[MacPorts] #53201: cmake, "compile features" and macports-clang

[MacPorts]

#53201: cmake, "compile features" and macports-clang
--------------------+-------------------
 Reporter:  RJVB    |      Owner:
     Type:  defect  |     Status:  new
 Priority:  Normal  |  Milestone:
Component:  ports   |    Version:
 Keywords:          |       Port:  cmake
--------------------+-------------------
 I just ran into an incomprehensible error where everything always worked
 just fine before, when using `configure.compiler=macports-clang-3.9`:

 {{{
 -- Configuring done
 CMake Error in src/platformtheme/CMakeLists.txt:
   No known features for CXX compiler

   "Clang"

   version 3.9.0.
 }}}

 After much head scratching and googling, I tracked that down to a line in
 the `Qt5CoreConfigExtras.cmake` file shipped by Qt 5.7.1 (I'm testing that
 Qt version):

 {{{
 set_property(TARGET Qt5::Core PROPERTY INTERFACE_COMPILE_FEATURES
 cxx_decltype)
 }}}

 From what I understand, CMake only supports compile[r] features with GCC
 and AppleClang, on Mac. Indeed, outcommenting that line fixes the
 configure error.

 I'm reporting this as a CMake bug in hope Michael can find a proper fix
 (to be reported upstream). I'm CC'ing the llvm/clang maintainers as a FYI,
 and Marcus so he's aware of this nasty little breaker too.

 https://bugreports.qt.io/browse/QTBUG-57886

--
Ticket URL: <https://trac.macports.org/ticket/53201>
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