On 14 June 2018 at 20:21, Ville Voutilainen <ville.voutilai...@gmail.com> wrote: > On 14 June 2018 at 20:08, Jonathan Wakely <jwak...@redhat.com> wrote: >>> Oops, indeed. But for gnu-attributes, surely we can decide whatever we >>> want about what's >>> valid and what's not? >> >> >> We could say that #defining 'nonnull' and/or 'gnu' as a macro is >> undefined, but then programs that the standard says are valid would >> fail to compile, and we'd be a non-conforming implementation. >> >> We can use __attribute__(__nonnull__)) so that we accept those >> programs (and be a conforming implementation). Why would we choose to >> be non-conforming when we don't have to? > > I can read the specification liberally enough that it might give us > the freedom to disallow programs > that #define names that our implementation uses for vendor attributes.
Namely "For an attribute-token (including an attribute-scoped-token) not specified in this document, the behavior is implementation-defined.", aka [dcl.attr.grammar]/6.
