Re: Switch buffers without modifying the buffer list ordering?

[martin rudalics <rudalics@gmx.at>]

 > 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