[Bug libstdc++/77395] [6/7 Regression] std::is_constructible is false for type constructible via implicit conversion operator affecting std::tuple

["j.s.mueller-roemer at gmx dot net" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77395

--- Comment #3 from Johannes S. Mueller-Roemer <j.s.mueller-roemer at gmx dot net> ---
(In reply to Daniel Krügler from comment #1)
> I think a better test-case is the following one, which does not depend on
> tuple at all:
> 
> //#################################
> #include <type_traits>
> 
> struct derived;
> struct base
> {
>   operator derived & () &;
>   operator derived const & () const &;
>   operator derived && () &&;
> };
> 
> struct derived : base {};
> 
> static_assert(std::is_constructible<derived&&, base&&>::value, "");
> 
> int main()
> {
> }
> //#################################

Probably. The failure in std::tuple is only due to now enforcing that
std::is_constructible needs to be true, which it wasn't before. The bug in
std::is_constructible might be older.