In https://github.com/msys2/MSYS2-packages/issues/5568 it seems that rust 1.89.0 is capable of being built (I had been building rust nightly snapshots, but haven't been keeping track of their release process).
I am neither a Rust person nor a Cygwin packaging person, but now that llvm 20.1 is packaged it should be possible for someone to package rust for Cygwin, and then it might be possbile to use it to do things like build newer fish versions for Cygwin. If any Cygwin packager out there is excited to take this on, you can look at https://github.com/jeremyd2019/cygwin-rust-bootstrap/blob/rust-1.89/.github/workflows/bootstrap_rust.yml for the workflow I have to cross-build a rust toolchain from windows-gnu to pc-cygwin and then use that to build a pc-cygwin toolchain natively. I'd be happy to collaborate to get a cygport going, but this is really not my thing so I can't commit to be a maintainer of it going forward ;) (that's why this is not an ITP).
