anchor.diff:  
       nativeBuildInputs =
         [ pkgconfig ]
  -      ++ lib.optionals (!is112) [ perl ]
  +      ++ lib.optionals (!is20) [ perl ]
         ++ lib.optionals fromGit [ autoreconfHook autoconf-archive bison flex libxml2 libxslt docbook5 docbook5_xsl ];
   
       buildInputs = [ curl openssl sqlite xz ]
         ++ lib.optional (stdenv.isLinux || stdenv.isDarwin) libsodium
         ++ lib.optionals fromGit [ brotli ] # Since 1.12
         ++ lib.optional stdenv.isLinux libseccomp
  -      ++ lib.optional ((stdenv.isLinux || stdenv.isDarwin) && is112)
  +      ++ lib.optional ((stdenv.isLinux || stdenv.isDarwin) && is20)
             (aws-sdk-cpp.override {
               apis = ["s3"];
               customMemoryManagement = false;
  
positive.code:   }) // { perl-bindings = nixStable; };
  
    nixUnstable = (lib.lowPrio (common rec {
      name = "nix-1.12${suffix}";
      suffix = "pre5873_b76e282d";
      src = fetchFromGitHub {
        owner = "NixOS";
        repo = "nix";
        rev = "b76e282da8824b679368370e43c994e588994a9a";
        sha256 = "11clfc8fh8q8s3k4canmn36xhh3zcl2zd8wwddp4pdvdal16b5n6";
      };
      fromGit = true;
    })) // { perl-bindings = perl-bindings { nix = nixUnstable; }; };
  
negative.code:     inherit name src;
      version = lib.getVersion name;
  
      is20 = lib.versionAtLeast version "2.0pre";
  
      VERSION_SUFFIX = lib.optionalString fromGit suffix;
  
  