[gtk+] gdkdnd: Stick to the first gdk_drag_drop_done() result

[Carlos Garnacho <carlosg src gnome org>]

commit 38d0d0a687c0c7416188cd6095ae4ebf69dc4f53
Author: Carlos Garnacho <carlosg gnome org>
Date:   Mon Feb 15 18:56:42 2016 +0100

    gdkdnd: Stick to the first gdk_drag_drop_done() result
    
    That way we can let ::cancel callers to override the visual
    result of the operation (eg. when detaching notebook tabs on
    NO_TARGET).
    
    Also, document gdk_drag_drop_done() so it is mentioned that
    this is a one-shot call.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=761954

 gdk/gdkdnd.c        |    9 +++++++++
 gdk/gdkdndprivate.h |    2 ++
 2 files changed, 11 insertions(+), 0 deletions(-)
---
diff --git a/gdk/gdkdnd.c b/gdk/gdkdnd.c
index b76b110..02d8d53 100644
--- a/gdk/gdkdnd.c
+++ b/gdk/gdkdnd.c
@@ -641,6 +641,10 @@ gdk_drag_context_set_hotspot (GdkDragContext *context,
  * be the last call before dropping the reference to the
  * @context.
  *
+ * The #GdkDragContext will only take the first gdk_drag_drop_done()
+ * call as effective, if this function is called multiple times,
+ * all subsequent calls will be ignored.
+ *
  * Since: 3.20
  */
 void
@@ -649,6 +653,11 @@ gdk_drag_drop_done (GdkDragContext *context,
 {
   g_return_if_fail (GDK_IS_DRAG_CONTEXT (context));
 
+  if (context->drop_done)
+    return;
+
+  context->drop_done = TRUE;
+
   if (GDK_DRAG_CONTEXT_GET_CLASS (context)->drop_done)
     GDK_DRAG_CONTEXT_GET_CLASS (context)->drop_done (context, success);
 }
diff --git a/gdk/gdkdndprivate.h b/gdk/gdkdndprivate.h
index 8eb94b8..c66de32 100644
--- a/gdk/gdkdndprivate.h
+++ b/gdk/gdkdndprivate.h
@@ -105,6 +105,8 @@ struct _GdkDragContext {
   guint32 start_time;
 
   GdkDevice *device;
+
+  guint drop_done : 1; /* Whether gdk_drag_drop_done() was performed */
 };
 
 GList *  gdk_drag_context_list (void);