We have weaned ourselves off of qExchange(), which, however, has C++23
semantics (is constexpr and noexcept), while we only require C++17 atm.
At the same time, we have more and more uses of a constexpr exchange(),
iow: the C++20 extension.
We have the qNN namespaces for this, so let's use it: Add
q20::exchange(), with C++20 semantics (constexpr, not noexcept), and
use it to port the only remaining qExchange() user (since ported to
2×std::move() to make the header compatible with QT_NO_QEXCHANGE),
QScopedValueRollback.
No user requires the C++23 noexcept on the function (compilers will
figure it out, because the std::exchange is fully inline), and we
can't provide a q23::exchange() even if we needed to, because the
author of P2401 forgot to ask to update the value of
__cpp_lib_exchange_function...
Conflict resolution for 6.8:
- worked around missing a313caca239638b384018aec18906de44aab2171,
by back-porting the relevant subset of it
Fixes: QTBUG-133038
Change-Id: I003df445001d1c5ab02402119c5e5106aa156263
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit b5ed7fb203335cef7b7b4f70f4130b07166cecf2)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit cebb2dd0681f7e4f8a838730a2b15e0c7384c711)
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
7f3539202f