anchor.diff:          '';
         };
   
  +      checkConfig = mkOption {
  +        type = types.bool;
  +        default = true;
  +        description = ''
  +          If enabled (the default), checks that Nix can parse the generated nix.conf.
  +        '';
  +      };
       };
   
     };
  
positive.code:         ''}
          $extraOptions
          END
        '';
  
  in
  
  
negative.code:       sh = pkgs.runtimeShell;
        binshDeps = pkgs.writeReferencesToFile sh;
      in
        pkgs.runCommand "nix.conf" { extraOptions = cfg.extraOptions; } (''
          ${optionalString (!isNix20) ''
            extraPaths=$(for i in $(cat ${binshDeps}); do if test -d $i; then echo $i; fi; done)
          ''}
  