[gcc r16-659] libstdc++: Fix class mandate for extents.

[Jonathan Wakely]

https://gcc.gnu.org/g:0babc6f29f7c29215674b3ee58d5dd17ce7b3849

commit r16-659-g0babc6f29f7c29215674b3ee58d5dd17ce7b3849
Author: Luc Grosheintz <luc.grosheintz@gmail.com>
Date:   Wed May 14 21:13:52 2025 +0200

    libstdc++: Fix class mandate for extents.
    
    The standard states that the IndexType must be a signed or unsigned
    integer. This mandate was implemented using `std::is_integral_v`. Which
    also includes (among others) char and bool, which neither signed nor
    unsigned integers.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/mdspan: Implement the mandate for extents as
            signed or unsigned integer and not any interal type. Remove
            leading underscores from names in static_assert message.
            * testsuite/23_containers/mdspan/extents/class_mandates_neg.cc:
            Check that extents<char,...> and extents<bool,...> are invalid.
            Adjust dg-prune-output pattern.
            * testsuite/23_containers/mdspan/extents/misc.cc: Update
            tests to avoid `char` and `bool` as IndexType.
    
    Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

Diff:
---
 libstdc++-v3/include/std/mdspan                              |  5 +++--
 .../23_containers/mdspan/extents/class_mandates_neg.cc       | 12 ++++++++----
 libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc  |  8 ++++----
 3 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index aee96dda7cd0..47cfa405e442 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -163,10 +163,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _IndexType, size_t... _Extents>
     class extents
     {
-      static_assert(is_integral_v<_IndexType>, "_IndexType must be integral.");
+      static_assert(__is_standard_integer<_IndexType>::value,
+		    "IndexType must be a signed or unsigned integer type");
       static_assert(
 	  (__mdspan::__valid_static_extent<_Extents, _IndexType> && ...),
-	  "Extents must either be dynamic or representable as _IndexType");
+	  "Extents must either be dynamic or representable as IndexType");
 
     public:
       using index_type = _IndexType;
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 b654e3920a8a..f9c1c0196669 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
@@ -1,8 +1,12 @@
 // { dg-do compile { target c++23 } }
 #include<mdspan>
 
-std::extents<char, size_t(1) << 9> e1; // { dg-error "from here" }
-std::extents<double, 1> e2;            // { dg-error "from here" }
-// { dg-prune-output "dynamic or representable as _IndexType" }
-// { dg-prune-output "must be integral" }
+#include <cstdint>
+
+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" }
diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc b/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc
index 16204aaaa75a..e71fdc542305 100644
--- a/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc
+++ b/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc
@@ -1,6 +1,7 @@
 // { dg-do run { target c++23 } }
 #include <mdspan>
 
+#include <cstdint>
 #include <testsuite_hooks.h>
 
 constexpr size_t dyn = std::dynamic_extent;
@@ -20,7 +21,6 @@ static_assert(std::is_same_v<std::extents<int, 1, 2>::rank_type, size_t>);
 static_assert(std::is_unsigned_v<std::extents<int, 2>::size_type>);
 static_assert(std::is_unsigned_v<std::extents<unsigned int, 2>::size_type>);
 
-static_assert(std::is_same_v<std::extents<char, 2>::index_type, char>);
 static_assert(std::is_same_v<std::extents<int, 2>::index_type, int>);
 static_assert(std::is_same_v<std::extents<unsigned int, 2>::index_type,
 	      unsigned int>);
@@ -49,7 +49,7 @@ static_assert(check_rank_return_types<int, 1>());
 
 // Check that the static extents don't take up space.
 static_assert(sizeof(std::extents<int, 1, dyn>) == sizeof(int));
-static_assert(sizeof(std::extents<char, 1, dyn>) == sizeof(char));
+static_assert(sizeof(std::extents<short, 1, dyn>) == sizeof(short));
 
 template<typename Extents>
 class Container
@@ -58,7 +58,7 @@ class Container
   [[no_unique_address]] std::extents<size_t> b0;
 };
 
-static_assert(sizeof(Container<std::extents<char, 1, 2>>) == sizeof(int));
+static_assert(sizeof(Container<std::extents<short, 1, 2>>) == sizeof(int));
 static_assert(sizeof(Container<std::extents<size_t, 1, 2>>) == sizeof(int));
 
 // operator=
@@ -103,7 +103,7 @@ test_deduction_all()
   test_deduction<0>();
   test_deduction<1>(1);
   test_deduction<2>(1.0, 2.0f);
-  test_deduction<3>(int(1), char(2), size_t(3));
+  test_deduction<3>(int(1), short(2), size_t(3));
   return true;
 }