[MacPorts] #52742: buildbot: add support for building ports with variants

[MacPorts]

#52742: buildbot: add support for building ports with variants
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  Reporter:  mojca          |      Owner:  admin@…
      Type:  enhancement    |     Status:  new
  Priority:  Normal         |  Milestone:
 Component:  buildbot/mpbb  |    Version:
Resolution:                 |   Keywords:  buildbot
      Port:                 |
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Comment (by neverpanic):

 You're right. I thought about this yesterday and came to the conclusion
 that this is really a bug in base, since base propagates these variants
 down the dependency tree and attempts to install a combination that will
 not work.

 Either the `glib2` Portfile should ignore the user's request to change the
 variant and forcefully set a variant, or base should not request this
 invalid combination.

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Ticket URL: <https://trac.macports.org/ticket/52742#comment:17>
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