[MacPorts] #65532: isl @0.25: builds failing for 10.13: call to unavailable member function 'value'

[MacPorts]

#65532: isl @0.25: builds failing for 10.13: call to unavailable member function
'value'
-------------------------+----------------------
  Reporter:  dyne2meter  |      Owner:  mascguy
      Type:  defect      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.7.2
Resolution:              |   Keywords:
      Port:  isl         |
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Comment (by mascguy):

 Replying to [comment:5 kencu]:
 > in both cases, it appears that the tests that isl is using to see if
 certain c++ standards are available during configure are not complete
 enough to detect when certain c++17 features are not actually available in
 the end on 10.7 or 10.13.
 >
 > System libc++ versions implemented c++17 gradually, and full support
 only comes in at 10.15 I believe. Before that you have partial support.
 >
 > You'll have to dig in on why 10.8 builds but 10.7 doesn't, but I would
 guess 10.8 uses the system compiler which tests as having no c++17
 support, whereas 10.7 uses clang-14 which seems to support c++17, but in
 the end, the overall system does not support it well enough and the link
 fails.
 >
 > My guess is turning off c++17 manually by some mechanism on systems
 before - 10.14? - is probably going to be needed.

 Ah, makes sense Ken, I'll take a closer look at all of this. Thanks for
 the thoughts/guidance, as always!

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Ticket URL: <https://trac.macports.org/ticket/65532#comment:8>
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