[Nix-dev] per-project nix-shell for Ruby (Gemfile) projects?

[Linus Arver]

On Tue, May 12, 2015 at 11:03:58PM +0200, Rok Garbas wrote:
> hi linus,
> 
> you might find a "recent" thread on mailing list interesting.
> http://article.gmane.org/gmane.linux.distributions.nixos/15702

Hello Rok!

I did read that thread, but I can't really understand how to adapt it
for installing a single gem and making it available in the current
environment. The example in there is for building the sup mail reader; I
followed the instructions and packaged the 'minitest' gem, but even
though I install it with

    nix-env -i minitest

and see it in my 'nix-env -q' like this:

    minitest-5.6.1

the Ruby script I wrote that uses it cannot find it.

What I want to do is write a single Ruby file (which defines a Class or
Module) that depends on a particular gem. I need, e.g.,

    require 'foo'

    class Bar
    ...
    end

to work.

How do NixOS users go about this? On Arch Linux, I use Rbenv to download
various Ruby versions, and then use 'bundle install' in a project's root
folder containing the Gemfile to get all the gems installed for the
currently active Ruby version.

I realize that I can just do the same thing on Nix, but I get a feeling
that the current tooling allows us to use the Nix mechanisms to achieve
the same thing (and avoid, e.g., re-downloading Rails or activerecord
every single time we start a new Rails project).

Cheers,
Linus