[MacPorts] #58858: [base]: default_variants could check variant conflicts

[MacPorts]

#58858: [base]: default_variants could check variant conflicts
-------------------------+--------------------
 Reporter:  RJVB         |      Owner:  (none)
     Type:  enhancement  |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  base         |    Version:
 Keywords:               |       Port:
-------------------------+--------------------
 Consider a port foo with

 {{{
 variant A conflicts B description {AAA} {}
 variant B conflicts A description {BBB} {}
 default_variants +A
 }}}

 {{{
 > port info foo +B
 Error: fpp: Variant A conflicts with B
 Error: Unable to open port: Error evaluating variants
 Exit 1
 }}}

 I'd argue that it isn't really too much to expect that `default_variants`
 would check check the user variant selection before applying the default;
 most APIs that I know of that prevent a default do something that boils
 down to the same thing.
 Note that I'm not saying it's easy, but it would remove (some of) the
 burden for conflict management and determining whether or not to set a
 default.

-- 
Ticket URL: <https://trac.macports.org/ticket/58858>
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