https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68524
--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- I believe the syntax in N2269 does allow [[]] attributes there (and disallows them as prefixes on old-style parameters to avoid ambiguity) - but they appertain to the function type (whereas the corresponding position for GNU attributes - after the full declarator and any following asm, before any initializer - appertains to the entity being declared).
