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bug#12208: yes-or-no-p escapes with-current-buffer


From: martin rudalics
Subject: bug#12208: yes-or-no-p escapes with-current-buffer
Date: Thu, 16 Aug 2012 11:38:10 +0200

> Open two buffers "buffer1" and  "buffer2" so that both are visible.
>
> Place the following in each buffer
>
> (with-current-buffer "buffer1"
>         (goto-char (point-min))
>    (yes-or-no-p "")
>    (insert "X"))
>
> C-xC-e from buffer1 places "X" at the beginning of the file, while
> C-xC-e from buffer2 places an "X" wherever the point was before moving
> from buffer1. This doesn't happen if only one buffer is visible; Nor
> does it happen if we replace "yes-or-no-p" with "y-or-n-p".
> This happens on both 23.3.1 and 24.1.

Indeed.  What you see is `save-window-excursion' at work.  Let's remove
`yes-or-no-p' from the example.  With emacs -Q in *scratch* evaluate the
following form:

(let ((form
       "(with-current-buffer \"*buffer1*\"
  (goto-char (point-min))
  (save-window-excursion
    nil)
  (setq x (1+ x))
  (insert (format \"%s\" x)))"))
  (setq x 0)
  (switch-to-buffer (get-buffer-create "*buffer1*"))
  (insert form)
  (split-window)
  (other-window 1)
  (switch-to-buffer (get-buffer-create "*buffer2*"))
  (insert form)
  (other-window 1))

Now in any of the two windows go to the end of the buffer and evaluate
the preceding form.  From the *buffer1* window the number is inserted at
position 1, from the *buffer2* window at the position of *buffer1*
before evaluating the form.  If, instead, you used the slightly
different form

(let ((form
       "(with-selected-window (get-buffer-window \"*buffer1*\")
  (goto-char (point-min))
  (save-window-excursion
    nil)
  (setq x (1+ x))
  (insert (format \"%s\" x)))"))
  (setq x 0)
  (switch-to-buffer (get-buffer-create "*buffer1*"))
  (insert form)
  (split-window)
  (other-window 1)
  (switch-to-buffer (get-buffer-create "*buffer2*"))
  (insert form)
  (other-window 1))

both insertions happen at position 1.

martin





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