Dependent quantification, GHC panic

While exploring Ryan's gist for term-level f :: forall a -> a -> Type.

{-# Language PolyKinds          #-}
{-# Language TypeApplications   #-}
{-# Language ImpredicativeTypes #-}

import Data.Kind

data A k :: k -> Type

f :: KindOf A
f a = undefined

type KindOf (a :: k) = k

a = f @Int

gives

$ ~/code/unmodifiedghc/inplace/bin/ghc-stage2 --interactive -ignore-dot-ghci 630_bug.hs
GHCi, version 8.7.20181029: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( 630_bug.hs, interpreted )
ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 8.7.20181029 for x86_64-unknown-linux):
        ASSERT failed!
  KindOf A
  forall k -> k -> *
  k_a1xQ[sk:0]
  k_a1xQ[sk:0] -> *
  k_a1xQ[sk:0]
  [req]
  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/TcExpr.hs:1336:94 in ghc:TcExpr

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

>

Trac metadata

Trac field	Value
Version	8.6.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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