[MacPorts] #15712: Add versions to platforms

[MacPorts]

#15712: Add versions to platforms
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  Reporter:  raimue       |      Owner:  larryv
      Type:  enhancement  |     Status:  assigned
  Priority:  Normal       |  Milestone:  MacPorts 2.6.0
 Component:  base         |    Version:
Resolution:               |   Keywords:
      Port:               |
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Comment (by raimue):

 For platforms, I think the best is to make this a declarative option in
 the Portfile. Specifiying support by matching on platform name and version
 should be sufficient. That would also make it possible to write this
 information into the PortIndex, so you could query for ports with this
 information (or present it accordingly on a web page).

 A new phase would mean that the Portfile needs to be evaluated, therefore
 you could not easily list all (non-)supported ports for a platform. Also,
 if the result of such a `check` phase is just "yes" or "no", it does not
 represent what platform would be required to be compatible.

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Ticket URL: <https://trac.macports.org/ticket/15712#comment:17>
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