Subject: bug#103: 23.0.60; Segmentation fault loading auto-lang.el

From: Chong Yidong <[email-masked]>
Date: Tue, 08 Apr 2008 12:50:11 -0400

Kenichi Handa <[email-masked]> writes:

> In article <[email-masked]>, Chong Yidong <[email-masked]> writes:
>
>> > - download http://www.marquardt-home.de/auto-lang.el to ~/.elisp/
>> > - run emacs -Q
>> > - M-x load-file
>> > - choose file ~/.elisp/auto-lang.el
>> > => Emacs segfaults (same result with emacs -Q -nw)
>
>> This is due to an infinite nesting depth in regexp-opt, which can be
>> tracked down to the following problem:
>
>> (let ((str (string-as-unibyte "ä")))
>>   (string-match (char-to-string (string-to-char str)) str))
>
>> evaluates to 0 in Emacs 22, and to nil in Emacs 23.  It turns out that
>> this screws up the use of all-completions in regexp-opt-group.
>
>> Anyone have any idea what's going on here?
>
> (string-as-unibyte "ä") => "\303\244"
> (string-to-char "\303\244") => 195 (because ?\303 == 195)
> (char-to-string 195) => "Ã" (because 195==0xC3 U+00C3=='Ã')
> (string-match "Ã" "ä") => nil (obvious)
>
> Any Lisp program that depends on the result of
> string-as-unibyte (thus Emacs' internal character
> representation) won't work in Emacs 23.

I see.  However, maybe the following change to regexp-opt-group in
regexp-opt.el would make things a little more predictable.  What do you
think?

*** trunk/lisp/emacs-lisp/regexp-opt.el.~1.37.~	2008-03-14 17:17:34.000000000 -0400
--- trunk/lisp/emacs-lisp/regexp-opt.el	2008-04-08 12:46:49.000000000 -0400
***************
*** 226,232 ****
  
  	      ;; Otherwise, divide the list into those that start with a
  	      ;; particular letter and those that do not, and recurse on them.
! 	      (let* ((char (char-to-string (string-to-char (car strings))))
  		     (half1 (all-completions char strings))
  		     (half2 (nthcdr (length half1) strings)))
  		(concat open-group
--- 226,232 ----
  
  	      ;; Otherwise, divide the list into those that start with a
  	      ;; particular letter and those that do not, and recurse on them.
! 	      (let* ((char (substring (car strings) 0 1))
  		     (half1 (all-completions char strings))
  		     (half2 (nthcdr (length half1) strings)))
  		(concat open-group