rake: associated Gem is not exposed

[vincentbernat]

Describe the bug

I am trying to package a Ruby application. Inside its gemspec, it does:

require 'rake'

So, to build Gemfile.lock and gemset.nix, I am using this shell.nix:

with import <nixpkgs> {};
stdenv.mkDerivation {
  name = "env";
  buildInputs = [
    ruby.devEnv
    rake
    git
    bundix
  ];
}

However, when running bundle lock, it complains:

$ bundle lock
[!] There was an error parsing `Gemfile`:
[!] There was an error while loading `jerakia.gemspec`: cannot load such file -- rake
Does it try to require a relative path? That's been removed in Ruby 1.9. Bundler cannot continue.

 #  from /home/bernat/code/blade/jerakia/jerakia.gemspec:1
 #  -------------------------------------------
 >  require 'rake'
 #  require './lib/jerakia/version'
 #  -------------------------------------------
. Bundler cannot continue.

 #  from /home/bernat/code/blade/jerakia/Gemfile:3
 #  -------------------------------------------
 #
 >  gemspec
 #
 #  -------------------------------------------

Unlike bundix, rake doesn't expose its gem for build. Note that I am not very experienced with Nix. Maybe I am missing something obvious.

To Reproduce Steps to reproduce the behavior:

1. git clone git@github.com:jerakia/jerakia.git
2. cd jerakia
3. Use above shell.nix
4. nix-shell
5. bundle lock

Alternative:

1. nix-shell -p rake ruby

2. require 'rake'
   Traceback (most recent call last):
       6: from /nix/store/c1y1h2qw06sql1vlwxixkqk9fpw33a8s-ruby-2.6.5/bin/irb:23:in `<main>'
       5: from /nix/store/c1y1h2qw06sql1vlwxixkqk9fpw33a8s-ruby-2.6.5/bin/irb:23:in `load'
       4: from /nix/store/c1y1h2qw06sql1vlwxixkqk9fpw33a8s-ruby-2.6.5/lib/ruby/gems/2.6.0/gems/irb-1.0.0/exe/irb:11:in `<top (required)>'
       3: from (irb):1
       2: from /nix/store/c1y1h2qw06sql1vlwxixkqk9fpw33a8s-ruby-2.6.5/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:92:in `require'
       1: from /nix/store/c1y1h2qw06sql1vlwxixkqk9fpw33a8s-ruby-2.6.5/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:92:in `require'
   LoadError (cannot load such file -- rake)

Expected behavior require 'rack' should load the appropriate lib.

Metadata

• system: "x86_64-linux"
• host os: Linux 5.4.0-3-amd64, Debian GNU/Linux, noversion
• multi-user?: no
• sandbox: yes
• version: nix-env (Nix) 2.3.2
• channels(bernat): "nixpkgs-20.03pre210705.a6b6fe115ea"
• nixpkgs: /home/bernat/.nix-defexpr/channels/nixpkgs

Maintainer information:

attribute: [ rake ]
module:

cc @manveru @nicknovitski

[manveru]

The rake derivation is only useful for its executable when you want to execute a Rakefile. To get a Ruby that can find rake, use this:

nix-shell -p 'ruby.withPackages (p: [ p.rake ])' --run 'ruby -rrake -e "p Rake::VERSION"'

Or for use in nix-shell:

let
  pkgs = import (fetchTarball {
    url = https://github.com/nixos/nixpkgs-channels/archive/690dd986b2349d2c9cd6437e820954ed400f37f7.tar.gz;
    sha256 = "0p7amn7raw5rahyxw3jq21378n7i7ld4122hm5dddlbcvmpw60p0";
  }) {};
in pkgs.mkShell {
  buildInputs = [
    (pkgs.ruby.withPackages (p: [ p.rake ]))
  ];
}

The ruby.withPackages will wrap Ruby with the appropriate GEM_PATH from a large selection of gems:

[nix-shell:~]$ cat $(which ruby)
#! /nix/store/715fljdrspphbdk255r729zxp4w7lcgk-bash-4.4-p23/bin/bash -e
export GEM_PATH='/nix/store/vcm0inyl5y59168ah5g7wy8z5bcfm2rm-ruby-gems/lib/ruby/gems/2.6.0'
exec "/nix/store/nni62pjp1f43x06hdd8mbxzspx7nsdqx-ruby-2.6.5/bin/ruby"  "$@"

[vincentbernat]

Thanks for your input! I thought I had already tried to do that, but I've always left ruby.devEnv in buildInputs and in this case, this doesn't work. With nix-shell:

$ nix-shell -p ruby.devEnv 'ruby.withPackages (p: [ p.rake ])' --run 'ruby -rrake -e "p Rake::VERSION"'
Traceback (most recent call last):
        1: from /nix/store/c1y1h2qw06sql1vlwxixkqk9fpw33a8s-ruby-2.6.5/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:92:in `require'
/nix/store/c1y1h2qw06sql1vlwxixkqk9fpw33a8s-ruby-2.6.5/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:92:in `require': cannot load such file -- rake (LoadError)

How to install gems when using ruby.devEnv?

Thanks!

[manveru]

The two are mutually exclusive, the ruby.devEnv is meant to be used with bundlerEnv, which you'll need to combine with a gemset.nix generated from Bundix. You cannot have two ruby executables be used in your environment at the same time easily.

[vincentbernat]

In my case, the gemspec is requiring rake, so to be able to generate Gemfile.lock and gemset.nix, I need to have both a ruby with rake as a gem and ability to execute bundle and bundix.

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