[MacPorts] #53201: cmake: doesn't recognize macports-clang (No known features for CXX compiler)

[MacPorts]

#53201: cmake: doesn't recognize macports-clang (No known features for CXX
compiler)
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  Reporter:  RJVB    |      Owner:  michaelld
      Type:  defect  |     Status:  assigned
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:
Resolution:          |   Keywords:
      Port:  cmake   |
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Comment (by RJVB):

 Replying to [comment:12 mojca]:

 > do the same thing as it's done on Linux for the stock Clang complier.

 Eh? Correct me if I'm wrong, but the same compiler module is used
 everywhere for Clang. Yes, there are AppleClang modules. I'm not certain
 where/when exactly they come into play, but as far as I can tell they're
 not where the CMP25 policy is enacted.

 Actually, I realise that it's possible that they are used when using an
 AppleClang version, and the regular Clang-C[XX].cmake modules when using a
 stock (and MacPorts) clang version. If that's the case there is indeed no
 need to worry about equivalence tables, and your concern that my patch
 might interfere with feature detection for the system compiler largely
 moot. Provided that the system compiler on the OS X versions you are
 considering is indeed detected as AppleClang.

 > Worrying about equivalence table should be left to CMake developers when
 supporting AppleClang. Our task is easier.

 Not if we want to be able to present a full-featured patch to make them
 reconsider their point of view.

 > Not that I understand this madness about trying to cover the database of
 all features of all compilers. Testing for features sounds way more
 useful.

 Look at the modules, not all features are concerned, only the important
 ones that often need to be tested for, and which may not be easy to verify
 with a true (but still cheap) compile check. A compiler version might have
 an option to select C++XY mode, but we know from experience that this
 doesn't guarantee that it has complete and reliable support. That's where
 this database comes in.

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Ticket URL: <https://trac.macports.org/ticket/53201#comment:13>
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