anchor.diff:  
     nixUnstable = (lib.lowPrio (common rec {
       name = "nix-1.12${suffix}";
  -    suffix = "pre5152_915f62fa";
  +    suffix = "pre5308_2f21d522";
       src = fetchFromGitHub {
         owner = "NixOS";
         repo = "nix";
  -      rev = "915f62fa19790d8f826aeb4dd3d2bb5bde2f67e9";
  -      sha256 = "0mf7y7hvzw2x5dp482qy8774djr3vzcjaqq58cp82zdil8l7kwjd";
  +      rev = "2f21d522c28b1e902bd7f0b5b9e7523975102d81";
  +      sha256 = "1r3jxz0ydnlxp4b3ggxjgx1q9dv7jyfjm8w1srqjanzn944wnmi9";
       };
       fromGit = true;
     })) // { perl-bindings = perl-bindings { nix = nixUnstable; }; };
  
positive.code: { lib, stdenv, fetchurl, fetchFromGitHub, perl, curl, bzip2, sqlite, openssl ? null, xz
  , pkgconfig, boehmgc, perlPackages, libsodium, aws-sdk-cpp, brotli
  , autoreconfHook, autoconf-archive, bison, flex, libxml2, libxslt, docbook5, docbook5_xsl
  , storeDir ? "/nix/store"
  , stateDir ? "/nix/var"
  
negative.code: 
      buildInputs = [ curl openssl sqlite xz ]
        ++ lib.optional (stdenv.isLinux || stdenv.isDarwin) libsodium
        ++ lib.optionals fromGit [ brotli readline ] # Since 1.12
        ++ lib.optional ((stdenv.isLinux || stdenv.isDarwin) && lib.versionAtLeast version "1.12pre")
            (aws-sdk-cpp.override {
              apis = ["s3"];
  