[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 mojca):

 Replying to [comment:30 raimue]:
 >
 > The example list from above would always evaluate to `YES` on macOS
 except for `darwin 10`

 See, that's where we completely disagree. The point of my example above is
 that the PortGroup specifying
 {{{
 platforms {darwin > 10}
 }}}
 means that a dependency (like Qt or wxWidgets or so) cannot be compiled on
 Snow Leopard or earlier, while (sorry for a not too realistic example) the
 following code in the Portfile
 {{{
 platforms {darwin < 10} {darwin 11}
 }}}
 means that the code in that port either requires some ancient SDK or no
 longer compiles with a newer compiler.

 The message I want to convey is that a PortGroup specifying `{darwin >
 10}` should not mean that a port using that PG can **additionally**
 (unconditionally) be compiled on any OS 10.7 or newer. It should mean that
 the port **cannot** be compiled on 10.6 and lower under any circumstances.
 Like the latest version of Qt.

 You are doing union. I claim we should be doing cross-section on compiler
 selection, else specifying any platforms in the PortGroup will be
 completely useless. This is why I consider blacklisting a better option.

-- 
Ticket URL: <https://trac.macports.org/ticket/15712#comment:31>
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