[GHC] #12144: GHC panic when using DeriveAnyClass with functor-like class and datatype with a type variable in a contravariant position

[GHC]

#12144: GHC panic when using DeriveAnyClass with functor-like class and datatype
with a type variable in a contravariant position
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.2.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  Generics
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #5462, #7346,     |  Differential Rev(s):  Phab:D2961
  #12423                             |
       Wiki Page:                    |
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Changes (by RyanGlScott):

 * status:  new => patch
 * differential:   => Phab:D2961


Comment:

 A WIP attempt at fixing this is at ​Phab:D2961.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12144#comment:3>
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