anchor.diff:  
   let
     inherit (lib) optional optionals optionalString;
  -  features = optional sqliteSupport "sqlite"
  -    ++ optional postgresqlSupport "postgres"
  -    ++ optional mysqlSupport "mysql";
   in
   
   rustPlatform.buildRustPackage rec {
  
positive.code:     ++ optional sqliteSupport sqlite
      ++ optional postgresqlSupport postgresql
      ++ optionals mysqlSupport [ mariadb zlib ];
  
    checkPhase = ''
      runHook preCheck
  
negative.code:     sha256 = "sha256-mRdDc4fHMkwkszY+2l8z1RSNMEQnrWI5/Y0Y2W+guQE=";
    };
  
    cargoSha256 = "sha256-sQ762Ss31sA5qALHzwkvwbfRXo00cCtqzQyoz3/zf6I=";
  
    nativeBuildInputs = [ installShellFiles pkg-config ];
  