macOS 14 SDK has a problematic use of __has_extension in TargetConditionals.h

[sezero]

Fixes #9632

CC: @Traace , @slime73

[sezero]

P.S.: If this is accepted, you may want to backport it to SDL2 branch.

[slouken]

I think it makes more sense to just include TargetConditionals.h in both branches rather than define a separate define to undefine.

[slouken]

Here's a proposed patch

diff --git a/include/SDL3/SDL_platform_defines.h b/include/SDL3/SDL_platform_defines.h
index 72b1ef260..b418ca411 100644
--- a/include/SDL3/SDL_platform_defines.h
+++ b/include/SDL3/SDL_platform_defines.h
@@ -65,7 +65,17 @@
 #define SDL_PLATFORM_APPLE  1
 /* lets us know what version of macOS we're compiling on */
 #include <AvailabilityMacros.h>
+/* The macOS 14 SDK uses __has_extension in TargetConditionals.h */
+#ifndef __has_extension
+# ifdef __has_feature
+#  define __has_extension __has_feature
+# else
+#  define __has_extension(x) 0
+# endif
 #include <TargetConditionals.h>
+#else
+#include <TargetConditionals.h>
+#endif

 /* Fix building with older SDKs that don't define these
    See this for more information:

[slouken]

Are we sure that __has_extension and __has_feature are equivalent? Have we heard back from the original bug reporter to find out what compiler they're using?

[sezero]

I think it makes more sense to just include TargetConditionals.h in both branches rather than define a separate define to undefine.

The undefine was suggested by @icculus in #9632 (and I kind'a agree with it)

[sezero]

Are we sure that __has_extension and __has_feature are equivalent?

They aren't exactly the same, but, as I said, that's what clang docs seem to suggest to use if __has_extension is absent: https://clang.llvm.org/docs/LanguageExtensions.html (search __has_extension on that page)

Have we heard back from the original bug reporter to find out what compiler they're using?

Nope. That's why I CC'd him here

[sezero]

find out what compiler they're using?

However, I do think they're using a version of gcc: all versions of clang I tried do have __has_extension. As for gcc, gcc-10 doesn't have either of __has_extension and __has_feature, however gcc-14 has both of them (EDIT: the features do seem to be added in gcc14: compare https://gcc.gnu.org/onlinedocs/gcc-13.2.0/cpp/Conditional-Syntax.html and https://gcc.gnu.org/onlinedocs/gcc-14.1.0/cpp/Conditional-Syntax.html).

[sezero]

Rebased and simplified the patch a bit.

[slouken]

@icculus and I chatted and we agreed we prefer separate include paths rather than the tap dance you have here. I'll go ahead and push that instead. Thanks for doing the legwork here!

[sezero]

OK. Please apply to SDL2, as well.

[slouken]

Done!