[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 ryandesign):

 Replying to [comment:18 mojca]:
 > the `platforms` variable currently represents the platforms where the
 port has been tested rather than platforms where the port works.

 Not particularly. `platforms macosx` means the port works on macOS, and
 does not work on pure Darwin because of the use of proprietary framework
 or other non-open-source technologies only available in macOS. `platforms
 darwin` means the port is not believed to use proprietary frameworks or
 other closed-source features so it should work on pure Darwin, though in
 practice nobody tests this of course, and I expect many ports that declare
 `platforms darwin` do actually use proprietary macOS features and don't
 work on pure Darwin.

 My guess is that most ports that list platforms other than `darwin` or
 `macosx` don't actually work on those other platforms because the portfile
 and the underlying software have undergone changes since those other
 platforms were added to the `platforms` directive. For example, the zlib
 port claims to work on freebsd, but that claim was added 11 years ago, and
 I certainly haven't ever tested it on freebsd. It might have worked on
 freebsd back then, but who knows if it does now.

 I'm not particularly concerned about addressing that problem. Everybody
 knows MacPorts is for macOS and it's not terrible that our support for
 non-Mac platforms isn't as good.

 I agree with Mojca that it would be good if it were possible for
 portgroups or subports to alter the set of supported macOS versions set by
 the port. As long as we design the syntax with that in mind, I don't think
 it particularly matters whether we design the syntax to use blacklisting
 or whitelisting. Using a blacklisting syntax seems to have worked well for
 choosing compilers, but I can't offer an opinion at this point as to
 whether it would make sense for platform versions.

-- 
Ticket URL: <https://trac.macports.org/ticket/15712#comment:22>
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