class Gem::Commands::ContentsCommand

def files_in_gem spec
  gem_path  = spec.full_gem_path
  extra     = "/{#{spec.require_paths.join ','}}" if options[:lib_only]
  glob      = "#{gem_path}#{extra}/**/*"
  prefix_re = /#{Regexp.escape(gem_path)}\//
  Dir[glob].map do |file|
    [gem_path, file.sub(prefix_re, "")]
  end
end