[gcc r16-2094] libstdc++: Check prerequisite of extents::extents.

[Tomasz Kaminski via Libstdc++-cvs]

https://gcc.gnu.org/g:74ddf1792ae3538ee829f2c399dfcb75bfae8fd3

commit r16-2094-g74ddf1792ae3538ee829f2c399dfcb75bfae8fd3
Author: Luc Grosheintz <luc.groshei...@gmail.com>
Date:   Fri Jul 4 10:29:44 2025 +0200

    libstdc++: Check prerequisite of extents::extents.
    
    Previously the prerequisite of the extents ctors that
    
        static_extent(i) == dynamic_extent || extent(i) == other.extent(i).
    
    was not checked. This commit adds the __glibcxx_assert and test them.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/mdspan (extents): Check prerequisite of the ctor that
            static_extent(i) == dynamic_extent || extent(i) == other.extent(i).
            * testsuite/23_containers/mdspan/extents/class_mandates_neg.cc:
            Test the implemented prerequisite.
    
    Reviewed-by: Tomasz Kamiński <tkami...@redhat.com>
    Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>

Diff:
---
 libstdc++-v3/include/std/mdspan                    | 13 ++++++++
 .../mdspan/extents/class_mandates_neg.cc           |  2 ++
 .../mdspan/extents/extents_mismatch_neg.cc         | 35 ++++++++++++++++++++++
 3 files changed, 50 insertions(+)

diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index 1fdcae634419..d97fa22e4f03 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -110,10 +110,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
            return __se;
        }
 
+       template<size_t _OtherRank, typename _GetOtherExtent>
+         static constexpr bool
+         _S_is_compatible_extents(_GetOtherExtent __get_extent) noexcept
+         {
+           if constexpr (_OtherRank == _S_rank)
+             for (size_t __i = 0; __i < _S_rank; ++__i)
+               if (_Extents[__i] != dynamic_extent
+                   && !cmp_equal(_Extents[__i], 
_S_int_cast(__get_extent(__i))))
+                 return false;
+           return true;
+         }
+
        template<size_t _OtherRank, typename _GetOtherExtent>
          constexpr void
          _M_init_dynamic_extents(_GetOtherExtent __get_extent) noexcept
          {
+           
__glibcxx_assert(_S_is_compatible_extents<_OtherRank>(__get_extent));
            for (size_t __i = 0; __i < _S_rank_dynamic; ++__i)
              {
                size_t __di = __i;
diff --git 
a/libstdc++-v3/testsuite/23_containers/mdspan/extents/class_mandates_neg.cc 
b/libstdc++-v3/testsuite/23_containers/mdspan/extents/class_mandates_neg.cc
index f9c1c0196669..67d18feda96c 100644
--- a/libstdc++-v3/testsuite/23_containers/mdspan/extents/class_mandates_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/mdspan/extents/class_mandates_neg.cc
@@ -7,6 +7,8 @@ std::extents<uint8_t, size_t(1) << 9> e1; // { dg-error "from 
here" }
 std::extents<char, 1> e2;                 // { dg-error "from here" }
 std::extents<bool, 1> e3;                 // { dg-error "from here" }
 std::extents<double, 1> e4;               // { dg-error "from here" }
+
 // { dg-prune-output "dynamic or representable as IndexType" }
 // { dg-prune-output "signed or unsigned integer" }
 // { dg-prune-output "invalid use of incomplete type" }
+// { dg-prune-output "non-constant condition for static assertion" }
diff --git 
a/libstdc++-v3/testsuite/23_containers/mdspan/extents/extents_mismatch_neg.cc 
b/libstdc++-v3/testsuite/23_containers/mdspan/extents/extents_mismatch_neg.cc
new file mode 100644
index 000000000000..b35e5310d415
--- /dev/null
+++ 
b/libstdc++-v3/testsuite/23_containers/mdspan/extents/extents_mismatch_neg.cc
@@ -0,0 +1,35 @@
+// { dg-do compile { target c++23 } }
+#include<mdspan>
+
+#include <cstdint>
+
+constexpr size_t dyn = std::dynamic_extent;
+
+constexpr bool
+test_dyn2sta_extents_mismatch_00()
+{
+  auto e0 = std::extents<int, dyn>{1};
+  [[maybe_unused]] auto e1 = std::extents<int, 2>{e0};        // { dg-error 
"expansion of" }
+  return true;
+}
+static_assert(test_dyn2sta_extents_mismatch_00());            // { dg-error 
"expansion of" }
+
+constexpr bool
+test_dyn2sta_extents_mismatch_01()
+{
+  [[maybe_unused]] auto e = std::extents<int, 1, dyn>{2, 2}; // { dg-error 
"expansion of" }
+  return true;
+}
+static_assert(test_dyn2sta_extents_mismatch_01());           // { dg-error 
"expansion of" }
+
+constexpr bool
+test_dyn2sta_extents_mismatch_02()
+{
+  std::array<int, 2> exts{2, 2};
+  [[maybe_unused]] auto e = std::extents<int, 1, dyn>{exts}; // { dg-error 
"expansion of" }
+  return true;
+}
+static_assert(test_dyn2sta_extents_mismatch_02());           // { dg-error 
"expansion of" }
+
+// { dg-prune-output "non-constant condition for static assertion" }
+// { dg-prune-output "__glibcxx_assert" }