[GHC] #15966: panic when using RebindableSyntax

28 Nov 2018

      #15966: panic when using RebindableSyntax
-------------------------------------+-------------------------------------
           Reporter:  mpickering     |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.3
          Component:  Compiler       |           Version:  8.6.2
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 https://gist.github.com/mpickering/216ecdd9d8766dce2ff1080a17f77a0e

 {{{
 {-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE KindSignatures #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE InstanceSigs #-}
 {-# LANGUAGE RebindableSyntax #-}

 {-# OPTIONS_GHC -Wall -Wno-missing-signatures -Wno-unticked-promoted-
 constructors
                -Wno-name-shadowing -fwarn-partial-type-signatures -Wno-
 partial-type-signatures #-}
 module Repro(main) where

 import Prelude hiding (Monad(..))
 import Control.Applicative

 data E (a :: * -> *) (n :: *) where
   VarE :: a n -> E a n

 instance IMonad E where
   return :: a n -> E a n
   return = VarE

   (>>=) :: E a n -> (forall n . a n -> E b n) -> E b n
   VarE x >>= f = f x

 class IMonad (m :: (* -> *) -> (* -> *)) where
   return :: forall a n . a n -> m a n
   (>>=) :: m a n -> (forall n . a n -> m b n) -> m b n

 one :: Const Int n
 one = (Const 1)

 example_4 :: E (Const Int) n
 example_4 = do
   x <- (return one)
   return x

 main = example_4 `seq` ()
 }}}

 Compiling this file with GHC leads to a StgCmmEnv panic.

 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.6.2 for x86_64-unknown-linux):
         StgCmmEnv: variable not found
   $dIMonad_a1lY
   local binds for:
   return
...
...
=
   $tc'VarE
   $tcE
   $tcIMonad
   $trModule
   $tc'VarE1_r1oI
   $tc'VarE2_r1ps
   $krep_r1pt
   $krep1_r1pu
   $krep2_r1pv
   $krep3_r1pw
   $krep4_r1px
   $tcE1_r1py
   $tcE2_r1pz
   $tcIMonad1_r1pA
   $tcIMonad2_r1pB
   $krep5_r1pC
   $krep6_r1pD
   $krep7_r1pE
   $trModule1_r1pF
   $trModule2_r1pG
   $trModule3_r1pH
   $trModule4_r1pI
   $krep8_r1pJ
   $krep9_r1pK
   sat_s1rG
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in
 ghc:Outputable
         pprPanic, called at compiler/codeGen/StgCmmEnv.hs:149:9 in
 ghc:StgCmmEnv
Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 Loading the file into GHCi succeeds but then when the `main` function is
 invoked, a `nameModule` panic occurs.

 {{{
 *Repro> main
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.6.2 for x86_64-unknown-linux):
         nameModule
   system $dIMonad_a1LV
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in
 ghc:Outputable
         pprPanic, called at compiler/basicTypes/Name.hs:240:3 in ghc:Name

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 Reproduced on 8.6.{2,1} 8.4.4 8.2.2

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15966
GHC http://www.haskell.org/ghc/
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