gistfile1.txt

Header AvailabilityInternal.h cannot be processed by non-clang C compilers

Summary: Compiling C or C++ code with older, non-clang compilers (such as GCC 4.9 and older) leads to error in the system header AvailabilityInternal.h

The header features this line:
#if defined(__has_feature) && defined(__has_attribute) && __has_attribute(availability)

This is totally incorrect, because C preprocessor does not shortcircuit the && evaluation, and thus if the compiler does not have support for __has_feature, i.e. defined(__has_attribute) is 0, it will still call __has_attribute(availability) which results in an error.

The correct usage, which is used everywhere in this same header and in other system headers, is to split it into two separate preprocessor directives:

    #if defined(__has_attribute) && defined(__has_feature)
        #if __has_attribute(availability)

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Steps to Reproduce: Take a simple C source file that includes a system header, like this:

$ cat a.c
#include <stdlib.h>

Then compile it with a C compiler that does not support __has_attribute, such as GCC 4.9.


Expected Results: This should compile fine.

Actual Results: It crashes with this error:
/usr/include/AvailabilityInternal.h:25584:74: error: missing binary operator before token "("
 #if defined(__has_feature) && defined(__has_attribute) && __has_attribute(availability)
                                                                          ^

Version/Build: macOS 10.13 beta 9 & Xcode 9 beta 6

I had to compile ruby 1.8.7 in high sierra and faced the same issue. I solved it using C headers from my old sierra's backup.