[GHC] #14880: GHC panic: updateRole

[GHC]

#14880: GHC panic: updateRole
-------------------------------------+-------------------------------------
           Reporter:  RyanGlScott    |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.2.2
  (Type checker)                     |
           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:
-------------------------------------+-------------------------------------
 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
 }}}

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