[MacPorts] #55637: allow port reactivation (WIP)

[MacPorts]

#55637: allow port reactivation (WIP)
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 Reporter:  RJVB         |      Owner:
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  base         |    Version:
 Keywords:               |       Port:
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 This is a little modification that allows doing something we've discussed
 this before, months ago: reactivating an already active port.
 The main intended application is to exclude almost the entire $prefix from
 (TimeMachine) incremental backup schemes except the crucial folders under
 var/macports (at least the port tree(s) and images and the registry).
 As an added bonus it make it trivial to repair or revert changes you made
 to an active port.

 The change does not introduce a new verb but simply reuses the `-f` option
 so that `port activate -f foo` acts deactivates and then reactivates the
 currently active port. I think this is intuitive enough not to require the
 introduction of a new verb, and probably even a bit more appropriate if
 you restore ports from the registry into an otherwise empty prefix.

 A priori a global restore should become possible with

 {{{
 > port activate -f active
 }}}

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Ticket URL: <https://trac.macports.org/ticket/55637>
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