master ebd5725e0b: Fix an infinite loop if the window manager pings Emacs during DND

[Po Lu]

branch: master
commit ebd5725e0b2f7e1dcf6dcb068bef638edd7f0cb4
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    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.
---
 src/xterm.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/xterm.c b/src/xterm.c
index 0543f152ed..fcc1f55ccb 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;