GNU bug report logs - #105
(split-string-and-unquote (combine-and-quote-strings STRINGS)) fails on trivial case

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

From: Joe Wells <jbw <at> macs.hw.ac.uk>
To: bug-gnu-emacs <at> gnu.org
Subject: (split-string-and-unquote (combine-and-quote-strings STRINGS))
	fails on trivial case
Date: Tue, 01 Apr 2008 02:17:23 +0100

The documentation strings for both split-string-and-unquote and
combine-and-quote-strings state that they attempt to achieve this
property:

  (split-string-and-unquote (combine-and-quote-strings strs)) == strs

Here is a trivial case that they fail on; the following sexp wrongly
evaluates to nil:

  (let ((l '("a b" "c")))
    (equal l
           (split-string-and-unquote (combine-and-quote-strings l))))

I hope this problem report is helpful.

Joe

======================================================================
In GNU Emacs 22.2.1 (i686-pc-linux-gnu, GTK+ Version 2.8.20)
 of 2008-04-01 on artemis
Windowing system distributor `The X.Org Foundation', version 11.0.70000000
configured using `configure  '--prefix=/home/jbw/local4' '--enable-debug' '--disable-nls' '--with-x-toolkit=gtk' 'CFLAGS=-O0 -g3 -ggdb -fno-crossjumping -DGLYPH_DEBUG=1''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: en_US.UTF-8
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: jbw
  value of $LANG: nil
  locale-coding-system: utf-8
  default-enable-multibyte-characters: t


-- 
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registered under charity number SC000278

Message #10 received at 105 <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Chong Yidong <cyd <at> stupidchicken.com>
To: Joe Wells <jbw <at> macs.hw.ac.uk>
Cc: 105 <at> debbugs.gnu.org, emacs-devel <at> gnu.org
Subject: Re: (split-string-and-unquote (combine-and-quote-strings STRINGS)) fails on trivial case
Date: Mon, 07 Apr 2008 01:31:34 -0400

> The documentation strings for both split-string-and-unquote and
> combine-and-quote-strings state that they attempt to achieve this
> property:
>
>   (split-string-and-unquote (combine-and-quote-strings strs)) == strs
>
> Here is a trivial case that they fail on; the following sexp wrongly
> evaluates to nil:
>
>   (let ((l '("a b" "c")))
>     (equal l
>            (split-string-and-unquote (combine-and-quote-strings l))))

I think this is a docstring mistake.  IIUC, the equation

 (split-string-and-unquote (combine-and-quote-strings strs)) == strs

only holds if STRS is a list containing a single string.  The point the
docstrings are trying to make is that combine-and-quote-strings performs
string quoting, while split-string-and-unquote performs unquoting.

If there are no objections to this interpretation, I'll check in a doc
fix shortly.

Message #15 received at 105-done <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: 105-done <at> debbugs.gnu.org
Subject: Re: (split-string-and-unquote (combine-and-quote-strings STRINGS)) fails on trivial case
Date: Mon, 07 Apr 2008 12:23:25 -0400

>> The documentation strings for both split-string-and-unquote and
>> combine-and-quote-strings state that they attempt to achieve this
>> property:
>> 
>> (split-string-and-unquote (combine-and-quote-strings strs)) == strs
>> 
>> Here is a trivial case that they fail on; the following sexp wrongly
>> evaluates to nil:
>> 
>> (let ((l '("a b" "c")))
>> (equal l
>> (split-string-and-unquote (combine-and-quote-strings l))))

> I think this is a docstring mistake.

I disagree.  This is a bug in the code.  I believe the patch below fixes it.


        Stefan


--- subr.el.~1.588.~	2008-04-07 10:23:51.000000000 -0400
+++ subr.el	2008-04-07 12:21:23.000000000 -0400
@@ -2987,10 +2987,11 @@
 This tries to quote the strings to avoid ambiguity such that
   (split-string-and-unquote (combine-and-quote-strings strs)) == strs
 Only some SEPARATORs will work properly."
-  (let ((sep (or separator " ")))
+  (let* ((sep (or separator " "))
+         (re (concat "[\\\"]" "\\|" (regexp-quote sep))))
     (mapconcat
      (lambda (str)
-       (if (string-match "[\\\"]" str)
+       (if (string-match re str)
 	   (concat "\"" (replace-regexp-in-string "[\\\"]" "\\\\\\&" str) "\"")
 	 str))
      strings sep)))

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