<section xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xml:id="sec-language-ruby">

<title>Ruby</title>

<para>There currently is support to bundle applications that are packaged as
Ruby gems. The utility "bundix" allows you to write a
<filename>Gemfile</filename>, let bundler create a
<filename>Gemfile.lock</filename>, and then convert this into a nix
expression that contains all Gem dependencies automatically.
</para>

<para>For example, to package sensu, we did:</para>

<screen>
<![CDATA[$ cd pkgs/servers/monitoring
$ mkdir sensu
$ cd sensu
$ cat > Gemfile
source 'https://rubygems.org'
gem 'sensu'
$ $(nix-build '<nixpkgs>' -A bundix --no-out-link)/bin/bundix --magic
$ cat > default.nix
{ lib, bundlerEnv, ruby }:

bundlerEnv rec {
  name = "sensu-${version}";

  version = (import gemset).sensu.version;
  inherit ruby;
  # expects Gemfile, Gemfile.lock and gemset.nix in the same directory
  gemdir = ./.;

  meta = with lib; {
    description = "A monitoring framework that aims to be simple, malleable, and scalable";
    homepage    = http://sensuapp.org/;
    license     = with licenses; mit;
    maintainers = with maintainers; [ theuni ];
    platforms   = platforms.unix;
  };
}]]>
</screen>

<para>Please check in the <filename>Gemfile</filename>,
<filename>Gemfile.lock</filename> and the
<filename>gemset.nix</filename> so future updates can be run easily.
</para>

<para>For tools written in Ruby - i.e. where the desire is to install
a package and then execute e.g. <command>rake</command> at the command
line, there is an alternative builder called <literal>bundlerApp</literal>.
Set up the <filename>gemset.nix</filename> the same way, and then, for
example:
</para>

<screen>
<![CDATA[{ lib, bundlerApp }:

bundlerApp {
  pname = "corundum";
  gemdir = ./.;
  exes = [ "corundum-skel" ];

  meta = with lib; {
    description = "Tool and libraries for maintaining Ruby gems.";
    homepage    = https://github.com/nyarly/corundum;
    license     = licenses.mit;
    maintainers = [ maintainers.nyarly ];
    platforms   = platforms.unix;
  };
}]]>
</screen>

<para>The chief advantage of <literal>bundlerApp</literal> over
<literal>bundlerEnv</literal> is the executables introduced in the
environment are precisely those selected in the <literal>exes</literal>
list, as opposed to <literal>bundlerEnv</literal> which adds all the
executables made available by gems in the gemset, which can mean e.g.
<command>rspec</command> or <command>rake</command> in unpredictable
versions available from various packages.
</para>

<para>Resulting derivations for both builders also have two helpful
attributes, <literal>env</literal> and <literal>wrappedRuby</literal>.
The first one allows one to quickly drop into
<command>nix-shell</command> with the specified environment present.
E.g. <command>nix-shell -A sensu.env</command> would give you an
environment with Ruby preset so it has all the libraries necessary
for <literal>sensu</literal> in its paths. The second one can be
used to make derivations from custom Ruby scripts which have
<filename>Gemfile</filename>s with their dependencies specified. It is
a derivation with <command>ruby</command> wrapped so it can find all
the needed dependencies. For example, to make a derivation
<literal>my-script</literal> for a <filename>my-script.rb</filename>
(which should be placed in <filename>bin</filename>) you should run
<command>bundix</command> as specified above and then use
<literal>bundlerEnv</literal> like this:
</para>

<programlisting>
<![CDATA[let env = bundlerEnv {
  name = "my-script-env";

  inherit ruby;
  gemfile = ./Gemfile;
  lockfile = ./Gemfile.lock;
  gemset = ./gemset.nix;
};

in stdenv.mkDerivation {
  name = "my-script";
  buildInputs = [ env.wrappedRuby ];
  script = ./my-script.rb;
  buildCommand = ''
    install -D -m755 $script $out/bin/my-script
    patchShebangs $out/bin/my-script
  '';
}]]>
</programlisting>

</section>
