Fix an infinite loop if the window manager pings Emacs during DND

* src/xterm.c (handle_one_xevent): Work around _NET_WM_PING
infinite loop during drag and drop.

1 files changed, 13 insertions, 1 deletions

diff --git a/src/xterm.c b/src/xterm.c
index 0543f152eda..fcc1f55ccb6 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -11014,7 +11014,19 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 
                 send_event.xclient.window = dpyinfo->root_window;
                 XSendEvent (dpyinfo->display, dpyinfo->root_window, False,
-                            SubstructureRedirectMask | SubstructureNotifyMask,
+                            /* FIXME: handling window stacking changes
+                               during drag-and-drop requires Emacs to
+                               select for SubstructureNotifyMask,
+                               which in turn causes the message to be
+                               sent to Emacs itself using the event
+                               mask specified by the EWMH.  To avoid
+                               an infinite loop, just use
+                               SubstructureRedirectMask when a
+                               drag-and-drop operation is in
+                               progress.  */
+                            ((x_dnd_in_progress || x_dnd_waiting_for_finish)
+                             ? SubstructureRedirectMask
+                             : SubstructureRedirectMask | SubstructureNotifyMask),
                             &send_event);
 
                 *finish = X_EVENT_DROP;