I have been using NixOS on my home machine and wanted to have a Rust development environment.

It's quite easy to get started I've found:

{ pkgs ? import <nixpkgs> {} }:
  pkgs.mkShell {
    # nativeBuildInputs is usually what you want -- tools you need to run
    nativeBuildInputs = with pkgs.buildPackages; [ 
        pkgs.cargo 
        pkgs.rustc
        pkgs.cargo-watch
    ];
}

Fun! I can then do cargo watch -x run.