bug#10196: 24.0.92; prolog-mode error

bug#10196: 24.0.92; prolog-mode error

[Simen Heggestøyl]

 Starting from 'emacs -Q', running 'M-x prolog-mode' gives the following
 error message:
       prolog-find-value-by-system: Wrong type argument: bufferp, nil

 In GNU Emacs 24.0.92.1 (i686-pc-linux-gnu, GTK+ Version 2.24.8)
  of 2011-12-02 on d610
 Windowing system distributor `The X.Org Foundation', version 
 11.0.11102000
 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_US.UTF-8
   value of $XMODIFIERS: nil
   locale-coding-system: utf-8-unix
   default enable-multibyte-characters: t

 Major mode: Prolog

 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:
 M-x p r o l <tab> <return> M-x r e p o r t - e m <tab>
 <return>

 Recent messages:
 For information about GNU Emacs and the GNU system, type C-h C-a.
 prolog-find-value-by-system: Wrong type argument: bufferp, nil

 Load-path shadows:
 None found.

 Features:
 (shadow sort gnus-util mail-extr message format-spec rfc822 mml mml-sec
 mm-decode mm-bodies mm-encode mail-parse rfc2231 rfc2047 rfc2045
 ietf-drums mm-util mail-prsvr mailabbrev mail-utils gmm-utils 
 mailheader
 emacsbug prolog align easymenu comint regexp-opt 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)

bug#10196: 24.0.92; prolog-mode error

[Stefan Monnier]

> Starting from 'emacs -Q', running 'M-x prolog-mode' gives the following
> error message:
>       prolog-find-value-by-system: Wrong type argument: bufferp, nil

Thanks, I've installed the patch below which should avoid this error,
tho it may hide some underlying problem, so if some other problem shows
up, make sure to come back here.


        Stefan


=== modified file 'lisp/progmodes/prolog.el'
--- lisp/progmodes/prolog.el	2011-11-26 08:26:37 +0000
+++ lisp/progmodes/prolog.el	2011-12-03 04:05:34 +0000
@@ -868,8 +868,9 @@
 (defun prolog-find-value-by-system (alist)
   "Get value from ALIST according to `prolog-system'."
   (let ((system (or prolog-system
-                    (buffer-local-value 'prolog-system
-                                        (prolog-inferior-buffer 'dont-run)))))
+                    (let ((infbuf (prolog-inferior-buffer 'dont-run)))
+                      (when infbuf
+                        (buffer-local-value 'prolog-system infbuf))))))
     (if (listp alist)
         (let (result
               id)