Add gem_group support to generators

railties/guides/source/generators.textile

@@ -449,6 +449,15 @@ The above code will put the following line into +Gemfile+:
 gem "devise", :git => "git://github.com/plataformatec/devise", :branch => "master"
 </ruby>
 
+h4. +gem_group+
+
+Wraps gem entries inside a group:
+
+<ruby>
+gem_group :development, :test do
+  gem "rspec-rails"
+end
+</ruby>
 
 h4. +add_source+
 

railties/guides/source/rails_application_templates.textile

@@ -60,6 +60,18 @@ Please note that this will NOT install the gems for you and you will have to run
 bundle install
 </ruby>
 
+h4. gem_group(*names, &block)
+
+Wraps gem entries inside a group.
+
+For example, if you want to load +rspec-rails+ only in +development+ and +test+ group:
+
+<ruby>
+gem_group :development, :test do
+  gem "rspec-rails"
+end
+</ruby>
+
 h4. add_source(source, options = {})
 
 Adds the given source to the generated application's +Gemfile+.

railties/lib/rails/generators/actions.rb

@@ -68,7 +68,32 @@ def gem(*args)
         end
 
         in_root do
-          append_file "Gemfile", "gem #{parts.join(", ")}\n", :verbose => false
+          str = "gem #{parts.join(", ")}\n"
+          str = "  " + str if @in_group
+          append_file "Gemfile", str, :verbose => false
+        end
+      end
+
+      # Wraps gem entries inside a group.
+      #
+      # ==== Example
+      #
+      #   gem_group :development, :test do
+      #     gem "rspec-rails"
+      #   end
+      #
+      def gem_group(*names, &block)
+        name = names.map(&:inspect).join(", ")
+        log :gemfile, "group #{name}"
+
+        in_root do
+          append_file "Gemfile", "\ngroup #{name} do\n", :force => true
+
+          @in_group = true
+          instance_eval &block
+          @in_group = false
+
+          append_file "Gemfile", "end\n", :force => true
         end
       end
 

railties/test/generators/actions_test.rb

@@ -102,6 +102,20 @@ def test_gem_should_insert_on_separate_lines
     assert_file 'Gemfile', /gem "rspec-rails"$/
   end
 
+  def test_gem_group_should_wrap_gems_in_a_group
+    run_generator
+
+    action :gem_group, :development, :test do
+      gem 'rspec-rails'
+    end
+
+    action :gem_group, :test do
+      gem 'fakeweb'
+    end
+
+    assert_file 'Gemfile', /\ngroup :development, :test do\n  gem "rspec-rails"\nend\n\ngroup :test do\n  gem "fakeweb"\nend/
+  end
+
   def test_environment_should_include_data_in_environment_initializer_block
     run_generator
     autoload_paths = 'config.autoload_paths += %w["#{Rails.root}/app/extras"]'