pkgs.mkShell is a special kind of derivation that is only useful when using it combined with nix-shell. It will in fact fail to instantiate when invoked with nix-build.

{} }: pkgs.mkShell { # this will make all the build inputs from hello and gnutar # available to the shell environment inputsFrom = with pkgs; [ hello gnutar ]; buildInputs = [ pkgs.gnumake ]; } ]]>