[GHC] #11480: UndecidableSuperClasses causes the compiler to spin with UndecidableInstances

[GHC]

#11480: UndecidableSuperClasses causes the compiler to spin with
UndecidableInstances
-------------------------------------+-------------------------------------
        Reporter:  ekmett            |                Owner:
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |             Keywords:  PolyKinds,
      Resolution:  fixed             |  UndecidableSuperClasses
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  GHC rejects       |            Test Case:
  valid program                      |  typecheck/should_compile/T11480,
                                     |  polykinds/T11480a
      Blocked By:                    |             Blocking:
 Related Tickets:  #10318            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by bgamari):

 * status:  merge => closed
 * resolution:   => fixed
 * milestone:   => 8.0.1


Comment:

 Cherry-picked to `ghc-8.0` as 6217147e0895e98b08e597660ea941a544943a4d and
 e37b571baabf18621eb3b471fddc015a021ecf46.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11480#comment:11>
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