[MacPorts] #51619: qt5.depends_component procedure

[MacPorts]

#51619: qt5.depends_component procedure
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  Reporter:  RJVB          |      Owner:  mkae
      Type:  enhancement   |     Status:  assigned
  Priority:  Normal        |  Milestone:
 Component:  ports         |    Version:
Resolution:                |   Keywords:
      Port:  qt5, qt5-kde  |
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Comment (by MarcusCalhoun-Lopez):

 Replying to [comment:27 mkae]:
 > Replying to [comment:24 mojca]:
 > > It's easy to get lost in this discussion,
 >
 > Yes, I'm already lost in this and wonder which way we could and should
 go now...
 I am sorry about losing people in this discussion.[[BR]]
 Hopefully, we can find our way forward.[[BR]]
 Attached is a patch that attempts to satisfy most concerns.
 * qt5 PG provides qt5kde variant (unless Portfile opts out).
 * if qt5kde is selected, qt5-kde is **required**
 * if qt5kde is not selected
  * path dependency on Qt component is used so qt5-kde could still satisfy
 dependency
  * default Qt port (qt55, q56, or qt5) is determined by values `os.major`
 and `cxx_stdlib`
  * if installed Qt is different than the default, a warning is given
 * Only one Qt installation is possible at a given time
  * qt5-qtbase, qt56-qtbase, and qt5-kde all conflict with each other.
  * every Qt component (e.g. qt5*-qtmultimedia) explicitly depends on
 qt5*-qtbase (**not** a path dependency)

 If there are no objections, I will commit the change, and we can proceed
 on other fronts.

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Ticket URL: <https://trac.macports.org/ticket/51619#comment:28>
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