anchor.diff:  
         nativeBuildInputs = [ cmake ];
         # spdlog <1.3 uses a bundled version of fmt
  -      propagatedBuildInputs = lib.optional (lib.versionAtLeast version "1.3") fmt;
  +      propagatedBuildInputs = lib.optional (lib.versionAtLeast version "1.3") fmt_8;
   
         cmakeFlags = [
           "-DSPDLOG_BUILD_SHARED=${if stdenv.hostPlatform.isStatic then "OFF" else "ON"}"
  
positive.code: in
  {
    spdlog_1 = generic {
      version = "1.8.5";
      sha256 = "sha256-D29jvDZQhPscaOHlrzGN1s7/mXlcsovjbqYpXd7OM50=";
    };
  
    spdlog_0 = generic {
  
negative.code: { lib, stdenv, fetchFromGitHub, cmake, fmt_8 }:
  
  let
    generic = { version, sha256 }:
  