Given kind equalities are discarded

The following program:

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}

module Bug where

data U (s :: *) = forall k. AA k [U s]

data I (u :: U *) (r :: [*]) :: * where
  A :: I (AA t as) r

-- fs unused, but needs to be present for the bug
class C (u :: U *) (r :: [*]) (fs :: [*]) where
  c :: I u r -> I u r

instance (C (AA (t (I a ps)) as) ps fs) => C (AA t (a ': as)) ps fs where
  c A = c undefined

crashes a fresh copy of GHC HEAD with the following:

ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 7.7.20131126 for i386-unknown-linux):
        kindFunResult k1{tv a24f} [ssk]

Trac metadata

Trac field	Value
Version	7.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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