[Bug libstdc++/115522] [13/14/15 Regression] std::to_array no longer works for struct which is trivial but not default constructible

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115522

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #3)
>        static_assert(is_constructible_v<_Tp, _Tp&>);
>        if constexpr (is_constructible_v<_Tp, _Tp&>)
>         {
> -         if constexpr (is_trivial_v<_Tp>)
> +         if constexpr (is_trivial_v<_Tp> && is_default_constructible_v<_Tp>
> +                          && is_copy_assignable_v<_Tp>)

For the testcase above, it would be sufficient to do:

         if constexpr (is_trivial_v<_Tp> && is_copy_assignable_v<_Tp>)

The type with const members isn't assignable.

I'm not sure if this covers all cases. I think combined with is_trivial it
should do, but then I don't understand why the struct ranges type is trivial in
the first place.