Subject: Re: bug#24494: 24.4; Trailing comma in emacs-module.h

From: Philipp Stephani <[email-masked]>
Date: Sun, 02 Jul 2017 15:28:55 +0000

Glenn Morris <[email-masked]> schrieb am Mo., 12. Dez. 2016 um 23:37 Uhr:

> Christopher Wellons wrote:
>
> > Building Emacs itself now requires a C99 compiler, but this requirement
> > needn't extend to dynamic modules. Removing a trailing comma (see patch)
> > makes emacs-module.h C89/C90 compatible, allowing modules to be built
> > using older C compilers. Trailing commas weren't permitted until C99.
>
> Thanks for the report. I don't have an opinion, but some comments:
>
> 1) I think it's going to be hard for developers to remember to use
> different conventions for emacs-module.h, so C99-isms are likely to
> creep back in.
>

emacs-module.h is used differently than other parts of the source code, so
different conventions apply: It should be more compatible with various
compilers, it has to be compatible with C++, all names have to start with
"emacs_", it can't depend on any headers not in the standard library, etc.
If it's hard to remember these requirements, maybe we should check for
them? E.g. add a unit test that including emacs-module.h always works, even
with '-pedantic-errors -Weverything -Werror -std=c++98'.
Aside: technically emacs-module.h already depends on C99/C++11, via
intmax_t and bool. However, these types are apparently often available even
in C++98/C89 mode.

>
> 2) Are people really likely to be building Emacs modules with set-ups
> that can't build Emacs itself?
>

Why not? Modules could be much simpler than Emacs, and module authors might
legitimately want to support older compilers.

>
> 3) It seems this feature was supported by gcc since 0.9? Ie, forever?
> https://www.gnu.org/software/gcc/c99status.html
>
> Hopefully someone who does have an opinion will quickly either fix or
> wontfix this issue. :)
>

I've independently just pushed the same change. I think not breaking
pre-C++11 builds (which probably still see signifcant use) is important
enough.