[MacPorts] #57578: __has_feature(cxx_exceptions) returns true but fails to compile std::uncaught_exceptions()

[MacPorts]

#57578: __has_feature(cxx_exceptions) returns true but fails to compile
std::uncaught_exceptions()
-------------------------------------------------+-------------------------
 Reporter:  noloader                             |      Owner:  (none)
     Type:  defect                               |     Status:  new
 Priority:  Normal                               |  Milestone:
Component:  ports                                |    Version:
 Keywords:  C++17 cxx_exceptions                 |       Port:
  std::uncaught_exceptions()                     |  clang++-mp-6.0
-------------------------------------------------+-------------------------
 I'm testing C++17 on OS X 10.8.5 and 10.9.5 using Macports Clang compiler
 versions 5.0 and 6.0. Attempting to compile the following program:

   $ cat test.cxx
   #if __EXCEPTIONS && __has_feature(cxx_exceptions)
   # include <exception>
   # define CXX17_EXCEPTIONS 1
   #endif

   void Foo()
   {
   #if defined(CXX17_EXCEPTIONS)
       if (std::uncaught_exceptions() == 0)
   #endif
       {
           int x = 0;
       }
   }

 Results in:

 $ /opt/local/bin/clang++-mp-5.0 -std=gnu++17 test.cxx -c
 test.cxx:9:14: error: 'uncaught_exceptions' is unavailable: introduced in
 macOS 10.12
     if (std::uncaught_exceptions() == 0)
              ^
 /opt/local/libexec/llvm-5.0/include/c++/v1/exception:130:63: note:
       'uncaught_exceptions' has been explicitly marked unavailable here
 _LIBCPP_FUNC_VIS _LIBCPP_AVAILABILITY_UNCAUGHT_EXCEPTIONS int
 uncaught_e...
                                                               ^
 -std=c++17 produces the same error.

 According to the LLVM 3.6 release notes
 (https://releases.llvm.org/3.6.0/tools/clang/docs/ReleaseNotes.html#the-
 exceptions-macro), I believe I am using the correct feature test:

     To reliably test if C++ exceptions are enabled,
     use __EXCEPTIONS && __has_feature(cxx_exceptions),
     else things won’t work in all versions of Clang in
     Objective-C++ files.

 ==========

 Upstream issue report at https://bugs.llvm.org/show_bug.cgi?id=39631

 ==========

 $ /opt/local/bin/clang++-mp-6.0 --version
 clang version 6.0.1 (tags/RELEASE_601/final)
 Target: x86_64-apple-darwin13.4.0
 Thread model: posix
 InstalledDir: /opt/local/libexec/llvm-6.0/bin

 $ /opt/local/bin/clang++-mp-5.0 --version
 clang version 5.0.2 (tags/RELEASE_502/final)
 Target: x86_64-apple-darwin13.4.0
 Thread model: posix
 InstalledDir: /opt/local/libexec/llvm-5.0/bin

 $ sw_vers
 ProductName:    Mac OS X
 ProductVersion: 10.9.5
 BuildVersion:   13F1911

-- 
Ticket URL: <https://trac.macports.org/ticket/57578>
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