Package: emacs;
Reported by: Eli Zaretskii <eliz <at> gnu.org>
Date: Sun, 15 Oct 2017 16:09:01 UTC
Severity: normal
Found in versions 27.0.50, 26.0.90
Done: Alan Mackenzie <acm <at> muc.de>
Bug is archived. No further changes may be made.
View this message in rfc822 format
From: Alan Mackenzie <acm <at> muc.de> To: Eli Zaretskii <eliz <at> gnu.org> Cc: 28850 <at> debbugs.gnu.org Subject: bug#28850: 26.0.90; Error running timer 'jit-lock-stealth-fontify': (error "Invalid search bound (wrong side of point)") Date: Sun, 22 Oct 2017 20:13:40 +0000
Hello again, Eli.
On Sun, Oct 15, 2017 at 19:07:50 +0300, Eli Zaretskii wrote:
> This bug is bugging me for quite some time now, and my hopes for it to
> be resolved are now gone, so I finally sat down to debug it.
> I have jit-lock-stealth turned on in my sessions, so whenever I
> restart Emacs (e.g., when I build a new binary, or after a system
> restart), and restore my session using desktop.el, Emacs starts
> fontifying in the background. At some point, sometimes more than
> once, I get this error:
> Error running timer 'jit-lock-stealth-fontify': (error "Invalid search bound (wrong side of point)")
> Today I ran Emacs under a debugger, and caught this error. The
> details are below, but in a nutshell, CC mode's fontification
> functions call re-search-forward with BOUND that is before point. I
> hope the data below is enough to understand why that happens and fix
> it; if not, please tell what additional data is needed to diagnose the
> problem.
The details you've given me are enough to form a strong hypothesis.
Thanks.
> Here're the C and Lisp backtraces from the error, and some relevant
> data that explains why the error happened:
[ .... ]
> Lisp Backtrace:
> "re-search-forward" (0x8898d0)
> "c-syntactic-re-search-forward" (0x889ed0)
> "c-forward-declarator" (0x88a410)
> "c-font-lock-declarators" (0x88a980)
> "c-font-lock-single-decl" (0x88ae50)
> 0xad881a0 PVEC_COMPILED
> "c-find-decl-spots" (0x88c040)
> "c-font-lock-declarations" (0x88c410)
> "font-lock-fontify-keywords-region" (0x88ca70)
> "font-lock-default-fontify-region" (0x88ce60)
> "c-font-lock-fontify-region" (0x88d230)
> "font-lock-fontify-region" (0x88d578)
> 0x83d89a8 PVEC_COMPILED
> "run-hook-wrapped" (0x88daf0)
> "jit-lock--run-functions" (0x88dee0)
> "jit-lock-fontify-now" (0x88e3e0)
> "jit-lock-stealth-fontify" (0x88e9d0)
> "apply" (0x88e9c8)
> "timer-event-handler" (0x88edb8)
> (gdb) p n
> $1 = 1
> (gdb) p lim
> $2 = <optimized out>
> (gdb) pp bound
> 123806
> (gdb) p PT
> $3 = 123811
> So point is 123811 and the BOUND argument of re-search-forward is
> 123806, too small.
What I think's happening is that c-forward-declarator has found a "["
which is before BOUND, but then sets point to the matching "]" which is
after BOUND. It then calls c-syntactic-re-search-forward again,
resulting in the error.
In master's process.c, there is a "]" very close to 123811.
> (gdb) up
> #1 0x011cd2c9 in Fre_search_forward (regexp=XIL(0x800000000ad97598),
> bound=..., noerror=..., count=...) at search.c:2271
> 2271 return search_command (regexp, bound, noerror, count, 1, 1, 0);
> (gdb) pp regexp
> "[;:,]\\|\\s)\\|\\(=\\|\\s(\\)"
> (gdb) p current_buffer
> $4 = (struct buffer *) 0xb362590
> (gdb) pp current_buffer->name_
> "process.c"
> These are the regexp argument to re-search-forward and the buffer
> which was being fontified.
> The problem happens in c-syntactic-re-search-forward in this snippet:
[ .... ]
> This is called from c-forward-declarator:
> ;; Search syntactically to the end of the declarator (";",
> ;; ",", a closing paren, eob etc) or to the beginning of an
> ;; initializer or function prototype ("=" or "\\s\(").
> ;; Note that square brackets are now not also treated as
> ;; initializers, since this broke when there were also
> ;; initializing brace lists.
> (let (found)
> (while
> (and (progn
> ;; In the next loop, we keep searching forward whilst
> ;; we find ":"s which aren't single colons inside C++
> ;; "for" statements.
> (while
> (and
> (setq found
> (c-syntactic-re-search-forward <<<<<<<<<<<
> "[;:,]\\|\\s)\\|\\(=\\|\\s(\\)"
> limit t t))
As already suggested, I think the bug is that there aren't enough checks
that (< (point) limit) in this function. I have added them in.
> It looks like c-syntactic-re-search-forward calls re-search-forward in
> a loop, but perhaps it fails to update the limit to be in sync with
> point that moves as the search proceeds?
A further problem is that c-font-lock-declarators is calling
c-forward-declarator with a limit; this is silly - if the end of a
declaration runs over a jit-lock chunk boundary, we still want to
fontify this declaration fully. So I've changed the LIMIT argument in
the pertinent two calls to nil. (There is a third call somewhere where
this LIMIT argument is the end of a macro, and it is absolutely needed).
> Let me know what other data I can provide to help fix this annoying
> problem.
I haven't reproduced the problem, but I admit I haven't tried all that
hard. Could you please try out the patch below, and let me know if it
fixes the bug.
> In GNU Emacs 26.0.90 (build 1, i686-pc-mingw32)
> of 2017-10-12 built on HOME-C4E4A596F7
> Windowing system distributor 'Microsoft Corp.', version 5.1.2600
> Recent messages:
> For information about GNU Emacs and the GNU system, type C-h C-a.
[ .... ]
diff --git a/lisp/progmodes/cc-engine.el b/lisp/progmodes/cc-engine.el
index 3792835752..07b9215046 100644
--- a/lisp/progmodes/cc-engine.el
+++ b/lisp/progmodes/cc-engine.el
@@ -8102,12 +8102,14 @@ c-forward-declarator
;; initializing brace lists.
(let (found)
(while
- (and (progn
+ (and (< (point) limit)
+ (progn
;; In the next loop, we keep searching forward whilst
;; we find ":"s which aren't single colons inside C++
;; "for" statements.
(while
(and
+ (< (point) limit)
(setq found
(c-syntactic-re-search-forward
"[;:,]\\|\\s)\\|\\(=\\|\\s(\\)"
@@ -8129,7 +8131,7 @@ c-forward-declarator
(c-go-up-list-forward))
(setq brackets-after-id t))
(when found (backward-char))
- t))
+ (<= (point) limit)))
(list id-start id-end brackets-after-id (match-beginning 1) decorated)
(goto-char here)
diff --git a/lisp/progmodes/cc-fonts.el b/lisp/progmodes/cc-fonts.el
index 02b685d240..b8dbe3c26b 100644
--- a/lisp/progmodes/cc-fonts.el
+++ b/lisp/progmodes/cc-fonts.el
@@ -1062,7 +1062,7 @@ c-font-lock-declarators
;; The following `while' fontifies a single declarator id each time round.
;; It loops only when LIST is non-nil.
(while
- (and pos (setq decl-res (c-forward-declarator limit)))
+ (and pos (setq decl-res (c-forward-declarator)))
(setq next-pos (point)
id-start (car decl-res)
id-face (if (and (eq (char-after) ?\()
@@ -1091,7 +1091,7 @@ c-font-lock-declarators
(throw 'is-function nil))
((not (eq got-type 'maybe))
(throw 'is-function t)))
- (c-forward-declarator limit t)
+ (c-forward-declarator nil t)
(eq (char-after) ?,))
(forward-char)
(c-forward-syntactic-ws))
--
Alan Mackenzie (Nuremberg, Germany).
GNU bug tracking system
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1997,2003 nCipher Corporation Ltd,
1994-97 Ian Jackson.