GNU bug report logs - #24377
25.1; CC-Mode (C++) uses font-lock-type-face for ordinary variable

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

From: Bastian Beischer <bastian.beischer <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.1; CC-Mode (C++) uses font-lock-type-face for ordinary variable
Date: Tue, 06 Sep 2016 13:16:41 +0200

This piece of C++ code is wrongly fontified by CC-Mode:

int b = 5;
int a = (b*3);

Reproduce as follows:

1) emacs -Q
2) Open file "test.C"
3) Paste snippet in buffer
4) Place cursor over "b" in second line
5) M-x describe-face -> font-lock-type-face

This appears to be correlated with the presence of the opening
parentheses and the '*' character, because:

1) int a = b*3;
does not have this problem

2) "b" gets fontified incorrectly after entering the '*' character:
int a = (b*



In GNU Emacs 25.1.2 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.30)
 of 2016-08-30 built on beischer-w520
Repository revision: 17197d0ae9eac100b56078b2a48964b29710b76e
Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --mandir=/usr/share/man --with-gameuser=:games
 --with-sound=alsa --with-xft --with-modules --with-x-toolkit=gtk2
 --with-gconf --without-gsettings 'CFLAGS=-march=native -O2 -pipe
 -fstack-protector-strong' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF NOTIFY ACL
GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK2 X11 MODULES

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: C++/l

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  diff-auto-refine-mode: t
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  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
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  abbrev-mode: t

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Message #8 received at 24377 <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: Bastian Beischer <bastian.beischer <at> gmail.com>
Cc: 24377 <at> debbugs.gnu.org
Subject: Re: bug#24377: 25.1;
 CC-Mode (C++) uses font-lock-type-face for ordinary variable
Date: 13 Sep 2016 18:35:14 -0000

Hello, Bastian.

In article <mailman.1977.1473362155.22741.bug-gnu-emacs <at> gnu.org> you wrote:

> This piece of C++ code is wrongly fontified by CC-Mode:

> int b = 5;
> int a = (b*3);

> Reproduce as follows:

> 1) emacs -Q
> 2) Open file "test.C"
> 3) Paste snippet in buffer
> 4) Place cursor over "b" in second line
> 5) M-x describe-face -> font-lock-type-face

> This appears to be correlated with the presence of the opening
> parentheses and the '*' character, because:

> 1) int a = b*3;
> does not have this problem

> 2) "b" gets fontified incorrectly after entering the '*' character:
> int a = (b*

Thanks for this bug report, and thanks even more for taking the trouble
to reduce the test case to just two lines.

> In GNU Emacs 25.1.2 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.30)
>  of 2016-08-30 built on beischer-w520
> Repository revision: 17197d0ae9eac100b56078b2a48964b29710b76e
> Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
> Configured using:
>  'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
>  --localstatedir=/var --mandir=/usr/share/man --with-gameuser=:games
>  --with-sound=alsa --with-xft --with-modules --with-x-toolkit=gtk2
>  --with-gconf --without-gsettings 'CFLAGS=-march=native -O2 -pipe
>  -fstack-protector-strong' CPPFLAGS=-D_FORTIFY_SOURCE=2
>  LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

[ .... ]

Yes, the CC Mode fontification code was confusing the "*" with an
indirection operator, such as you might get in "int (*b) (....);"

The solution seems to be to recognise the case where an arithmetic
operator (including "=") precedes the open parenthesis.  This is what the
following patch does.  Would you please try out this patch on real code,
and let me know whether the problem is completely fixed, and if not,
what's still going wrong.  Thanks!

After applying the patch, plese recompile all of CC Mode, since the
change is partly in Lisp macros, which need to propagate to other files.

Here's the patch:



diff -r 9ff65a2d07bd cc-fonts.el
--- a/cc-fonts.el	Sun Sep 11 20:46:35 2016 +0000
+++ b/cc-fonts.el	Tue Sep 13 18:22:17 2016 +0000
@@ -1310,6 +1310,13 @@
 		     ;; multiline declaration.
 		     (c-put-char-property (1- match-pos)
 					  'c-type 'c-decl-arg-start))
+		    ;; Got an open paren preceded by an arith operator.
+		    ((and (eq (char-before match-pos) ?\()
+			  (save-excursion
+			    (and (zerop (c-backward-token-2 2))
+				 (looking-at c-arithmetic-op-regexp))))
+		     (setq context nil
+			   c-restricted-<>-arglists nil))
 		    (t (setq context 'arglist
 			     c-restricted-<>-arglists t))))
 
diff -r 9ff65a2d07bd cc-langs.el
--- a/cc-langs.el	Sun Sep 11 20:46:35 2016 +0000
+++ b/cc-langs.el	Tue Sep 13 18:22:17 2016 +0000
@@ -1231,6 +1231,22 @@
 (c-lang-defvar c-assignment-op-regexp
   (c-lang-const c-assignment-op-regexp))
 
+(c-lang-defconst c-arithmetic-operators
+  "List of all arithmetic operators, including \"+=\", etc."
+  ;; Note: in the following, there are too many operators for AWK and IDL.
+  t (append (c-lang-const c-assignment-operators)
+	    '("+" "-" "*" "/" "%"
+	      "<<" ">>"
+	      "<" ">" "<=" ">="
+	      "==" "!="
+	      "&" "^" "|"
+	      "&&" "||")))
+
+(c-lang-defconst c-arithmetic-op-regexp
+  t (c-make-keywords-re nil
+      (c-lang-const c-arithmetic-operators)))
+(c-lang-defvar c-arithmetic-op-regexp (c-lang-const c-arithmetic-op-regexp))
+
 (c-lang-defconst c-:$-multichar-token-regexp
   ;; Regexp matching all tokens ending in ":" which are longer than one char.
   ;; Currently (2016-01-07) only used in C++ Mode.



-- 
Alan Mackenzie (Nuremberg, Germany).

Message #11 received at 24377 <at> debbugs.gnu.org (full text, mbox):

From: Bastian Beischer <bastian.beischer <at> gmail.com>
To: Alan Mackenzie <acm <at> muc.de>
Cc: 24377 <at> debbugs.gnu.org
Subject: Re: bug#24377: 25.1; CC-Mode (C++) uses font-lock-type-face for
 ordinary variable
Date: Tue, 13 Sep 2016 22:24:40 +0200

Hello Alan,

First of all, thanks for the patch - it's appreciated. My comments
below:

Alan Mackenzie <acm <at> muc.de> writes:

> Hello, Bastian.
>
> In article <mailman.1977.1473362155.22741.bug-gnu-emacs <at> gnu.org> you wrote:
>
>> This piece of C++ code is wrongly fontified by CC-Mode:
>
>> int b = 5;
>> int a = (b*3);
>
>> Reproduce as follows:
>
>> 1) emacs -Q
>> 2) Open file "test.C"
>> 3) Paste snippet in buffer
>> 4) Place cursor over "b" in second line
>> 5) M-x describe-face -> font-lock-type-face
>
>> This appears to be correlated with the presence of the opening
>> parentheses and the '*' character, because:
>
>> 1) int a = b*3;
>> does not have this problem
>
>> 2) "b" gets fontified incorrectly after entering the '*' character:
>> int a = (b*
>
> Thanks for this bug report, and thanks even more for taking the trouble
> to reduce the test case to just two lines.
>
>> In GNU Emacs 25.1.2 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.30)
>>  of 2016-08-30 built on beischer-w520
>> Repository revision: 17197d0ae9eac100b56078b2a48964b29710b76e
>> Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
>> Configured using:
>>  'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
>>  --localstatedir=/var --mandir=/usr/share/man --with-gameuser=:games
>>  --with-sound=alsa --with-xft --with-modules --with-x-toolkit=gtk2
>>  --with-gconf --without-gsettings 'CFLAGS=-march=native -O2 -pipe
>>  -fstack-protector-strong' CPPFLAGS=-D_FORTIFY_SOURCE=2
>>  LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'
>
> [ .... ]
>
> Yes, the CC Mode fontification code was confusing the "*" with an
> indirection operator, such as you might get in "int (*b) (....);"
>
> The solution seems to be to recognise the case where an arithmetic
> operator (including "=") precedes the open parenthesis.  This is what the
> following patch does.  Would you please try out this patch on real code,
> and let me know whether the problem is completely fixed, and if not,
> what's still going wrong.  Thanks!
>

Yes this helps in the example above, but I'm not sure this is a fully
correct solution. One can write something like this:

void f(int arg)  {
     printf("%d\n", arg)
}

f(a*5);

Another example:

int d(a*5)

In both cases a is also wrongly fontified (and still is after applying
the patch).

> After applying the patch, plese recompile all of CC Mode, since the
> change is partly in Lisp macros, which need to propagate to other files.
>
> Here's the patch:
>

Thanks a lot again!

On Tue, Sep 13, 2016 at 8:35 PM, Alan Mackenzie <acm <at> muc.de> wrote:
> Hello, Bastian.
>
> In article <mailman.1977.1473362155.22741.bug-gnu-emacs <at> gnu.org> you wrote:
>
>> This piece of C++ code is wrongly fontified by CC-Mode:
>
>> int b = 5;
>> int a = (b*3);
>
>> Reproduce as follows:
>
>> 1) emacs -Q
>> 2) Open file "test.C"
>> 3) Paste snippet in buffer
>> 4) Place cursor over "b" in second line
>> 5) M-x describe-face -> font-lock-type-face
>
>> This appears to be correlated with the presence of the opening
>> parentheses and the '*' character, because:
>
>> 1) int a = b*3;
>> does not have this problem
>
>> 2) "b" gets fontified incorrectly after entering the '*' character:
>> int a = (b*
>
> Thanks for this bug report, and thanks even more for taking the trouble
> to reduce the test case to just two lines.
>
>> In GNU Emacs 25.1.2 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.30)
>>  of 2016-08-30 built on beischer-w520
>> Repository revision: 17197d0ae9eac100b56078b2a48964b29710b76e
>> Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
>> Configured using:
>>  'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
>>  --localstatedir=/var --mandir=/usr/share/man --with-gameuser=:games
>>  --with-sound=alsa --with-xft --with-modules --with-x-toolkit=gtk2
>>  --with-gconf --without-gsettings 'CFLAGS=-march=native -O2 -pipe
>>  -fstack-protector-strong' CPPFLAGS=-D_FORTIFY_SOURCE=2
>>  LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'
>
> [ .... ]
>
> Yes, the CC Mode fontification code was confusing the "*" with an
> indirection operator, such as you might get in "int (*b) (....);"
>
> The solution seems to be to recognise the case where an arithmetic
> operator (including "=") precedes the open parenthesis.  This is what the
> following patch does.  Would you please try out this patch on real code,
> and let me know whether the problem is completely fixed, and if not,
> what's still going wrong.  Thanks!
>
> After applying the patch, plese recompile all of CC Mode, since the
> change is partly in Lisp macros, which need to propagate to other files.
>
> Here's the patch:
>
>
>
> diff -r 9ff65a2d07bd cc-fonts.el
> --- a/cc-fonts.el       Sun Sep 11 20:46:35 2016 +0000
> +++ b/cc-fonts.el       Tue Sep 13 18:22:17 2016 +0000
> @@ -1310,6 +1310,13 @@
>                      ;; multiline declaration.
>                      (c-put-char-property (1- match-pos)
>                                           'c-type 'c-decl-arg-start))
> +                   ;; Got an open paren preceded by an arith operator.
> +                   ((and (eq (char-before match-pos) ?\()
> +                         (save-excursion
> +                           (and (zerop (c-backward-token-2 2))
> +                                (looking-at c-arithmetic-op-regexp))))
> +                    (setq context nil
> +                          c-restricted-<>-arglists nil))
>                     (t (setq context 'arglist
>                              c-restricted-<>-arglists t))))
>
> diff -r 9ff65a2d07bd cc-langs.el
> --- a/cc-langs.el       Sun Sep 11 20:46:35 2016 +0000
> +++ b/cc-langs.el       Tue Sep 13 18:22:17 2016 +0000
> @@ -1231,6 +1231,22 @@
>  (c-lang-defvar c-assignment-op-regexp
>    (c-lang-const c-assignment-op-regexp))
>
> +(c-lang-defconst c-arithmetic-operators
> +  "List of all arithmetic operators, including \"+=\", etc."
> +  ;; Note: in the following, there are too many operators for AWK and IDL.
> +  t (append (c-lang-const c-assignment-operators)
> +           '("+" "-" "*" "/" "%"
> +             "<<" ">>"
> +             "<" ">" "<=" ">="
> +             "==" "!="
> +             "&" "^" "|"
> +             "&&" "||")))
> +
> +(c-lang-defconst c-arithmetic-op-regexp
> +  t (c-make-keywords-re nil
> +      (c-lang-const c-arithmetic-operators)))
> +(c-lang-defvar c-arithmetic-op-regexp (c-lang-const c-arithmetic-op-regexp))
> +
>  (c-lang-defconst c-:$-multichar-token-regexp
>    ;; Regexp matching all tokens ending in ":" which are longer than one char.
>    ;; Currently (2016-01-07) only used in C++ Mode.
>
>
>
> --
> Alan Mackenzie (Nuremberg, Germany).
>



-- 
Bastian Beischer
RWTH Aachen University of Technology

@CERN
Office: Bdg 32-4-B12
Phone: +41-22-76-75750
E-mail: bastian.beischer <at> cern.ch
Address: CERN, CH-1211 Geneve 23

@RWTH Aachen
Office: 28 C 203
Phone: +49-241-80-27205
E-mail: beischer <at> physik.rwth-aachen.de
Address: I. Physikalisches Institut B, Sommerfeldstr. 14, D-52074 Aachen

Message #16 received at 24377-done <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: Bastian Beischer <bastian.beischer <at> gmail.com>
Cc: 24377-done <at> debbugs.gnu.org
Subject: Re: bug#24377: 25.1; CC-Mode (C++) uses font-lock-type-face for
 ordinary variable
Date: Thu, 29 Dec 2016 15:50:04 +0000

Hello, Bastian.

On Tue, Sep 13, 2016 at 10:24:40PM +0200, Bastian Beischer wrote:
> Hello Alan,

> First of all, thanks for the patch - it's appreciated. My comments
> below:

> Alan Mackenzie <acm <at> muc.de> writes:

> > In article <mailman.1977.1473362155.22741.bug-gnu-emacs <at> gnu.org> you wrote:

> >> This piece of C++ code is wrongly fontified by CC-Mode:

> >> int b = 5;
> >> int a = (b*3);

> >> Reproduce as follows:

> >> 1) emacs -Q
> >> 2) Open file "test.C"
> >> 3) Paste snippet in buffer
> >> 4) Place cursor over "b" in second line
> >> 5) M-x describe-face -> font-lock-type-face

> >> This appears to be correlated with the presence of the opening
> >> parentheses and the '*' character, because:

> >> 1) int a = b*3;
> >> does not have this problem

> >> 2) "b" gets fontified incorrectly after entering the '*' character:
> >> int a = (b*

> > Thanks for this bug report, and thanks even more for taking the trouble
> > to reduce the test case to just two lines.

> >> In GNU Emacs 25.1.2 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.30)
> >>  of 2016-08-30 built on beischer-w520
> >> Repository revision: 17197d0ae9eac100b56078b2a48964b29710b76e
> >> Windowing system distributor 'The X.Org Foundation', version 11.0.11804000
> >> Configured using:
> >>  'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
> >>  --localstatedir=/var --mandir=/usr/share/man --with-gameuser=:games
> >>  --with-sound=alsa --with-xft --with-modules --with-x-toolkit=gtk2
> >>  --with-gconf --without-gsettings 'CFLAGS=-march=native -O2 -pipe
> >>  -fstack-protector-strong' CPPFLAGS=-D_FORTIFY_SOURCE=2
> >>  LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

> > [ .... ]

> > Yes, the CC Mode fontification code was confusing the "*" with an
> > indirection operator, such as you might get in "int (*b) (....);"

> > The solution seems to be to recognise the case where an arithmetic
> > operator (including "=") precedes the open parenthesis.  This is what the
> > following patch does.  Would you please try out this patch on real code,
> > and let me know whether the problem is completely fixed, and if not,
> > what's still going wrong.  Thanks!


> Yes this helps in the example above, but I'm not sure this is a fully
> correct solution. One can write something like this:

> void f(int arg)  {
>      printf("%d\n", arg)
> }

> f(a*5);

> Another example:

> int d(a*5)

> In both cases a is also wrongly fontified (and still is after applying
> the patch).

Sorry, but in the end I wasn't able to fix this problem.

There is now just too much ambiguity in C++'s syntax.  The "int d(a*5)"
is a sort of special case variant of "int d(a*b)".  This could either be
a declaration of d which is initialised to a*b, or the declaration of a
function d taking one parameter b whose type is a pointer to a.

C++ Mode, being an almost purely syntactic editor has no way to resolve
these ambiguities.  It seems not really worthwhile to handle the special
case of a literal integer following the "*".  So I have left that
construct being fontified as the function declaration, which is probably
the more common case.

So, I have committed the patch as it was when I last sent it to you for
review in September, and I am closing this bug.  Sorry, again.

> Thanks a lot again!


> -- 
> Bastian Beischer
> RWTH Aachen University of Technology

-- 
Alan Mackenzie (Nuremberg, Germany).

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