Tools like those exist. The problem with them is that they use unsafe blocks a lot, and the code usually isn't very idiomatic. Translating global variable state machines into more idiomatic Rust state machines based on things like named enums, for instance, would be very difficult.
With the help of powerful enough AI we might be able to get a tool like this, but as AI still very much sucks at actually doing what it's supposed to do, I don't think we're quite ready yet. I imagine you'd also need enough memory to keep the entire C and Rust code base inside of your context window, which would quickly require very expensive hardware once your code grows beyond a certain threshold. If you don't, you end up like many code assisting LLMs, generating code independently that's incompatible with itself.
Still, if you're looking to take a C project and extend it in Rust, or perhaps slowly rewrite it piece by piece, https://c2rust.com/ is ready for action.
With the help of powerful enough AI we might be able to get a tool like this, but as AI still very much sucks at actually doing what it's supposed to do, I don't think we're quite ready yet. I imagine you'd also need enough memory to keep the entire C and Rust code base inside of your context window, which would quickly require very expensive hardware once your code grows beyond a certain threshold. If you don't, you end up like many code assisting LLMs, generating code independently that's incompatible with itself.
Still, if you're looking to take a C project and extend it in Rust, or perhaps slowly rewrite it piece by piece, https://c2rust.com/ is ready for action.