avoid unnecessary files in wrapper-lib's source directory in the nix store

    inherit version;

  };

  # wraps `fopen()` for finding firmware files

  wrapperLibName = "wrapper-lib.so";

  wrapperLibSource = "wrapper-lib.c";

  # wraps `fopen()` for finding firmware files

  wrapperLib = stdenv.mkDerivation {

    pname = "${pname}-wrapper-lib";

    inherit version;

    src = ./.;

    src = builtins.path {

      name = "${pname}-source";

      path = ./.;

      filter = (path: type: baseNameOf path == wrapperLibSource);

    };

    postPatch = ''

      substitute wrapper-lib.c lib.c \

      substitute ${wrapperLibSource} lib.c \

        --subst-var-by to "${src}/var/lib/fprint/fw"

      cc -fPIC -shared lib.c -o ${wrapperLibName}

    '';