[Bug libstdc++/125024] [reflection] `std::is_scalar_v<std::meta::info>` incorrectly yields `false`

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125024

--- Comment #3 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:7f4cc8140e3eae85e77c755fc14991456649af7e

commit r17-101-g7f4cc8140e3eae85e77c755fc14991456649af7e
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Mon Apr 27 13:30:58 2026 +0200

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

    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.

    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.

    Reviewed-by: Jonathan Wakely <jwakely@redhat.com>