Adding docs for bundlerApp.

1 files changed, 24 insertions, 3 deletions

diff --git a/doc/languages-frameworks/ruby.xml b/doc/languages-frameworks/ruby.xml
index 3c6e4f5e01a4..6a14854b5c56 100644
--- a/doc/languages-frameworks/ruby.xml
+++ b/doc/languages-frameworks/ruby.xml
@@ -41,12 +41,34 @@ bundlerEnv rec {
 <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>Resulting derivations also have two helpful items, <literal>env</literal> and <literal>wrapper</literal>. The first one allows one to quickly drop into
+<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;
+  };
+}]]>
+
+<para>The chief advantage of <literal>bundlerApp</literal> over <literal>bundlerEnv</literal> is the 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 unpredicable versions available from various packages.
+
+<para>Resulting derivations for both builders also have two helpful items, <literal>env</literal> and <literal>wrapper</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> lile this:</para>
+run <command>bundix</command> as specified above and then use <literal>bundlerEnv</literal> like this:</para>
 
 <programlisting>
 <![CDATA[let env = bundlerEnv {
@@ -74,4 +96,3 @@ in stdenv.mkDerivation {
 </programlisting>
 
 </section>
-