r224012 - Emit warning if define or undef reserved identifier or keyword.

[Joerg Sonnenberger]

On Mon, Dec 15, 2014 at 11:47:23AM -0500, Aaron Ballman wrote:
> On Mon, Dec 15, 2014 at 11:35 AM, Joerg Sonnenberger
> <joerg at britannica.bec.de> wrote:
> > On Mon, Dec 15, 2014 at 11:32:02AM -0500, Aaron Ballman wrote:
> >> On Sat, Dec 13, 2014 at 2:46 PM, Joerg Sonnenberger
> >> > (2) #define restrict __restrict__ --> code that has to deal with pre-C99
> >> > default in GCC.
> >>
> >> I'm not certain this should have triggered the warning in the first
> >> place. Either restrict is a keyword (at which point, the #define
> >> should be considered possibly harmful), or restrict isn't a keyword
> >> (and then there's no reason for the warning in the first place).
> >
> > It happens in code that has to deal with different compilers. Consider a
> > pre-generated config.h. In NetBSD we have to deal with different GCC
> > versions and Clang, at least the former doesn't default to C99 :(
> 
> I'm confused. Are you talking about vendors where restrict is a
> keyword, but it's not implemented (properly)?

configure will not pick it up for GCC with the C90 default.

> >> > (3) #define extern, #define static --> debug, code sharing
> >>
> >> I think these should be a warning. If you're doing a debug build where
> >> you want to turn off keywords, you can add a -Wno-keyword-macro flag
> >> to your command line.
> >
> > I disagree. Having to change the warning settings just to get a debug
> > build to work is stupid.
> 
> Redefining keywords to be empty macros in production code is equally stupid. ;-)
> 
> > My question remains: what bugs has this warning caught? I've heard that
> > Microsoft believes this to be reasonable to warn about, but that's about
> > it.
> 
> CERT also feels this is reasonable to diagnose:
> ...

Well, keep in mind that C and restricted interface contracts don't
necessarily agree with each other, so often various tricks are played.
So summarize, I think the following should be accepted silently by
default:

(1) macro name equals macro body.
(2) macro name is a "storage" class keyword (extern, static, inline) and
the body is empty.
(3) macro name is const.
(4) macro body wrapped with __ equals macro name.

Joerg