Hello! The Clang community is currently considering a patch (https://reviews.llvm.org/D93630) that would further impact the way GNU-style __attribute__ attributes affect parsing. Clang and GCC already deviate in this case in that Clang accepts GNU-style attributes at the start of a statement at function body scope, and it appears that GCC only accepts these attributes at the start of a statement in a more deeply nested block scope (like within a switch or while statement body).
In Clang, currently, when a GNU-style attribute appears at the start of a line, what follows is treated as a declaration. The proposed Clang patch is to look at all of the attributes named in the attribute list and if all of the attributes are (exclusively) statement attributes and what follows is not known to be a declaration statement, then parse the remainder of the line without assuming that what follows must be a declaration. This would allow GNU-style attributes at the beginning of a statement without causing parsing diagnostics. We believe that this change does not break existing code, but the potential exists for code like: __attribute__((attr-that-is-both-decl-and-stmt)) i = 12; where the use of the GNU-style attribute implies that what follows is a ANSI C-style declaration with an implied 'int' type specifier. However, we could not find any existing attributes that act as both a declaration and a statement attribute that would cause a problem in practice. I wanted to make the GCC community aware of the change in case this change would cause problems for GCC (either due to existing or planned attributes that could not support such a scheme, or because of other design reasons) beyond portability concerns. If you have opinions on the proposed Clang patch, I'd appreciate knowing what concerns you have. Thanks! ~Aaron
