Ruby Nix

This is technically a fork of bundlerEnv that attempts to better meet the needs of ruby app developers instead of package maintainers.

This flake exports a function that is suitable for application development (eg. Rails).

Tl;dr

The gemset.nix file, generated by executing the bundix command, manages your environment. Bundix depends on the contents of Gemfile.lock, which is produced by running the bundle lock command after modifying the Gemfile.

Gemfile --[bundle lock]-->
Gemfile.lock --[bundix]-->
gemset.nix --[nix develop (actual build)]-->
reproducible ruby environment

Features

1. supports local, path-based gems
2. supports git sources
3. supports pre-compiled native gems on multiple platforms (see this discussion)
4. bundix out of the box
5. A starter template based on flake

How is it different from bundlerEnv?

1. it does not track the entire directory as inputSrc when gemDir is specified, requiring only gemset.nix.
2. it does not use BUNDLE_GEMFILE variable.
3. it works without Gemfile and Gemfile.lock.

The gist

      let
        pkgs = import nixpkgs {
          inherit system;
          overlays = [ ruby-nix.overlays.ruby ];
        };
        rubyNix = ruby-nix.lib pkgs;

        inherit (rubyNix {
          name = "simple-ruby-app";
          gemset = ./gemset.nix;
        })
          env ruby;
      in {
        devShells = rec {
          default = dev;
          dev = pkgs.mkShell { buildInputs = [ env ruby ]; };
        };
      });

Global Bundix Installation (optional)

My bundix fork is needed to generate the correct gemset.nix. It is available in nix shell out of the box.

# installation
nix profile install github:inscapist/bundix/main

# upgrade
nix profile upgrade '.*'

Usage

With nix installed and optionally direnv, you can run:

1. Initialize flake

cd myapp
nix flake init -t github:inscapist/ruby-nix/main

2. Enter nix shell

If you are a direnv user, add the following content to .envrc and run direnv allow. Otherwise, run nix develop -c zsh.

if ! has nix_direnv_version || ! nix_direnv_version 3.0.4; then
    source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/3.0.4/direnvrc" "sha256-DzlYZ33mWF/Gs8DDeyjr8mnVmQGx7ASYqA5WlxwvBG4="
fi

watch_file gemset.nix
use flake

Or use the latest version here. Don't forget to add watch_file /path_to/gemset.nix to ensure direnv picks up gem changes.

3. In nix shell

In a nix shell, you have ruby, irb, bundle at your disposal. Additional gems will only be available if they are specified in gemset.nix. To generate that, ensure Gemfile and Gemfile.lock are present, then run bundix.

FAQs

1. When does my environment gets build?

If you use direnv, running git add gemset.nix would trigger a rebuild automatically.

Otherwise, Ctrl-D to exit the current nix shell, and enter again.

2. How to bundle?

With ruby-nix, you shouldn't install gems using bundle. Nix will build the gems for you. Always run bundix to update your gemset after making changes to Gemfile.lock.. If you faced error with git fetch, set BUNDLE_PATH=vendor/bundle in your environment.

bundle add

run bundle add GEM --skip-install instead

bundle install (after modifying Gemfile)

run bundle lock instead

bundle update GEM

run bundle lock --update=GEM instead

Adding multiple platforms to Gemfile.lock

One example could be:

bundle lock --update --add-platform ruby arm64-darwin-21 x86_64-darwin-20 x86_64-linux

You can retrieve the platform names by running bundle platform. Having multiple platforms would allow your colleagues to use precompiled gems, if they are available.

In your Gemfile.lock, it should show up as:

   sorbet-runtime (0.5.10626)
    sorbet-static (0.5.10626-universal-darwin-20)
    sorbet-static (0.5.10626-universal-darwin-21)
    sorbet-static (0.5.10626-universal-darwin-22)
    sorbet-static (0.5.10626-x86_64-linux)
    sorbet-static-and-runtime (0.5.10626)
      sorbet (= 0.5.10626)
@@ -1232,6 +1233,7 @@ GEM
PLATFORMS
  arm64-darwin-20
  arm64-darwin-21
  arm64-darwin-22
  x86_64-darwin-20
  x86_64-darwin-21
  x86_64-linux

3. bundle lock fails with Permission denied when Gemfile contains git sources

You can either set this permanently at .bundle

bundle config set --local path 'vendor/bundle'

Or temporarily using:

export BUNDLE_PATH=vendor/bundle

4. How to use a different ruby version?

Code comment of simple-app shows how to use ruby_3_1 instead of the current default version (2.7.6). You can also write your own overlay that overrides globally with your own ruby derivation.

Common issues

I want to use a custom ruby version

Check the sample. @bobvanderlinden maintains it at the nixpkgs-ruby project.

Local bundle config overriding environment

Check your .bundle/config

Ruby or gems don't come from nix

Check that you have removed .rbenv or .rvm

Bundle install doesn't work

Check the previous section. You should only use bundler to lock your dependencies, not install them.

I don't like that nix develop is a bash shell

Use nix develop -c zsh or even better install .envrc, following this guide.

Roadmap

1. Try out more ruby versions, both old and new
2. Make bundix runs faster
3. More documentations

Credits

All credits goes to the original authors of buildRubyGem, bundlerEnv, and bundix (@manveru, @lavoiesl, @jdelStrother). This is only a thin layer with a different take on top of these solid foundation.

PRs welcomed :)