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

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From: Tino Calancha <tino.calancha <at> gmail.com>
To: 13122-done <at> debbugs.gnu.org
Subject: bug#13122: save-excursion not saving point
Date: Sat, 4 May 2019 17:39:11 +0900 (JST)

Saving the point, in the general case, would rely on unspecified 
behaviour; so I close this bug.
>>>> ;; 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
> 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.

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