Is it possible to use myst_substitutions or myst_url_schemes within a URL argument of a directive?

[matterhorn103]

Hi!

We're using Sphinx/MyST-Parser/MyST Markdown/Sphinx-Design.

Various external URLs used on our site need to automatically adapt to the current release version being changed in conf.py.

This is in general done using f-strings within myst_substitutions in conf.py. This works fine up until wanting to use it in some Sphinx-Design buttons that I am trying to make.

Previously a particular set of buttons were created within a Sphinx-Design card like so:

{{ '<a class="sd-sphinx-override sd-btn sd-text-wrap sd-btn-outline-primary reference external" href="' + winurl + '"><span>Download Installer</span></a>'}}

The resulting link works fine but the created button has awkward formatting and looks out of place next to the native Sphinx-Design ones, so I tried to turn them into proper buttons:

:::{button-link} {{winurl}}
:color: primary
:outline:
Download Installer
:::

but the substitution doesn't work.

I've scoured the web and tried myst_url_schemes as well as what feels like every possible syntax and nothing works. Why don't any of the syntaxes with ', {, <, ", `, do anything other than pass the literal characters in this situation? Is there any way with MyST-Parser to give a URL argument to a directive as anything other than a simple string?

Any help appreciated.