Despite being move-only, std::vector<unique_ptr> advertizes
is_copyable:
https://quuxplusone.github.io/blog/2020/02/05/vector-is-copyable-except-when-its-not/
Our combined reallocation and resizing function, reallocate_impl(),
runs afoul of this when it uses std::is_copyable in a constexpr-if to
implement resize(n, v) without running into problems with move-only
types: the trait is true, but actual instantation runs into a
static_assert in the STL implementation.
To fix, move the problematic resize functionality out of
reallocate_impl() and into the resp. resize_impl overloads. The shrink
functionality remains in reallocate_impl(), because there are many
more users, and it only requires destructible<T>, which isn't
constraining at all.
Amends a00a1d8806.
Fixes: QTBUG-109745
Pick-to: 6.5 6.4
Change-Id: Ibc5b9cf5375108eb3d8f6c8a16d4fd02dadd73b1
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
800ebd84f5