GNU bug report logs - #68235
29.1.90; Switching tabs stops following process output in selected window

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From: martin rudalics <rudalics <at> gmx.at>
To: Juri Linkov <juri <at> linkov.net>
Cc: daniel.c.mccarthy <at> gmail.com, Eli Zaretskii <eliz <at> gnu.org>, 68235 <at> debbugs.gnu.org
Subject: bug#68235: 29.1.90; Switching tabs stops following process output in selected window
Date: Tue, 23 Jan 2024 10:30:49 +0100

> 1. 'post-set-window-configuration-functions' is called even
> after 'delete-other-windows' and 'kill-buffer', albeit with
> windows=nil, so no problems.

I don't understand what you mean here.  Do you mean that it gets called
because for some reason 'set-window-configuration' gets called after
'delete-other-windows' and 'kill-buffer'?

> 2. It seems there is no way to get the name of the killed buffer
> from '(nth 1 quad)'?

No way.  'buffer-name' with a killed buffer as argument has to return
nil - too many functions may rely on that.

> Here is what I tried:
>
> (defun foo (frame windows)
>    (while windows
>      (let* ((quad (car windows))
> 	   (window (car quad))
> 	   (buffer (generate-new-buffer
>                      (format " *Old buffer %s*" (nth 1 quad)))))
>        (with-current-buffer buffer
>          (insert (format "Restore the original buffer named %s:\n"
> 			(nth 1 quad)))
> 	(insert-button
> 	 "[Restore]"
>           'action
> 	 (lambda (_button)
>             (set-window-buffer window (find-file-noselect
>                                        (buffer-file-name (nth 1 quad))))
> 	   (set-window-point window (nth 3 quad))
> 	   (set-window-start window (nth 2 quad) t)))
> 	(set-window-buffer window buffer)))
>      (setq windows (cdr windows))))
>
> It inserts to the transient buffer this text without the real buffer name:
>
>    Restore the original buffer named #<killed buffer>:
>    [Restore]

I'd say Restore buffer from ... and use the file name here.

> But the button really restores the original buffer.

Because many functions with a buffer as argument like 'buffer-file-name'
don't check whether that buffer is live.  You can find such functions by
looking for "decode_buffer (buffer)" in buffer.c.  'buffer-name' fails
because the name of the buffer _is_ reset to nil when the buffer is
killed.  We could add a new field to the buffer structure and a function
say 'buffer-last-name' which would return the last name a buffer had
before it was renamed: nil for a new buffer, the old name before the
last 'rename-buffer' and the last buffer name for a dead buffer.

And always think about what to propose when a new buffer with the same
name has been created meanwhile.

> 3. It seems the buffer-local value of 'revert-buffer-function'
>     is not preserved in the killed buffer?

'kill-buffer' calls reset_buffer_local_variables which scans the local
variables alist of the buffer and resets all values to their default
values.  Giving the variable either a 'permanent-local' property or
binding the default value to the buffer local value around 'kill-buffer'
could work around that but I'd rather try to save this (and other buffer
local values) in a separate alist for buffers stored in a configuration.

martin

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