#11520: GHC falls into a hole if given incorrect kind signature -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler (Type | Version: 8.0.1-rc1 checker) | Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by bgamari: @@ -1,1 +1,2 @@ - This non-sense, + If one provides an incorrect kind signature GHC throws up. For instance, + this non-sense, @@ -11,2 +12,0 @@ - data TyCon (a :: k) = TyCon - @@ -14,1 +13,1 @@ - TypeCon :: forall (a :: k). TyCon a -> TypeRep k -> TypeRep a + TypeCon :: forall (a :: k). String -> TypeRep k -> TypeRep a @@ -25,3 +24,1 @@ - composeTyCon :: TyCon Compose - composeTyCon = TyCon Fingerprint "Compose" - + -- Note how the kind signature on g is incorrect @@ -30,2 +27,1 @@ - typeRep = TypeApp (TypeApp (TypeCon composeTyCon typeRep) typeRep) - typeRep + typeRep = undefined @@ -33,4 +29,0 @@ - instance (Typeable f, Typeable g, Typeable a) => Typeable (Compose f g a) - where - typeRep = TypeApp (TypeApp (TypeApp (TypeCon composeTyCon typeRep) - typeRep) typeRep) typeRep New description: If one provides an incorrect kind signature GHC throws up. For instance, this non-sense, {{{#!hs {-# LANGUAGE RankNTypes, PolyKinds, TypeInType, GADTs, UndecidableSuperClasses #-} module Play where import GHC.Types hiding (TyCon) data TypeRep (a :: k) where TypeCon :: forall (a :: k). String -> TypeRep k -> TypeRep a TypeApp :: forall k1 k2 (a :: k1 -> k2) (b :: k1). TypeRep a -> TypeRep b -> TypeRep (a b) class Typeable k => Typeable (a :: k) where typeRep :: TypeRep a data Compose (f :: k1 -> *) (g :: k2 -> k1) (a :: k2) = Compose (f (g a)) -- Note how the kind signature on g is incorrect instance (Typeable f, Typeable (g :: k), Typeable k) => Typeable (Compose f g) where typeRep = undefined }}} fails with {{{ λ> :load Bug.hs [1 of 1] Compiling Play ( Bug.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.1.20160122 for x86_64-unknown-linux): fvProv falls into a hole {abet} Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11520#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler