[MacPorts] #15712: Add versions to platforms

[MacPorts]

#15712: Add versions to platforms
--------------------------+----------------------------
  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 mojca):

 One thought. A good point has been raised: the `platforms` variable
 currently represents the platforms where the port has been tested rather
 than platforms where the port works. If we try to be strict, most likely
 it will no longer be possible to install any port on linux since linux is
 almost nowhere listed as a platform (then again, if we did that, we would
 suddenly get enough pull requests to list the missing platform variable
 and thus get feedback when something actually works).

 We could potentially introduce something like
 {{{
 platforms-blacklist {darwin < 10} darwin12
 }}}
 to signal that Mac OS X < 10.6 and 10.8 don't work with this port. Or
 {{{
 platforms-whitelist darwin15 darwin16 linux
 }}}
 to signal that the port only works on linux and macOS 10.11 and 10.12. I
 don't know whether
 {{{
 platform-blacklist {darwin > 11}
 }}}
 should match darwin11.1 in that case or not.

 I'm not saying that this is necessarily the best idea, just thinking loud.

--
Ticket URL: <https://trac.macports.org/ticket/15712#comment:18>
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