[Bug libstdc++/91541] [C++17] Exception specification of operator= of node-based containers may be broken

[frankhb1989 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91541

--- Comment #3 from frankhb1989 at gmail dot com ---
(In reply to Jonathan Wakely from comment #2)
> (In reply to frankhb1989 from comment #0)
> 
> This type does not meet the allocator requirements. For a valid allocator,
> A::rebind<A::value_type>::other must be the same type as A, and
> A::rebind<U>::other::rebind<A::value_type>::other must also be the same type
> as A.

Oops, I missed those requirements. How about this?

#include <utility>
#include <map>
#include <functional>

using P = std::pair<const int, int>;

template<typename T>
struct AT
{
        using value_type = T;

        template<typename U>
        struct rebind
        {
                using other = AT<U>;
        };

        using is_always_equal = std::is_same<T, P>;

        template<typename U>
        AT(const AT<U>&);

        T* allocate(std::size_t);

        void deallocatoe(T*, std::size_t);
};

using A = AT<P>;

int main()
{
        static_assert(std::is_same_v<A::template rebind<A::value_type>::other,
A>);
        // For any U:
        using U = int;
        static_assert(std::is_same_v<A::template rebind<U>::other::template
rebind<A::value_type>::other, A>);
        using always_equal = std::allocator_traits<A>::is_always_equal;
        using C = std::less<>;
        constexpr bool std_nothrow = always_equal::value &&
std::is_nothrow_move_assignable_v<C>;
        static_assert(std_nothrow);
        static_assert(!(std_nothrow &&
!std::is_nothrow_move_assignable<std::map<int, int, C, A>>::value));
}