[MacPorts] #52161: mp-buildbot: incorrect error message when a port cannot be installed due to arch mismatch

[MacPorts]

#52161: mp-buildbot: incorrect error message when a port cannot be installed due to
arch mismatch
-------------------------+--------------------------------
  Reporter:  ryandesign  |      Owner:  macports-tickets@…
      Type:  defect      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  contrib     |    Version:  2.3.4
Resolution:              |   Keywords:
      Port:              |
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Comment (by jmroot):

 Replying to [comment:2 ryandesign]:
 > Actually, it cannot install svn2git for ppc because its dependency
 qt5-qtbase only builds for x86_64.
 Not sure if anything changed since you wrote this, but currently svn2git
 includes the qmake5 portgroup which in turn includes the qt5 portgroup,
 which sets supported_archs.

 Basically the issue here is that check_supported_archs (which produces the
 error seen in the wine example) is only called when you execute a target
 on the port. The incorrect error being seen here is generated during
 dependency calculation, before any targets are run. The reason for the
 ppc/powerpc mismatch is that unsupported archs are filtered out of
 configure.build_arch, which in this case leaves it empty. So
 get_canonical_archs falls back to returning ${os.arch} rather than return
 an empty string.

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Ticket URL: <https://trac.macports.org/ticket/52161#comment:3>
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