On Tue, 18 Jul 2023, Ken Matsui via Libstdc++ wrote:
> This patch defines _GLIBCXX_HAS_BUILTIN_TRAIT, which will be used as a
> flag to toggle built-in traits in the type_traits header. Through this
> macro function and _GLIBCXX_NO_BUILTIN_TRAITS macro, we can switch the
> use of built-in traits without needing to modify the source code.
>
> libstdc++-v3/ChangeLog:
>
> * include/bits/c++config (_GLIBCXX_HAS_BUILTIN_TRAIT): Define.
The ChangeLog entry should also mention the change to _GLIBCXX_HAS_BUILTIN,
e.g.
(_GLIBCXX_HAS_BUILTIN): Keep defined.
>
> Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
> ---
> libstdc++-v3/include/bits/c++config | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/include/bits/c++config
> b/libstdc++-v3/include/bits/c++config
> index dd47f274d5f..de13f61db71 100644
> --- a/libstdc++-v3/include/bits/c++config
> +++ b/libstdc++-v3/include/bits/c++config
> @@ -854,7 +854,11 @@ namespace __gnu_cxx
> # define _GLIBCXX_HAVE_BUILTIN_LAUNDER 1
> #endif
>
> -#undef _GLIBCXX_HAS_BUILTIN
> +// Returns true if _GLIBCXX_NO_BUILTIN_TRAITS is not defined and the compiler
> +// has a corresponding built-in type trait. _GLIBCXX_NO_BUILTIN_TRAITS is
> +// defined to disable the use of built-in traits.
> +#define _GLIBCXX_HAS_BUILTIN_TRAIT(BT) \
> + (!defined(_GLIBCXX_NO_BUILTIN_TRAITS) && _GLIBCXX_HAS_BUILTIN(BT))
Since we don't expect _GLIBCXX_NO_BUILTIN_TRAITS to get
defined/undefined in the middle of preprocessing, perhaps we should
factor out the _GLIBCXX_NO_BUILTIN_TRAITS test from the macro function
and instead conditionally define the macro function to 0 according
_GLIBCXX_NO_BUILTIN_TRAITS?
>
> // Mark code that should be ignored by the compiler, but seen by Doxygen.
> #define _GLIBCXX_DOXYGEN_ONLY(X)
> --
> 2.41.0
>
>
