GNU bug report logs - #36492
c-mode fails with errors during fontification

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Alan Mackenzie <acm <at> muc.de>
Cc: tracker <at> debbugs.gnu.org
Subject: bug#36492: closed (c-mode fails with errors during fontification)
Date: Mon, 08 Jul 2019 12:54:01 +0000

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

Your message dated Mon, 8 Jul 2019 12:53:32 +0000
with message-id <20190708125332.GA5244 <at> ACM>
and subject line Re: bug#36492: c-mode fails with errors during fontification
has caused the debbugs.gnu.org bug report #36492,
regarding c-mode fails with errors during fontification
to be marked as done.

(If you believe you have received this mail in error, please contact
help-debbugs <at> gnu.org.)


-- 
36492: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=36492
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

[Message part 2 (message/rfc822, inline)]

From: Juri Linkov <juri <at> linkov.net>
To: bug-gnu-emacs <at> gnu.org
Subject: c-mode fails with errors during fontification
Date: Wed, 03 Jul 2019 23:56:19 +0300

[Message part 3 (text/plain, inline)]

Opening this message in Gnus fails with the following backtrace
after setting (setq diff-font-lock-syntax 'hunk-also)
because c-mode fails to fontify the attachment.

Debugger entered--Lisp error: (wrong-type-argument integer-or-marker-p nil)
  c-forward-decl-or-cast-1(0 top nil)
  (setq decl-or-cast (c-forward-decl-or-cast-1 match-pos context last-cast-end))
  (if (eq context 'not-decl) ...)
  (if (or (and (eq (get-text-property (point) 'face) 'font-lock-keyword-face) ...) ...) t ...)
  (if (if (or (and (eq (get-text-property (point) 'face) 'font-lock-keyword-face) ...) ...) t ...) ...)
  (lambda (match-pos inside-macro &optional toplev) ...)(0 nil t)
  c-find-decl-spots(11 "[[:alpha:]_]" (nil font-lock-type-face font-lock-constant-face font-lock-keyword-face) ...)
  (let (start-pos context ...) ... nil)
  (save-restriction (let (start-pos context ...) ... nil))
  (progn (save-restriction (let (start-pos context ...) ... nil)))
  (if (< (point) limit) (progn (save-restriction (let (start-pos context ...) ... nil))))
  c-font-lock-declarations(11)
  font-lock-fontify-keywords-region(1 11 nil)
  font-lock-default-fontify-region(1 11 nil)
  funcall(font-lock-default-fontify-region 1 11 nil)
  (let (new-beg new-end new-region case-fold-search) ...)
  c-font-lock-fontify-region(1 11 nil)
  font-lock-fontify-region(1 11)
  #f(compiled-function (beg end) #<bytecode 0x1fd6e1a05171>)(1 11)
  font-lock-ensure(1 11)
  diff-syntax-fontify-props(#("a/test.c" 0 8 (face (diff-file-header diff-header))) "int i)\n{\n1" (1 3) t)
  diff-syntax-fontify-hunk(78 111 t)
  diff-syntax-fontify(78 111)
  #f(compiled-function (beg end) #<bytecode 0x158f39208a39>)(78 111)
  diff--iterate-hunks(113 #f(compiled-function (beg end) #<bytecode 0x158f39208a39>))
  diff--font-lock-syntax(113)
  font-lock-fontify-keywords-region(1 113 nil)
  font-lock-default-fontify-region(1 113 nil)
  font-lock-fontify-region(1 113)
  #f(compiled-function (beg end) #<bytecode 0x1fd6e1a05171>)(1 113)
  font-lock-ensure()
  (if (eq major-mode 'fundamental-mode) nil (font-lock-ensure))
  (progn (if mode (let ((#:wconfig (current-window-configuration))) ...) ...) ...)
  (condition-case #:err (progn ...) ((debug error) (message "Error: %S" #:err) nil))
  (let ((font-lock-verbose nil) (enable-local-variables nil)) ...)
  (progn (buffer-disable-undo) (mm-enable-multibyte) ...)
  (unwind-protect (progn (buffer-disable-undo) (mm-enable-multibyte) ...) ...)
  (save-current-buffer (set-buffer #:temp-buffer) (unwind-protect ...))
  (let ((#:temp-buffer (generate-new-buffer " *temp*"))) (save-current-buffer ...))
  (let ((charset (mail-content-type-get (nth 1 handle) 'charset)) text coding-system ovs) ...)
  mm-display-inline-fontify(... diff-mode)
  mm-display-patch-inline(...)
  mm-display-inline(...)
  gnus-mime-display-single(...)
  gnus-mime-display-part(...)
  mapcar(gnus-mime-display-part (...))
  gnus-mime-display-mixed((...))
  gnus-mime-display-part((#("multipart/mixed" 0 15 ...) ...))
  gnus-display-mime()
  gnus-article-prepare-display()
  gnus-article-prepare(5460 nil)
  funcall(gnus-article-prepare 5460 nil)
  (prog1 (funcall (or gnus-summary-display-article-function ...) article all-header) ...)
  (if (null article) nil (prog1 (funcall (or gnus-summary-display-article-function ...) article all-header)))
  gnus-summary-display-article(5460 nil)
  (progn (gnus-summary-display-article article all-headers) ...)
  (if (or (and gnus-single-article-buffer ...)) ... 'old)
  (save-current-buffer (set-buffer gnus-summary-buffer) ...)
  (let ((article (or article (gnus-summary-article-number))) ...) ...)
  gnus-summary-select-article(nil nil pseudo)
  (eq (gnus-summary-select-article nil nil 'pseudo) 'old)
  (if (eq (gnus-summary-select-article nil nil 'pseudo) 'old) ...)
  gnus-summary-scroll-up(1)
  funcall-interactively(gnus-summary-scroll-up 1)
  call-interactively(gnus-summary-scroll-up nil nil)
  command-execute(gnus-summary-scroll-up)

I don't know if it's possible to fix c-mode to not raise the error
during fontification.  But at least the patch below will avoid this error
while displaying such attachments in Gnus.  Normally calling font-lock-ensure
ignores the fontification errors when called from font-lock.
But in mm-display-inline-fontify font-lock-ensure is called directly
from top-level, so this patch ignores its errors.

diff --git a/lisp/gnus/mm-view.el b/lisp/gnus/mm-view.el
index 6ffa1fc168..ebaf8435c0 100644
--- a/lisp/gnus/mm-view.el
+++ b/lisp/gnus/mm-view.el
@@ -500,7 +500,7 @@ mm-display-inline-fontify
 	      (setq mode major-mode)))
 	  ;; Do not fontify if the guess mode is fundamental.
 	  (unless (eq major-mode 'fundamental-mode)
-	    (font-lock-ensure))))
+	    (ignore-errors (font-lock-ensure)))))
       (setq text (buffer-string))
       (when (eq mode 'diff-mode)
 	(setq ovs (mapcar (lambda (ov) (list ov (overlay-start ov)

Then visiting such attachments will just leave this line in *Messages*
without wreaking much havoc:

  Error during redisplay: (jit-lock-function 1) signaled (wrong-type-argument integer-or-marker-p nil)

[test.diff (text/x-diff, inline)]

diff --git a/test.c b/test.c
index aaa..bbb 100644
--- a/test.c
+++ b/test.c
@@ -1,3 +2,3 @@
 int i)
 {
-1
+2

[Message part 5 (message/rfc822, inline)]

From: Alan Mackenzie <acm <at> muc.de>
To: Juri Linkov <juri <at> linkov.net>
Cc: 36492-done <at> debbugs.gnu.org
Subject: Re: bug#36492: c-mode fails with errors during fontification
Date: Mon, 8 Jul 2019 12:53:32 +0000

Hello, Juri.

On Mon, Jul 08, 2019 at 00:52:02 +0300, Juri Linkov wrote:
> >>> Opening this message in Gnus fails with the following backtrace
> >>> because c-mode fails to fontify the attachment.

> >> Actually, with the attachment in this message the bug in c-mode
> >> font-lock is much easier to reproduce.

> > That is one ugly piece of erroneous C.  ;-)

> > What triggers the bug is the ) without a preceding (.  A variable
> > recording the position of the opening ( is still set to nil, and we
> > tried to use it in the given buffer with the unbalanced ).

> >> [-- text/x-csrc, encoding 7bit, charset: US-ASCII, 3 lines, name: test.c --]

> > The following patch fixes it, I hope.  Would you please do the usual,
> > and confirm that it does indeed fix the bug (or tell me what's still
> > wrong).

> Thanks, Alan.  Now there is no error anymore.

Thanks.  I've committed the fix, and I'm closing the bug.

> I wonder if ignore-errors around font-lock-ensure in mm-display-inline-fontify
> is still necessary to ensure no more bugs in other modes disrupt Gnus
> by erroneous code in attachments?  Or maybe raising such errors will help
> to find fontification bugs sooner?

My feeling is that it's better to let the errors happen, so that we can
debug them.  But on the other hand, it's not me that gets inconvenienced
by such an error (I don't use gnus).

-- 
Alan Mackenzie (Nuremberg, Germany).

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