#12512: UnboxedTupleRep-related panic involving typeclasses -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash Test Case: | Blocked By: Blocking: | Related Tickets: #11723 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- You can trigger a GHC panic by abusing `UnboxedTupleRep` in just the right way: {{{#!hs {-# LANGUAGE DataKinds #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE StandaloneDeriving #-} {-# LANGUAGE UnboxedTuples #-} import GHC.Exts class Wat (a :: TYPE 'UnboxedTupleRep) deriving instance Wat (# a, b #) }}} {{{ $ /opt/ghc/8.0.1/bin/ghc Bug.hs [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.0.1 for x86_64-unknown-linux): newTyConEtadArity (#,#) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} This is probably a leak that #11723 didn't plug, as it only considered datatypes, not typeclasses. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12512 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler