[GHC] #14561: Panic on levity polymorphic very unsafe coerce

6 Dec 2017

      #14561: Panic on levity polymorphic very unsafe coerce
-------------------------------------+-------------------------------------
           Reporter:  goldfire       |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.3
           Keywords:                 |  Operating System:  Unknown/Multiple
  LevityPolymorphism                 |
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{#!hs
 {-# LANGUAGE TypeInType #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE PolyKinds #-}
 {-# LANGUAGE MagicHash #-}

 module LevityId where

 import GHC.Types
 import GHC.Prim

 levityPolymorphicId :: forall (a :: TYPE r). a -> a
 levityPolymorphicId = unsafeCoerce#
 }}}

 {{{
   (GHC version 8.3.20170928 for x86_64-apple-darwin):
         runtimeRepPrimRep
   typePrimRep (a_aW0 :: TYPE r_aVZ)
   r_aVZ
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1144:37 in
 ghc:Outputable
         pprPanic, called at compiler/simplStg/RepType.hs:358:5 in
 ghc:RepType
         runtimeRepPrimRep, called at compiler/simplStg/RepType.hs:344:5 in
 ghc:RepType
         kindPrimRep, called at compiler/simplStg/RepType.hs:307:18 in
 ghc:RepType
         typePrimRep, called at compiler/simplStg/UnariseStg.hs:666:8 in
 ghc:UnariseStg

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

 As originally mentioned [https://github.com/ghc-proposals/ghc-
 proposals/pull/98#issuecomment-349727273 here].

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14561
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