[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:  merge
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |             Keywords:  PolyKinds,
      Resolution:                    |  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 simonpj):

 * status:  new => merge
 * testcase:   => typecheck/should_compile/T11480, polykinds/T11480a


Comment:

 OK I've fixed both the original report (with the commit in comment:9) and
 comment:2 (the commit in comment:8).  Pls merge both.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11480#comment:10>
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