GNU bug report logs - #78690
31.0.50; split string: args out of range with TRIM

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: bug-gnu-emacs <at> gnu.org
Subject: 31.0.50; split string: args out of range with TRIM
Date: Wed, 04 Jun 2025 04:36:26 +0200

Hello,

I stumbled across this:

#+begin_src emacs-lisp
(split-string
 "-*- lexical-binding: t; -*-"
 "-\\*-" nil "[ \t\n\r-]+")
#+end_src

~~>

| Debugger entered--Lisp error: (args-out-of-range "-*- lexical-binding: t; -*-" 1 0)
|   (substring "-*- lexical-binding: t; -*-" 1 0)
|   (let ((this (substring string this-start this-end))) (if trim (progn (let ((tem (string-match (concat trim "\\'") this 0))) (and tem (< tem (length this)) (setq this (substring this 0 tem)))))) (if (or keep-nulls (> (length this) 0)) (progn (setq list (cons this list)))))
|   (progn (let ((this (substring string this-start this-end))) (if trim (progn (let ((tem (string-match ... this 0))) (and tem (< tem (length this)) (setq this (substring this 0 tem)))))) (if (or keep-nulls (> (length this) 0)) (progn (setq list (cons this list))))))
|   (if (or keep-nulls (< this-start this-end)) (progn (let ((this (substring string this-start this-end))) (if trim (progn (let ((tem ...)) (and tem (< tem ...) (setq this ...))))) (if (or keep-nulls (> (length this) 0)) (progn (setq list (cons this list)))))))
|   (#f(lambda () [(list nil) (this-end 0) (this-start 1) (keep-nulls t) (trim "[ \11\n\15-]+") (string "-*- lexical-binding: t; -*-")] (if trim (progn (let ((tem (string-match trim string this-start))) (and (eq tem this-start) (setq this-start (match-end 0)))))) (if (or keep-nulls (< this-start this-end)) (progn (let ((this (substring string this-start this-end))) (if trim (progn (let ... ...))) (if (or keep-nulls (> ... 0)) (progn (setq list ...))))))))
|   (funcall #f(lambda () [(list nil) (this-end 0) (this-start 1) (keep-nulls t) (trim "[ \11\n\15-]+") (string "-*- lexical-binding: t; -*-")] (if trim (progn (let ((tem (string-match trim string this-start))) (and (eq tem this-start) (setq this-start (match-end 0)))))) (if (or keep-nulls (< this-start this-end)) (progn (let ((this (substring string this-start this-end))) (if trim (progn (let ... ...))) (if (or keep-nulls (> ... 0)) (progn (setq list ...))))))))
|   (while (and (string-match rexp string (if (and notfirst (= start (match-beginning 0)) (< start (length string))) (1+ start) start)) (< start (length string))) (setq notfirst t) (progn (setq this-start start) (setq this-end (match-beginning 0)) (setq start (match-end 0))) (funcall push-one))
|   (let* ((keep-nulls (not (if separators omit-nulls t))) (rexp (or separators split-string-default-separators)) (start 0) this-start this-end notfirst (list nil) (push-one #'(lambda nil (if trim (progn (let ... ...))) (if (or keep-nulls (< this-start this-end)) (progn (let ... ... ...)))))) (while (and (string-match rexp string (if (and notfirst (= start (match-beginning 0)) (< start (length string))) (1+ start) start)) (< start (length string))) (setq notfirst t) (progn (setq this-start start) (setq this-end (match-beginning 0)) (setq start (match-end 0))) (funcall push-one)) (progn (setq this-start start) (setq this-end (length string))) (funcall push-one) (nreverse list))
|   (split-string "-*- lexical-binding: t; -*-" "-\\*-" nil "[ \11\n\15-]+")

No problem without TRIM arg in the call.


TIA,

Michael.



In GNU Emacs 31.0.50 (build 23, x86_64-pc-linux-gnu, cairo version
 1.16.0) of 2025-06-03 built on drachen
Repository revision: 8e4a0ea35908e08c2220bafee33a05c33f24bbc3
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101007
System Description: Debian GNU/Linux 12 (bookworm)

Configured using:
 'configure --with-x-toolkit=no --with-native-compilation=no'

Message #8 received at 78690 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: 78690 <at> debbugs.gnu.org
Subject: Re: bug#78690: 31.0.50; split string: args out of range with TRIM
Date: Thu, 05 Jun 2025 18:48:44 +0300

> Date: Wed, 04 Jun 2025 04:36:26 +0200
> From:  Michael Heerdegen via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs <at> gnu.org>
> 
> 
> Hello,
> 
> I stumbled across this:
> 
> #+begin_src emacs-lisp
> (split-string
>  "-*- lexical-binding: t; -*-"
>  "-\\*-" nil "[ \t\n\r-]+")
> #+end_src
> 
> ~~>
> 
> | Debugger entered--Lisp error: (args-out-of-range "-*- lexical-binding: t; -*-" 1 0)
> |   (substring "-*- lexical-binding: t; -*-" 1 0)
> |   (let ((this (substring string this-start this-end))) (if trim (progn (let ((tem (string-match (concat trim "\\'") this 0))) (and tem (< tem (length this)) (setq this (substring this 0 tem)))))) (if (or keep-nulls (> (length this) 0)) (progn (setq list (cons this list)))))

It is quite obvious that split-string is not prepared to deal with a
situation where the argument STRING begins with a match for
SEPARATORS.  The breakage here happens because the match for
SEPARATORS at the very beginning of STRING also matches TRIM, but even
if that is not so, a match for SEPARATORS at the beginning of STRING
sets THIS-START incorrectly for the first call to push-one inside the
while-loop.

Message #11 received at 78690 <at> debbugs.gnu.org (full text, mbox):

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 78690 <at> debbugs.gnu.org
Subject: Re: bug#78690: 31.0.50; split string: args out of range with TRIM
Date: Fri, 06 Jun 2025 03:53:47 +0200

Eli Zaretskii <eliz <at> gnu.org> writes:

> It is quite obvious that split-string is not prepared to deal with a
> situation where the argument STRING begins with a match for
> SEPARATORS.  The breakage here happens because the match for
> SEPARATORS at the very beginning of STRING also matches TRIM, but even
> if that is not so, a match for SEPARATORS at the beginning of STRING
> sets THIS-START incorrectly for the first call to push-one inside the
> while-loop.

I read that as "confirmed, a bug".  Ok, thanks for the analysis.

The original use case is in Helm btw, which does a call like this.  I
made the example a bit shorter for this report - in the original issue
the string starts with whitespace, like

  "            -*- lexical-binding: t; -*-"

but as you already mentioned the issue is the same.


Michael.

Message #14 received at 78690 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: 78690 <at> debbugs.gnu.org
Subject: Re: bug#78690: 31.0.50; split string: args out of range with TRIM
Date: Fri, 06 Jun 2025 10:10:25 +0300

> From: Michael Heerdegen <michael_heerdegen <at> web.de>
> Cc: 78690 <at> debbugs.gnu.org
> Date: Fri, 06 Jun 2025 03:53:47 +0200
> 
> Eli Zaretskii <eliz <at> gnu.org> writes:
> 
> > It is quite obvious that split-string is not prepared to deal with a
> > situation where the argument STRING begins with a match for
> > SEPARATORS.  The breakage here happens because the match for
> > SEPARATORS at the very beginning of STRING also matches TRIM, but even
> > if that is not so, a match for SEPARATORS at the beginning of STRING
> > sets THIS-START incorrectly for the first call to push-one inside the
> > while-loop.
> 
> I read that as "confirmed, a bug".  Ok, thanks for the analysis.

It's more than that: I'm working on this bug.  It just takes time to
unlock all the subtleties of the implementation and understand how to
fix it in a most economical and safe way.  I've just succeeded to
understand what was the root cause when I ran out of time.

The interim analysis was intended to attract others to the problem and
perhaps nudge someone to work out a solution.  Also to serve a
reminder to myself when I get to look at this next time.

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