[cfe-dev] Possible bug with __has_cpp_attribute

[Kal]

Hi,
The following seems like a clang bug.

You can't use __has_cpp_attribute with namespaces in a header that is 
included from C. For example:
#if __has_cpp_attribute(clang::fallthrough)
    ...
#endif

Yields:
error: builtin feature check macro requires a parenthesized identifier.

Shouldn't __has_cpp_attribute() evaluate to 0 for C programs?

I worked around the issue with something like:

#ifndef __has_cpp_attribute
#define __has_cpp_attribute(x) 0
#elif defined(__clang__) && !defined(__cplusplus)
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wbuiltin-macro-redefined"
#define __has_cpp_attribute(x) 0
#pragma clang diagnostic pop
#endif

Is there a better way?

-Kal