From: Jeff Norden <jnorden@tntech.edu>
To: 40317@debbugs.gnu.org
Cc: Damien Cassou <damien@cassou.me>, Alan Mackenzie <acm@muc.de>
Subject: bug#40317: 27.0.90; Reverting a buffer that visits C file signals an error
Date: Thu, 17 Sep 2020 20:21:47 -0500 [thread overview]
Message-ID: <fd7dsr3mms.fsf@norden.tntech.edu> (raw)
In-Reply-To: <87k0wtmvod.fsf@cassou.me> (message from Damien Cassou on Wed, 16 Sep 2020 20:19:14 +0200)
I came across this by searching for args-out-of-range bugs. I recently found
a bug in forward-comment (which I'll post separately) that was causing
out-of-range errors for me, and I wondered if forward-comment might be
relevant to other issues. It isn't in this case, but I think I did find the
source of the problem.
The function c-after-change (in cc-mode.el) was changed between 26.3 and 27.1,
to handle more cases where the before and/or after change functions get called
multiple times. The function now begins (line numbers are from the current
master version) with:
1993 ;; Note: c-just-done-before-change is nil, t, or 'whole-buffer.
1994 (unless (c-called-from-text-property-change-p)
1995 (save-restriction
1996 (widen)
1997 (unless c-just-done-before-change
1998 (c-before-change (point-min) (point-max)))
1999 (unless (eq c-just-done-before-change t)
2000 (setq beg (point-min)
2001 end (point-max)
2002 old-len (- end beg)
2003 c-new-BEG (point-min)
2004 c-new-END (point-max)))
2005 (setq c-just-done-before-change nil)))
2006
2007 ;; (c-new-BEG c-new-END) will be the region to fontify. It may become
2008 ;; larger than (beg end).
2009 (setq c-new-END (- (+ c-new-END (- end beg)) old-len))
It looks like it is now possible for the last line above, which increments
c-new-END, to run even if c-new-END has been set to the after-change value
of point-max. That will make c-new-END point past the end of the buffer.
---
In the backtrace from March,
> c-after-change(214738 215088 0)
indicates that 350 bytes have been added to the buffer, although not at end.
If point-max was 216785 (which would be the value if the buffer-length was
actually 216784), then line-2009 would set c-new-END to 216785+350 = 217135,
which would then be used by c-after-change-mark-abnormal-strings when calling
parse-partial-sexp. This fits the args-out-of-range error in the backtrace.
---
A simple fix would be to change line-2009 to
(setq c-new-END (min (- (+ c-new-END (- end beg)) old-len) (point-max)))
But, maybe the third 'unless' could be changed to 'if' instead, with the
increment as the else. I don't know if c-new-END might need to be
incremented when c-called-from-text-property-change-p is true.
Unfortunately, I can't figure out how to trigger this bug myself. If you want
to be 100% sure about it, you might try adding
(if (> c-new-END (point-max))
(error "c-new-END is too big! %d > %d" c-new-END (point-max)))
right after line-2009 and see if it raises an error before it gets to
parse-partial-sexp.
Hope this helps,
-Jeff
next prev parent reply other threads:[~2020-09-18 1:21 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-29 13:26 bug#40317: 27.0.90; Reverting a buffer that visits C file signals an error Eli Zaretskii
2020-09-16 12:24 ` Damien Cassou
2020-09-16 14:26 ` Eli Zaretskii
2020-09-16 14:51 ` Damien Cassou
2020-09-16 15:09 ` Eli Zaretskii
2020-09-16 18:19 ` Damien Cassou
2020-09-18 1:21 ` Jeff Norden [this message]
2020-09-18 19:46 ` Damien Cassou
2020-09-18 20:13 ` Alan Mackenzie
2020-09-18 22:03 ` Jeff Norden
2020-09-19 7:35 ` Eli Zaretskii
2020-09-19 11:48 ` Alan Mackenzie
2020-09-20 17:25 ` Alan Mackenzie
2020-10-29 14:19 ` Damien Cassou
2022-02-20 15:11 ` Lars Ingebrigtsen
2022-02-21 10:09 ` Damien Cassou
2022-02-21 14:08 ` Lars Ingebrigtsen
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