It's the result of automated c2rust[1] conversion. Of course it will be cleaned up. C2rust itself provides handy refactoring tools scriptable in Lua language. A lot of the code will be removed, for example image handling can be done through image-rs crate, etc.
All that's fine, and good luck to you; I wish you well.
But I guess I wasn't clear. This project is described as a TeX engine “in Rust”. Has any code been actually written in Rust—as opposed to either Rust code that wraps C code (as in the main repo), or autogenerated Rust code (as in this one you linked)—for any of the core parts (as opposed to system-dependencies like I/O or whatever) of the TeX engine?
I'm genuinely curious, and if there is any such code I'd like to read it (and compare it to the equivalent WEB code).
I completely understand that this could be done at some future date. The question is about the description of the current state of the project. The impression from a statement like “Efforts to ditch any C remnants are being made” is that the C code is only a few “remnants”, when in fact it appears to be the entire TeX engine itself.
(Also, I do not foresee any refactoring tool being able to convert, for instance, “108” into “fi_or_else”, recovering information that's already lost. The point here is that it would have been better to start with the original WEB code, not the lossy and autogenerated C code.)
[1] https://github.com/immunant/c2rust