message: keep `QueryState` private
diff: @@ -27,7 +27,7 @@ where
  /// Defines the "current state" of query's memoized results.
  #[derive(Debug)]
  -pub enum QueryState<V> {
  +enum QueryState<V> {
  /// We are currently computing the result of this query; if we see
  /// this value in the table, it indeeds a cycle.
  InProgress,
  