GNU bug report logs - #4803
Undo fails to restore marker position correctly

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Message #5 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Toby Cubitt <tsc25 <at> cantab.net>
To: bug-gnu-emacs <at> gnu.org
Subject: Undo fails to restore marker position correctly
Date: Sat, 24 Oct 2009 17:18:48 -0700

In GNU Emacs 23.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.16.6)
  of 2009-10-17


Steps to reproduce:
-------------------
(switch-to-buffer "*scratch*")  ; any buffer containing some text will do
(setq mrk (make-marker))
(move-marker mrk 5)             ; any position within text will do
(set-marker-insertion-type mrk t)
(delete-region 1 10)
(undo)

Marker mrk is now at position 15 in *scratch* instead of 5.


Toby
--
Dr T. S. Cubitt
Quantum Information Theory group
Department of Mathematics
University of Bristol
United Kingdom

email: tsc25 <at> cantab.net
web: www.dr-qubit.org

Message #10 received at 4803-done <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Stefan Monnier <monnier <at> IRO.UMontreal.CA>
To: Toby Cubitt <toby-dated-1256861956.bb6a54 <at> dr-qubit.org>
Subject: Re: Undo fails to restore marker position correctly
Date: Tue, 24 Nov 2009 16:33:39 -0500

> (switch-to-buffer "*scratch*")  ; any buffer containing some text will do
> (setq mrk (make-marker))
> (move-marker mrk 5)             ; any position within text will do
> (set-marker-insertion-type mrk t)
> (delete-region 1 10)
> (undo)

> Marker mrk is now at position 15 in *scratch* instead of 5.

I've just installed the patch below should should fix it.
Thanks for catching it!


        Stefan


=== modified file 'src/insdel.c'
--- src/insdel.c	2009-11-24 15:30:54 +0000
+++ src/insdel.c	2009-11-24 21:28:22 +0000
@@ -377,7 +377,7 @@
 	       upon re-inserting the deleted text, so we have to arrange
 	       for them to move backward to the correct position.  */
 	      XSETMISC (marker, m);
-	    record_marker_adjustment (marker, charpos - to);
+	      record_marker_adjustment (marker, to - charpos);
 	    }
 	  m->charpos = from;
 	  m->bytepos = from_byte;

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