Ruby-Nix: Generates reproducible Ruby/bundler app environment with Nix

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 rubyNix that is suitable for local development (eg. Rails).

Features

1. supports local, path-based gems
2. supports pre-compiled native gems on multiple platforms (see this discussion)
3. bundix and bundler out of the box
4. Two starter templates based on flakes

How is it different from bundlerEnv?

1. it does not track the entire directory as inputSrc when gemDir is specified, requiring only the 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; };
    rubyNix = ruby-nix.lib pkgs;

    inherit (rubyNix {
        name = "simple-ruby-app";
        gemset = ./gemset.nix;
        # run `bundle platform` to find your platform
        gemPlatforms = [ "ruby" "arm64-darwin-20" "x86_64-linux" ];
    }) env envMinimal; 
in
{
    devShells = rec {
        default = dev;
        dev = pkgs.mkShell {
            buildInputs = [ env ];
        };
    };
}

Usage

With nix installed and optionally direnv, you can run:

1. Initialize flake

cd myapp
nix flake init -t github:sagittaros/ruby-nix

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 2.2.0; then
  source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/2.2.0/direnvrc" "sha256-5EwyKnkJNQeXrRkYbwwRBcXbibosCJqyIUuz9Xq+LRc="
fi
use flake

3. In nix shell

Replace Gemfile and Gemfile.lock with your own and run generate-gemset. Otherwise, use relock-gems to generate both Gemfile.lock and gemset.nix.

Building a Docker image

nix flake init -t sagittaros/ruby-nix#docker-app
nix build
docker load < result
docker images

Screencast (WIP)

/tmp
▲ mkdir t1

/tmp
▲ cd t1

/tmp/t1
▲ nix flake init -t github:sagittaros/ruby-nix

wrote: /tmp/t1/gemset.nix
wrote: /tmp/t1/Gemfile
wrote: /tmp/t1/Gemfile.lock
wrote: /tmp/t1/flake.nix

/tmp/t1
▲ ls
flake.nix  Gemfile  Gemfile.lock  gemset.nix

/tmp/t1
▲ nix develop -c zsh
warning: creating lock file '/tmp/t1/flake.lock'
/tmp/t1
nix-shell ▲ irb
irb(main):001:0> require 'puma'
=> true
irb(main):002:0>

/tmp/t1 6s
nix-shell ▲ rails
Usage:
  rails new APP_PATH [options]

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 :)

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