anchor.diff:          inherit src;
           overrideSrc = drv: lib.overrideDerivation drv (orig: { inherit src; });
         };
  +
       updateScript = ''
         #!${runtimeShell}
         set -e
  
positive.code:         --modify-nix default.nix
      '';
    };
    meta = {
      description = "Utility to automate updating of nix derivation sources";
      maintainers = with lib.maintainers; [ timbertson ];
  
negative.code: { lib, pkgs, fetchFromGitHub, python3Packages, nix-prefetch-scripts, runtimeShell }:
  
  python3Packages.buildPythonApplication rec {
    pname = "nix-update-source";
    version = "0.6.3";
  
    src = fetchFromGitHub {
      owner = "timbertson";
      repo = "nix-update-source";
      rev = "version-${version}";
      sha256 = "157wvv9vnaszzwbj68jpdc0imcm1hdab3z760bx2axbsgfpqqilz";
    };
  
    propagatedBuildInputs = [ nix-prefetch-scripts ];
    passthru = {
      # NOTE: `fetch` should not be used within nixpkgs because it
  