[MacPorts] #46956: base should keep track of explicitly requested variants on install and only preserve those on upgrade

[MacPorts]

#46956: base should keep track of explicitly requested variants on install and only
preserve those on upgrade
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  Reporter:  neverpanic   |      Owner:  neverpanic
      Type:  enhancement  |     Status:  closed
  Priority:  Normal       |  Milestone:  MacPorts 2.7.0
 Component:  base         |    Version:  2.3.3
Resolution:  fixed        |   Keywords:
      Port:               |
--------------------------+----------------------------

Comment (by neverpanic):

 Thanks. I wanted to fix this before bringing `port migrate` to mainline,
 so that it'll only preserve requested variants (since otherwise guessing
 which variants you actually wanted, and which ones you didn't is quite
 complicated).

 Could you write a Changelog entry and document how the conversion from
 current state to requested variants works?

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Ticket URL: <https://trac.macports.org/ticket/46956#comment:12>
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