[PATCH] libstdc++: Fix up std::is_scalar for std::meta::info [PR125024]

[Jakub Jelinek]

Hi!

https://eel.is/c++draft/basic.types.general#9.sentence-1 says that
std::meta::info and its cv-qualified versions are scalar types too
(and in https://eel.is/c++draft/basic.fundamental#19.sentence-1
that they are fundamental types too).
Now, on the reflection side, eval_is_scalar_type is handled
in the compiler and uses SCALAR_TYPE_P (type) which includes
REFLECTION_TYPE_P check and eval_is_fundamental_type includes that
explicitly too.
std::is_fundamental uses
   template<typename _Tp>
     struct is_fundamental
     : public __or_<is_arithmetic<_Tp>, is_void<_Tp>,
                    is_null_pointer<_Tp>
 #if __cpp_impl_reflection >= 202506L
                    , is_reflection<_Tp>
 #endif
                    >::type
     { };
but for std::is_scalar we apparently forgot to include is_reflection.

The following patch fixes that.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/16.2?

2026-04-26  Jakub Jelinek  <jakub@redhat.com>

	PR libstdc++/125024
	* include/std/type_traits (std::is_scalar): For
	__cpp_impl_reflection >= 202506L handle is_reflection types as
	scalar.
	* testsuite/20_util/is_scalar/reflection.cc: New test.

--- libstdc++-v3/include/std/type_traits.jj	2026-04-09 18:09:11.002020134 +0200
+++ libstdc++-v3/include/std/type_traits	2026-04-26 19:20:37.109205308 +0200
@@ -871,7 +871,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     struct is_scalar
     : public __or_<is_arithmetic<_Tp>, is_enum<_Tp>, is_pointer<_Tp>,
-                   is_member_pointer<_Tp>, is_null_pointer<_Tp>>::type
+                   is_member_pointer<_Tp>, is_null_pointer<_Tp>
+#if __cpp_impl_reflection >= 202506L
+		   , is_reflection<_Tp>
+#endif
+		   >::type
     { };
 
   /// is_compound
--- libstdc++-v3/testsuite/20_util/is_scalar/reflection.cc.jj	2026-04-26 20:30:15.661943601 +0200
+++ libstdc++-v3/testsuite/20_util/is_scalar/reflection.cc	2026-04-26 20:49:40.107965736 +0200
@@ -0,0 +1,13 @@
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+
+#include <type_traits>
+#include <testsuite_tr1.h>
+
+void test01()
+{
+  using std::is_scalar;
+  using namespace __gnu_test;
+
+  static_assert(test_category<is_scalar, decltype (^^::)>(true), "");
+}

	Jakub