anchor.diff:    config = {
   
       system.activationScripts.checks.text = ''
  -      set +e
  -
         ${darwinChanges}
         ${buildUsers}
         ${nixPath}
  
positive.code:   '';
  
    buildUsers = optionalString config.services.nix-daemon.enable ''
      buildUser=$(dscl . -read /Groups/nixbld GroupMembership 2>&1 | awk '/^GroupMembership: / {print $2}')
      if [ -z $buildUser ]; then
          echo "[1;31merror: Using the nix-daemon requires build users, aborting activation[0m" >&2
          echo "Create the build users or disable the daemon:" >&2
  
negative.code:         echo "ok" >&2
          exit 0
        fi
      '';
  
    };
  