[GHC] #7035: `deriving instance Generic (HsExpr Id)` raises panic

[GHC]

#7035: `deriving instance Generic (HsExpr Id)` raises panic
--------------------------------+-------------------------------------------
 Reporter:  Daniel Schuessler   |          Owner:                  
     Type:  bug                 |         Status:  new             
 Priority:  normal              |      Component:  Compiler        
  Version:  7.4.2               |       Keywords:                  
       Os:  Linux               |   Architecture:  Unknown/Multiple
  Failure:  Compile-time crash  |       Testcase:                  
Blockedby:                      |       Blocking:                  
  Related:                      |  
--------------------------------+-------------------------------------------
 Input file:

 {{{

 {-# LANGUAGE FlexibleInstances, DeriveGeneric, StandaloneDeriving #-}
 module GHCGeneric where

 import GHC
 import GHC.Generics

 deriving instance Generic (HsExpr Id)

 }}}

 Result:

 {{{
 GHCi, version 7.4.2: http://www.haskell.org/ghc/  :? for help
 Loading package ghc-prim ... linking ... done.
 Loading package integer-gmp ... linking ... done.
 Loading package base ... linking ... done.
 [1 of 1] Compiling GHCGeneric       (
 /home/daniel/dev/dataflow/GHCGeneric.hs, interpreted )
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.4.2 for i386-unknown-linux):
         tcTyVarDetails ( id{tv a3cX} [tv] :: *{(w) tc 34d} )

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

 Regards,[[BR]]
 Daniel

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7035>
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