module Rails::Generators::Actions

def add_source(source, options = {}, &block)

end
gem "rspec-rails"
add_source "http://gems.github.com/" do

add_source "http://gems.github.com/"

If block is given, gem entries in block are wrapped into the source group.

Add the given source to +Gemfile+ 
def add_source(source, options = {}, &block)
  log :source, source
  in_root do
    if block
      append_file_with_newline "Gemfile", "\nsource #{quote(source)} do", force: true
      with_indentation(&block)
      append_file_with_newline "Gemfile", "end", force: true
    else
      prepend_file "Gemfile", "source #{quote(source)}\n", verbose: false
    end
  end
end