C++26: QPointer forward declaration now fails

#include <QPointer>
QPointer<QObject> obj;

clang++ foo.cpp  -I/usr/include/qt6/QtCore -I/usr/include/qt6 -DQT_CORE_LIB -I/usr/lib/qt6/mkspecs/linux-g++ -lQt6Core -std=c++26 -w -stdlib=libc++
In file included from foo.cpp:1:
In file included from /usr/include/qt6/QtCore/QPointer:1:
In file included from /usr/include/qt6/QtCore/qpointer.h:7:
In file included from /usr/include/qt6/QtCore/qcompare.h:12:
In file included from /usr/include/qt6/QtCore/qglobal.h:13:
In file included from /usr/bin/../include/c++/v1/type_traits:449:
/usr/bin/../include/c++/v1/__type_traits/is_base_of.h:38:109: error: incomplete type 'QObject' where a complete type is required
   38 | _LIBCPP_NO_SPECIALIZATIONS inline constexpr bool is_virtual_base_of_v = __builtin_is_virtual_base_of(_Base, _Derived);
      |                                                                                                             ^
/usr/include/qt6/QtCore/qsharedpointer_impl.h:601:60: note: in instantiation of variable template specialization 'std::is_virtual_base_of_v<QObject, QObject>' requested here
  601 |     using IfNotVirtualBase = typename std::enable_if<!qxp::is_virtual_base_of_v<T, X>, bool>::type;
      |                                                            ^
/usr/include/qt6/QtCore/qsharedpointer_impl.h:632:68: note: in instantiation of template type alias 'IfNotVirtualBase' requested here
  632 |     template <class X, IfCompatible<X> = true, IfNotVirtualBase<X> = true>
      |                                                                    ^
/usr/include/qt6/QtCore/qsharedpointer_impl.h:634:5: note: while substituting prior template arguments into non-type template parameter [with X = QObject, $1 = true]
  634 |     QWeakPointer(QWeakPointer<X> &&other) noexcept
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  635 |         : d(std::exchange(other.d, nullptr)),
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  636 |           value(std::exchange(other.value, nullptr))
      |           ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  637 |     {
      |     ~
  638 |     }
      |     ~
/usr/include/qt6/QtCore/qsharedpointer_impl.h:591:7: note: while substituting deduced template arguments into function template 'QWeakPointer' [with X = QObject, $1 = (no value), $2 = (no value)]
  591 | class QWeakPointer
      |       ^
/usr/include/qt6/QtCore/qpointer.h:18:7: note: while declaring the implicit copy constructor for 'QPointer<QObject>'
   18 | class QPointer
      |       ^
foo.cpp:1516:22: note: in instantiation of template class 'QPointer<QObject>' requested here
 1516 |    QPointer<QObject> obj;
      |                      ^
/usr/include/qt6/QtCore/qtclasshelpermacros.h:139:7: note: forward declaration of 'QObject'
  139 | class QObject;
      |       ^
1 error generated.