anchor.diff:  
         lib.addPassthru (derivation (
           (removeAttrs attrs ["meta" "passthru" "crossAttrs"])
  -        // (let
  -          buildInputs = attrs.buildInputs or [];
  -          nativeBuildInputs = attrs.nativeBuildInputs or [];
  -          propagatedBuildInputs = attrs.propagatedBuildInputs or [];
  -          propagatedNativeBuildInputs = attrs.propagatedNativeBuildInputs or [];
  -          crossConfig = attrs.crossConfig or null;
  -        in
  +        //
           {
             builder = attrs.realBuilder or shell;
             args = attrs.args or ["-e" (attrs.builder or ./default-builder.sh)];
  
positive.code:           nativeBuildInputs = nativeBuildInputs ++ (if crossConfig == null then buildInputs else []);
            propagatedNativeBuildInputs = propagatedNativeBuildInputs ++
              (if crossConfig == null then propagatedBuildInputs else []);
          }))) (
        {
          # The meta attribute is passed in the resulting attribute set,
          # but it's not part of the actual derivation, i.e., it's not
  
negative.code:         # include it in the result, it *is* available to nix-env for
          # queries.  We also a meta.position attribute here to
          # identify the source location of the package.
          meta = meta // (if pos != null then {
            position = pos.file + ":" + toString pos.line;
          } else {});
          inherit passthru;
        } //
        # Pass through extra attributes that are not inputs, but
        # should be made available to Nix expressions using the
        # derivation (e.g., in assertions).
        passthru);
  
    # The stdenv that we are producing.
    result =
  