QPlatformWindow functions to move or resize the window

On Wayland, geometry updates occur asynchronously. With some protocols, Qt cannot resize until it receives an acknowledgement from the compositor. For example, one such protocol is layer-shell. In the layer-shell protocol, Qt needs to tell the compositor the desired size, then the compositor will re-layout the windows and tell Qt the size that it should paint at.

The problem is that if QWindow::move() is called while there are pending resize requests, the window may end up with a wrong size. It's due to QWindow::move() being implemented as setGeometry(newX, newY, oldWidth, oldHeight). QPA can't determine whether it's asked to move the window, resize the window, or both.

• QWindow::resize(geometryA.size()): call QWaylandWindow::setGeometry(), which in its turn will ask the compositor to resize the window to geometryA.size()
• QWindow::resize(geometryB.size()): call QWaylandWindow::setGeometry(), which in its turn will ask the compositor to resize the window to geometryB.size()
• the compositor has processed geometryA, and the window is resized to geometryA.size() by calling QWaylandWindow::setGeometry() (but with the code path that asks the compositor to resize the window disabled)
• QWindow::move(other position) -> it's going to result in the window also asking the compositor to resize it to geometryA.size()
• the compositor has processed geometryB, and the window is resized to geometryB.size()
• the compositor has processed geometryA (caused by QWindow::move()), and the window is resized to geometryA.size()

Ideally, such an asynchronous geometry issue would be fixed by introducing a new geometry, e.g. QWindow::desiredGeometry(), that would be used exclusively for window resizing. QWindow::geometry() would reflect the current geometry, it could be used for painting and input processing. A huge problem with it is that it's going to be a too API breaking design change even though it's a reasonable API choice in long term.

An alternative option might be to add QPlatformWindow::move() and QPlatformWindow::resize() functions so QPA has more context when it's requested to change the window geometry. This approach was attempted in https://github.com/zzag/qtbase/tree/work/zzag/qpa-move-resize and https://github.com/zzag/qtwayland/tree/work/zzag/qpa-move-resize, and it was confirmed that it helps to mitigate windows ending up with wrong size due to async geometry issues.