://keats.github.io/tera/docs/#for. ↩

2. Quoted from https://keats.github.io/tera/docs/#assignments except I changed the phrase "can use" to "must". ↩

3. From https://keats.github.io/tera/docs/#safe "Marks a variable as safe: HTML will not be escaped anymore. safe only works if it is the last filter of the expression" ↩

4. From https://github.com/Keats/tera/issues/913, valid characters are: a-zA-Z_0-9 but cannot start with 0-9 ↩