GHC Panic in ByteCodeGen

Try to load the following problem with ghc --interactive of the latest HEAD.

{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}

class Search id a where
  search :: a -> ()

instance Search id () where
  search d = undefined

-- works:
-- instance Search () () where  search d = undefined

You get an irrefutable pattern match error in ByteCodeGen:644

The code calls splitApp and expects an AnnVar v. What it gets instead is:

\ (@ id{tv af0} [sk]) -> search1{v rfK} [gid] @ id{tv af0} [sk]

The argument to splitApp was:

((((\ (@ id{tv af0} [sk]) ->
          search1{v rfK} [gid] @ id{tv af0} [sk])
       `cast` (forall id{tv af0} [sk].
               ghc-prim:GHC.Prim.sym{(w) tc 34v}
                 (main:Main.NTCo:T:Search{tc rfe}
                    id{tv af0} [sk] ghc-prim:GHC.Unit.(){(w) tc 40})
               :: <pred>forall id{tv af0} [sk].
                        ghc-prim:GHC.Unit.(){(w) tc 40} -> ghc-prim:GHC.Unit.(){(w) tc 40}
                          ~
                        forall id{tv af0} [sk].
                        main:Main.T:Search{tc rf8}
                          id{tv af0} [sk] ghc-prim:GHC.Unit.(){(w) tc 40}))
        @ etaT_sg1{tv} [tv])
     `cast` (main:Main.NTCo:T:Search{tc rfe}
               etaT_sg1{tv} [tv] ghc-prim:GHC.Unit.(){(w) tc 40}
             :: <pred>main:Main.T:Search{tc rf8}
                        etaT_sg1{tv} [tv] ghc-prim:GHC.Unit.(){(w) tc 40}
                        ~
                      ghc-prim:GHC.Unit.(){(w) tc 40}
                      -> ghc-prim:GHC.Unit.(){(w) tc 40}))
      eta_sg2{v} [lid]

Trac metadata

Trac field	Value
Version	6.11
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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