required_location (Gem)

    # File lib/rubygems.rb, line 417
        def required_location(gemname, libfile, *version_constraints)
          version_constraints = Gem::Requirement.default if version_constraints.empty?
          matches = Gem.source_index.find_name(gemname, version_constraints)
          return nil if matches.empty?
          spec = matches.last
          spec.require_paths.each do |path|
            result = File.join(spec.full_gem_path, path, libfile)
            return result if File.exist?(result)
          end
          nil
        end