[MacPorts] #66953: cmake @3.24.3: Does not compile with SDK 10.12

[MacPorts]

#66953: cmake @3.24.3: Does not compile with SDK 10.12
---------------------+-----------------------
  Reporter:  lukaso  |      Owner:  michaelld
      Type:  defect  |     Status:  assigned
  Priority:  Normal  |  Milestone:
 Component:  ports   |    Version:  2.8.1
Resolution:          |   Keywords:
      Port:  cmake   |
---------------------+-----------------------

Comment (by ryandesign):

 Ok. Cross-OS-version compilation is prone to problems like this. However,
 it [https://gitlab.kitware.com/cmake/cmake/-/issues/20054#note_663424
 sounds like this is supposed to work], so it may be a simple bug that can
 be fixed.

 The cmake port requires a C++14 compiler but will use features from C++17
 (like "optional") if they are detected to work. It sounds like maybe
 something has gone wrong with the detection, and it has perhaps determined
 that "optional" is available on the basis of your Big Sur / Ventura libc++
 when it needs to be looking at the Sierra libc++ in the 10.12 SDK that
 doesn't support it.

 Please attach the main.log file. I'm expecting to see a line like:

 {{{
 :info:configure -- Checking if compiler supports needed C++17 constructs -
 yes
 }}}

 I have not checked but I assume that what the line should say, when
 compiling for 10.12, is:

 {{{
 :info:configure -- Checking if compiler supports needed C++17 constructs -
 no
 }}}

 MacPorts contains a patch to that detection which was intended to improve
 it, but maybe it doesn't work correctly or maybe it recently broke. The
 [changeset:09819f74ebbdfe1b3beb042ce40d642f8e1a6d7d/macports-ports patch
 was added 4 years ago]. I don't know why we have this patch in MacPorts
 rather than submitting it to the developers of cmake. You could try
 removing the patch to see if that changes anything; maybe in the
 intervening years upstream fixed the problem a different way that
 interferes with our patch.

-- 
Ticket URL: <https://trac.macports.org/ticket/66953#comment:5>
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