Get the keys of a nested object in a flat data structure in nix

flatkeys.nix

let
  flatkeys = cur:
    if builtins.isAttrs cur then
      (builtins.concatMap
        (k: builtins.map (x: [ k ] ++ x) (flatkeys cur."${k}"))
        (builtins.attrNames cur))
    else if builtins.isList cur then
      builtins.concatLists (builtins.genList
        (i: builtins.map (x: [ i ] ++ x) (flatkeys (builtins.elemAt cur i)))
        (builtins.length cur))
    else
      [ [ ] ];
in
  flatkeys