GNU bug report logs - #35161
26.1; follow-mode spurious motion

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Devon Sean McCullough <Emacs-Hacker2018 <at> jovi.net>
To: bug-gnu-emacs <at> gnu.org
Subject: 26.1; follow-mode spurious motion
Date: Fri, 5 Apr 2019 11:58:23 -0400

bash$ /Applications/Emacs.app/Contents/MacOS/Emacs -Q -eval '(progn (insert-file-contents-literally "/dev/stdin") (eval-buffer))' <<.
(xref-find-definitions 'set-frame-font)
(toggle-frame-maximized)
(follow-mode)
(delete-other-windows)
(mark-defun)
(split-window-right)
(setq s1 0
      t1 (run-at-time 1 1 (lambda (&rest args)
			    (other-window 1)
			    (sit-for 0)
			    (when (> (setq s1 (1+ s1)) 3)
			      (cancel-timer t1)
			      (message "Now when you type C-x o the unselected cursor will spuriously move to the bottom line.")))))
.
bash$ ## Both windows' cursors should stay put, but instead one of them moves.

		Peace
			--Devon

P.S. I'm curious why programmatic (other-window 1) (sit-for 0)
doesn't exhibit this bug.
Perhaps ELisp manual chapter 28.21 Windows and Point
should mention relevant pitfalls?

In GNU Emacs 26.1 (build 1, x86_64-apple-darwin14.5.0, NS appkit-1348.17 Version 10.10.5 (Build 14F2511))
 of 2018-05-30 built on builder10-10.porkrind.org
Windowing system distributor 'Apple', version 10.3.1404
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
uncompressing frame.el.gz...done
Mark set [2 times]
Now when you type C-x o the unselected cursor will spuriously move to the bottom line.

Configured using:
 'configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-modules'

Configured features:
NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES THREADS

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
  follow-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq dired
dired-loaddefs format-spec rfc822 mml mml-sec password-cache epa derived
epg epg-config gnus-util rmail rmail-loaddefs mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils follow pulse
jka-compr help-fns radix-tree help-mode easymenu find-func xref cl-seq
project ring eieio byte-opt bytecomp byte-compile cconv eieio-core
cl-macs gv eieio-loaddefs cl-loaddefs cl-lib elec-pair time-date tooltip
eldoc electric uniquify ediff-hook vc-hooks lisp-float-type mwheel
term/ns-win ns-win ucs-normalize mule-util term/common-win tool-bar dnd
fontset image regexp-opt fringe tabulated-list replace newcomment
text-mode elisp-mode lisp-mode prog-mode register page menu-bar
rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core term/tty-colors frame cl-generic cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
ethiopic indian cyrillic chinese composite charscript charprop
case-table epa-hook jka-cmpr-hook help simple abbrev obarray minibuffer
cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote kqueue cocoa ns
multi-tty make-network-process emacs)

Memory information:
((conses 16 213238 12101)
 (symbols 48 21064 1)
 (miscs 40 50 228)
 (strings 32 31333 1806)
 (string-bytes 1 844158)
 (vectors 16 36768)
 (vector-slots 8 740380 12142)
 (floats 8 50 379)
 (intervals 56 575 60)
 (buffers 992 12))

Message #8 received at 35161 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Devon Sean McCullough <Emacs-Hacker2018 <at> jovi.net>
Cc: 35161 <at> debbugs.gnu.org
Subject: Re: bug#35161: 26.1; follow-mode spurious motion
Date: Sat, 06 Apr 2019 12:19:54 +0300

> From: Devon Sean McCullough <Emacs-Hacker2018 <at> jovi.net>
> Date: Fri, 5 Apr 2019 11:58:23 -0400
> 
> bash$ /Applications/Emacs.app/Contents/MacOS/Emacs -Q -eval '(progn (insert-file-contents-literally "/dev/stdin") (eval-buffer))' <<.
> (xref-find-definitions 'set-frame-font)
> (toggle-frame-maximized)
> (follow-mode)
> (delete-other-windows)
> (mark-defun)
> (split-window-right)
> (setq s1 0
>       t1 (run-at-time 1 1 (lambda (&rest args)
> 			    (other-window 1)
> 			    (sit-for 0)
> 			    (when (> (setq s1 (1+ s1)) 3)
> 			      (cancel-timer t1)
> 			      (message "Now when you type C-x o the unselected cursor will spuriously move to the bottom line.")))))
> .
> bash$ ## Both windows' cursors should stay put, but instead one of them moves.
> 
> 		Peace
> 			--Devon
> 
> P.S. I'm curious why programmatic (other-window 1) (sit-for 0)
> doesn't exhibit this bug.
> Perhaps ELisp manual chapter 28.21 Windows and Point
> should mention relevant pitfalls?

It's not a bug, not in redisplay anyway.  The last line of the left
window is not fully visible, at least on my system, and that causes
the effects you see (if I understand correctly the issue you find
unexpected).

Btw, calling sit-for from a timer function is not a good idea, but
this is a tangent.

Thanks.

Message #11 received at 35161 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Kangas <stefan <at> marxist.se>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: Devon Sean McCullough <Emacs-Hacker2018 <at> jovi.net>, 35161 <at> debbugs.gnu.org
Subject: Re: bug#35161: 26.1; follow-mode spurious motion
Date: Tue, 25 Aug 2020 18:07:36 -0700

tags 35161 + notabug
close 35161
thanks

Eli Zaretskii <eliz <at> gnu.org> writes:

>> From: Devon Sean McCullough <Emacs-Hacker2018 <at> jovi.net>
>> Date: Fri, 5 Apr 2019 11:58:23 -0400
>>
>> bash$ /Applications/Emacs.app/Contents/MacOS/Emacs -Q -eval '(progn (insert-file-contents-literally "/dev/stdin") (eval-buffer))' <<.
>> (xref-find-definitions 'set-frame-font)
>> (toggle-frame-maximized)
>> (follow-mode)
>> (delete-other-windows)
>> (mark-defun)
>> (split-window-right)
>> (setq s1 0
>>       t1 (run-at-time 1 1 (lambda (&rest args)
>> 			    (other-window 1)
>> 			    (sit-for 0)
>> 			    (when (> (setq s1 (1+ s1)) 3)
>> 			      (cancel-timer t1)
>> 			      (message "Now when you type C-x o the unselected cursor will spuriously move to the bottom line.")))))
>> .
>> bash$ ## Both windows' cursors should stay put, but instead one of them moves.
>>
>> 		Peace
>> 			--Devon
>>
>> P.S. I'm curious why programmatic (other-window 1) (sit-for 0)
>> doesn't exhibit this bug.
>> Perhaps ELisp manual chapter 28.21 Windows and Point
>> should mention relevant pitfalls?
>
> It's not a bug, not in redisplay anyway.  The last line of the left
> window is not fully visible, at least on my system, and that causes
> the effects you see (if I understand correctly the issue you find
> unexpected).
>
> Btw, calling sit-for from a timer function is not a good idea, but
> this is a tangent.

Eli explains here that this is not a bug and there has been no further
replies within a year.  I'm going to assume this answer is satisfactory
and close this bug now.

If this conclusion is incorrect and this is still an issue, please reply
to this email (use "Reply to all" in your email client) and we can
reopen the bug report.

Best regards,
Stefan Kangas

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