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Re: Switch buffers without modifying the buffer list ordering?
From: |
martin rudalics |
Subject: |
Re: Switch buffers without modifying the buffer list ordering? |
Date: |
Mon, 31 Jan 2022 09:42:10 +0100 |
> With the following code, I can verify that the NORECORD argument of
> `switch-to-buffer' does what it promises:
>
> ```
> (progn
> (switch-to-buffer "A")
> (switch-to-buffer "B" 'norecord)
> (car (buffer-list)))
> ```
>
> Namely, this makes buffer B current, but returns #<buffer A>.
>
> Now, here's a catch: if next I type `M-x (car (buffer-list))',
... M-: (car (buffer-list)) I suppose ...
> I get
> #<buffer B> instead of #<buffer A>. Why does that happen, and is there
> a way to switch to buffer B and *really* not modify the buffer list
> ordering?
It's restoring the window configuration after reading from the
minibuffer but before evaluating the expression you typed that gets in
the way. Try with emacs -Q and evaluate the forms below step by step
(display-buffer "*Messages*")
(defun foo ()
(message
"%s - %s" (selected-window) (car (buffer-list))))
(add-hook 'buffer-list-update-hook 'foo)
(progn
(switch-to-buffer "A")
(switch-to-buffer "B" 'norecord)
(car (buffer-list)))
and now type M-: (car (buffer-list)). This gets me in the *Messages*
buffer
#<window 3 on A> - A [3 times]
#<buffer A>
#<window 3 on B> - A
#<window 4 on *Minibuf-1*> - *Minibuf-1* [4 times]
#<window 3 on B> - B [2 times]
#<buffer B>
Now try again the same scenario but first evaluate
(setq read-minibuffer-restore-windows nil)
which gets me here the
#<window 3 on A> - A [3 times]
#<buffer A>
you probably expected.
> I'm asking this because of an issue with the live preview feature of the
> Consult package. Very succinctly, the idea here is to temporarily
> change the current buffer during a `completing-read' call, in order to
> display more information about the candidates. When the
> `completing-read' ends, we would like to restore the original order of
> the buffer list. There seems to be no simple way to achieve that, and
> some kludge like the following seems necessary. Any better suggestions?
>
> ```
> (let ((buffers (buffer-list)))
> (unwind-protect
> <do the completing-read with live preview>
> (save-window-excursion
> ;; Restore the original buffer list ordering
> (dolist (buffer buffers)
> (when (buffer-live-p buffer)
> (bury-buffer-internal buffer))))))
That's a different issue. 'buffer-list' is a function that returns a
list from the internal C variable Vbuffer_alist - a variable, Lisp code
is not allowed to modify directly. In order to modify Vbuffer_alist, a
Lisp programmer has to bury buffers in precisely the same way as you do.
You could try coming up with a macro, say 'with-buffer-list-unmodified'
(where you probably should suspend calling 'buffer-list-update-hook'
while running it).
martin