modules/sshd: print the offending keys when we detect duplicate sshd keys.

    assertions = [{ assertion = if cfg.settings.X11Forwarding then cfgc.setXAuthLocation else true;

                    message = "cannot enable X11 forwarding without setting xauth location";}

                  { assertion = lib.lists.unique (map (x: lib.strings.toLower x) (attrNames cfg.settings))

                      == (map (x: lib.strings.toLower x) (attrNames cfg.settings));

                    message = "Duplicate sshd config key; does your capitalization match the option's?"; } ]

                  (let

                    duplicates =

                      # Filter out the groups with more than 1 element

                      lib.filter (l: lib.length l > 1) (

                        # Grab the groups, we don't care about the group identifiers

                        lib.attrValues (

                          # Group the settings that are the same in lower case

                          lib.groupBy lib.strings.toLower (attrNames cfg.settings)

                        )

                      );

                    formattedDuplicates = lib.concatMapStringsSep ", " (dupl: "(${lib.concatStringsSep ", " dupl})") duplicates;

                  in

                  {

                    assertion = lib.length duplicates == 0;

                    message = ''Duplicate sshd config key; does your capitalization match the option's? Duplicate keys: ${formattedDuplicates}'';

                  })]

      ++ forEach cfg.listenAddresses ({ addr, ... }: {

        assertion = addr != null;

        message = "addr must be specified in each listenAddresses entry";

      });

  };

}