GNU bug report logs - #4312
23.1; save-excursion and goto-char fail

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

From: RSridhar <rsridar50 <at> dataone.in>
To: bug-gnu-emacs <at> gnu.org
Subject: 23.1;  save-excursion and goto-char fail
Date: Wed, 02 Sep 2009 15:33:05 +0530

1. I have a lisp code which saves file buffer and does some manipulation
on the 
file in shell. subsequently it is reverted. However I have tried
save-excursion 
before saving file which did not restore the file position on reverting.
So I tr
ied setq point to some var and after reverting restore point with
goto-char. Thi
s also did not ork in restoring previous position although (point)
function did 
return the correct  value from the goto-char function in lisp. 

2. The file manipulated contains utf-8 chars. Every now and then octal
values di
splay as language text but most of the time only octal utf-8 chars are
displayed
. Also the devanaagari font that is displayed incorrectly when it is
displayed..
. The (itrans) short i is to be to the left of the consonant but gets
associated
 with the right consonant. 

3. re-search-forward function fails regular expression with octal code
   
In GNU Emacs 23.1.1 (i386-redhat-linux-gnu, GTK+ Version 2.16.5)
 of 2009-08-26 on x86-2.fedora.phx.redhat.com
Windowing system distributor `The X.Org Foundation', version
11.0.10602000
configured using `configure  '--build=i386-redhat-linux-gnu'
'--host=i386-redhat-linux-gnu' '--target=i586-redhat-linux-gnu'
'--program-prefix=' '--prefix=/usr' '--exec-prefix=/usr'
'--bindir=/usr/bin' '--sbindir=/usr/sbin' '--sysconfdir=/etc'
'--datadir=/usr/share' '--includedir=/usr/include' '--libdir=/usr/lib'
'--libexecdir=/usr/libexec' '--localstatedir=/var'
'--sharedstatedir=/var/lib' '--mandir=/usr/share/man'
'--infodir=/usr/share/info' '--with-dbus' '--with-gif' '--with-jpeg'
'--with-png' '--with-rsvg' '--with-tiff' '--with-xft' '--with-xpm'
'--with-x-toolkit=gtk' 'build_alias=i386-redhat-linux-gnu'
'host_alias=i386-redhat-linux-gnu' 'target_alias=i586-redhat-linux-gnu'
'CFLAGS=-DMAIL_USE_LOCKF -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2
-fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32
-march=i586 -mtune=generic -fasynchronous-unwind-tables''

Important settings:
  value of $LC_ALL: C
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: nil
  default-enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  show-paren-mode: t
  cua-mode: t
  tooltip-mode: t
  tool-bar-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <menu-bar> 
<help-menu> <send-emacs-bug-report>

Recent messages:
Loading /usr/share/emacs/site-lisp/site-start.d/focus-init.el
(source)...done
Loading /usr/share/emacs/site-lisp/site-start.d/nxml-init.el (source)...
Loading /usr/share/emacs/site-lisp/nxml-mode/rng-auto.el (source)...done
Loading /usr/share/emacs/site-lisp/site-start.d/nxml-init.el
(source)...done
Loading /usr/share/emacs/site-lisp/site-start.d/php-mode-init.el
(source)...done
Loading /usr/share/emacs/site-lisp/site-start.d/po-mode-init.el
(source)...done
Loading /usr/share/emacs/site-lisp/site-start.d/rpm-spec-mode-init.el
(source)...done
Loading cua-base...done
Loading paren...done
For information about GNU Emacs and the GNU system, type C-h C-a.

-- 
RSridhar <rsridar50 <at> dataone.in>

Message #12 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: RSridhar <rsridar50 <at> dataone.in>
Cc: 4312 <at> debbugs.gnu.org, bug-gnu-emacs <at> gnu.org
Subject: Re: bug#4312: 23.1;  save-excursion and goto-char fail
Date: Thu, 03 Sep 2009 09:51:04 -0400

> 1. I have a lisp code which saves file buffer and does some
> manipulation on the file in shell.  subsequently it is reverted.
> However I have tried save-excursion before saving file which did not
> restore the file position on reverting.

save-excursion uses markers to remember the position.  But markers only
keep track of positions by keeping track of insertions/deletions and
adjusting the position accordingly.  When the changes happen outside
Emacs, this doesn't work too well, because Emacs sees your revert-buffer
as just one big delete&insert.

> So I tried setq point to some var and after reverting restore point
> with goto-char. Thi s also did not ork in restoring previous position
> although (point) function did return the correct  value from the
> goto-char function in lisp. 

This should "work" in the sense that it will keep point at the same
numerical position (same distance from the beginning of the file, when
counted in chars).  But it may very well not be pointing at the same
conceptual place in the file if you've added/removed content.

Maybe you should use bookmarks for that: bookmarks remember the position
together with the context (the text immediately before and after point),
so as to be able to find the "same spot" again, even if it moved in
the file.

> 3. re-search-forward function fails regular expression with octal code

IIRC, we already have a bug report about that (bug#3822).  But no
I haven't had time to look at it yet.
   

        Stefan

Message #22 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Andreas Schwab <schwab <at> linux-m68k.org>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 4312 <at> debbugs.gnu.org, RSridhar <rsridar50 <at> dataone.in>,
        bug-gnu-emacs <at> gnu.org
Subject: Re: bug#4312: 23.1;  save-excursion and goto-char fail
Date: Thu, 03 Sep 2009 18:33:01 +0200

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

>> 1. I have a lisp code which saves file buffer and does some
>> manipulation on the file in shell.  subsequently it is reverted.
>> However I have tried save-excursion before saving file which did not
>> restore the file position on reverting.
>
> save-excursion uses markers to remember the position.  But markers only
> keep track of positions by keeping track of insertions/deletions and
> adjusting the position accordingly.  When the changes happen outside
> Emacs, this doesn't work too well, because Emacs sees your revert-buffer
> as just one big delete&insert.

insert-file-contents tries to keep markers if possible, but that only
works if the marker points into the unchanged head or tail of the
replaced contents.

Andreas.

-- 
Andreas Schwab, schwab <at> linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

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