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