FileUtils#fu_clean_components

# File tmp/rubies/ruby-3.2.0/lib/fileutils.rb, line 2539
def fu_clean_components(*comp)
  comp.shift while comp.first == "."
  return comp if comp.empty?
  clean = [comp.shift]
  path = File.join(*clean, "") # ending with File::SEPARATOR
  while c = comp.shift
    if c == ".." and clean.last != ".." and !(fu_have_symlink? && File.symlink?(path))
      clean.pop
      path.chomp!(%r((?<=\A|/)[^/]+/\z), "")
    else
      clean << c
      path << c << "/"
    end
  end
  clean
end