message: visiting an out-of-range variant index is UB
  Fixes
diff: @@ -306,6 +306,7 @@ namespace ranges
  template<typename Fun, typename Proj = indexed_element_fn>
  constexpr int variant_visit_(std::size_t, variant_nil, Fun, Proj = {})
  {
  + RANGES_EXPECT(false);
  return 0;
  }
  template<typename Data, typename Fun, typename Proj = indexed_element_fn>
  