GNU bug report logs - #34100
26.1; Incomplete ? and ?? handling in rx

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#34100: closed (26.1; Incomplete ? and ?? handling in rx)
Date: Fri, 01 Feb 2019 09:45:01 +0000

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Your message dated Fri, 01 Feb 2019 11:44:20 +0200
with message-id <83va23yhaj.fsf <at> gnu.org>
and subject line Re: bug#34100: Acknowledgement (26.1; Incomplete ? and ?? handling in rx)
has caused the debbugs.gnu.org bug report #34100,
regarding 26.1; Incomplete ? and ?? handling in rx
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


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34100: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=34100
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From: Mattias Engdegård <mattiase <at> acm.org>
To: bug-gnu-emacs <at> gnu.org
Subject: 26.1; Incomplete ? and ?? handling in rx
Date: Wed, 16 Jan 2019 12:39:58 +0100

In rx, the ? and ?? operators can be written verbatim as ? and ?? (space and ? character), or by using symbols whose leading character needs to be escaped, \? and \?? respectively. The names come from Olin Shivers's SRE, but ? is not a special character in Scheme syntax, hence the character syntax hack.

However, the symbols only partially work:

(rx (\? "x") (\?? "y"))       --> "x?y?"  ; expected "x?y??"
(rx (minimal-match (\? "x"))) --> "x??"   ; expected "x?"

While it could be argued that only the character-based syntax should be used, the fact is that the symbols are accepted and seem to work, just in a subtly broken way.

The documentation is also not clear on this point, and a programmer knowing the elisp syntax might very well assume that the symbols are the ones to use.

Suggested fix:

diff --git a/lisp/emacs-lisp/rx.el b/lisp/emacs-lisp/rx.el
index a39fe55c32..8b4551d0d3 100644
--- a/lisp/emacs-lisp/rx.el
+++ b/lisp/emacs-lisp/rx.el
@@ -733,8 +733,8 @@
 is non-nil."
   (rx-check form)
   (setq form (rx-trans-forms form))
-  (let ((suffix (cond ((memq (car form) '(* + ?\s)) "")
-		      ((memq (car form) '(*? +? ??)) "?")
+  (let ((suffix (cond ((memq (car form) '(* + \? ?\s)) "")
+		      ((memq (car form) '(*? +? \?? ??)) "?")
 		      (rx-greedy-flag "")
 		      (t "?")))
 	(op (cond ((memq (car form) '(* *? 0+ zero-or-more)) "*")

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From: Eli Zaretskii <eliz <at> gnu.org>
To: mattiase <at> acm.org
Cc: Michael Heerdegen <michael_heerdegen <at> web.de>, 34100-done <at> debbugs.gnu.org
Subject: Re: bug#34100: Acknowledgement (26.1;
 Incomplete ? and ?? handling in rx)
Date: Fri, 01 Feb 2019 11:44:20 +0200

> From: Michael Heerdegen <michael_heerdegen <at> web.de>
> Date: Mon, 28 Jan 2019 16:53:28 +0100
> Cc: 34100 <at> debbugs.gnu.org
> 
> Mattias Engdegård <mattiase <at> acm.org> writes:
> 
> > Anything more I can do? I thought this one would be rather
> > straightforward.  I do understand that there are more pressing
> > matters.
> 
> I guess you just have to be patient until someone has a look.  That can
> sometimes take some time, there are a lot of open bug reports...
> 
> For me what you suggest looks like a good idea btw.

Sorry for the long delay, Mattias.  I've now pushed your changes to
the master branch, and I'm marking this bug done.

Thanks.

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