package gim-nix and document it

doc/language-support.xml

@@ -233,6 +233,17 @@ twisted = buildPythonPackage {
 </section>
 
 
+<section xml:id="ssec-language-java"><title>Ruby</title>
+  <para>For example, to package yajl-ruby package, use gem-nix:</para>
+  
+  <screen>
+    $ nix-env -i gem-nix
+    $ gem-nix --no-user-install --nix-file=pkgs/development/interpreters/ruby/generated.nix yajl-ruby
+    $ nix-build -A rubyLibs.yajl-ruby
+  </screen>
+</section>
+
+
 <section xml:id="ssec-language-java"><title>Java</title>
 
 <para>Ant-based Java packages are typically built from source as follows:

pkgs/development/interpreters/ruby/rubygems.nix

@@ -29,13 +29,7 @@ rec {
     longDescription = ''
       Nix can create nix packages from gems.
 
-      To use it do the following:
+      To use it by installing gem-nix package.
-      1. Install rubygems and rubyLibs.nix.
-      2. Add $your_profile/${ruby.gemPath} to GEM_PATH.
-      3. export RUBYLIB=$your_profile/lib RUBYOPT=rubygems.
-      4. Run `gem nix --[no-]user-install gem1 gem2 ...` to generate Nix
-      expression from gem repository.
-      5. Install rubyLibs.gem1 etc.
     '';
   };
 

pkgs/tools/package-management/gem-nix/default.nix

@@ -0,0 +1,23 @@
+{ stdenv, rubygems, rubyLibs, ruby, makeWrapper }:
+
+stdenv.mkDerivation rec {
+  name = "gem-nix";
+
+  buildInputs = [ ruby rubygems rubyLibs.nix makeWrapper ];
+
+  phases = ["installPhase"];
+
+  installPhase = ''
+    mkdir -p $out/bin
+    echo 'exec ${rubygems}/bin/gem nix "$@"' >> $out/bin/gem-nix
+    chmod +x $out/bin/gem-nix
+    wrapProgram $out/bin/gem-nix \
+      --set GEM_PATH $GEM_PATH
+  '';
+
+  meta = with stdenv.lib; {
+    description = "gem nix command in a nice wrapper";
+    platforms = platforms.linux;
+    maintainers = [ maintainers.iElectric ];
+  };
+}

pkgs/top-level/all-packages.nix

@@ -3087,6 +3087,8 @@ let
 
   fsharp = callPackage ../development/compilers/fsharp {};
 
+  gem-nix = callPackage ../tools/package-management/gem-nix { };
+
   go_1_0 = callPackage ../development/compilers/go { };
 
   go_1_1 =