InScope set assertion failure from monad-skeleton

{-# LANGUAGE PolyKinds, GADTs, Rank2Types, ScopedTypeVariables, Trustworthy #-} 
module Control.Monad.Skeleton.Internal where                                    
                                                                                
data Cat k a b where                                                            
  Empty :: Cat k a a                                                            
  Leaf :: k a b -> Cat k a b                                                    
  Tree :: Cat k a b -> Cat k b c -> Cat k a c                                   
                                                                                
viewL :: forall k a b r. Cat k a b                                              
  -> ((a ~ b) => r)                                                             
  -> (forall x. k a x -> Cat k x b -> r)                                        
  -> r                                                                          
viewL Empty e _ = e                                                             
viewL (Leaf k) _ r = k `r` Empty                                                
viewL (Tree a b) e r = go a b where                                             
  go :: Cat k a x -> Cat k x b -> r                                             
  go Empty t = viewL t e r                                                      
  go (Leaf k) t = r k t                                                         
  go (Tree c d) t = go c (Tree d t)

Leads to the assertion failure

[1 of 1] Compiling Control.Monad.Skeleton.Internal ( Internal.hs, Internal.o )
WARNING: file compiler/simplCore/OccurAnal.hs, line 2160 Just 3 []
ghc: panic! (the 'impossible' happened)
  (GHC version 8.2.0.20170708 for x86_64-unknown-linux):
	ASSERT failed!
  in_scope InScope {x_avF ds_d14c}
  tenv [avF :-> x_avF]
  tenvFVs [avF :-> x_avF, a11Z :-> k_a11Z]
  cenv []
  cenvFVs []
  tys [k1_a120 a_a121 x_avF]
  cos []
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1188:22 in ghc:Outputable
        assertPprPanic, called at compiler/types/TyCoRep.hs:2088:56 in ghc:TyCoRep
        checkValidSubst, called at compiler/types/TyCoRep.hs:2121:29 in ghc:TyCoRep
        substTy, called at compiler/coreSyn/CoreArity.hs:1197:19 in ghc:CoreArity
  Call stack:
      CallStack (from HasCallStack):
        prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable
        callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable
        pprPanic, called at compiler/utils/Outputable.hs:1186:5 in ghc:Outputable
        assertPprPanic, called at compiler/types/TyCoRep.hs:2088:56 in ghc:TyCoRep
        checkValidSubst, called at compiler/types/TyCoRep.hs:2121:29 in ghc:TyCoRep
        substTy, called at compiler/coreSyn/CoreArity.hs:1197:19 in ghc:CoreArity

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

Trac metadata

Trac field	Value
Version	8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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