[PATCH] libstdc++: Implement LWG 3535 changes to ranges::join_view

[Patrick Palka via Gcc-patches]

Tested on x86_64-pc-linux-gnu, does this look OK for trunk, and branches
after a while?

libstdc++-v3/ChangeLog:

        * include/std/ranges (join_view::__iter_cat::_S_iter_cat): Adjust
        criteria for returning bidirectional_iterator_tag as per LWG3535.
        (join_view::_Iterator::_S_iter_concept): Likewise.
---
 libstdc++-v3/include/std/ranges | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 273699aa790..c1519c7dbd5 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -2523,7 +2523,8 @@ namespace views::__adaptor
            using _OuterCat = typename 
iterator_traits<_Outer_iter>::iterator_category;
            using _InnerCat = typename 
iterator_traits<_Inner_iter>::iterator_category;
            if constexpr (derived_from<_OuterCat, bidirectional_iterator_tag>
-                         && derived_from<_InnerCat, 
bidirectional_iterator_tag>)
+                         && derived_from<_InnerCat, bidirectional_iterator_tag>
+                         && common_range<range_reference_t<_Base<_Const>>>)
              return bidirectional_iterator_tag{};
            else if constexpr (derived_from<_OuterCat, forward_iterator_tag>
                               && derived_from<_InnerCat, forward_iterator_tag>)
@@ -2575,7 +2576,8 @@ namespace views::__adaptor
          {
            if constexpr (_S_ref_is_glvalue
                          && bidirectional_range<_Base>
-                         && bidirectional_range<range_reference_t<_Base>>)
+                         && bidirectional_range<range_reference_t<_Base>>
+                         && common_range<range_reference_t<_Base>>)
              return bidirectional_iterator_tag{};
            else if constexpr (_S_ref_is_glvalue
                               && forward_range<_Base>
-- 
2.33.1.711.g9d530dc002