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

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

[Christopher Wellons]

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.

diff --git a/src/emacs-module.h b/src/emacs-module.h
--- a/src/emacs-module.h
+++ b/src/emacs-module.h
@@ -67,7 +67,7 @@ enum emacs_funcall_exit
   emacs_funcall_exit_signal = 1,

   /* Function has exit using `throw'.  */
-  emacs_funcall_exit_throw = 2,
+  emacs_funcall_exit_throw = 2
 };

 struct emacs_env_25

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

[Glenn Morris]

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.

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

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. :)


> diff --git a/src/emacs-module.h b/src/emacs-module.h
> --- a/src/emacs-module.h
> +++ b/src/emacs-module.h
> @@ -67,7 +67,7 @@ enum emacs_funcall_exit
>    emacs_funcall_exit_signal = 1,
>
>    /* Function has exit using `throw'.  */
> -  emacs_funcall_exit_throw = 2,
> +  emacs_funcall_exit_throw = 2
>  };
>
>  struct emacs_env_25

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

[npostavs]

tags 24494 fixed
close 24494 26.1
quit

Glenn Morris <rgm@gnu.org> writes:

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

This has now been done in [1: 0489f2ca5a].

[1: 0489f2ca5a]: 2017-07-01 20:02:24 +0200
  Improve C++98 compatibility
  http://git.savannah.gnu.org/cgit/emacs.git/commit/?id=0489f2ca5a01445d3abb39aea18d54257fedd5f1

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

[Philipp Stephani]

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Glenn Morris <rgm@gnu.org> 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.

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