#14326: Panic on COMPLETE pragma with mismatched type variable order -------------------------------------+------------------------------------- Reporter: dailectic | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- The motivating example is to allow patterns with phantom types to interact nicely with TypeApplications, so in the below we can do `L @Int :: a -> L a Int` to specify the phantom. {{{#!hs data E a b = L' a | R b pattern L :: forall b a. a -> E a b pattern L a = L' a {-# COMPLETE L, R #-} }}} The compiler balks {{{ ghc: panic! (the 'impossible' happened) (GHC version 8.2.1 for x86_64-unknown-linux): mkOneConFull: Not TyConApp: c_a50V 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/deSugar/Check.hs:976:30 in ghc:Check Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14326 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler