The initial step used c2rust[1] tool for automated conversion of C to Rust, and automated refactoring of the resulting Rust code. You can see the original issue[2] in Tectonic about oxidation plans. And there is a bunch of issues[3] if you want to help the project.
[1] https://github.com/immunant/c2rust
[2] https://github.com/tectonic-typesetting/tectonic/issues/459
[3] https://github.com/crlf0710/tectonic/issues