GNU bug report logs - #48670
27.2; cc-mode and constexpr if

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

From: John Eivind Helset <jehelset <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 27.2; cc-mode and constexpr if
Date: Wed, 26 May 2021 05:08:03 +0200

cc-mode has problems with constexpr-if-statements whose true-statement
is not a compound statement.

From 'emacs -Q' open a buffer in cc-mode and compare the formatting of:

void f(){
  if(a == 4)
    return 4;
  else if(a == 3)
    return 3;
  else
    return 2;
}

void f_constexpr(){
  if constexpr(a == 4)
                return 4;
  else if constexpr(a == 3)
         return 3;
  else
    return 2;
}


In GNU Emacs 27.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.27, cairo version 1.17.4)
 of 2021-03-26 built on juergen
Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
System Description: Arch Linux

Recent messages:
Loading /home/jeh/.config/emacs/custom.el (source)...done
Turning on magit-auto-revert-mode...done
For information about GNU Emacs and the GNU system, type C-h C-a.
Package cl is deprecated

Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-wide-int
 --with-modules --with-cairo --with-harfbuzz 'CFLAGS=-march=x86-64
 -mtune=generic -O2 -pipe -fno-plt' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'

Configured features:
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INOTIFY ACL GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD JSON
PDUMPER LCMS2 GMP

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  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
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Load-path shadows:
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Memory information:
((conses 16 557252 409165)
 (symbols 48 41880 568)
 (strings 32 164504 45552)
 (string-bytes 1 4903026)
 (vectors 16 61227)
 (vector-slots 8 754212 496078)
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 (buffers 1000 11))

-- 
John Eivind Helset

Message #8 received at 48670 <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: John Eivind Helset <jehelset <at> gmail.com>
Cc: acm <at> muc.de, 48670 <at> debbugs.gnu.org
Subject: Re: bug#48670: 27.2; cc-mode and constexpr if
Date: Sun, 30 May 2021 16:29:17 +0000

Hello, John.

On Wed, May 26, 2021 at 05:08:03 +0200, John Eivind Helset wrote:

> cc-mode has problems with constexpr-if-statements whose true-statement
> is not a compound statement.

> >From 'emacs -Q' open a buffer in cc-mode and compare the formatting of:

> void f(){
>   if(a == 4)
>     return 4;
>   else if(a == 3)
>     return 3;
>   else
>     return 2;
> }

> void f_constexpr(){
>   if constexpr(a == 4)
>                 return 4;
>   else if constexpr(a == 3)
>          return 3;
>   else
>     return 2;
> }

Thanks for taking the trouble to report this bug, and thanks even more
for creating a minimal, easy to work with, test case.

The bug has in fact already been fixed in the development version of
Emacs, and should be getting released with Emacs 28.1, whenever that
will happen.

In the mean time, please apply the following patch to
..../emacs/lisp/progmodes/cc-engine.el, and then byte compile that file.
Should you want any help with the patching or byte compilation, feel
free to send me private email.



--- cc-engine.el.orig	2021-05-30 16:08:48.855885223 +0000
+++ cc-engine.el	2021-05-30 16:16:47.785903083 +0000
@@ -1181,6 +1181,15 @@
 			  ;; suitable error.
 			  (setq pre-stmt-found t)
 			  (throw 'loop nil))
+			;; Handle C++'s `constexpr', etc.
+			(if (save-excursion
+			      (and (looking-at c-block-stmt-hangon-key)
+				   (progn
+				     (c-backward-syntactic-ws lim)
+				     (c-safe (c-backward-sexp) t))
+				   (looking-at c-block-stmt-2-key)
+				   (setq pos (point))))
+			    (goto-char pos))
 			(cond
 			 ;; Have we moved into a macro?
 			 ((and (not macro-start)


> In GNU Emacs 27.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.27, cairo version 1.17.4)
>  of 2021-03-26 built on juergen
> Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
> System Description: Arch Linux

[ .... ]

> -- 
> John Eivind Helset

-- 
Alan Mackenzie (Nuremberg, Germany).

Message #11 received at 48670 <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: control <at> debbugs.gnu.org
Cc: 48670 <at> debbugs.gnu.org
Subject: Re: bug#48670: 27.2; cc-mode and constexpr if
Date: Sun, 30 May 2021 16:35:10 +0000

tags 48670 fixed 28.1
close 48670
quit

On Wed, May 26, 2021 at 05:08:03 +0200, John Eivind Helset wrote:

> cc-mode has problems with constexpr-if-statements whose true-statement
> is not a compound statement.

[ .... ]

-- 
Alan Mackenzie (Nuremberg, Germany).

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