[mutter] wayland/data-offer: Accept final preferrence of drop destination

[Marge Bot <marge-bot src gnome org>]

commit 33b834c43373b715219d1b911813b59b2d0e2477
Author: Robert Mader <robert mader posteo de>
Date:   Wed Oct 6 20:08:12 2021 +0200

    wayland/data-offer: Accept final preferrence of drop destination
    
    Quoting the spec for `wl_data_device::drop`:
    > If the resulting action is "ask", the action will not be considered
    > final. The drag-and-drop destination is expected to perform one last
    > wl_data_offer.set_actions request, or wl_data_offer.destroy in order
    > to cancel the operation.
    
    We did not respect the action choosen by the drop destination when
    it called `wl_data_offer::set_actions` after `wl_data_device::drop`
    if a user override was still active. This eventually resulted in
    a protocol error in `wl_data_offer::finish`, as the current action
    could still be `ask`.
    
    Fix this by only allowing a user override to `ask` before `drop` is
    called, thus making sure the final `set_actions` preference is
    honored.
    
    Closes https://gitlab.gnome.org/GNOME/mutter/-/issues/1952
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2043>

 src/wayland/meta-wayland-data-offer.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/src/wayland/meta-wayland-data-offer.c b/src/wayland/meta-wayland-data-offer.c
index c686aee6f6..c4ec2a701a 100644
--- a/src/wayland/meta-wayland-data-offer.c
+++ b/src/wayland/meta-wayland-data-offer.c
@@ -276,7 +276,9 @@ data_offer_choose_action (MetaWaylandDataOffer *offer)
     return WL_DATA_DEVICE_MANAGER_DND_ACTION_NONE;
 
   /* If the user is forcing an action, go for it */
-  if ((user_action & available_actions) != 0)
+  if ((user_action & available_actions) != 0 &&
+      !(user_action == WL_DATA_DEVICE_MANAGER_DND_ACTION_ASK &&
+        meta_wayland_data_source_get_drop_performed (source)))
     return user_action;
 
   /* If the dest side has a preferred DnD action, use it */