tuple_size_v fails with optional<unique_ptr<...>> field in the structure

[dragon-dreamer]

This code fails to compile with both clang and gcc trunk (but compiles with the latest MSVC):

#include <memory>
#include <optional>

#include <boost/pfr/core.hpp>

struct optional_linked_list
{
	int value;
	std::optional<std::unique_ptr<optional_linked_list>> next;
};

int main()
{
    return boost::pfr::tuple_size_v<optional_linked_list>;
}

Also see https://godbolt.org/z/1d9W5e4b3 (tested with Boost 1.80.0).

This is the clang-trunk compile error:

In file included from <source>:4:
In file included from /opt/compiler-explorer/libs/boost_1_80_0/boost/pfr/core.hpp:12:
In file included from /opt/compiler-explorer/libs/boost_1_80_0/boost/pfr/detail/core.hpp:17:
In file included from /opt/compiler-explorer/libs/boost_1_80_0/boost/pfr/detail/core17.hpp:11:
In file included from /opt/compiler-explorer/libs/boost_1_80_0/boost/pfr/detail/fields_count.hpp:13:
/opt/compiler-explorer/libs/boost_1_80_0/boost/pfr/detail/unsafe_declval.hpp:29:12: error: static_cast from 'typename std::remove_reference<unique_ptr<optional_linked_list>>::type' (aka 'std::unique_ptr<optional_linked_list>') to 'std::unique_ptr<optional_linked_list>' uses deleted function
    return static_cast<T>(*ptr);
           ^~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/libs/boost_1_80_0/boost/pfr/detail/fields_count.hpp:45:24: note: in instantiation of function template specialization 'boost::pfr::detail::unsafe_declval<std::unique_ptr<optional_linked_list>>' requested here
        return detail::unsafe_declval<Type>();
                       ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/13.0.0/../../../../include/c++/13.0.0/optional:244:17: note: in instantiation of function template specialization 'boost::pfr::detail::ubiq_rref_constructor::operator unique_ptr<std::unique_ptr<optional_linked_list>>' requested here
            : _M_value(std::forward<_Args>(__args)...)
                       ^
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/13.0.0/../../../../include/c++/13.0.0/bits/unique_ptr.h:523:7: note: candidate constructor has been explicitly deleted
      unique_ptr(const unique_ptr&) = delete;
      ^