master 73237458ba: Improve safety of various DND callbacks

[Po Lu]

branch: master
commit 73237458ba305506d42293beb88d26054f8a353c
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Improve safety of various DND callbacks
    
    * src/xterm.c (x_dnd_begin_drag_and_drop): Restore selection
    events if DND is no longer in progress and don't call
    x-dnd-movement-function.
---
 src/xterm.c | 31 +++++++++++++++++++++++--------
 1 file changed, 23 insertions(+), 8 deletions(-)

diff --git a/src/xterm.c b/src/xterm.c
index 94c996a11d..5c59113469 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -10646,7 +10646,12 @@ x_dnd_begin_drag_and_drop (struct frame *f, Time time, 
Atom xaction,
              /* FIXME: how come this can end up with movement frames
                 from other displays on GTK builds?  */
              && (FRAME_X_DISPLAY (x_dnd_movement_frame)
-                 == FRAME_X_DISPLAY (f)))
+                 == FRAME_X_DISPLAY (f))
+             /* If both those variables are false, then F is no
+                longer protected from deletion by Lisp code.  This
+                can only happen during the final iteration of the DND
+                event loop.  */
+             && (x_dnd_in_progress || x_dnd_waiting_for_finish))
            {
              XSETFRAME (frame_object, x_dnd_movement_frame);
              XSETINT (x, x_dnd_movement_x);
@@ -10677,14 +10682,24 @@ x_dnd_begin_drag_and_drop (struct frame *f, Time 
time, Atom xaction,
            {
              if (hold_quit.kind == SELECTION_REQUEST_EVENT)
                {
-                 x_dnd_old_window_attrs = root_window_attrs;
-                 x_dnd_unwind_flag = true;
+                 /* It's not safe to run Lisp inside this function if
+                    x_dnd_in_progress and x_dnd_waiting_for_finish
+                    are unset, so push it back into the event queue.  */
+
+                 if (!x_dnd_in_progress && !x_dnd_waiting_for_finish)
+                   kbd_buffer_store_event (&hold_quit);
+                 else
+                   {
+                     x_dnd_old_window_attrs = root_window_attrs;
+                     x_dnd_unwind_flag = true;
+
+                     ref = SPECPDL_INDEX ();
+                     record_unwind_protect_ptr (x_dnd_cleanup_drag_and_drop, 
f);
+                     x_handle_selection_event ((struct selection_input_event 
*) &hold_quit);
+                     x_dnd_unwind_flag = false;
+                     unbind_to (ref, Qnil);
+                   }
 
-                 ref = SPECPDL_INDEX ();
-                 record_unwind_protect_ptr (x_dnd_cleanup_drag_and_drop, f);
-                 x_handle_selection_event ((struct selection_input_event *) 
&hold_quit);
-                 x_dnd_unwind_flag = false;
-                 unbind_to (ref, Qnil);
                  continue;
                }