It's possible to use hieracles 0.4.3 directly by using a Nix Shell.
$ git clone https://github.com/Gandi/hieracles.git
$ cd hieracles
# Need to patch Gemfile to avoir a DEPRECATED warning
$ cat Gemfile
source 'https://rubygems.org'
gem 'hieracles'
# Bundler version will be updated
$ nix-shell -p bundler bundix --run 'bundle lock && bundix'
$ cat << EOF > shell.nix
with import <nixpkgs> {};
let
gems = pkgs.bundlerEnv {
name = "hieracles";
gemdir = ./.;
};
in mkShell { buildInputs = [ gems gems.wrappedRuby ]; }
EOF
$ nix-shell
... waiting to build ...
$ ./bin/hieracles -v
0.4.3