Usually the "dnd-finished" signal will be used to unref the GdkDrag. In
those cases, we would lose the object, so that when we do the final
drag_drop_done() afterwards, we wouldn't have a remaining reference.
With the reference guard, this now works.
We must call gdk_drag_drop_done() when the drag ends,
successfully or not. Without this, we get an unwarranted
emission of ::cancel after a successful drop.
Since only the first call to gdk_drag_drop_done() is taking
effect, it is safe to call as a fallback, after emitting
::dnd-finished. If the application connects to that signal
and calls gdk_drag_drop_done() itself, its call will take
precedence.
This matches what the X11 implementation does.
Otherwise the compositor gets all confused when it's trying to make
drag happen but we know it's not going to happen.
After all, we exchange data behind its back, we just need to keep it
informed.
We need to set the drag to NULL in gdk_wayland_drag_drop_done,
otherwise, all future drags will be considered local after the
first local one. Worse, they will also provide the wrong data.
We want to use a gdk_surface_new_popup for popups,
and align the constructor names with the surface
types, so rename
gdk_surface_new_popup -> gdk_surface_new_temp
gdk_surface_new_popup_full -> gdk_surface_new_popup
The temp surface type will disappear eventually.
GLib master propagates argument types in g_clear_pointer(), which causes
the usual function pointer casts to GDestroyNotify to trip compiler
warnings. Additionally, this commit changes some cleanup functions where
appropriate (wl_data_source_destroy ->
gtk_primary_selection_source_destroy for struct
gtk_primary_selection_source).
