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bug#45952: Correction to: Re: 27.1; Certain regexps can cause comint-red


From: Richard Sharman
Subject: bug#45952: 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

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@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
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Configured features:
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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))


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