Make it easier to clear the Motif drag window for debugging

* src/xterm.c (xm_get_drag_window_1): Add comment explaining
side effect of x_special_window_exists_p.
(handle_one_xevent): Clear Motif drag window upon DestroyNotify.
In addition to debugging, it also reduces syncs necessary to
communicate via the Motif protocol after a defective/old client
sets the drag window without setting the disconnect mode.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/xterm.c b/src/xterm.c
index 4ac42a91384..12234351a32 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -1971,6 +1971,10 @@ xm_get_drag_window_1 (struct x_display_info *dpyinfo)
       && tmp_data)
     {
       drag_window = *(Window *) tmp_data;
+
+      /* This has the side effect of selecting for
+	 StructureNotifyMask, meaning that we will get notifications
+	 once it is deleted.  */
       rc = x_special_window_exists_p (dpyinfo, drag_window);
 
       if (!rc)
@@ -20707,6 +20711,15 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 	  == dpyinfo->net_supported_window)
 	dpyinfo->net_supported_window = None;
 
+      if (event->xdestroywindow.window
+	  == dpyinfo->motif_drag_window)
+	/* We get DestroyNotify events for the drag window because
+	   x_special_window_exists_p selects for structure
+	   notification.  The drag window is not supposed to go away
+	   but not all clients obey that requirement when setting the
+	   drag window property.  */
+	dpyinfo->motif_drag_window = None;
+
       xft_settings_event (dpyinfo, event);
       break;