nixos/mandoc: use MANPATH environment variable

        default = [ "share/man" ];

        example = lib.literalExpression "[ \"share/man\" \"share/man/fr\" ]";

        description = lib.mdDoc ''

          Change the manpath, i. e. the directories where

          {manpage}`man(1)`

          Change the paths included in MANPATH environment variable,

          i. e. the directories where {manpage}`man(1)`

          looks for section-specific directories of man pages.

          You only need to change this setting if you want extra man pages

          (e. g. in non-english languages). All values must be strings that

          are a valid path from the target prefix (without including it).

          The first value given takes priority.

          The first value given takes priority. Note that this is not

          adding manpath in {manpage}`man.conf(5)`.

        '';

      };

          configuration options used for the package.

        '';

      };

      extraConfig = lib.mkOption {

        type = lib.types.lines;

        default = "";

        description = lib.mdDoc ''

          Configuration to write to {manpage}`man.conf(5)`.

        '';

      };

    };

  };

    environment = {

      systemPackages = [ cfg.package ];

      # tell mandoc about man pages

      etc."man.conf".text = lib.concatMapStrings (path: ''

        manpath /run/current-system/sw/${path}

      '') cfg.manPath;

      etc."man.conf".text = cfg.extraConfig;

      # create mandoc.db for whatis(1), apropos(1) and man(1) -k

      # TODO(@sternenseemman): fix symlinked directories not getting indexed,

          [[ -d "$man_path" ]] && ${makewhatis} -T utf8 $man_path

        done

      '';

      # tell mandoc the paths containing man pages

      profileRelativeSessionVariables."MANPATH" = map (path: "/${path}") cfg.manPath;

    };

  };

}