[mutter] wayland/data-device: Cancel drag source when the drag finished unsuccessfully

[Carlos Garnacho <carlosg src gnome org>]

commit 6cc748cce9bb7cb47a4098cdc251c554d9f99b6b
Author: Robert Mader <robert mader posteo de>
Date:   Wed Jan 29 00:11:18 2020 +0100

    wayland/data-device: Cancel drag source when the drag finished unsuccessfully
    
    When a drag was performed but did not finish successfully, e.g. because no
    mimetype was accepted, we need to send the source cancel event so clients
    know they can destroy the drag source (since version 3).
    
    Fixes https://gitlab.gnome.org/GNOME/mutter/issues/740
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/1031

 src/wayland/meta-wayland-data-device.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)
---
diff --git a/src/wayland/meta-wayland-data-device.c b/src/wayland/meta-wayland-data-device.c
index 7e0a254b4..9a4ba9a92 100644
--- a/src/wayland/meta-wayland-data-device.c
+++ b/src/wayland/meta-wayland-data-device.c
@@ -75,6 +75,7 @@ typedef struct _MetaWaylandDataSourcePrivate
   MetaWaylandSeat *seat;
   guint actions_set : 1;
   guint in_ask : 1;
+  guint drop_performed : 1;
 } MetaWaylandDataSourcePrivate;
 
 typedef struct _MetaWaylandDataSourcePrimary
@@ -95,6 +96,9 @@ meta_wayland_data_source_new (struct wl_resource *resource);
 static MetaWaylandDataSource *
 meta_wayland_data_source_primary_new (struct wl_resource *resource);
 
+static void
+meta_wayland_source_cancel (MetaWaylandDataSource *source);
+
 static void
 drag_grab_data_source_destroyed (gpointer data, GObject *where_the_object_was);
 
@@ -363,6 +367,15 @@ meta_wayland_data_source_set_user_action (MetaWaylandDataSource *source,
     data_offer_update_action (offer);
 }
 
+static gboolean
+meta_wayland_data_source_get_drop_performed (MetaWaylandDataSource *source)
+{
+  MetaWaylandDataSourcePrivate *priv =
+    meta_wayland_data_source_get_instance_private (source);
+
+  return priv->drop_performed;
+}
+
 static void
 data_offer_accept (struct wl_client *client,
                    struct wl_resource *resource,
@@ -577,11 +590,17 @@ destroy_data_offer (struct wl_resource *resource)
 
       if (offer == meta_wayland_data_source_get_current_offer (offer->source))
         {
-          if (seat->data_device.dnd_data_source == offer->source &&
-              wl_resource_get_version (offer->resource) <
-              WL_DATA_OFFER_ACTION_SINCE_VERSION)
+          if (seat->data_device.dnd_data_source == offer->source)
             {
-              meta_wayland_data_source_notify_finish (offer->source);
+              if (wl_resource_get_version (offer->resource) <
+                  WL_DATA_OFFER_ACTION_SINCE_VERSION)
+                meta_wayland_data_source_notify_finish (offer->source);
+              else if (meta_wayland_data_source_get_drop_performed (offer->source) &&
+                       meta_wayland_data_source_get_resource(offer->source) &&
+                       wl_resource_get_version(
+                       meta_wayland_data_source_get_resource(offer->source)) >=
+                       WL_DATA_SOURCE_DND_FINISHED_SINCE_VERSION)
+                meta_wayland_source_cancel (offer->source);
             }
           else
             {
@@ -1390,6 +1409,8 @@ meta_wayland_source_drop_performed (MetaWaylandDataSource *source)
   MetaWaylandDataSourcePrivate *priv =
     meta_wayland_data_source_get_instance_private (source);
 
+  priv->drop_performed = TRUE;
+
   if (wl_resource_get_version (priv->resource) >=
       WL_DATA_SOURCE_DND_DROP_PERFORMED_SINCE_VERSION)
     wl_data_source_send_dnd_drop_performed (priv->resource);
@@ -1440,6 +1461,7 @@ meta_wayland_data_source_init (MetaWaylandDataSource *source)
 
   wl_array_init (&priv->mime_types);
   priv->current_dnd_action = -1;
+  priv->drop_performed = FALSE;
 }
 
 static void