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
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