This project doesn’t have that as a goal. In fact, it doesn’t even have “Rust to C compiler” as a goal. https://github.com/FractalFir/rustc_codegen_clr:

“ The project aims to provide a way to easily use Rust libraries in .NET. It comes with a Rust/.NET interop layer, which allows you to easily interact with .NET code from Rust

[…]

While .NET is the main focus of my work, this project can also be used to compile Rust to C, by setting the C_MODE enviroment flag to 1.

This may seem like a strange and unrelated feature, but the project was written in such a way that this is not only possible, but relatively easy.”

It also doesn’t mention for which version of C it produces code. That may or may not hinder attempts to use this to run rust on obscure platforms.

The README is slightly out of date, sorry. Supporting old platforms is one of the goals.

Truth be told, the support for C was at first added as a proff-of-concept that a Rust to C compiler is possible. But it worked surprisingly well, so I just decided to roll with it, and see where it takes me.

My policy in regards to C version is: I want to be as close to ANSI C as possible. So, I avoid modern C features as much as I can. I don't know if full compatibility is achievable, but I certainly hope so. Only time will tell.

Some simpler pieces of Rust work just fine with ANSI C compilers, but more complex code breaks(eg. due to unsupported intrinsics). If I will be able to solve that(+ some potential soundness issues) then I'll be able to use ANSI C.

The article mentions ANSI-C at places. So seems like the old c standard is targeted.

This is a fairly common technique in compiler construction and programming language research: Don't try to emit some machine code, instead emit C or an IR for clang or GCC. And suddenly your little research language (not that rust is one) is executable on many, many platforms, can rely on optimizations the compilers can do, has potential access to debug handling, ..

Vala [1] is, perhaps, the most prominent example of practically used programming language with such compiler.

[1] https://en.wikipedia.org/wiki/Vala_(programming_language)

Regarding the other way, I guess a lot of (practically) legal C wouldn't compile to Rust at all due to the language's restrictions and C's laxness, while I think all Rust could be translated to C.

Exactly. Btw rust toolchain is quite complicated while a code that was tanspiled to C might be as well compiled to e.g. 6052