class Bundler::Definition

def rubygems_index

spec, even if (say) a git gem is not checked out.
used when frozen is enabled so we can find the bundler 
def rubygems_index
  @rubygems_index ||= Index.build do |idx|
    sources.rubygems_sources.each do |rubygems|
      idx.add_source rubygems.specs
    end
  end
end