
#14270: GHC HEAD's ghc-stage1 panics on Data.Typeable.Internal -------------------------------------+------------------------------------- Reporter: hvr | Owner: bgamari Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #14236 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I attempted to create a minimal example of this bug. This is as small as I was able to make it (~110 lines): {{{#!hs {-# LANGUAGE TypeInType #-} {-# LANGUAGE ViewPatterns #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE PatternSynonyms #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE UndecidableInstances #-} {-# LANGUAGE TypeApplications #-} module DataTypeableInternal (pattern App) where import Data.Kind (Type) import GHC.Fingerprint (Fingerprint, fingerprintFingerprints) import GHC.Types (RuntimeRep, TYPE, TyCon) data (a :: k1) :~~: (b :: k2) where HRefl :: a :~~: a data TypeRep (a :: k) where TrTyCon :: {-# UNPACK #-} !Fingerprint -> !TyCon -> [SomeTypeRep] -> TypeRep (a :: k) TrApp :: forall k1 k2 (a :: k1 -> k2) (b :: k1). {-# UNPACK #-} !Fingerprint -> TypeRep (a :: k1 -> k2) -> TypeRep (b :: k1) -> TypeRep (a b) TrFun :: forall (r1 :: RuntimeRep) (r2 :: RuntimeRep) (a :: TYPE r1) (b :: TYPE r2). {-# UNPACK #-} !Fingerprint -> TypeRep a -> TypeRep b -> TypeRep (a -> b) data SomeTypeRep where SomeTypeRep :: forall k (a :: k). !(TypeRep a) -> SomeTypeRep typeRepFingerprint :: TypeRep a -> Fingerprint typeRepFingerprint = undefined mkTrApp :: forall k1 k2 (a :: k1 -> k2) (b :: k1). TypeRep (a :: k1 -> k2) -> TypeRep (b :: k1) -> TypeRep (a b) mkTrApp rep@(TrApp _ (TrTyCon _ con _) (x :: TypeRep x)) (y :: TypeRep y) | con == funTyCon -- cheap check first , Just (IsTYPE (rx :: TypeRep rx)) <- isTYPE (typeRepKind x) , Just (IsTYPE (ry :: TypeRep ry)) <- isTYPE (typeRepKind y) , Just HRefl <- withTypeable x $ withTypeable rx $ withTypeable ry $ typeRep @((->) x :: TYPE ry -> Type) `eqTypeRep` rep = undefined mkTrApp a b = TrApp fpr a b where fpr_a = typeRepFingerprint a fpr_b = typeRepFingerprint b fpr = fingerprintFingerprints [fpr_a, fpr_b] pattern App :: forall k2 (t :: k2). () => forall k1 (a :: k1 -> k2) (b :: k1). (t ~ a b) => TypeRep a -> TypeRep b -> TypeRep t pattern App f x <- (splitApp -> Just (IsApp f x)) where App f x = mkTrApp f x data IsApp (a :: k) where IsApp :: forall k k' (f :: k' -> k) (x :: k'). () => TypeRep f -> TypeRep x -> IsApp (f x) splitApp :: forall k (a :: k). () => TypeRep a -> Maybe (IsApp a) splitApp (TrApp _ f x) = Just (IsApp f x) splitApp rep@(TrFun _ a b) = Just (IsApp (mkTrApp arr a) b) where arr = bareArrow rep splitApp (TrTyCon{}) = Nothing withTypeable :: forall a r. TypeRep a -> (Typeable a => r) -> r withTypeable = undefined eqTypeRep :: forall k1 k2 (a :: k1) (b :: k2). TypeRep a -> TypeRep b -> Maybe (a :~~: b) eqTypeRep = undefined typeRepKind :: TypeRep (a :: k) -> TypeRep k typeRepKind = undefined bareArrow :: forall (r1 :: RuntimeRep) (r2 :: RuntimeRep) (a :: TYPE r1) (b :: TYPE r2). () => TypeRep (a -> b) -> TypeRep ((->) :: TYPE r1 -> TYPE r2 -> Type) bareArrow = undefined data IsTYPE (a :: Type) where IsTYPE :: forall (r :: RuntimeRep). TypeRep r -> IsTYPE (TYPE r) isTYPE :: TypeRep (a :: Type) -> Maybe (IsTYPE a) isTYPE = undefined class Typeable (a :: k) where typeRep :: Typeable a => TypeRep a typeRep = undefined funTyCon :: TyCon funTyCon = undefined instance (Typeable f, Typeable a) => Typeable (f a) instance Typeable ((->) :: TYPE r -> TYPE s -> Type) instance Typeable TYPE }}} I wasn't able to reproduce the exact panic in this ticket, but if you compile with `-O1` and `-dcore-lint`, then you do experience a Core Lint that is very reminiscent of the panic: {{{ $ /opt/ghc/8.2.1/bin/ghc -O1 -fforce-recomp Bug.hs -dcore-lint [1 of 1] Compiling DataTypeableInternal ( Bug.hs, Bug.o ) *** Core Lint errors : in result of Float out(FOS {Lam = Just 0, Consts = True, OverSatApps = True}) *** <no location info>: warning: In the type ‘forall (a :: TYPE r1) k1. (k1 :: *) ~# (* :: *) => TypeRep ((->) a |> <TYPE r2>_N ->_N Sym cobox)’ cobox_a2ym :: (k2_aVY :: *) ~# (* :: *) [LclId[CoVarId]] is out of scope *** Offending Program *** <elided> *** End of Offense *** <no location info>: error: Compilation had errors }}} `cobox_a2ym` appears in `$mApp` (the matcher for the `App` pattern synonym). I've reproduced this with GHC 8.0.2 and HEAD. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14270#comment:15 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler