Ever tried to build a rust project and gotten an error because the openssl-sys build script doesn't find openssl, because there's no way for a project maintainer to instruct cargo to run rustc and build scripts inside the appropriate nix-shell invocation, so you have to figure that out for yourself?
No more! Just apply this one weird trick: Put your app into a subdirectory, add the nix attr paths to your Cargo.toml, and your users can just invoke cargo from inside this wrapper app! It will work, as if by magic!1
1 May require some modification of all the hardcoded bits. Also your crate better only has one binary at src/main.rs, no tests, etc.