bug#1948: confusion and bug in dabbrev.el

[Fred <fred@fperrin.net>]

Follow-up to http://debbugs.gnu.org/cgi/bugreport.cgi?bug=1948

I seem to be experiencing a bad version of this bug. In some instances,
dabbrev seems to feel like not only inserting text at point (which is
expected) but also modifying some text in other parts of the buffer. 
For
some reason, TCL code seems to trigger the bug quite easily. To see 
what
I experienced:

Save the following as blah.tcl:

====== beginning of blah.tcl
proc check { topology } {
     set network [ blahblah ]
     preconfig $topology $networks
     do_check  $topology $networks
}

# Apply the default pre-config steps for each device
proc preconfig { topology networks } {
     foreach node [ keylkeys topology ] {
	set config [ get_config -device $node -type pre ]
	apply_config $node $config
     }
}

# do the actual check
proc do_check {
====== end of blah.tcl

Start `emacs -Q', and either look at the `view-lossage' output included
below, or in plain English:

- Open blah.tcl
- Put the point after the opening brace of do_check;
- Insert `SPC top' and complete with `dabbrev-expand' (M-/) to get
   `topology';
- Insert `SPC' and try to complete (M-/) until you get `topology 
network'.

Expected:

After a round or two, dabbrev inserts networks, based on the prototype
of `preconfig'. At worse, it inserts rubbish and I have to give a 
longer
hint to dabbrev.

Actual result:

Some text after the last occurence of `topology' is replaced, point has
been moved, and procedure prototype has not been completed.

With Peter Tury's patch to `dabbrev--substitute-expansion', point does
not seem to start jumping around, replacing text in remote places
(though I don't have the correct replacement, but whatever)


In GNU Emacs 24.2.1 (x86_64-pc-linux-gnu, GTK+ Version 2.24.10)
  of 2012-09-09 on trouble, modified by Debian
Windowing system distributor `The X.Org Foundation', version 
11.0.11203902
Configured using:
  `configure '--build' 'x86_64-linux-gnu' '--build' 'x86_64-linux-gnu'
  '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib'
  '--localstatedir=/var/lib' '--infodir=/usr/share/info'
  '--mandir=/usr/share/man' '--with-pop=yes'
  
'--enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.2/site-lisp:/usr/share/emacs/site-lisp'
  '--with-crt-dir=/usr/lib/x86_64-linux-gnu' '--with-x=yes'
  '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars'
  'build_alias=x86_64-linux-gnu' 'CFLAGS=-g -O2 -fstack-protector
  --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall'
  'CPPFLAGS=-D_FORTIFY_SOURCE=2''

Important settings:
   value of $LC_ALL: nil
   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_GB.UTF-8
   value of $XMODIFIERS: nil
   locale-coding-system: utf-8-unix
   default enable-multibyte-characters: t

Major mode: Tcl

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

Recent input:
C-x C-f / t m p / b l a h . t c l <return> C-s d o
_ c C-s C-e SPC t o p M-/ SPC M-/ M-/ C-/ C-/ M-x r
e p o <tab> r t - e m <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark saved where search started
Undo! [2 times]
Making completion list...

Load-path shadows:
/usr/share/emacs/24.2/site-lisp/flim/hex-util hides 
/usr/share/emacs/24.2/lisp/hex-util
/usr/share/emacs/24.2/site-lisp/flim/md4 hides 
/usr/share/emacs/24.2/lisp/md4
/usr/share/emacs/24.2/site-lisp/dictionaries-common/flyspell hides 
/usr/share/emacs/24.2/lisp/textmodes/flyspell
/usr/share/emacs/24.2/site-lisp/dictionaries-common/ispell hides 
/usr/share/emacs/24.2/lisp/textmodes/ispell
/usr/share/emacs/24.2/site-lisp/flim/sasl-ntlm hides 
/usr/share/emacs/24.2/lisp/net/sasl-ntlm
/usr/share/emacs/24.2/site-lisp/flim/sasl-digest hides 
/usr/share/emacs/24.2/lisp/net/sasl-digest
/usr/share/emacs/24.2/site-lisp/flim/hmac-def hides 
/usr/share/emacs/24.2/lisp/net/hmac-def
/usr/share/emacs/24.2/site-lisp/flim/sasl hides 
/usr/share/emacs/24.2/lisp/net/sasl
/usr/share/emacs/24.2/site-lisp/flim/hmac-md5 hides 
/usr/share/emacs/24.2/lisp/net/hmac-md5
/usr/share/emacs/24.2/site-lisp/flim/ntlm hides 
/usr/share/emacs/24.2/lisp/net/ntlm
/usr/share/emacs/24.2/site-lisp/flim/sasl-cram hides 
/usr/share/emacs/24.2/lisp/net/sasl-cram

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 
mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
mail-prsvr mail-utils help-mode view dabbrev misearch multi-isearch tcl
easymenu comint regexp-opt ansi-color ring time-date tooltip ediff-hook
vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image
fringe lisp-mode register page menu-bar rfn-eshadow timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core frame 
cham
georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese hebrew greek romanian slovak czech european ethiopic
indian cyrillic chinese case-table epa-hook jka-cmpr-hook help simple
abbrev minibuffer loaddefs button faces cus-face files text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote make-network-process dbusbind
dynamic-setting system-font-setting font-render-setting move-toolbar 
gtk
x-toolkit x multi-tty emacs)

-- 
Fred -- http://tar-jx.bz