don't raise SystemExit in process_options

mypy/main.py

@@ -70,6 +70,10 @@ def main(script_path: Optional[str], args: Optional[List[str]] = None) -> None:
  fscache = FileSystemCache()
  sources, options = process_options(args, fscache=fscache)
 
+ if sources is None:
+ # indicates early out
+ sys.exit(0)
+
  messages = []
 
  def flush_errors(new_messages: List[str], serious: bool) -> None:
@@ -299,7 +303,7 @@ def process_options(args: List[str],
  fscache: Optional[FileSystemCache] = None,
  program: str = 'mypy',
  header: str = HEADER,
- ) -> Tuple[List[BuildSource], Options]:
+ ) -> Tuple[Optional[List[BuildSource]], Options]:
  """Parse command line arguments.
 
  If a FileSystemCache is passed in, and package_root options are given,
@@ -704,19 +708,19 @@ def add_invertible_flag(flag: str,
  # filename for the config file and know if the user requested all strict options.
  dummy = argparse.Namespace()
  parser.parse_args(args, dummy)
+ options = Options()
 
  if dummy.list_error_codes:
  import mypy.messages
  for msg_id in sorted(mypy.messages.MessageBuilder.get_message_ids()):
  print(msg_id)
- raise SystemExit(0)
+ return None, options
 
  config_file = dummy.config_file
  if config_file is not None and not os.path.exists(config_file):
  parser.error("Cannot find config file '%s'" % config_file)
 
  # Parse config file first, so command line can override.
- options = Options()
  parse_config_file(options, config_file)
 
  # Set strict flags before parsing (if strict mode enabled), so other command