[MacPorts] #58881: libgcc 9 dependency cctools requires libunwind-headers with which libgcc9 cannot be build

[MacPorts]

#58881: libgcc 9 dependency cctools requires libunwind-headers with which libgcc9
cannot be build
-------------------------+-------------------------------------------------
  Reporter:  vdoublie    |      Owner:  (none)
      Type:  update      |     Status:  new
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:
Resolution:              |   Keywords:  dependencies conflicts cctools
      Port:  libgcc9     |  libgcc9
-------------------------+-------------------------------------------------

Comment (by kencu):

 You've correctly described the problem.

 It turns out to be quite difficult to force gcc9 to ignore the libunwind
 headers during the build if they are already installed. You might think we
 could find a way to get gcc9 to build correctly against the current
 libunwind headers, but so far that has eluded us, at least on some
 systems. Even if we did fix that issue, propagating it back through all
 the gcc versions we support would be big job.

 I think only a few ports need the libunwind headers, and then only to
 build, but there is no sanctioned way to have a port deactivate a build
 dependency after it is installed. There is a way to make macports forcibly
 deactivate a port during a build of another port, the "deactivate hack",
 but this has been frowned upon (disallowed) for use in this situation in
 other ports, so I have not bothered to pursue that approach to solving
 this issue.

 The buildbots purge all ports prior to building, and reinstall only the
 listed build deps for a given port, and so they escape this issue. So most
 people never see this.

 It could be that we would discover this issue only affects certain system
 versions, and the conflicts-build might not need to apply to every os
 version; that would lessen the problem a bit, at least.

-- 
Ticket URL: <https://trac.macports.org/ticket/58881#comment:1>
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