$ nix-env -f default.nix -i dwm --show-trace
installing ‘dwm-6.1’
error: while evaluating the attribute ‘buildInputs’ of the derivation ‘dwm-6.1’ at /nix/store/3iz298whbyg9zpbpnllym4c0aafxlfps-nixos-17.09.3194.edf1079d43f/nixos/pkgs/stdenv/generic/make-derivation.nix:98:11:
while evaluating ‘chooseDevOutputs’ at /nix/store/3iz298whbyg9zpbpnllym4c0aafxlfps-nixos-17.09.3194.edf1079d43f/nixos/lib/attrsets.nix:460:22, called from undefined position:
undefined variable ‘libX11’ at /home/blob/default.nix:11:19