[GHC] #15817: Visible kind application + data family = GHC panic, ‘impossible’ happened

[GHC]

#15817: Visible kind application + data family = GHC panic, ‘impossible’ happened
-------------------------------------+-------------------------------------
           Reporter:  Iceland_jack   |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.6.1
           Keywords:                 |  Operating System:  Unknown/Multiple
  TypeApplications                   |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 {{{#!hs
 {-# Language RankNTypes       #-}
 {-# Language TypeApplications #-}
 {-# Language PolyKinds        #-}
 {-# Language KindSignatures   #-}
 {-# Language TypeFamilies     #-}

 data family   Pair :: forall a. forall b. *
 data instance Pair @a @b = MkPair a b
 }}}

 {{{
 $ ghci -ignore-dot-ghci 593_bug.hs
 GHCi, version 8.7.20181017: http://www.haskell.org/ghc/  :? for help
 [1 of 1] Compiling Main             ( 593_bug.hs, interpreted )
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.7.20181017 for x86_64-unknown-linux):
         ASSERT failed!
   kind axiom D:R:Pairabab0 ::
          forall a b (a :: a) (b :: b).
            Pair = R:Pairabab -- Defined at 593_bug.hs:8:15
   forall k k (a :: k) (b :: k). *
   forall a b -> a -> b -> *
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in
 ghc:Outputable
         pprPanic, called at compiler/utils/Outputable.hs:1219:5 in
 ghc:Outputable
         assertPprPanic, called at compiler/typecheck/FamInst.hs:158:61 in
 ghc:FamInst

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

 >
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15817>
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