compareThreeWay() was supposed to be an operator<=>(), but for C++17.
The idea was that at some point when we unconditionally demand C++20,
people could just replace all the usages of compareThreeWay() with
operator<=>().
However, the Qt::compareThreeWay() overload for pointers is different
from the operator<=>() for pointers, because it is actually using
std::less{} or std::compare_three_way{} to do the comparison, thus
avoiding an UB. This is not bad as such, but can potentially lead to
UB when mass-replacing all compareThreeWay() calls with operator<=>().
To avoid this problem, deprecate the overload, and suggest to use
the Qt::totally_ordered_wrapper together with the respective overload
instead.
Found in API Review.
[ChangeLog][QtCore][QtCompare] Deprecate Qt::compareThreeWay()
overload for pointers.
Change-Id: I9c57871145dc3cb9656d6006db88b48a1553bef4
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
(cherry picked from commit b1ae4334ea11f6942c7ce37a80a3aa98a3447809)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
e37c0a33a4