[GHC] #11399: Ill-kinded instance head involving -XTypeInType can invoke GHC panic

[GHC]

#11399: Ill-kinded instance head involving -XTypeInType can invoke GHC panic
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        Reporter:  RyanGlScott       |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.1
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by ekmett):

 You don't even need `-XTypeInType`.

 I had this bite me earlier when I accidentally gave one too many type
 parameters to `K1`.

 {{{
 class GEq1 t where
   gliftEq :: (a -> b -> Bool) -> t a -> t b -> Bool

 instance Eq c => GEq1 (K1 i c) where gliftEq _ (K1 c) (K1 d) = c == d
 }}}

 If you replace the instance with

 {{{
 instance Eq c => GEq1 (K1 i c oops) where gliftEq _ (K1 c) (K1 d) = c == d
 }}}

 You get the same `fpProv falls into a hole` error.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11399#comment:1>
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