Tectonic doesn't support woff2 format fonts
I'm using the current 0.15.0 package from the Nix store and a document fails with
error: Cannot proceed without the font: /nix/store/k090.....montserrat-9.000/share/fonts/woff2/Montserrat-LightItalic.woff2
Looking at the offending function causing the error, the checks directly prior to the abort https://github.com/tectonic-typesetting/tectonic/blob/09b1c14e89a8f2cf0c5b6d4bfb08fde07caa2725/crates/pdf_io/pdf_io/dpx-dvi.c#L1135-L1142 seem to hint at this function not expecting .woff2 paths to be passed to it?
The file does exist at the location.
Minimal example
\documentclass{article}
\usepackage{fontspec}
\setmainfont{Montserrat}
\begin{document}
Text
\end{document}
The version of XeTeX Tectonic uses as a backend doesn't support woff/woff2 font files. There are workarounds to make freetype not list them, so if other formats exist they will be used. If you need woff2 support specifically though, Tectonic can't do it currently.
Thanks, there are alternative .ttf fonts available, this fixed the problem.