Feature request: custom fonts

[thangleiter]

First off, thanks to everyone who worked on this project. I think it's high time the TeX stack has been rethought and tectonic looks very promising, especially in its V2/Tectonic.toml guise. Setting up my first not-very-simple project has been a bit of a bumpy road, though, partly because the docs are sometimes in the future, and partly because of what I now understand are constraints imposed by the "reproducibility" target, which is of course one reason why tectonic is so promising!

One of the major bumps I encountered was dealing with fonts. The style I used had various different fonts declared using fontspec, and compiled fine with XeLaTeX. Moving to tectonic, I first had to find all the precise font names (fine, using nextonic bundle search). However, one of the fonts (Liberation Mono) is not present in the bundle but XeLaTeX finds it because it's installed on my system.

Of course, this would not be reproducible across different systems, so my question is if it's possible to allow shipping fonts with the document. That is, I'd include a folder root/resources/fonts in my project directory and point to it from doc.extra_paths in Tectonic.toml, similar to my suggestion in #1166 for tectonic-biber. That would ensure reproducible builds while at the same time allowing users to "extend" what's included in the bundle.