anchor.diff:                  [node]
                   nickname = ${settings.nickname}
                   tub.port = ${toString settings.tub.port}
  +                ${optionalString (settings.tub.location != null)
  +                  "tub.location = ${settings.tub.location}"}
                   # This is a Twisted endpoint. Twisted Web doesn't work on
                   # non-TCP. ~ C.
                   web.port = tcp:${toString settings.web.port}
  
positive.code:               The port on which the introducer will listen.
              '';
            };
            package = mkOption {
              default = pkgs.tahoelafs;
              defaultText = "pkgs.tahoelafs";
  
negative.code:                 [node]
                  nickname = ${settings.nickname}
                  tub.port = ${toString settings.tub.port}
                  ${optionalString (settings.tub.location != null)
                    "tub.location = ${settings.tub.location}"}
                '';
              });
            # Actually require Tahoe, so that we will have it installed.
  