It actually works in trunk gcc/clang: https://godbolt.org/z/oKasW8zqf.

On Fri, May 19, 2023 at 1:29 PM Pavel Vazharov via Std-Proposals <
std-proposals_at_[hidden]> wrote:

> if constexpr ( .... ) { . . . }
>> else if constexpr ( ... ) { . . . }
>> else
>> {
>> std::terminate_compilation();
>> }
>
> I think this proposal covers the above case
> https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2593r0.html
> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals
>

-- 
Regards,
Oleksandr Koval.