docs: def list_locations(self):
          """Print known dist-locations and exit.
          """
          known = self.defaults.get_known_locations()
          for default in self.defaults.distdefault:
              if default not in known:
                  known.add(default)
          if not known:
              err_exit('No locations', 0)
          for location in sorted(known):
              if location in self.defaults.distdefault:
                  print(location, '(default)')
              else:
                  print(location)
          sys.exit(0)