#15598: RebindableSyntax with RankNTypes and type class method call yields panic. -------------------------------------+------------------------------------- Reporter: romanb | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.3 Resolution: | Keywords: | RebindableSyntax, RankNTypes Operating System: Linux | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by romanb: Old description:
The following program in a file `ghc-panic.hs`
{{{
{-# LANGUAGE GADTSyntax , RankNTypes , RebindableSyntax #-}
import Prelude hiding ((>>=))
data InfDo where InfDo :: String -> (forall a. a -> InfDo) -> InfDo
prog :: InfDo prog = do _ <- show (42 :: Int) prog where (>>=) = InfDo
main :: IO () main = let x = prog in x `seq` return () }}}
when loaded into GHCi yields
{{{ λ> main ghc: panic! (the 'impossible' happened) (GHC version 8.4.3 for x86_64-unknown-linux): nameModule system $dShow_abfY Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/basicTypes/Name.hs:241:3 in ghc:Name }}}
and separate compilation yields
{{{ $ ghc ghc-panic.hs [1 of 1] Compiling Main ( ghc-panic.hs, ghc-panic.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.4.3 for x86_64-unknown-linux): StgCmmEnv: variable not found $dShow_a1qI local binds for: $tcInfDo $trModule $tcInfDo1_r1th $tcInfDo2_r1tH $trModule1_r1tI $trModule2_r1tJ $trModule3_r1tK $trModule4_r1tL sat_s1E4 Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/codeGen/StgCmmEnv.hs:149:9 in ghc:StgCmmEnv }}}
The problem disappears when either the rank-2 type is removed from `InfDo` or when the call to `show` is replaced by a static string.
Besides 8.4.3, also reproduced with 8.6.0.20180714
New description: The following program in a file `ghc-panic.hs` {{{#!hs {-# LANGUAGE GADTSyntax , RankNTypes , RebindableSyntax #-} import Prelude hiding ((>>=)) data InfDo where InfDo :: String -> (forall a. a -> InfDo) -> InfDo prog :: InfDo prog = do _ <- show (42 :: Int) prog where (>>=) = InfDo main :: IO () main = let x = prog in x `seq` return () }}} when loaded into GHCi yields {{{ λ> main ghc: panic! (the 'impossible' happened) (GHC version 8.4.3 for x86_64-unknown-linux): nameModule system $dShow_abfY Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/basicTypes/Name.hs:241:3 in ghc:Name }}} and separate compilation yields {{{ $ ghc ghc-panic.hs [1 of 1] Compiling Main ( ghc-panic.hs, ghc-panic.o ) ghc: panic! (the 'impossible' happened) (GHC version 8.4.3 for x86_64-unknown-linux): StgCmmEnv: variable not found $dShow_a1qI local binds for: $tcInfDo $trModule $tcInfDo1_r1th $tcInfDo2_r1tH $trModule1_r1tI $trModule2_r1tJ $trModule3_r1tK $trModule4_r1tL sat_s1E4 Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/codeGen/StgCmmEnv.hs:149:9 in ghc:StgCmmEnv }}} The problem disappears when either the rank-2 type is removed from `InfDo` or when the call to `show` is replaced by a static string. Besides 8.4.3, also reproduced with 8.6.0.20180714 -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15598#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler