docs: def debug(s, *args):
      """debug(s, x1, ..., xn) logs s.format(x1, ..., xn)."""
      # Get the path name and line number of the function which called us.
      previous_frame = inspect.currentframe().f_back
      try:
          pathname, lineno, _, _, _ = inspect.getframeinfo(previous_frame)
          # if path is in cwd, simplify it
          cwd = os.path.abspath(os.getcwd())
          pathname = os.path.abspath(pathname)
          if os.path.commonprefix([cwd, pathname]) == cwd:
              pathname = os.path.relpath(pathname, cwd)
      except Exception:  # pylint: disable=broad-except
          pathname = '<UNKNOWN-FILE>.py'
          lineno = 0
      if _FORMATTER: # log could have not been initialized.
          _FORMATTER.pathname = pathname
          _FORMATTER.lineno = lineno
      logger = logging.getLogger(__package__)
      logger.debug(s.format(*args))