GNU bug report logs - #11982
24.1.50; (Contains ERT Test) show-paren-mode doesn't work in C comments if there's a quote between the parenthesis (affects c-mode and modes derived from it)

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Rolando Pereira <rolando_pereira <at> sapo.pt>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.1.50;
	(Contains ERT Test) show-paren-mode doesn't work in C comments if
	there's a quote between the parenthesis (affects c-mode and
	modes derived from it)
Date: Wed, 18 Jul 2012 21:16:17 +0100

In c-mode if you type the following comment with M-x show-paren-mode
activated, the closing parenthesis is highlighted correctly:

// Lorem ipsum (dolor sit amet)

However, if the ' character appears inside the parenthesis, then
show-paren-mode won't match them.

For example, when typing the following comment, show-paren-mode highlights
the closing parenthesis using show-paren-mismatch:

// Comments are good (aren't they?)


I tried to make an ERT test that would check if the parenthesis was
highlighted correctly, but I couldn't get the overlay that
show-paren-mode uses.

However I found out that forward-sexp also doesn't work when the '
character appears between parenthesis, which makes me think the problem
may be somewhere in the syntax-table used by c-mode.

Here's the ERT test:

(ert-deftest cc-mode-should-forward-sexp-with-quotes-inside ()
  "Check if `forward-sexp' works in c-mode when the cursor is
inside a comment and there's a ' character inside the
parenthesis"
  (with-temp-buffer
    (c-mode)
    (insert "// Comments are good (aren't they?)")
    (goto-char (point-min))
    (search-forward "(")
    (backward-char 1)
    (forward-sexp)
    (ert-should (= (point) 36))))


Also, the reason I think that the problem only affects c-mode and modes that
derive from it is because this problem doesn't show up in
emacs-lisp-mode or lisp-mode.


Here's how to see the problem when starting emacs with the -Q flag:

1. Create the temporary buffer "temp-buffer" with C-x b temp-buffer RET
2. Activate c-mode with M-x c-mode
3. Activate show-paren-mode with M-x show-paren-mode
4. Write "// Comments are good (aren't they?)"
5. When typing the closing parenthesis, notice that it's highlighted
with the face show-paren-mismatch


Another test that can be used that doesn't use show-paren-mode but still
shows wrong behaviour is the following:

1. Create the temporary buffer as before
2. Activate c-mode as before
2. Write "// Comments are good (aren't they?)"
3. When typing the closing parenthesis, notice that the minibuffer shows
the message "No matching parenthesis found".




In GNU Emacs 24.1.50.1 (i686-pc-linux-gnu, GTK+ Version 2.20.1)
 of 2012-07-15 on rolando-desktop
Bzr revision: 109096 dmantipov <at> yandex.ru-20120715111709-pa3d1hni2gmjdux0
Windowing system distributor `The X.Org Foundation', version 11.0.10706000
Important settings:
  value of $LANG: pt_PT.utf8
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-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

Recent input:
M-x r e p o r <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Starting new Ispell process [/usr/bin/aspell::default] ...
Checking spelling of PARENTHESIS...
byte-code: Window #<window 4 on  *Minibuf-1*> too small for splitting

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr ispell emacsbug message format-spec
rfc822 mml easymenu mml-sec mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils time-date tooltip ediff-hook
vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment lisp-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer loaddefs
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format env code-pages mule custom widget hashtable-print-readable
backquote make-network-process dbusbind dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty emacs)

Message #14 received at 11982 <at> debbugs.gnu.org (full text, mbox):

From: Vincent Lefevre <vincent <at> vinc17.net>
To: 11982 <at> debbugs.gnu.org
Subject: Re: 24.1.50; (Contains ERT Test) show-paren-mode doesn't work in C
 comments if there's a quote between the parenthesis (affects c-mode and
 modes derived from it)
Date: Thu, 22 Aug 2019 15:45:01 +0200

On 2012-07-18 21:16:17 +0100, Rolando Pereira wrote:
> In c-mode if you type the following comment with M-x show-paren-mode
> activated, the closing parenthesis is highlighted correctly:
> 
> // Lorem ipsum (dolor sit amet)
> 
> However, if the ' character appears inside the parenthesis, then
> show-paren-mode won't match them.
> 
> For example, when typing the following comment, show-paren-mode highlights
> the closing parenthesis using show-paren-mismatch:
> 
> // Comments are good (aren't they?)

I can reproduce this bug with Emacs 26.1 from the Debian package,
but the current development version seems fine. Has this bug been
fixed?

-- 
Vincent Lefèvre <vincent <at> vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

Message #17 received at 11982 <at> debbugs.gnu.org (full text, mbox):

From: Noam Postavsky <npostavs <at> gmail.com>
To: Vincent Lefevre <vincent <at> vinc17.net>
Cc: 11982 <at> debbugs.gnu.org
Subject: Re: bug#11982: 24.1.50;
 (Contains ERT Test) show-paren-mode doesn't work in C comments if
 there's a quote between the parenthesis (affects c-mode and modes derived
 from it)
Date: Thu, 22 Aug 2019 11:05:04 -0400

found 11982 25.3
tags 11982 fixed
close 11982 26.1
quit

Vincent Lefevre <vincent <at> vinc17.net> writes:

> On 2012-07-18 21:16:17 +0100, Rolando Pereira wrote:
>> In c-mode[...] when typing the following comment, show-paren-mode highlights
>> the closing parenthesis using show-paren-mismatch:
>> 
>> // Comments are good (aren't they?)
>
> I can reproduce this bug with Emacs 26.1 from the Debian package,
> but the current development version seems fine. Has this bug been
> fixed?

I can reproduce up to 25.3, but it seems to be fixed in 26.1.

Message #26 received at 11982 <at> debbugs.gnu.org (full text, mbox):

From: Vincent Lefevre <vincent <at> vinc17.net>
To: Noam Postavsky <npostavs <at> gmail.com>
Cc: 11982 <at> debbugs.gnu.org
Subject: Re: bug#11982: 24.1.50; (Contains ERT Test) show-paren-mode doesn't
 work in C comments if there's a quote between the parenthesis (affects
 c-mode and modes derived from it)
Date: Thu, 22 Aug 2019 17:20:20 +0200

On 2019-08-22 11:05:04 -0400, Noam Postavsky wrote:
> I can reproduce up to 25.3, but it seems to be fixed in 26.1.

No, not fixed in 26.1, where this depends on some context.
This is rather random, but here's a way to reproduce the
bug in Debian:

1. emacs-gtk -Q foo.c
   (where foo.c does not exist)

2. Paste "// Comments are good (aren't they?)"

3. Type C-M-p

I get an error:

forward-list: Scan error: "Unbalanced parentheses", 35, 1

This problem does not occur without the apostrophe.

-- 
Vincent Lefèvre <vincent <at> vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

Message #29 received at 11982 <at> debbugs.gnu.org (full text, mbox):

From: Noam Postavsky <npostavs <at> gmail.com>
To: Vincent Lefevre <vincent <at> vinc17.net>
Cc: 11982 <at> debbugs.gnu.org
Subject: Re: bug#11982: 24.1.50;
 (Contains ERT Test) show-paren-mode doesn't work in C comments if
 there's a quote between the parenthesis (affects c-mode and modes derived
 from it)
Date: Thu, 22 Aug 2019 11:48:48 -0400

fixed 11982 27.1
notfixed 11982 26.1
quit

Vincent Lefevre <vincent <at> vinc17.net> writes:

> On 2019-08-22 11:05:04 -0400, Noam Postavsky wrote:
>> I can reproduce up to 25.3, but it seems to be fixed in 26.1.
>
> No, not fixed in 26.1, where this depends on some context.
> This is rather random, but here's a way to reproduce the
> bug in Debian:
>
> 1. emacs-gtk -Q foo.c
>    (where foo.c does not exist)
>
> 2. Paste "// Comments are good (aren't they?)"
>
> 3. Type C-M-p
>
> I get an error:
>
> forward-list: Scan error: "Unbalanced parentheses", 35, 1
>
> This problem does not occur without the apostrophe.

Oh, interesting, if I delete and re-insert the apostrophe, it stops
happening, i.e., there is some hidden state which affects things as
well.

Message #36 received at 11982 <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: Vincent Lefevre <vincent <at> vinc17.net>
Cc: 11982 <at> debbugs.gnu.org, Noam Postavsky <npostavs <at> gmail.com>
Subject: Re: bug#11982: 24.1.50;
 (Contains ERT Test) show-paren-mode doesn't work in C comments if
 there's a quote between the parenthesis (affects c-mode and modes derived
 from it)
Date: 25 Aug 2019 14:10:58 -0000

Hello, Vincent and Noam.

In article <mailman.72.1566487266.1922.bug-gnu-emacs <at> gnu.org> you wrote:
> On 2019-08-22 11:05:04 -0400, Noam Postavsky wrote:
>> I can reproduce up to 25.3, but it seems to be fixed in 26.1.

> No, not fixed in 26.1, where this depends on some context.

This "context" is a syntax-table text property on the apostrophe which
"neutralises" it's normal string syntax.  Without this text property,
the apostrophe, a string opener, breaks the association of the two
parentheses.

The code which applies and removes these syntax-table text properties is
somewhat involved.  I believe it is working correctly in the master
branch, but wasn't in Emacs-26.

> This is rather random, but here's a way to reproduce the
> bug in Debian:

> 1. emacs-gtk -Q foo.c
>    (where foo.c does not exist)

> 2. Paste "// Comments are good (aren't they?)"

For some value of "paste".  Inserting the text on a Linux tty with the GPM
mouse utility (in 26.1) causes the text property to be correctly set.
Killing the entire line with C-k, followed by yanking it with C-y leaves
the text property unset (again in 26.1).

> 3. Type C-M-p

> I get an error:

> forward-list: Scan error: "Unbalanced parentheses", 35, 1

> This problem does not occur without the apostrophe.

No.  The apostrophe is a "string opener", see above.  It's normal use is
to delimit character constants, as:

    char foo = 'F';

> -- 
> Vincent Lefèvre <vincent <at> vinc17.net> - Web: <https://www.vinc17.net/>
> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

-- 
Alan Mackenzie (Nuremberg, Germany).

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