First of all, sorry for the big patch.
Currently, we implement Wayland protocol wrappers in KWayland and then
add necessary "glue" code here in KWin. Because KWayland is a KF library,
we are not able to change existing API in ways that may break API or
ABI compatibility. So, if some particular wrapper has been implemented
incorrectly, we can't do that much about it except maybe leaving
comments that look like "// TODO KF6".
Another problem with KWayland is that we try to build abstractions over
something that is unstable. We do this in the name of the "don't repeat
yourself" mantra. While it is a good approach to keep the amount of
duplicated code as low as possible, we basically ask for trouble. If a
new version of an unstable protocol comes along with dramatic changes,
we are screwed.
The current xdg-shell wrappers in KWayland were designed for xdg-shell
v5, which didn't have objects such as xdg-toplevel or xdg-positioner.
Unfortunately, we can't change existing classes because of the API and
ABI compatibility promises we made.
This change splits the XdgShellClient class to better match existing
abstractions in the xdg-shell protocol. Unfortunately, since xdg-shell
wrappers in KWayland weren't designed for xdg-shell v6+, I had to
re-implement them here in KWin. The new wrappers weren't implemented in
KWayland because I cannot guarantee that the future versions of the
wrappers will be API compatible.
The XdgSurface{V6}Client class is concerned mainly about things such as
mapped/unmapped state and geometry, while XdgToplevel{V6}Client and
XdgPopup{V6}Client are concerned about role-specific things, for example
the window state, etc.
In the new client classes, configure events are handled differently.
Instead of blocking configure events, we try to send them as late as
possible. Delaying configure events will let us merge changeMaximize()
for X11 clients and Wayland clients and it also fixes the bug where
we don't send the final configure event when user has finished resizing
a window.
Given that configure events are not sent immediately, XdgSurfaceClient
and XdgSurfaceV6Client keep the last requested frame geometry and the
last requested client geometry.
This change doesn't intend to fix all things that are currently broken
in the xdg-shell wrappers and the XdgShellClient class. For example,
we don't reset XdgSurfaceInterface when the wl_surface is unmapped, we
handle xdg-popup grabs poorly, etc. Instead, this change lays the
foundation for the future improvements.