scrub.nix

with import <nixpkgs> {};

let
  collectDeps = drv:
    (lib.collect (v: (lib.isDerivation v && v != drv))) drv;

  scrubDrv = f: drv: {
    name = drv.name;
    drv = drv;
    deps = map f (collectDeps drv.drvAttrs);
    meta = {
      maintainers = drv.meta.maintainers or [];
    };
  };
  scrub = lib.fix scrubDrv;

in { inherit collectDeps scrubDrv scrub; }

https://github.com/NixOS/nix/blob/master/corepkgs/derivation.nix is where drvAttrs comes from, btw.