docs: def tcl_add_fileset_file(filename: str):
      """
      :param filename: relative filename with .vhdl or .v
  
      :return: add_fileset_file command string
      """
      if filename.endswith(".vhd"):
          t = "VHDL"
      elif filename.endswith(".v") or filename.endswith(".sv"):
          t = "VERILOG"
      else:
          raise NotImplementedError(
              "Can not resolve type of file by extension", filename)
      name = basename(filename)
  
      return "add_fileset_file %s %s PATH %s" % (name, t, filename)