[MacPorts] #70384: opencv3 fails to provide legacy module in contrib variant, which is required by digikam port

[MacPorts]

#70384: opencv3 fails to provide legacy module in contrib variant, which is
required by digikam port
-------------------------------+----------------------
  Reporter:  barracuda156      |      Owner:  mascguy
      Type:  defect            |     Status:  assigned
  Priority:  Normal            |  Milestone:
 Component:  ports             |    Version:  2.9.3
Resolution:                    |   Keywords:
      Port:  opencv3, digikam  |
-------------------------------+----------------------

Comment (by barracuda156):

 Replying to [comment:1 ryandesign]:
 > The digikam port already sets `known_fail yes` so it is known that it
 does not build.
 >
 > It's also years out of date. This problem may already have been fixed in
 the latest version. See #62755.

 Thank you. I have found what was going wrong for me: I needed
 `-DENABLE_OPENCV3:BOOL=ON` to make it use `opencv3` correctly.

 Updating it beyond 4.14.0 will not work for me, since it is the last
 version to support Qt4, but I am trying to build that one, of course, not
 our archaic portfile.

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Ticket URL: <https://trac.macports.org/ticket/70384#comment:2>
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