On Tue, Feb 7, 2023 at 10:50 AM Timur Doumler <cpp@timur.audio> wrote:
@SG22: Can you confirm this? What is the intent of __has_c_attribute in C: what Poll 1 says or what Poll 2 says?
The intent in C is the same as Poll 1:
__has_c_attribute should return a positive value for a standard attribute only if it implements the semantics suggested in the specification of the attribute.
The C Standard contains the following example in Subclause 6.10.1 Conditional inclusion, paragraph 17:
/* Fallback for compilers not yet implementing this feature. */
#ifndef __has_c_attribute
#define __has_c_attribute(x) 0
#endif /* __has_c_attribute */
#if __has_c_attribute(fallthrough)
/* Standard attribute is available, use it. */
#define FALLTHROUGH [[fallthrough]]
#elif __has_c_attribute(vendor::fallthrough)
/* Vendor attribute is available, use it. */
#define FALLTHROUGH [[vendor::fallthrough]]
#else
/* Fallback implementation. */
#define FALLTHROUGH
#endif
How should we resolve this contradiction? Should we re-discuss that aspect of the paper in EWG, with someone from SG22 present?
Aaron Ballman would be the ideal person to represent the SG22 and WG14 positions, but if he is not available I would be willing to act as a poor substitute.
rCs