os/lib/recursive-merge.nix

{lib}: attrList: let
  f = attrPath:
    zipAttrsWith (
      n: values:
        if tail values == []
        then head values
        else if all isList values
        then unique (concatLists values)
        else if all isAttrs values
        then f (attrPath ++ [n]) values
        else last values
    );
in
  f [] attrList