module RuboCop::PathUtil

def relative_path(path, base_dir = PathUtil.pwd)
  # Optimization for the common case where path begins with the base
  # dir. Just cut off the first part.
  if path.start_with?(base_dir)
    base_dir_length = base_dir.length
    result_length = path.length - base_dir_length - 1
    return path[base_dir_length + 1, result_length]
  end
  path_name = Pathname.new(File.expand_path(path))
  begin
    path_name.relative_path_from(Pathname.new(base_dir)).to_s
  rescue ArgumentError
    path
  end
end