nixpkgs/pkgs/development/tools/build-managers/rake/gemset.nix

{
  rake = {
    source = {
      remotes = ["https://rubygems.org"];
      sha256 = "01j8fc9bqjnrsxbppncai05h43315vmz9fwg28qdsgcjw9ck1d7n";
      type = "gem";
    };
    version = "12.0.0";
  };
}