anchor.diff: -{ lib, fetchurl, fetchFromGitHub, callPackage
  +{ lib, fetchurl, callPackage
   , storeDir ? "/nix/store"
   , stateDir ? "/nix/var"
   , confDir ? "/etc"
  
positive.code:   });
  
    nixUnstable = lib.lowPrio (callPackage common rec {
      name = "nix-2.3${suffix}";
      suffix = "pre6895_84de821";
      src = fetchFromGitHub {
        owner = "NixOS";
        repo = "nix";
        rev = "84de8210040580ce7189332b43038d52c56a9689";
        sha256 = "062pdly0m2hk8ly8li5psvpbj1mi7m1a15k8wyzf79q7294l5li3";
      };
      fromGit = true;
  
      inherit storeDir stateDir confDir boehmgc;
    });
  
    nixFlakes = lib.lowPrio (callPackage common rec {
      name = "nix-2.4${suffix}";
      suffix = "pre20191022_9cac895";
      src = fetchFromGitHub {
        owner = "NixOS";
        repo = "nix";
        rev = "9cac895406724e0304dff140379783c4d786e855";
        hash = "sha256-Y1cdnCNoJmjqyC/a+Nt2N+5L3Ttg7K7zOD7gmtg1QzA=";
      };
      fromGit = true;
  
      inherit storeDir stateDir confDir boehmgc;
    });
  
negative.code:       version = lib.getVersion name;
  
        is20 = lib.versionAtLeast version "2.0pre";
        is24 = lib.versionAtLeast version "2.4pre";
  
        VERSION_SUFFIX = suffix;
  
        outputs = [ "out" "dev" "man" "doc" ];
  
        nativeBuildInputs =
          [ pkgconfig ]
          ++ lib.optionals (!is20) [ curl perl ]
          ++ lib.optionals is24 [ jq ];
  
        buildInputs = [ curl openssl sqlite xz bzip2 nlohmann_json ]
          ++ lib.optional (stdenv.isLinux || stdenv.isDarwin) libsodium
          ++ lib.optionals is20 [ brotli boost editline ]
          ++ lib.optionals is24 [ libarchive rustc cargo ]
          ++ lib.optional withLibseccomp libseccomp
          ++ lib.optional (withAWS && is20)
              ((aws-sdk-cpp.override {
  