[gcc r13-7817] libstdc++: Add workaround for std::make_integer_sequence bug [PR111357]

[gcc r13-7817] libstdc++: Add workaround for std::make_integer_sequence bug [PR111357]

[Jonathan Wakely]

https://gcc.gnu.org/g:7b0abd4a8ee9d2057febe443de67009dcdfe7574

commit r13-7817-g7b0abd4a8ee9d2057febe443de67009dcdfe7574
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Sep 14 09:18:34 2023 +0100

    libstdc++: Add workaround for std::make_integer_sequence bug [PR111357]
    
    The compiler bug has been fixed on trunk, but we need this workaround on
    the branches.
    
    libstdc++-v3/ChangeLog:
    
            PR c++/111357
            * include/bits/utility.h (make_integer_sequence): Add cast.
            * testsuite/20_util/integer_sequence/pr111357.cc: New test.

Diff:
---
 libstdc++-v3/include/bits/utility.h                |  2 +-
 .../testsuite/20_util/integer_sequence/pr111357.cc | 34 ++++++++++++++++++++++
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/include/bits/utility.h b/libstdc++-v3/include/bits/utility.h
index abaaae2dd33..714e2c02680 100644
--- a/libstdc++-v3/include/bits/utility.h
+++ b/libstdc++-v3/include/bits/utility.h
@@ -173,7 +173,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #if __has_builtin(__make_integer_seq)
       = __make_integer_seq<integer_sequence, _Tp, _Num>;
 #else
-      = integer_sequence<_Tp, __integer_pack(_Num)...>;
+      = integer_sequence<_Tp, __integer_pack(_Tp(_Num))...>;
 #endif
 
   /// Alias template index_sequence
diff --git a/libstdc++-v3/testsuite/20_util/integer_sequence/pr111357.cc b/libstdc++-v3/testsuite/20_util/integer_sequence/pr111357.cc
new file mode 100644
index 00000000000..1ad06b732af
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/integer_sequence/pr111357.cc
@@ -0,0 +1,34 @@
+// { dg-do compile { target c++14 } }
+
+// PR c++/111357 - __integer_pack fails to work with values of dependent type
+// convertible to integers in noexcept context
+
+#include <utility>
+
+using std::integer_sequence;
+using std::make_integer_sequence;
+
+template<int... V>
+void g(integer_sequence<int,V...>)
+{}
+
+template<typename ...T>
+struct c1
+{
+  static constexpr int value = 1;
+  constexpr operator int() { return value; }
+};
+
+template<typename T>
+struct R
+{
+  using S = make_integer_sequence<int,c1<T>{}>;
+
+  R() noexcept(noexcept(g(S()))) // { dg-bogus "argument to .__integer_pack." }
+  {}
+};
+
+int main()
+{
+  R<int>();
+}