[GHC] #14880: GHC panic: updateRole

[GHC]

#14880: GHC panic: updateRole
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  8.2.2
  checker)                           |
      Resolution:                    |             Keywords:  Roles
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by RyanGlScott:

Old description:

> The following program panics on GHC 8.0.2, 8.2.2, 8.4.1, and HEAD:
>
> {{{#!hs
> {-# LANGUAGE ConstraintKinds #-}
> {-# LANGUAGE GADTs #-}
> {-# LANGUAGE ScopedTypeVariables #-}
> {-# LANGUAGE TypeFamilies #-}
> {-# LANGUAGE TypeInType #-}
> {-# LANGUAGE TypeOperators #-}
> module Bug where
>
> import Data.Kind
> import Data.Type.Equality ((:~:)(..))
>
> type SameKind (a :: k) (b :: k) = (() :: Constraint)
>
> data TyFun :: Type -> Type -> Type
> type a ~> b = TyFun a b -> Type
> infixr 0 ~>
>
> type family Apply (f :: k1 ~> k2) (x :: k1) :: k2
> type f @@ x = f `Apply` x
> infixl 9 @@
>
> type family WhyCong (x :: Type) (y :: Type) (f :: x ~> y)
>                     (a :: x) (z :: x) (e :: a :~: z) :: Type where
>   WhyCong _ _ f a z _ = f @@ a :~: f @@ z
>
> data WhyCongSym1 (x :: Type) :: forall (a :: x)
>                                        (y :: Type)
>                                        (z :: x).
>                                 Type ~> (x ~> y) ~> x ~> x ~> a :~: z ~>
> Type
>
> data WhyCongSym0 :: forall (x :: Type)
>                            (a :: x)
>                            (y :: Type)
>                            (z :: x).
>                     Type ~> Type ~> (x ~> y) ~> x ~> x ~> a :~: z ~> Type
>   where
>     WhyCongSym0KindInference :: forall x arg.
>                                 SameKind (Apply WhyCongSym0 arg)
> (WhyCongSym1 arg) =>
>                                 WhyCongSym0 x
> }}}
>
> {{{
> $ /opt/ghc/8.2.2/bin/ghc Bug.hs
> [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
> ghc: panic! (the 'impossible' happened)
>   (GHC version 8.2.2 for x86_64-unknown-linux):
>         updateRole
>   WhyCongSym0
>   arg_aYV[sk:1]
>   [aYU :-> 4, a22o :-> 0, a22p :-> 1, a22q :-> 2, a22r :-> 3]
>   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/typecheck/TcTyDecls.hs:656:23 in
> ghc:TcTyDecls
> }}}

New description:

 The following program panics on GHC 8.0.2, 8.2.2, 8.4.1, and HEAD:

 {{{#!hs
 {-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE TypeInType #-}
 {-# LANGUAGE TypeOperators #-}
 module Bug where

 import Data.Kind
 import Data.Type.Equality ((:~:))

 type SameKind (a :: k) (b :: k) = (() :: Constraint)

 data TyFun :: Type -> Type -> Type
 type a ~> b = TyFun a b -> Type
 infixr 0 ~>
 type family Apply (f :: k1 ~> k2) (x :: k1) :: k2

 data WhyCongSym1 (x :: Type) :: forall (a :: x)
                                        (y :: Type)
                                        (z :: x).
                                 Type ~> (x ~> y) ~> x ~> x ~> (a :~: z) ~>
 Type

 data WhyCongSym0 :: forall (x :: Type)
                            (a :: x)
                            (y :: Type)
                            (z :: x).
                     Type ~> Type ~> (x ~> y) ~> x ~> x ~> (a :~: z) ~>
 Type
   where
     WhyCongSym0KindInference :: forall x arg.
                                 SameKind (Apply WhyCongSym0 arg)
 (WhyCongSym1 arg) =>
                                 WhyCongSym0 x
 }}}

 {{{
 $ /opt/ghc/8.2.2/bin/ghci Bug.hs
 GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Bug              ( Bug.hs, interpreted )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.2.2 for x86_64-unknown-linux):
         updateRole
   WhyCongSym0
   arg_a1A6[sk:1]
   [a1A5 :-> 4, a2Cy :-> 0, a2Cz :-> 1, a2CA :-> 2, a2CB :-> 3]
   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/typecheck/TcTyDecls.hs:656:23 in
 ghc:TcTyDecls
 }}}

--

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14880#comment:1>
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