line.filename = guess_source(line.filename)

end
function guess_source(filename)
  local possible_source = filename:gsub('%.lua$', '%.splua')
  if file_exists(possible_source) then
    return possible_source
  else
    return filename
  end

  local candidate = guess_source(s..'.lua')
  source.switch_to_file(candidate)

  source.switch_to_file(s..'.lua')