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

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From: martin rudalics <rudalics <at> gmx.at>
To: Jyothis V <jyothisv <at> gmail.com>
Cc: 13122 <at> debbugs.gnu.org
Subject: bug#13122: save-excursion not saving point
Date: Sat, 08 Dec 2012 12:21:08 +0100

> I wrote the following version of transpose-chars which is supposed to
> always transform the last two chars without moving the point.
> (defun gosmacs-tranpose-chars (n)
>   (interactive "p")
>   (save-excursion
>     (forward-char (- n))
>     (transpose-chars 1)))
>
> The trouble is, even though I have used save-excursion, the point does
> move 2 characters backwards when n=1! For other values of n, this seems to
> be working fine.

This is a limitation (or bug) in the code of `transpose-subr' and
`transpose-subr-1' due to the use of `delete-and-extract-region' (IIRC
transposing mangles `undo' as well.)

martin

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