GNU bug report logs - #45952
Correction to: Re: 27.1; Certain regexps can cause comint-redirect-results-list-from-process to loop.

Previous Next

To add a comment to this bug, you must first unarchive it, by sending
a message to control AT debbugs.gnu.org, with unarchive 45952 in the body.
You can then email your comments to 45952 AT debbugs.gnu.org in the normal way.

Toggle the display of automated, internal messages from the tracker.

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

From: Richard Sharman <rsharman <at> pobox.com>
To: bug-gnu-emacs <at> gnu.org
Subject: Correction to: Re: 27.1; Certain regexps can cause 
 comint-redirect-results-list-from-process to loop.
Date: Sun, 17 Jan 2021 21:48:16 -0800

[Message part 1 (text/plain, inline)]

Sorry, there was a mistake on the patch on my previous message; 
the (re-search-forward regexp nil t)) was inadvertently changed to (re-search-forward regexp nil).

Sorry.

Here’s the corrected version:

--- comint.el.orig	2021-01-17 21:35:02.000000000 -0800
+++ comint.el	2021-01-17 21:36:23.000000000 -0800
@@ -3822,7 +3822,7 @@
 Return a list of expressions in the output which match REGEXP.
 REGEXP-GROUP is the regular expression group in REGEXP to use."
   (let ((output-buffer " *Comint Redirect Work Buffer*")
-	results)
+	results last-point)
     (with-current-buffer (get-buffer-create output-buffer)
       (erase-buffer)
       (comint-redirect-send-command-to-process command
@@ -3837,13 +3837,18 @@
       ;; Skip past the command, if it was echoed
       (and (looking-at command)
 	   (forward-line))
+      (setq last-point (point))
       (while (and (not (eobp))
 		  (re-search-forward regexp nil t))
-	(push (buffer-substring-no-properties
-               (match-beginning regexp-group)
-               (match-end regexp-group))
-              results))
+	(if (equal (point) last-point)
+	    (forward-line 1)
+	  (push (buffer-substring-no-properties
+		 (match-beginning regexp-group)
+		 (match-end regexp-group))
+		results))
+	(setq last-point (point)))
       (nreverse results))))
+
 
 ;; Converting process modes to use comint mode
 ;; ===========================================================================



> On Jan 17, 2021, at 5:24 PM, Richard Sharman <rsharman <at> pobox.com> wrote:
> 
> Certain regexps can cause comint-redirect-results-list-from-process to loop.
> 
> For example, when attempting to match whole lines with the regexp
> "^.*$" if the output buffer contains an empty line, then the
> re-search-forward expression returns (point) but does not advance point,
> and since (eobp) is false the loop never terminates. 
> 
> This could avoided by testing if point advances.  If it doesn't, one
> could either exit the loop or, preferably, advance a line which would
> allow for further matches. 
> 
> Function loop.el demonstrates the problem.  It sends to a shell buffer a
> command that outputs 4 lines, the 3rd of which is empty.  Trying to
> match all lines with "^.*$" causes it to loop. 
> 
> (defun loop ()
>  (interactive)
>  ;; create shell if not done
>  (save-window-excursion
>    (shell))
>  ;; send a command that outputs 4 lines, the 3rd of which is empty
>  (let ((p (get-process "shell"))
> 	(command "(echo a; echo b ; echo ; echo d)\n")
> 	reply)
>    (setq reply (comint-redirect-results-list-from-process p command "^.*$" 0))
>    ;; we never get to here!
>    (message (car reply))
>    reply
>    ))
> 
> Note:  Starting from emacs -Q it is necessary to run M-x shell before
> invoking loop,  otherwise the error "No prompt found or
> ‘comint-prompt-regexp’ not set properly" is produced.
> 
> With this patch correct results are obtained:
> --- comint.el.orig	2021-01-17 14:22:17.000000000 -0800
> +++ comint.el	2021-01-17 14:23:54.000000000 -0800
> @@ -3822,7 +3822,7 @@
> Return a list of expressions in the output which match REGEXP.
> REGEXP-GROUP is the regular expression group in REGEXP to use."
>   (let ((output-buffer " *Comint Redirect Work Buffer*")
> -	results)
> +	results last-point)
>     (with-current-buffer (get-buffer-create output-buffer)
>       (erase-buffer)
>       (comint-redirect-send-command-to-process command
> @@ -3837,13 +3837,18 @@
>       ;; Skip past the command, if it was echoed
>       (and (looking-at command)
> 	   (forward-line))
> +      (setq last-point (point))
>       (while (and (not (eobp))
> -		  (re-search-forward regexp nil t))
> -	(push (buffer-substring-no-properties
> -               (match-beginning regexp-group)
> -               (match-end regexp-group))
> -              results))
> +		  (re-search-forward regexp nil))
> +	(if (equal (point) last-point)
> +	    (forward-line 1)
> +	  (push (buffer-substring-no-properties
> +		 (match-beginning regexp-group)
> +		 (match-end regexp-group))
> +		results))
> +	(setq last-point (point)))
>       (nreverse results))))
> +
> 
> ;; Converting process modes to use comint mode
> ;; ===========================================================================
> 
> 
> 
> In GNU Emacs 27.1 (build 2, x86_64-apple-darwin17.7.0, NS appkit-1561.61 Version 10.13.6 (Build 17G14033))
> of 2020-12-13 built on henry.local
> Windowing system distributor 'Apple', version 10.3.1561
> System Description:  Mac OS X 10.13.6
> 
> Recent messages:
> For information about GNU Emacs and the GNU system, type C-h C-a.
> loop
> Quit
> Quit
> Configured features:
> NOTIFY KQUEUE ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES
> THREADS JSON PDUMPER GMP
> 
> Important settings:
>  value of $LANG: en_CA.UTF-8
>  locale-coding-system: utf-8-unix
> 
> Major mode: Emacs-Lisp
> 
> Minor modes in effect:
>  shell-dirtrack-mode: t
>  tooltip-mode: t
>  global-eldoc-mode: t
>  eldoc-mode: t
>  electric-indent-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
> 
> Load-path shadows:
> None found.
> 
> Features:
> (shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
> format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
> epg-config gnus-util rmail rmail-loaddefs text-property-search time-date
> subr-x seq byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies
> mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
> cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
> shell pcomplete comint ansi-color ring tooltip eldoc electric uniquify
> ediff-hook vc-hooks lisp-float-type mwheel term/ns-win ns-win
> ucs-normalize mule-util term/common-win tool-bar dnd fontset image
> regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode
> lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch
> timer select scroll-bar mouse jit-lock font-lock syntax facemenu
> font-core term/tty-colors frame minibuffer cl-generic cham georgian
> utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
> japanese eucjp-ms cp51932 hebrew greek romanian slovak czech european
> ethiopic indian cyrillic chinese composite charscript charprop
> case-table epa-hook jka-cmpr-hook help simple abbrev obarray
> cl-preloaded nadvice loaddefs button faces cus-face macroexp files
> text-properties overlay sha1 md5 base64 format env code-pages mule
> custom widget hashtable-print-readable backquote threads kqueue cocoa ns
> multi-tty make-network-process emacs)
> 
> Memory information:
> ((conses 16 49326 43672)
> (symbols 48 6380 11)
> (strings 32 17163 4847)
> (string-bytes 1 570096)
> (vectors 16 10970)
> (vector-slots 8 134400 67778)
> (floats 8 19 151)
> (intervals 56 211 86)
> (buffers 1000 14))

[Message part 2 (text/html, inline)]

Message #10 received at 45952 <at> debbugs.gnu.org (full text, mbox):

From: Richard Sharman <rsharman <at> pobox.com>
To: 45952 <at> debbugs.gnu.org
Subject: bug#45952 was really a correction to 45950
Date: Mon, 18 Jan 2021 09:17:47 -0800

Sorry, I when I found a problem with 45950 I hadn’t received the acknowledgement message (and didn’t know it was coming) and  so submitted this one (45952) to fix the path.
Richard

Message #13 received at 45952 <at> debbugs.gnu.org (full text, mbox):

From: Lars Ingebrigtsen <larsi <at> gnus.org>
To: Richard Sharman <rsharman <at> pobox.com>
Cc: 45952 <at> debbugs.gnu.org, 45950 <at> debbugs.gnu.org
Subject: Re: bug#45950: 27.1; Certain regexps can cause
 comint-redirect-results-list-from-process to loop.
Date: Tue, 19 Jan 2021 05:16:02 +0100

Richard Sharman <rsharman <at> pobox.com> writes:

> Sorry, there was a mistake on the patch on my previous message; 
> the (re-search-forward regexp nil t)) was inadvertently changed to
> (re-search-forward regexp nil).
>
> Sorry.
>
> Here’s the corrected version:

[...]

> + (if (equal (point) last-point)
> +    (forward-line 1)
> +  (push (buffer-substring-no-properties
> + (match-beginning regexp-group)
> + (match-end regexp-group))
> + results))
> + (setq last-point (point)))
>        (nreverse results))))

I can reproduce the infloop in Emacs 28, but I don't think this is quite
the correct fix -- if you've asked for "^.*$", then you should get an
empty string in the result set, and not just "a" "b" "d".  So I've
installed a variant of what you suggest in Emacs 28.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Previous Next

GNU bug tracking system
Copyright (C) 1999 Darren O. Benham, 1997,2003 nCipher Corporation Ltd, 1994-97 Ian Jackson.