Rust with Nix on MacOS

flake.nix

{
  inputs.flake-utils.url = "github:numtide/flake-utils";

  outputs =
    { flake-utils, nixpkgs, ... }:
    flake-utils.lib.eachDefaultSystem (
      system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
      in
      with pkgs;
      {
        devShells.default = mkShell {
          buildInputs = [ rustup ];
          RUSTC_VERSION = lib.readFile ./rust-toolchain.toml;
          shellHook = ''
            export PATH=$PATH:''${CARGO_HOME:-~/.cargo}/bin
            export PATH=$PATH:''${RUSTUP_HOME:-~/.rustup}/toolchains/$RUSTC_VERSION-x86_64-apple-darwin/bin/
          '';
        };
      }
    );
}