On Tue, Apr 13, 2021 at 02:07:13PM -0700, Junio C Hamano wrote:
> Jeff King <peff@xxxxxxxx> writes:
>
> >> + * We restrict this trick to gcc, though, because while we rely on the
> >> + * presence of C99 variadic macros, this code also relies on the
> >> + * non-standard behavior of GCC's __VA_ARGS__, allowing error() to
> >> + * work even if no format specifiers are passed to error().
>
> The last part of this comment is puzzlling. Do we ever call error()
> without any format specifier? There may be GCC-ism behaviour around
> the __VA_ARGS__ stuff, but are we relying on that GCC-ism?
I took "format specifier" to mean the "%" code within the format. E.g.:
error("foo");
has no format specifier, and thus no arguments after the format. But
every call will have at least the format string itself.
AFAIK, portably using variadic macros means you need there to always be
at least one argument. Hence "error(fmt, ...)" is wrong (the "..." may
have no arguments) but "error(...)" is OK (you always have a format
string). I'm not sure if Ævar knows about some other portability gotcha,
or if he just didn't realize that this was written in the portable way.
-Peff
