Dir.tmpdir

# File tmp/rubies/ruby-4.1.0-preview1/lib/tmpdir.rb, line 25
def self.tmpdir
  Tmpname::TMPDIR_CANDIDATES.find do |name, dir|
    unless dir
      next if !(dir = ENV[name] rescue next) or dir.empty?
    end
    dir = File.expand_path(dir)
    stat = File.stat(dir) rescue next
    case
    when !stat.directory?
      warn "#{name} is not a directory: #{dir}"
    when !File.writable?(dir)
      # We call File.writable?, not stat.writable?, because you can't tell if a dir is actually
      # writable just from stat; OS mechanisms other than user/group/world bits can affect this.
      warn "#{name} is not writable: #{dir}"
    when stat.world_writable? && !stat.sticky?
      warn "#{name} is world-writable: #{dir}"
    else
      break dir
    end
  end or raise ArgumentError, "could not find a temporary directory"
end