bug#74924: 29.3; Buffer showing manpage jumps back to beginning

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[Ture Pålsson]

1. Run in a terminal window. Operating system seems not to matter; I can
reproduce on both macOS and Linux.

2. Set environment variable MANWIDTH to 80 .

3. Start Emacs ('emacs -nw -Q').

4. Do M-x man, enter the name of some manpage, and type RET.

5. Switch to the manpage window (C-x o), and scroll down by typing 'C-v'
a few times.

6. Switch back to the *scratch* window (C-x o again).

7. After about a second, the manpage window jumps back to the beginning
of the buffer.

My *guess* is that this is related to the changes in commit
7e387c9e5265b98dbb3b986f8ab8ac2217052831, but that may well be a red
herring.



In GNU Emacs 29.3 (build 1, aarch64-apple-darwin23.4.0, NS
 appkit-2487.50 Version 14.4.1 (Build 23E224)) of 2024-04-28 built on
 agaton
Repository revision: 8d7918ec1f42048ed994dfd0e4d582d8acaabd45
Repository branch: master
System Description:  macOS 15.1.1

Configured using:
 'configure --prefix=/Users/ture/Nobackup/emacsbuild --with-ns
 --without-gif CPPFLAGS=-I/Users/ture/Nobackup/emacsbuild/include
 LDFLAGS=-L/Users/ture/Nobackup/emacsbuild/lib'

Configured features:
ACL GMP GNUTLS JPEG LIBXML2 MODULES NOTIFY KQUEUE NS PDUMPER PNG SQLITE3
THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER ZLIB

Important settings:
  value of $LC_CTYPE: sv_SE.UTF-8
  value of $LC_MESSAGES: C
  value of $LANG: sv_SE.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  blink-cursor-mode: t
  buffer-read-only: t
  line-number-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  view-mode: t

Load-path shadows:
/Users/ture/Library/Emacs Lisp/python hides /Applications/Emacs.app/Contents/Resources/lisp/progmodes/python

Features:
(shadow sort mail-extr emacsbug message yank-media puny dired
dired-loaddefs rfc822 mml mml-sec epa derived epg rfc6068 epg-config
gnus-util text-property-search time-date mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils view term/screen
term/xterm xterm ture-theme ansi-color finder-inf package browse-url url
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generate-lisp-file url-domsuf url-util mailcap url-handlers url-parse
auth-source cl-seq eieio eieio-core cl-macs password-cache json subr-x
map byte-opt gv bytecomp byte-compile url-vars cl-loaddefs cl-lib rmc
iso-transl tooltip cconv eldoc paren electric uniquify ediff-hook
vc-hooks lisp-float-type elisp-mode mwheel term/ns-win ns-win
ucs-normalize mule-util term/common-win tool-bar dnd fontset image
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prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine 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 emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads kqueue cocoa ns multi-tty
make-network-process emacs)

Memory information:
((conses 16 81755 10005)
 (symbols 48 8456 0)
 (strings 32 27783 2349)
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 (buffers 984 12))

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[Stefan Kangas]

found 74924 29.3
found 74924 31.0.50
tags 74924 + confirmed
thanks

Ture Pålsson <ture@turepalsson.se> writes:

> 1. Run in a terminal window. Operating system seems not to matter; I can
> reproduce on both macOS and Linux.
>
> 2. Set environment variable MANWIDTH to 80 .
>
> 3. Start Emacs ('emacs -nw -Q').
>
> 4. Do M-x man, enter the name of some manpage, and type RET.
>
> 5. Switch to the manpage window (C-x o), and scroll down by typing 'C-v'
> a few times.
>
> 6. Switch back to the *scratch* window (C-x o again).
>
> 7. After about a second, the manpage window jumps back to the beginning
> of the buffer.
>
> My *guess* is that this is related to the changes in commit
> 7e387c9e5265b98dbb3b986f8ab8ac2217052831, but that may well be a red
> herring.

I can reproduce this on both 29.3 and master on GNU/Linux.

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[Robert Pluim]

>>>>> On Tue, 17 Dec 2024 13:19:00 +0000, Stefan Kangas <stefankangas@gmail.com> said:

    Stefan> found 74924 29.3
    Stefan> found 74924 31.0.50
    Stefan> tags 74924 + confirmed
    Stefan> thanks

    Stefan> Ture Pålsson <ture@turepalsson.se> writes:

    >> 1. Run in a terminal window. Operating system seems not to matter; I can
    >> reproduce on both macOS and Linux.
    >> 
    >> 2. Set environment variable MANWIDTH to 80 .
    >> 
    >> 3. Start Emacs ('emacs -nw -Q').
    >> 
    >> 4. Do M-x man, enter the name of some manpage, and type RET.
    >> 
    >> 5. Switch to the manpage window (C-x o), and scroll down by typing 'C-v'
    >> a few times.
    >> 
    >> 6. Switch back to the *scratch* window (C-x o again).
    >> 
    >> 7. After about a second, the manpage window jumps back to the beginning
    >> of the buffer.
    >> 
    >> My *guess* is that this is related to the changes in commit
    >> 7e387c9e5265b98dbb3b986f8ab8ac2217052831, but that may well be a red
    >> herring.

    Stefan> I can reproduce this on both 29.3 and master on GNU/Linux.


This code from man.el should be setq-localʼing Man-columns
unconditionally, I think (itʼs nil by default):

    (when (or window-system
	      (not (or (getenv "MANWIDTH") (getenv "COLUMNS"))))
      ;; Since the page buffer is displayed beforehand,
      ;; we can select its window and get the window/frame width.
      (setq-local Man-columns (Man-columns))
      (setenv "COLUMNS" (number-to-string Man-columns)))



Robert
-- 

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[Eli Zaretskii]

> From: Ture Pålsson <ture@turepalsson.se>
> Date: Tue, 17 Dec 2024 10:07:18 +0100
> 
> 
> 1. Run in a terminal window. Operating system seems not to matter; I can
> reproduce on both macOS and Linux.
> 
> 2. Set environment variable MANWIDTH to 80 .
> 
> 3. Start Emacs ('emacs -nw -Q').
> 
> 4. Do M-x man, enter the name of some manpage, and type RET.
> 
> 5. Switch to the manpage window (C-x o), and scroll down by typing 'C-v'
> a few times.
> 
> 6. Switch back to the *scratch* window (C-x o again).
> 
> 7. After about a second, the manpage window jumps back to the beginning
> of the buffer.

Does the async command ('man' and the filter into which 'man' is
piped) still run when you do the above?  Or is this after the
background formatting has ended?  I'm guessing the former.

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[Eli Zaretskii]

> Cc: Ture Pålsson <ture@turepalsson.se>, 74924@debbugs.gnu.org
> From: Robert Pluim <rpluim@gmail.com>
> Date: Tue, 17 Dec 2024 14:34:37 +0100
> 
> >>>>> On Tue, 17 Dec 2024 13:19:00 +0000, Stefan Kangas <stefankangas@gmail.com> said:
> 
>     Stefan> found 74924 29.3
>     Stefan> found 74924 31.0.50
>     Stefan> tags 74924 + confirmed
>     Stefan> thanks
> 
>     Stefan> Ture Pålsson <ture@turepalsson.se> writes:
> 
>     >> 1. Run in a terminal window. Operating system seems not to matter; I can
>     >> reproduce on both macOS and Linux.
>     >> 
>     >> 2. Set environment variable MANWIDTH to 80 .
>     >> 
>     >> 3. Start Emacs ('emacs -nw -Q').
>     >> 
>     >> 4. Do M-x man, enter the name of some manpage, and type RET.
>     >> 
>     >> 5. Switch to the manpage window (C-x o), and scroll down by typing 'C-v'
>     >> a few times.
>     >> 
>     >> 6. Switch back to the *scratch* window (C-x o again).
>     >> 
>     >> 7. After about a second, the manpage window jumps back to the beginning
>     >> of the buffer.
>     >> 
>     >> My *guess* is that this is related to the changes in commit
>     >> 7e387c9e5265b98dbb3b986f8ab8ac2217052831, but that may well be a red
>     >> herring.
> 
>     Stefan> I can reproduce this on both 29.3 and master on GNU/Linux.
> 
> 
> This code from man.el should be setq-localʼing Man-columns
> unconditionally, I think (itʼs nil by default):
> 
>     (when (or window-system
> 	      (not (or (getenv "MANWIDTH") (getenv "COLUMNS"))))
>       ;; Since the page buffer is displayed beforehand,
>       ;; we can select its window and get the window/frame width.
>       (setq-local Man-columns (Man-columns))
>       (setenv "COLUMNS" (number-to-string Man-columns)))

If this fixes the problem, please install on master, and thanks.

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[Juri Linkov]

> This code from man.el should be setq-localʼing Man-columns
> unconditionally, I think (itʼs nil by default):
>
>     (when (or window-system
> 	      (not (or (getenv "MANWIDTH") (getenv "COLUMNS"))))
>       ;; Since the page buffer is displayed beforehand,
>       ;; we can select its window and get the window/frame width.
>       (setq-local Man-columns (Man-columns))
>       (setenv "COLUMNS" (number-to-string Man-columns)))

The problem is that the number returned by '(Man-columns)'
is inapplicable in case of "MANWIDTH".

So I will add a check for 'Man-columns' like below.

However, before pushing the patch, let's solve another problem
that the manpage window jumps back to the beginning
even on a window system.  Here is the reproducible test case:

1. emacs -Q
2. M-x man RET man RET
3. C-M-v (scroll-other-window)
4. Reduce the width of the frame
5. manpage window jumps back to the beginning

So unless Martin has objections, I will also change
'with-current-buffer' to 'with-selected-window':

diff --git a/lisp/man.el b/lisp/man.el
index 29c3dec501c..ba4f01122e2 100644
--- a/lisp/man.el
+++ b/lisp/man.el
@@ -1300,8 +1300,9 @@ Man--window-state-change
 (defun Man-fit-to-window (window)
   "Adjust width of the buffer to fit columns into WINDOW boundaries."
   (when (window-live-p window)
-    (with-current-buffer (window-buffer window)
+    (with-selected-window window
       (when (and (derived-mode-p 'Man-mode)
+                 Man-columns
                  (not (eq Man-columns (Man-columns))))
         (let ((proc (get-buffer-process (current-buffer))))
           (unless (and proc (not (eq (process-status proc) 'exit)))

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[martin rudalics via Bug reports for GNU Emacs, the Swiss army knife of text editors]

 > However, before pushing the patch, let's solve another problem
 > that the manpage window jumps back to the beginning
 > even on a window system.  Here is the reproducible test case:
 >
 > 1. emacs -Q
 > 2. M-x man RET man RET
 > 3. C-M-v (scroll-other-window)
 > 4. Reduce the width of the frame
 > 5. manpage window jumps back to the beginning

Why does it do that?  I can try to find out by myself but I hope you
already know better.

 > So unless Martin has objections, I will also change
 > 'with-current-buffer' to 'with-selected-window':

I don't have any objections but we'd have to say why it is necessary for
curing the above problem.

martin

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[Juri Linkov]

>> However, before pushing the patch, let's solve another problem
>> that the manpage window jumps back to the beginning
>> even on a window system.  Here is the reproducible test case:
>>
>> 1. emacs -Q
>> 2. M-x man RET man RET
>> 3. C-M-v (scroll-other-window)
>> 4. Reduce the width of the frame
>> 5. manpage window jumps back to the beginning
>
> Why does it do that?  I can try to find out by myself but I hope you
> already know better.

After resizing the frame, 'man' have to regenerate the buffer's contents
with new width.

>> So unless Martin has objections, I will also change
>> 'with-current-buffer' to 'with-selected-window':
>
> I don't have any objections but we'd have to say why it is necessary for
> curing the above problem.

I didn't realize that the problem is worse and actually
'with-selected-window' is not much of help.  This is the same
problem how to restore the point position after reverting Dired buffer,
but much worse.  In Dired we can remember a file name under point.
But for the Man buffer we can't even use some context around point
because after regeneration, the text layout changes significantly.

For example, in 'M-x man RET man RET' there is such text:

  The  manual  page associated with each of these arguments

We could remember the context "The  manual  page".  But after
resizing it's split to next line:

                                                    The
 manual page associated with each  of  these  arguments

Ok, need to try using 'window-point-context-use-default-function'
and modify it to ignore whitespace changes in context strings.

But first need to move 'window-point-context-use-default-function'
to the new file lisp/window-x.el after you will push
Pranshu's patch that creates the new file lisp/window-x.el ;-)

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[martin rudalics via Bug reports for GNU Emacs, the Swiss army knife of text editors]

 > After resizing the frame, 'man' have to regenerate the buffer's contents
 > with new width.

I see.

 > Ok, need to try using 'window-point-context-use-default-function'
 > and modify it to ignore whitespace changes in context strings.

I would make it a two step procedure.

- In a first step try to find an exact fix.

- In the second step ignore whitespace changes.

The second step is slightly more dangerous because it might get us false
positives.

 > But first need to move 'window-point-context-use-default-function'
 > to the new file lisp/window-x.el after you will push
 > Pranshu's patch that creates the new file lisp/window-x.el ;-)

I'm still waiting for Eli's approval.

martin

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[Eli Zaretskii]

> Cc: Robert Pluim <rpluim@gmail.com>,
>  Ture Pålsson <ture@turepalsson.se>,
>  Stefan Kangas <stefankangas@gmail.com>, 74924@debbugs.gnu.org
> Date: Thu, 9 Jan 2025 09:53:17 +0100
> From:  martin rudalics via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
>  > After resizing the frame, 'man' have to regenerate the buffer's contents
>  > with new width.
> 
> I see.
> 
>  > Ok, need to try using 'window-point-context-use-default-function'
>  > and modify it to ignore whitespace changes in context strings.
> 
> I would make it a two step procedure.
> 
> - In a first step try to find an exact fix.
> 
> - In the second step ignore whitespace changes.
> 
> The second step is slightly more dangerous because it might get us false
> positives.
> 
>  > But first need to move 'window-point-context-use-default-function'
>  > to the new file lisp/window-x.el after you will push
>  > Pranshu's patch that creates the new file lisp/window-x.el ;-)
> 
> I'm still waiting for Eli's approval.

Sorry, I wasn't aware you were waiting for my approval.  Where's the
message asking for the approval, so I could re-read it?

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[martin rudalics via Bug reports for GNU Emacs, the Swiss army knife of text editors]

 > Sorry, I wasn't aware you were waiting for my approval.  Where's the
 > message asking for the approval, so I could re-read it?

https://lists.gnu.org/archive/html/emacs-devel/2024-12/msg00702.html

Pranshu's last take on this is here

https://lists.gnu.org/archive/html/emacs-devel/2025-01/msg00002.html

martin

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[Eli Zaretskii]

> Date: Thu, 9 Jan 2025 10:35:39 +0100
> Cc: juri@linkov.net, rpluim@gmail.com, ture@turepalsson.se,
>  stefankangas@gmail.com, 74924@debbugs.gnu.org
> From: martin rudalics <rudalics@gmx.at>
> 
>  > Sorry, I wasn't aware you were waiting for my approval.  Where's the
>  > message asking for the approval, so I could re-read it?
> 
> https://lists.gnu.org/archive/html/emacs-devel/2024-12/msg00702.html
> 
> Pranshu's last take on this is here
> 
> https://lists.gnu.org/archive/html/emacs-devel/2025-01/msg00002.html

Thanks.

The NEWS entry should quote the function names 'like this'.

Other than that, please feel to install, unless there are specific
aspects or portions of the patch you'd like me to look closer at.

bug#74924: 29.3; Buffer showing manpage jumps back to beginning

[Juri Linkov]

>> After resizing the frame, 'man' have to regenerate the buffer's contents
>> with new width.
>
> I see.
>
>> Ok, need to try using 'window-point-context-use-default-function'
>> and modify it to ignore whitespace changes in context strings.
>
> I would make it a two step procedure.
>
> - In a first step try to find an exact fix.
>
> - In the second step ignore whitespace changes.
>
> The second step is slightly more dangerous because it might get us false
> positives.

Ok, now I pushed the immediate fix for this bug report that checks
for 'Man-columns'.  Then later will do this two step procedure
for a more general problem in window-x.el.