Re: [RFC PATCH] compiler_attributes.h: Add 'fallthrough' pseudo keyword for switch/case use

[Joe Perches <joe@perches.com>]

On Wed, 2019-07-31 at 19:14 +0200, Pavel Machek wrote:
> On Tue 2019-07-30 22:35:18, Joe Perches wrote:
> > Reserve the pseudo keyword 'fallthrough' for the ability to convert the
> > various case block /* fallthrough */ style comments to appear to be an
> > actual reserved word with the same gcc case block missing fallthrough
> > warning capability.
> 
> Acked-by: Pavel Machek <pavel@ucw.cz>
> 
> > +/*
> > + * Add the pseudo keyword 'fallthrough' so case statement blocks
> > + * must end with any of these keywords:
> > + *   break;
> > + *   fallthrough;
> > + *   goto <label>;
> > + *   return [expression];
> > + *
> > + *  gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes
> > + */
> > +#if __has_attribute(__fallthrough__)
> > +# define fallthrough                    __attribute__((__fallthrough__))
> > +#else
> > +# define fallthrough                    do {} while (0)  /* fallthrough */
> > +#endif
> > +
> 
> Will various checkers (and gcc) recognize, that comment in a macro,
> and disable the warning accordingly?

Current non-gcc tools:  I doubt it.

And that's unlikely as the comments are supposed to be stripped
before the macro expansion phase.

gcc 7+, which by now probably most developers actually use, will
though
and likely that's sufficient.

> Explanation that the comment is "magic" might not be a bad idea.

The comment was more for the reader.

cheers, Joe