[GHC] #12968: GHC crash with TypeInType and pattern synonym

[GHC]

#12968: GHC crash with TypeInType and pattern synonym
-------------------------------------+-------------------------------------
           Reporter:  dfeuer         |             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 or panic
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 I decided to try playing with the proposed new `Typeable` interface,
 faking up types and functions in GHC 8.0.1. Unfortunately, it seems I did
 something impossible:

 {{{#!hs
 {-# LANGUAGE TypeInType, GADTs, ScopedTypeVariables, PatternSynonyms,
       ViewPatterns #-}

 module TypeReflection where

 data TypeRep (a :: k)

 data TRAppG (fun :: k2) where
   TRAppG :: forall k1 (a :: k1 -> k2) (b :: k1) . TypeRep a -> TypeRep b
 -> TRAppG (a b)

 pattern TRApp :: forall k2 (fun :: k2). ()
               => forall k1 (a :: k1 -> k2) (b :: k1). (fun ~ a b)
               => TypeRep a -> TypeRep b -> TypeRep fun
 pattern TRApp a b <- ((undefined :: TypeRep fun -> TRAppG fun) -> TRAppG a
 b)
 }}}

 The error:

 {{{
 [1 of 1] Compiling TypeReflection   ( TypeReflectionTemplate.hs,
 TypeReflectionTemplate.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-unknown-linux):
         StgCmmEnv: variable not found
   $dIP_a1Aj
   local binds for:
   typeRep
   $tcTypeable
   $tc'C:Typeable
   $tcTypeRep
   $tc'TRAppG
   $WTRAppG
   $tcTRAppG
   $trModule
   $tcTRAppG1_r1KE
   $tc'TRAppG1_r1KS
   $tcTypeRep1_r1KT
   $tcTypeable1_r1KU
   $tc'C:Typeable1_r1KV
   $trModule1_r1KW
   $trModule2_r1KX
   scrut_s1Lg
   cont_s1Lh
   fail_s1Li
   sat_s1Lj
   sat_s1Lk
   sat_s1Ll
   sat_s1Lm
   sat_s1Ln
   sat_s1Lo
   sat_s1Lp
   sat_s1Lq
   sat_s1Lr
   sat_s1Ls
   sat_s1Lt
 }}}

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12968>
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