[PATCH 2/2 v2] libstdc++: add std::is_virtual_base_of

[Jonathan Wakely]

On Tue, 30 Jul 2024 at 23:49, Giuseppe D'Angelo
<giuseppe.dangelo@kdab.com> wrote:
>
> Hello,
>
> On 30/07/2024 15:04, Jonathan Wakely wrote:
> > On Mon, 29 Jul 2024 at 21:58, Giuseppe D'Angelo wrote:
> >>
> >> Hi,
> >>
> >> And this is the corresponding change libstdc++.
> >
> > Thanks for the patch.
>
> Again, thanks for the guidance, should be all fixed.


The new built-in won't be available when compiling with older versions
of Clang, so it needs to be used conditionally. I think the feature
test macro should only be defined if the built-in is available. See
the version.def entry for bit_cast, for example.

If __cpp_lib_is_virtual_base_of depends on __has_builtin, then that
will do the right thing for #ifdef __cpp_lib_is_virtual_base_of in
<type_traits>.