bug#64750: 30.0.50; [PATCH] Clicking at screen edge in X11 echoes "<nil> <mouse-1> is undefined"

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

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When clicking along the left edge of screen in a maximized emacs X11
window, the message "<left-fringe> <mouse-1> is undefined" or
"<nil> <mouse-1> is undefined" will appear. This can also be done with
the right fringe, and with the top edge of the screen if the menu and
tool bars are disabled. It can also be done using mouse events besides
<mouse-1>, like <mouse-2>, <down-mouse-1>, or <drag-mouse-1>.

This occurs with emacs -Q, regardless of fringe mode or internal border
settings. It is easier to reproduce with larger internal borders (-ib 10
or so) or larger fringes, because that expands the size of the nil or
fringe area. When internal border and fringes are disabled, there is
still a 1-pixel wide area with this problem.

This bug makes using programs with clickable UI elements at the edge of
the frame annoying. The cursor tends to land in the nil or fringe areas,
then the distracting/irrelevant message appears in the echo area when
you attempt to click.

The attached patch globally ignores all inputs for those areas in
fringe.el.


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From bcf7e7a528620f830c54ec2ad9457acf1259416b Mon Sep 17 00:00:00 2001
From: Antero Mejr <antero@mailbox.org>
Date: Thu, 20 Jul 2023 17:30:07 +0000
Subject: [PATCH] Ignore input in the fringe and nil areas

* lisp/fringe.el: Add global key bindings to ignore clicks in the
left-fringe, right-fringe, and nil areas.
---
 lisp/fringe.el | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lisp/fringe.el b/lisp/fringe.el
index b5ab4f9f605..f5a85365a89 100644
--- a/lisp/fringe.el
+++ b/lisp/fringe.el
@@ -336,6 +336,10 @@ options to pick a fringe bitmap."
     (put symbol 'fringe (get value 'fringe))
     (force-window-update)))
 
+(global-set-key [left-fringe] #'ignore)
+(global-set-key [right-fringe] #'ignore)
+(global-set-key [nil] #'ignore)
+
 (provide 'fringe)
 
 ;;; fringe.el ends here
-- 
2.41.0