Nix expression for finding derivations with missing licenses

missing_licenes.nix

with builtins;

let
   pkgs = import ./nixpkgs { overlays = []; };

   # clean evals
   cc1 = pkgs.lib.mapAttrs (n: v: (builtins.tryEval v).value ) pkgs;
   # Only top level derivations
   cc2 = pkgs.lib.filterAttrs (n: v: pkgs.lib.isDerivation v) cc1;
   # Filter for meta tags
   cc3 = pkgs.lib.filterAttrs (n: v: v ? "meta") cc2;

   noLic = with pkgs.lib; concatStringsSep "\n"
        (
          mapAttrsToList (name: v: "${v.meta.position}") (
            filterAttrs (n: v: (! hasAttr "license" v.meta) && (hasAttr "position" v.meta) ) cc3
          )
        );

in pkgs.runCommand "missing-licenses"
  {}
  ''
    mkdir $out

    cat << EOF > $out/unsorted
    ${noLic}
    EOF
    cat $out/unsorted  | sort | uniq > $out/unique
  ''