[GHC] #15778: GHC HEAD-only panic (zonkTcTyVarToTyVar)

[GHC]

#15778: GHC HEAD-only panic (zonkTcTyVarToTyVar)
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.8.1
       Component:  Compiler (Type    |              Version:  8.7
  checker)                           |
      Resolution:                    |             Keywords:  TypeInType
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by RyanGlScott):

 * keywords:   => TypeInType


Comment:

 Marginally simpler example:

 {{{#!hs
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeInType #-}
 module Bug where

 import Data.Kind

 data Flarble (a :: Type) where
   MkFlarble :: Flarble Bool
 data SFlarble (z :: Flarble a) where
   SMkFlarble :: SFlarble MkFlarble

 foo :: SFlarble z -> ()
 foo s at SMkFlarble =
   case s of
     (_ :: SFlarble (MkFlarble :: Flarble probablyABadIdea))
       -> ()
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15778#comment:3>
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