GNU bug report logs - #13122
transpose-subr defeats save-excursion

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From: Andreas Schwab <schwab <at> linux-m68k.org>
To: Tino Calancha <tino.calancha <at> gmail.com>
Cc: Eli Zaretskii <eliz <at> gnu.org>, 13122 <at> debbugs.gnu.org
Subject: bug#13122: save-excursion not saving point
Date: Sat, 27 Apr 2019 11:59:48 +0200

On Apr 27 2019, Tino Calancha <tino.calancha <at> gmail.com> wrote:

> On Sat, 27 Apr 2019, Eli Zaretskii wrote:
>
>>> From: Tino Calancha <tino.calancha <at> gmail.com>
>>> Date: Sat, 27 Apr 2019 04:53:56 +0900
>>>
>>> ;; Following expression should eval as non-nil
>>> (let ((pos 3))
>>>   (with-temp-buffer
>>>     (insert "abcdef")
>>>     (goto-char pos)
>>>     (save-excursion (transpose-chars 2))
>>>     (= pos (point))))
>>> => nil
>
> I read that warning; maybe getting `nil' is above is expected; if that's
> the case then we can close the report again.

Since the form inside save-excursion can modify the text before point,
there is never a guarantee that the numeric value of point stays the
same.  And if point points inside the modified text, it is generally
unspecified how point moves during the modification.

Andreas.

-- 
Andreas Schwab, schwab <at> linux-m68k.org
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