ghc panics

{-# LANGUAGE DataKinds, StandaloneDeriving, TypeOperators, GADTs, FlexibleInstances #-}

data A a where
  A :: A (a:as) -> a -> A as

deriving instance Show a => Show (A a)

gives

% ghci -ignore-dot-ghci Panic.hs
GHCi, version 8.1.20160117: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( Panic.hs, interpreted )
ghc: panic! (the 'impossible' happened)
  (GHC version 8.1.20160117 for x86_64-unknown-linux):
        fvProv falls into a hole {a1aV}

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

> 

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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