bug#67173: 27.1; support raw string literals in C mode (a GNU C extension)

bug#67173: 27.1; support raw string literals in C mode (a GNU C extension)

[Rasmus Villemoes via Bug reports for GNU Emacs, the Swiss army knife of text editors]

gcc, when using -std=gnu99 or newer, supports using raw string literals
in C code. But emacs' C mode does not do proper syntax highlighting for
that case.

I do not know if that can be fixed by simply adding
c-before-change-check-raw-strings to C mode's
c-get-state-before-change-functions.

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --enable-libsystemd --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/27.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/27.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --build
 x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --enable-libsystemd
 --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/27.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/27.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --with-cairo
 --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars
 'CFLAGS=-g -O2
 -ffile-prefix-map=/build/emacs-WL9mhG/emacs-27.1+1=.
-fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro''

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 LIBSYSTEMD
JSON PDUMPER LCMS2 GMP

Important settings:
  value of $LANG: en_DK.UTF-8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix

Major mode: C/*l

Minor modes in effect:
  shell-dirtrack-mode: t
  yas-global-mode: t
  yas-minor-mode: t
  cscope-minor-mode: t
  desktop-save-mode: t
  display-time-mode: t
  electric-pair-mode: t
  show-paren-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t
  abbrev-mode: t

bug#67173: 27.1; support raw string literals in C mode (a GNU C extension)

[Eli Zaretskii]

> Date: Tue, 14 Nov 2023 11:30:53 +0100
> From:  Rasmus Villemoes via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> gcc, when using -std=gnu99 or newer, supports using raw string literals
> in C code. But emacs' C mode does not do proper syntax highlighting for
> that case.
> 
> I do not know if that can be fixed by simply adding
> c-before-change-check-raw-strings to C mode's
> c-get-state-before-change-functions.

Alan, are you looking into this?

bug#67173: 27.1; support raw string literals in C mode (a GNU C extension)

[Alan Mackenzie]

Hello, Eli and Rasmus.

On Wed, Nov 15, 2023 at 15:03:39 +0200, Eli Zaretskii wrote:
> > Date: Tue, 14 Nov 2023 11:30:53 +0100
> > From:  Rasmus Villemoes via "Bug reports for GNU Emacs,
> >  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>

> > gcc, when using -std=gnu99 or newer, supports using raw string literals
> > in C code. But emacs' C mode does not do proper syntax highlighting for
> > that case.

Thanks!  I didn't know about that.  I can't find any mention of raw
strings in C in the GCC manual for version 10.3.0.

> > I do not know if that can be fixed by simply adding
> > c-before-change-check-raw-strings to C mode's
> > c-get-state-before-change-functions.

That's the basic idea, yes, with another function to be added to
c-before-font-lock-functions.  But there are several detailed changes
necessary, too.

> Alan, are you looking into this?

I am now.  What's bothering me at the moment is that this is going to
make C Mode slower.  I suppose I could add an option into C Mode so that
raw strings can be enabled only when they're needed, but this would be
quite awkward, and a new departure for CC Mode.

-- 
Alan Mackenzie (Nuremberg, Germany)

bug#67173: 27.1; support raw string literals in C mode (a GNU C extension)

[Eli Zaretskii]

> Date: Wed, 15 Nov 2023 22:23:15 +0000
> Cc: Rasmus Villemoes <ravi@prevas.dk>, 67173@debbugs.gnu.org
> From: Alan Mackenzie <acm@muc.de>
> 
> > > I do not know if that can be fixed by simply adding
> > > c-before-change-check-raw-strings to C mode's
> > > c-get-state-before-change-functions.
> 
> That's the basic idea, yes, with another function to be added to
> c-before-font-lock-functions.  But there are several detailed changes
> necessary, too.
> 
> > Alan, are you looking into this?
> 
> I am now.  What's bothering me at the moment is that this is going to
> make C Mode slower.  I suppose I could add an option into C Mode so that
> raw strings can be enabled only when they're needed, but this would be
> quite awkward, and a new departure for CC Mode.

We could support fontification of raw strings only when
font-lock-maximum-decoration is set, or something.  Any solution that
makes this optional behavior is okay from where I stand, since I don't
believe raw string literals will be used frequently enough to make
this a UX issue.

bug#67173: 27.1; support raw string literals in C mode (a GNU C extension)

[Rasmus Villemoes via Bug reports for GNU Emacs, the Swiss army knife of text editors]

On 15/11/2023 23.23, Alan Mackenzie wrote:
> Hello, Eli and Rasmus.
> 
> On Wed, Nov 15, 2023 at 15:03:39 +0200, Eli Zaretskii wrote:
>>> Date: Tue, 14 Nov 2023 11:30:53 +0100
>>> From:  Rasmus Villemoes via "Bug reports for GNU Emacs,
>>>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
>>> gcc, when using -std=gnu99 or newer, supports using raw string literals
>>> in C code. But emacs' C mode does not do proper syntax highlighting for
>>> that case.
> 
> Thanks!  I didn't know about that.  I can't find any mention of raw
> strings in C in the GCC manual for version 10.3.0.

No, it's not mentioned anywhere, and I don't know why they don't
document it, but it's most definitely deliberate (see the
lang_defaults[] table in libcpp/init.cc).

>>> I do not know if that can be fixed by simply adding
>>> c-before-change-check-raw-strings to C mode's
>>> c-get-state-before-change-functions.
> 
> That's the basic idea, yes, with another function to be added to
> c-before-font-lock-functions.  But there are several detailed changes
> necessary, too.

That explains why my quick hacking didn't work...

>> Alan, are you looking into this?
> 
> I am now.  What's bothering me at the moment is that this is going to
> make C Mode slower.  

Urgh, I didn't think about that. I agree that it's probably not very
widely used (probably partly due to not being documented...). I myself
only use it very rarely, and for now just use C++ mode for the file in
question where I noticed this.

So if "slower" is actually noticeable, I would probably prefer to
retract this bug report or ask that support becomes some explicit
opt-in, because 99.99% of the .c files I touch do not use raw strings.

Regardless, thanks for taking this up so quickly.

Rasmus