Gem::Package::TarWriter#mkdir

# File tmp/rubies/ruby-3.4.1/lib/rubygems/package/tar_writer.rb, line 287
def mkdir(name, mode)
  check_closed

  name, prefix = split_name(name)

  header = Gem::Package::TarHeader.new name: name, mode: mode,
                                       typeflag: "5", size: 0,
                                       prefix: prefix,
                                       mtime: Gem.source_date_epoch

  @io.write header

  self
end