lib/modules: short-circuit mergeDefinitions for plain singletons (#509195)

          else

            defsFiltered.values;

      in

      # Fast path: the overwhelming majority of options have exactly one

      # definition whose value carries no property wrapper

      # (mkIf/mkMerge/mkOverride/mkOrder/definition). In that case the

      # discharge/filter/sort pipeline above is a no-op but still allocates

      # several intermediate lists and closures. Detect it up front and hand

      # the original singleton straight to the type merge. The let-bindings

      # above are lazy and thus never forced on this branch.

      if

        length defs == 1

        && (

          let

            d = head defs;

          in

          addErrorContext "while evaluating definitions from `${d.file}':" (

            !(isAttrs d.value && d.value ? _type)

          )

        )

      then

        {

          values = defs;

          highestPrio = defaultOverridePriority;

        }

      else

        {

          values = defsSorted;

          inherit (defsFiltered) highestPrio;