A Nix repository with all Ruby versions being kept up-to-date automatically.

Consider this an experiment to make all versions of a tool available in a separate Nixpkgs repo.

Open a shell with Ruby 2.7.x available:

$ nix shell github:bobvanderlinden/nixpkgs-ruby#'"ruby-2.7"'
$ ruby --version
ruby 2.7.7p221 (2022-11-24 revision 168ec2b1e5) [x86_64-linux]

Run Ruby 2.7.x interpreter directly:

$ nix shell github:bobvanderlinden/nixpkgs-ruby#'"ruby-2.7"' --command irb
irb(main):001:0> RUBY_VERSION
=> "2.7.7"

When you are in a Ruby project that uses .ruby-version and Bundle, you can use the following:

nix flake init --template github:bobvanderlinden/nixpkgs-ruby#

This creates flake.nix that includes a development shell with a Ruby version that it reads from .ruby-version.

To use the shell use:

nix develop

This opens a new shell where Ruby (and any other build inputs) are available.

To let Nix handle your gems run:

bundix

This creates gemset.nix based on your Gemfile.lock. You can now uncomment gems in buildInputs in flake.nix.

direnv is a convenient way to automatically load environments into your shell when entering a project directory.

To use this for nixpkgs-ruby, you'll need nix-direnv.

Once installed, you can do:

nix flake init --template github:bobvanderlinden/nixpkgs-ruby#
direnv allow

After that every time you enter your project directory, the correct Ruby version is automatically available.

When you want to use a specific Ruby version inside a Nix expression, you can use ruby-${version}.

{
  inputs = {
    nixpkgs-ruby.url = "github:bobvanderlinden/nixpkgs-ruby";
  };
  outputs = { self, nixpkgs-ruby }: {
    ...
    # You can now refer to packages like:
    #   nixpkgs-ruby.packages.x86_64-linux."ruby-3"
    #   nixpkgs-ruby.packages.x86_64-linux."ruby-2.7"
    #   nixpkgs-ruby.packages.x86_64-linux."ruby-3.0.1"
  };
}

It is also possible to use overlays so that the packages are available in pkgs alongside other packages from nixpkgs:

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-22.11";
    nixpkgs-ruby.url = "github:bobvanderlinden/nixpkgs-ruby";
  };
  outputs = { self, nixpkgs, nixpkgs-ruby }: let
    pkgs = import nixpkgs {
      system = "x86_64-linux";
      overlays = [
        nixpkgs-ruby.overlays.default
      ];
    };
  in {
    # You can now refer to packages like:
    #   pkgs."ruby-3"
    #   pkgs."ruby-2.7"
    #   pkgs."ruby-3.0.1"
  };
}

Note that when using overlays, the Ruby packages are built against the nixpkgs that you have specified. nixpkgs-ruby only tests against a single version of nixpkgs, so when building against a different nixpkgs it'll result in a different package hash compared to what nixpkgs-ruby builds and tests against.

You can also use nixpkgs-ruby in devenv.sh. First add nixpkgs-ruby to devenv.yaml:

inputs:
  nixpkgs:
    url: github:NixOS/nixpkgs/nixpkgs-unstable
  nixpkgs-ruby:
    url: github:bobvanderlinden/nixpkgs-ruby

Next, use a specific Ruby package in devenv.nix:

{ pkgs, nixpkgs-ruby, ... }:
{
  languages.ruby.enable = true;
  languages.ruby.package = nixpkgs-ruby.packages.${pkgs.system}."ruby-2.7";
}