[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()
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  Reporter:  noloader   |      Owner:  jeremyhu
      Type:  defect     |     Status:  assigned
  Priority:  Normal     |  Milestone:
 Component:  ports      |    Version:
Resolution:             |   Keywords:
      Port:  clang-6.0  |
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Comment (by noloader):

 Replying to [comment:6 jmroot]:
 > Replying to [ticket:57578 noloader]:
 > > 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.
 >
 > This doesn't say anything about C++17 features, just that it tells you
 whether C++ exceptions are enabled at all. Since uncaught_exceptions is
 part of the standard library and not the compiler, I would guess its
 absence isn't a problem with clang++ as such.

 Thanks Joshua.

 Maybe I am parsing something incorrectly, but according to
 [https://en.cppreference.com/w/User:D41D8CD98F/feature_testing_macros C++
 feature test macros], `__has_feature(cxx_exceptions)` is supposed to give
 me the correct answer:

 > [feature test macros] provide a set of preprocessor macros which give a
 simple and portable way to detect the presence of C++ standards and
 experimental features.

 If I understand the concept correctly, then
 `__has_feature(cxx_exceptions)` should return false because
 `std::uncaught_exceptions()` is not available.

 Or maybe I am not understanding the word-smithing that's happening here.
 As an analogy, are you saying I'm buying a car with a anti-lock brake
 system but the brakes don't work and the car won't stop? (This kind of
 reasoning makes no sense to me).

-- 
Ticket URL: <https://trac.macports.org/ticket/57578#comment:7>
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