[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):

 Rainer, yes, in your example above I would consider all platforms
 blacklisted. If you don't like "whitelisting" (you could call it
 `platforms-blacklisteverythingbut` :), we can drop it. My idea only needs
 blacklisting to work.

 Now, to explain why your suggestion might be tricky to implement and
 understand, imagine that your port declares
 {{{
 platforms {darwin < 10} {darwin 11}
 }}}
 and one the portgroup it includes declares
 {{{
 platforms {darwin > 10}
 }}}
 and one dependency would declare
 {{{
 platforms {darwin > 12}
 }}}
 etc. How do you then combine these together? Users might just as well
 start thinking of using something like `platforms-append {darwin 13}`

 How will you determine whether the port can be installed on a particular
 platform? You would need to use cross-sections of options which is not
 quite easy for users to understand either.

-- 
Ticket URL: <https://trac.macports.org/ticket/15712#comment:28>
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