As struct wlr_drag is destroyed on drop and in the process resets
the focus, a xwayland dnd listener would also reset xwm->drag_focus.
This prevents the xcb replies from being processed and also prevents
the transfer if a compositor would not additionally request new focus
in its wlr_drag destroy handler (which is something usually only done
when in a focus-follows-mouse setting).
This patch creates a new xwm->drop_focus pointer which is a copy of
xwm->drag_focus at drop time. The xcb reply handler and transfer
logic now use the new xwm->drop_focus for their authorization checks.
The wlr_drag takes care of resetting the focused wlr_surface when
it's destroyed, however we store the wlr_xwayland_surface, which
may be destroyed before.
Instead of calling xcb_flush() directly, wait until the FD is
writable.
Ideally we'd have a non-blocking variant instead of xcb_flush(),
but libxcb doesn't have this. Also libxcb blocks when its internal
buffer is full, but not much we can do here.
Previously, the clipboard and primary selections shared the same window.
This was racey, and could have led to pasting failures.
On xfixes selection owner change notification, the logic for requesting
the supported mimetypes of the new owner's selection looks like:
xcb_convert_selection(
xwm->xcb_conn,
selection->window,
selection->atom,
xwm->atoms[TARGETS],
xwm->atoms[WL_SELECTION],
selection->timestamp
);
This means ask the selection owner to write its TARGETS for the
`selection->atom` selection (one of PRIMARY, CLIPBOARD, DND_SELECTION)
to `selection->window`'s WL_SELECTION atom.
However, `selection->window` is shared for both PRIMARY and CLIPBOARD
selections, and WL_SELECTION is used as the target atom in both cases.
So, there's a race when both selections change at the same time.
The CLIPBOARD selection might support mimetypes {A, B, C}, and the
PRIMARY only {A, B}. If the ConvertSelection requests/responses "cross
on the wire", so to speak, wlroots can end up believing that the PRIMARY
selection also supports C.
A Wayland client may then ask for the PRIMARY selection in C format,
which will fail with "convert selection failed".
This commit fixes this by using a separate window for PRIMARY and
CLIPBOARD target requests, so that WL_SELECTION can be used as the
target atom in both cases.
This supersedes f24e17259e and
04c9ca4198. These commits were manually removing
wlr_data_source destroy handlers when starting a new drag. This is error-prone.
Instead, this commit destroys the previous source whenever we start a new drag.
