bug#42805: 27.1; cc-mode/syntax/font-lock bug

bug#42805: 27.1; cc-mode/syntax/font-lock bug

[Gustavo Tavares Cabral]

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Hi,

I have found two related issues. Both are evident in csharp-mode, but
can easily be reproduced in c-mode.

Issue 1 (cc-mode.el):

  When c-multiline-string-start-char is set, font locking breaks after
  changes in string literals. The issue started after commit 2ca12bb3de:
  I believe that '(c-remove-string-fences (car end-limits))' should be
  '(c-remove-string-fences (1- (cdr end-limits)))'

  Steps to reproduce:
    1. Open a .c file;
    2. Eval '(setq c-multiline-string-start-char ?@)';
    3. Delete/insert double quotes.

  I think this issue is related:
  https://github.com/Fuco1/smartparens/issues/992


Issue 2 (maybe syntax.el):

  When syntax-propertize-function is set (to '(lambda (beg end) nil)',
  for example), a similar problem occurs if electric-pair-mode (or even
  smartparens) is enabled. The symptoms started after commit 585fb95739,
  but I don't know if it is related.

  Steps to reproduce:
    1. Open a .c file;
    2. Eval '(setq syntax-propertize-function (lambda (beg end) nil)';
    3. Enable electric-pair-mode;
    4. Insert/delete empty strings.




In GNU Emacs 27.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30,
cairo version 1.16.0)
of 2020-08-06 built on gustavo-Lenovo-ideapad-330-15IKB
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Ubuntu 18.04.5 LTS

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Making completion list...

Configured using:
'configure --with-x-toolkit=gtk3 --with-modules --with-sound=yes
--with-file-notification=yes --with-mailutils --with-cairo'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS PDUMPER LCMS2
GMP

Important settings:
value of $LANG: en
value of $XMODIFIERS:
locale-coding-system: iso-latin-1-unix

Major mode: Lisp Interaction

Minor modes in effect:
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
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lisp-float-type mwheel term/x-win x-win term/common-win x-dnd 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
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custom widget hashtable-print-readable backquote threads dbusbind
inotify lcms2 dynamic-setting system-font-setting font-render-setting
cairo move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 44286 8232)
(symbols 48 5980 1)
(strings 32 15464 904)
(string-bytes 1 505487)
(vectors 16 9275)
(vector-slots 8 124610 9084)
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bug#42805: 27.1; cc-mode/syntax/font-lock bug

[Eli Zaretskii]

> From: Gustavo Tavares Cabral <gustavotcabral@gmail.com>
> Date: Mon, 10 Aug 2020 16:55:40 -0300
> Cc: bug-cc-mode@gnu.org
> 
> I have found two related issues. Both are evident in csharp-mode, but 
> can easily be reproduced in c-mode. 
> 
> Issue 1 (cc-mode.el): 
> 
>   When c-multiline-string-start-char is set, font locking breaks after 
>   changes in string literals. The issue started after commit 2ca12bb3de:
>   I believe that '(c-remove-string-fences (car end-limits))' should be 
>   '(c-remove-string-fences (1- (cdr end-limits)))' 
> 
>   Steps to reproduce: 
>     1. Open a .c file; 
>     2. Eval '(setq c-multiline-string-start-char ?@)'; 
>     3. Delete/insert double quotes. 
> 
>   I think this issue is related:
>   https://github.com/Fuco1/smartparens/issues/992 
> 
> Issue 2 (maybe syntax.el): 
> 
>   When syntax-propertize-function is set (to '(lambda (beg end) nil)', 
>   for example), a similar problem occurs if electric-pair-mode (or even 
>   smartparens) is enabled. The symptoms started after commit 585fb95739,
>   but I don't know if it is related.
> 
>   Steps to reproduce: 
>     1. Open a .c file; 
>     2. Eval '(setq syntax-propertize-function (lambda (beg end) nil)'; 
>     3. Enable electric-pair-mode; 
>     4. Insert/delete empty strings.

Alan, could you please take a look?  Would it be possible to fix this
for Emacs 27.2?

bug#42805: 27.1; cc-mode/syntax/font-lock bug

[Alan Mackenzie]

Hello, Gustavo and Eli.

On Mon, Nov 23, 2020 at 19:10:11 +0200, Eli Zaretskii wrote:
> > From: Gustavo Tavares Cabral <gustavotcabral@gmail.com>
> > Date: Mon, 10 Aug 2020 16:55:40 -0300
> > Cc: bug-cc-mode@gnu.org

> > I have found two related issues. Both are evident in csharp-mode, but 
> > can easily be reproduced in c-mode. 

I'll answer the second issue now (which is easy) and hopefully get round
to the first one soon.

> > Issue 1 (cc-mode.el): 

[ .... ]

> > Issue 2 (maybe syntax.el): 

> >   When syntax-propertize-function is set (to '(lambda (beg end) nil)', 
> >   for example), a similar problem occurs if electric-pair-mode (or even 
> >   smartparens) is enabled. The symptoms started after commit 585fb95739,
> >   but I don't know if it is related.

> >   Steps to reproduce: 
> >     1. Open a .c file; 
> >     2. Eval '(setq syntax-propertize-function (lambda (beg end) nil)'; 
> >     3. Enable electric-pair-mode; 
> >     4. Insert/delete empty strings.

This is simple.  syntax-propertize-function is utterly incompatible with
CC Mode, and _will_ foul it up.  To quote from the Emacs Lisp manual
(recently added text):

     *Caution:* When this variable is non-`nil', Emacs removes
     `syntax-table' text properties arbitrarily and relies on
     `syntax-propertize-function' to reapply them.  Thus if this
     facility is used at all, the function must apply *all*
     `syntax-table' text properties used by the major mode.  In
     particular, Modes derived from a CC Mode mode must not use this
     variable, since CC Mode uses other means to apply and remove these
     text properties.

> Alan, could you please take a look?  Would it be possible to fix this
> for Emacs 27.2?

I hope so.  Are there any firm plans for a release date, yet?

-- 
Alan Mackenzie (Nuremberg, Germany).

bug#42805: 27.1; cc-mode/syntax/font-lock bug

[Eli Zaretskii]

> Date: Mon, 23 Nov 2020 18:57:18 +0000
> Cc: 42805@debbugs.gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> > Alan, could you please take a look?  Would it be possible to fix this
> > for Emacs 27.2?
> 
> I hope so.  Are there any firm plans for a release date, yet?

Plans, yes: soon.  Firm, no.  I have a few bug reports that I'd like
to see fixed if possible; this is one of them.  I hope to have an
up-to-date status for all of them in a week or so, and if that
succeeds, I will probably start preparing a pretest of 27.2.

bug#42805: 27.1; cc-mode/syntax/font-lock bug

[Alan Mackenzie]

Hello, Gustavo.

On Mon, Nov 23, 2020 at 19:10:11 +0200, Eli Zaretskii wrote:
> > From: Gustavo Tavares Cabral <gustavotcabral@gmail.com>
> > Date: Mon, 10 Aug 2020 16:55:40 -0300
> > Cc: bug-cc-mode@gnu.org

> > I have found two related issues. Both are evident in csharp-mode, but 
> > can easily be reproduced in c-mode. 

> > Issue 1 (cc-mode.el): 

> >   When c-multiline-string-start-char is set, font locking breaks after 
> >   changes in string literals. The issue started after commit 2ca12bb3de:
> >   I believe that '(c-remove-string-fences (car end-limits))' should be 
> >   '(c-remove-string-fences (1- (cdr end-limits)))' 

> >   Steps to reproduce: 
> >     1. Open a .c file; 
> >     2. Eval '(setq c-multiline-string-start-char ?@)'; 
> >     3. Delete/insert double quotes. 

I've just done this, and not noticed anything adrift other than
exceptionally long delays in making the changes.  Would you please state
more precisely what the problem is that you see.  Thanks!

> >   I think this issue is related:
> >   https://github.com/Fuco1/smartparens/issues/992 

> > Issue 2 (maybe syntax.el): 

[ Dealt with in a separate post. ]

> Alan, could you please take a look?  Would it be possible to fix this
> for Emacs 27.2?

-- 
Alan Mackenzie (Nuremberg, Germany).

bug#42805: 27.1; cc-mode/syntax/font-lock bug

[Lars Ingebrigtsen]

Alan Mackenzie <acm@muc.de> writes:

>> >   When c-multiline-string-start-char is set, font locking breaks after 
>> >   changes in string literals. The issue started after commit 2ca12bb3de:
>> >   I believe that '(c-remove-string-fences (car end-limits))' should be 
>> >   '(c-remove-string-fences (1- (cdr end-limits)))' 
>
>> >   Steps to reproduce: 
>> >     1. Open a .c file; 
>> >     2. Eval '(setq c-multiline-string-start-char ?@)'; 
>> >     3. Delete/insert double quotes. 
>
> I've just done this, and not noticed anything adrift other than
> exceptionally long delays in making the changes.  Would you please state
> more precisely what the problem is that you see.  Thanks!

This was half a year ago, and there was no response (and I can't
reproduce the problem either in 27.1 or the current trunk), so I'm
closing this bug report.  If the problem still exists, please respond to
this email and we'll reopen the bug report.

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