[MacPorts] #51310: ImageMagick: update to 7.x

[MacPorts]

#51310: ImageMagick: update to 7.x
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  Reporter:  mopihopi     |      Owner:  ryandesign
      Type:  update       |     Status:  assigned
  Priority:  Normal       |  Milestone:
 Component:  ports        |    Version:
Resolution:               |   Keywords:
      Port:  ImageMagick  |
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Comment (by ryandesign):

 The process to do that would be:
 * Make the ImageMagick6 and ImageMagick7 ports, making sure the files get
 installed to different locations so that the two ports do not conflict
 * Modify all ports that declare a dependency on ImageMagick so that they
 depend on ImageMagick6 instead, and modify each port's build system so
 that it knows how to find the ImageMagick6 files at their new locations,
 and increase the ports' revisions
 * Keep an empty ImageMagick port for 1 year that is `replaced_by
 ImageMagick6` (using the obsolete-1.0 portgroup) to help users upgrade

 The above should all happen simultaneously. Not necessarily in one commit,
 but in one pull request that is merged to master all at once.

 "Make the ImageMagick6 and ImageMagick7 ports" could mean make separate
 Portfiles in ImageMagick6 and ImageMagick7 directories, or, since it is
 possible/likely that the ImageMagick6 and ImageMagick7 Portfiles would
 have a lot in common, one could make both ImageMagick6 and ImageMagick7
 subports of the single ImageMagick Portfile. That way they can share as
 much code as they wish.

 Since the above necessitates visiting each port that depends on
 ImageMagick anyway, this might also be a good opportunity to tackle
 another longstanding issue, which is that the ImageMagick program and
 libraries are in a single port. Ideally the libraries should be in a
 separate subport so that ports that need the program can declare a
 dependency on that and ports that need the libraries can declare a
 dependency on that (like the netpbm port and its libnetpbm subport for
 example). That way, when ImageMagick is updated and its library version
 increases, it is easy for us to tell which ports need a revbump and which
 ones don't. It may even be desirable to put each library in its own
 subport, since they are versioned separately, and since not all ports that
 use the libraries link with all three of them. But this is a more
 difficult task, as it requires figuring out how to make the build system
 build each part separately, as well as identifying which parts of
 ImageMagick each port that declares a dependency on it uses.

-- 
Ticket URL: <https://trac.macports.org/ticket/51310#comment:17>
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