#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: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Here's as minimal of an example as I can conjure up: {{{#!hs {-# LANGUAGE GADTs #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeInType #-} module Bug where import Data.Kind import Data.Proxy data Foo (x :: Type) :: forall (a :: x). Proxy a -> Type data Bar :: Type -> Type where MkBar :: forall x arg. -- Commenting out the line below makes the issue go away Foo arg ~ Foo arg => Bar 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 Bar arg_a1vT[sk:1] [a1vS :-> 0] 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:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler