support the ruby version option

features/ruby_gemfile.feature

@@ -411,3 +411,14 @@ Feature: Gemfiles
       gem "one"
       """
 
+  Scenario: Pass through the Ruby version
+    Given I have the file "Gemfile.penchant" with the content:
+      """
+      ruby '1.9.3'
+      """
+    When I rebuild the Gemfile for "local" mode
+    Then the file "Gemfile" should have the following content:
+      """
+      # generated by penchant, environment: local
+      ruby "1.9.3"
+      """

lib/penchant/gemfile.rb

@@ -203,6 +203,10 @@ module Penchant
         end
       end
 
+      def ruby(version)
+        @output << %{ruby "#{version}"}
+      end
+
       protected
       def args_to_string(args)
         args.inspect[1..-2]
@@ -218,9 +222,9 @@ module Penchant
         [ args, template ]
       end
 
-      def call_and_indent_output(block)
+      def call_and_indent_output(block = nil, &given_block)
         index = @output.length
-        block.call
+        (block || given_block).call
         index.upto(@output.length - 1) do |i|
           @output[i] = "  " + @output[i]
         end