Correctly detect cancelled drag-and-drop operations in wxGTK.

The status of the drop operation wasn't propagated back to the initiator of
drag and drop, so failing to drop data over a possibly accepting recipient
could result in wrong behaviour and even data loss.

Closes #15930.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75745 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

docs/changes.txt

@@ -33,6 +33,7 @@ All (GUI):
 wxGTK:
 
 - Support building wxGTK3 under Windows (Kolya Kosenko).
+- Correctly detect cancelled drag-and-drop operations (Kinaou Hervé).
 
 wxMSW:
 

src/gtk/dnd.cpp

@@ -311,6 +311,9 @@ static gboolean target_drag_drop( GtkWidget *widget,
     {
         wxLogTrace(TRACE_DND, wxT( "Drop target: OnDrop returned FALSE") );
 
+        // change drag and drop status if drop operation failed
+        gdk_drag_status( context, (GdkDragAction)0, time );
+
         /* cancel the whole thing */
         gtk_drag_finish( context,
                           FALSE,        /* no success */
@@ -365,6 +368,9 @@ static void target_drag_data_received( GtkWidget *WXUNUSED(widget),
 
     if (gtk_selection_data_get_length(data) <= 0 || gtk_selection_data_get_format(data) != 8)
     {
+        // change drag and drop status if drop operation failed
+        gdk_drag_status( context, (GdkDragAction)0, time );
+
         /* negative data length and non 8-bit data format
            qualifies for junk */
         gtk_drag_finish (context, FALSE, FALSE, time);
@@ -384,6 +390,9 @@ static void target_drag_data_received( GtkWidget *WXUNUSED(widget),
     {
         wxLogTrace(TRACE_DND, wxT( "Drop target: OnData returned true") );
 
+        // change drag and drop status if drop operation failed
+        gdk_drag_status( context, (GdkDragAction)0, time );
+
         /* tell GTK that data transfer was successful */
         gtk_drag_finish( context, TRUE, FALSE, time );
     }
@@ -880,6 +889,14 @@ wxDragResult wxDropSource::DoDragDrop(int flags)
     while (m_waiting)
         gtk_main_iteration();
 
+    if ( m_retValue != wxDragCancel &&
+         m_retValue != wxDragError )
+    {
+        // if wxDropTarget::OnDrop has been processed and has succeeded
+        // check the return value of wxDropTarget::OnData
+        m_retValue = ConvertFromGTK( context->action );
+    }
+
     g_signal_handlers_disconnect_by_func (m_iconWindow,
                                           (gpointer) gtk_dnd_window_configure_callback, this);