bug#57476: 29.0.50; Mouse wheel event ignored on Lucid build

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Stephen Berman <stephen.berman@gmx.net> writes:

> 1.79769e+308

Please instrument this piece of xterm.c, around line 20724, as follows:

  	      xi_reset_scroll_valuators_for_device_id (dpyinfo, enter->deviceid,
						       true);
#endif
	      printf ("Enter %d %d\n", enter->mode, enter->detail); <===

	      {
#ifdef HAVE_XWIDGETS
		struct xwidget_view *xwidget_view = xwidget_view_from_window (enter->event);

and this piece of the same function, around line 20843, as follows:

	      if (device)
		xi_report_motion_window_clear (device);
	      printf ("Leave %d %d\n", leave->mode, leave_detail); <====

and see what is printed as you move the mouse wheel.

Should it print "Enter" and "Leave" repetitively, please try the
following patch:

diff --git a/src/xfns.c b/src/xfns.c
index 0b1f707e9f..bebac747fb 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -3996,6 +3996,9 @@ x_window (struct frame *f, long window_prompting)
   /* Make all the standard events reach the Emacs frame.  */
   attributes.event_mask = STANDARD_EVENT_SET;
 
+  if (FRAME_DISPLAY_INFO (f)->supports_xi2)
+    attributes.event_mask &= ~(ButtonPressMask | ButtonReleaseMask);
+
 #ifdef HAVE_X_I18N
   if (FRAME_XIC (f))
     {

Thanks in advance.

P.S. I can't see anything wrong with that patch at first glance;
however, it is a big change to very old code, so please report any
issues that show up with it applied.