uncaught_exceptions requires macOS 10.12 or iOS 10.0

[gjasny]

Hello,

due to backward compatibility reasons we build boost with -mmacosx-version-min=10.8. This results in a compilation error in boost/core/uncaught_exceptions.hpp due to unavailability of the API in older macOS versions despite libc++ announces support. Locally I applied the following patch to fix compilation:

diff --git a/boost/core/uncaught_exceptions.hpp b/boost/core/uncaught_exceptions.hpp
index 27e2491bda..ff71e1925b 100644
--- a/boost/core/uncaught_exceptions.hpp
+++ b/boost/core/uncaught_exceptions.hpp
@@ -32,6 +32,16 @@
 #define BOOST_CORE_HAS_UNCAUGHT_EXCEPTIONS
 #endif
 
+// At least macOS 10.12 or iOS 10.0 is required
+#if defined(BOOST_CORE_HAS_UNCAUGHT_EXCEPTIONS) && defined(__APPLE__)
+#   if defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && __MAC_OS_X_VERSION_MIN_REQUIRED < 101200
+#      undef BOOST_CORE_HAS_UNCAUGHT_EXCEPTIONS
+#   endif
+#   if defined(__IPHONE_OS_VERSION_MIN_REQUIRED) && __IPHONE_OS_VERSION_MIN_REQUIRED < 100000
+#      undef BOOST_CORE_HAS_UNCAUGHT_EXCEPTIONS
+#   endif
+#endif
+
 #if !defined(BOOST_CORE_HAS_UNCAUGHT_EXCEPTIONS)
 
 // cxxabi.h availability macro

But I guess Boost already provides a more elegant way to check for availability like a Boost.Config Feature Check.

Thanks,
Gregor

[gjasny]

Availability for watchOS and tvOS (libc++ config.h):

#  define _LIBCPP_AVAILABILITY_UNCAUGHT_EXCEPTIONS                             \
     __attribute__((availability(macosx,strict,introduced=10.12)))             \
     __attribute__((availability(ios,strict,introduced=10.0)))                 \
     __attribute__((availability(tvos,strict,introduced=10.0)))                \
     __attribute__((availability(watchos,strict,introduced=3.0)))

[Lastique]

We are using __cpp_lib_uncaught_exceptions to detect availability of std::uncaught_exceptions. Do I understand correctly that the library defines the macro but does not actually provide the function? If so, please, report the bug to libc++ developers.