[gcc r12-10254] libstdc++: Add static_assert to std::integer_sequence [PR112473]

[Jonathan Wakely <redi@gcc.gnu.org>]

https://gcc.gnu.org/g:dc0964f43dcee46dcd1843287a541668fd08a4a8

commit r12-10254-gdc0964f43dcee46dcd1843287a541668fd08a4a8
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Nov 10 12:21:52 2023 +0000

    libstdc++: Add static_assert to std::integer_sequence [PR112473]
    
    C++20 allows class types as non-type template parameters, but
    std::integer_sequence explicitly disallows them. Enforce that.
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/112473
            * include/bits/utility.h (integer_sequence): Add static_assert.
            * testsuite/20_util/integer_sequence/112473.cc: New test.
    
    (cherry picked from commit 0953497a81f1e320989b9f2aaa7f56747eddd4a0)

Diff:
---
 libstdc++-v3/include/bits/utility.h                       | 3 +++
 libstdc++-v3/testsuite/20_util/integer_sequence/112473.cc | 8 ++++++++
 2 files changed, 11 insertions(+)

diff --git a/libstdc++-v3/include/bits/utility.h b/libstdc++-v3/include/bits/utility.h
index 180866e3581..6483a8e537e 100644
--- a/libstdc++-v3/include/bits/utility.h
+++ b/libstdc++-v3/include/bits/utility.h
@@ -163,6 +163,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp, _Tp... _Idx>
     struct integer_sequence
     {
+#if __cplusplus >= 202002L
+      static_assert(is_integral_v<_Tp>);
+#endif
       typedef _Tp value_type;
       static constexpr size_t size() noexcept { return sizeof...(_Idx); }
     };
diff --git a/libstdc++-v3/testsuite/20_util/integer_sequence/112473.cc b/libstdc++-v3/testsuite/20_util/integer_sequence/112473.cc
new file mode 100644
index 00000000000..14abfbc8149
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/integer_sequence/112473.cc
@@ -0,0 +1,8 @@
+// { dg-do compile { target c++20 } }
+
+// PR libstdc++/112473 - integer_sequence accepts non-integer types
+
+#include <utility>
+
+std::integer_sequence<std::pair<int, int>, std::pair<int, int>{0, 0}> ic;
+// { dg-error "static assertion failed" "" { target *-*-* } 0 }