[GHC] #3886: Standalone deriving of NFData causes panic

[GHC]

#3886: Standalone deriving of NFData causes panic
---------------------------------+------------------------------------------
    Reporter:  blarsen           |       Owner:                    
        Type:  bug               |      Status:  new               
    Priority:  normal            |   Component:  Compiler          
     Version:  6.12.1            |    Keywords:                    
          Os:  Unknown/Multiple  |    Testcase:                    
Architecture:  Unknown/Multiple  |     Failure:  Compile-time crash
---------------------------------+------------------------------------------
 Using the -XStandaloneDeriving option, I tried to generate an NFData
 instance for the CNF type from the funsat 0.60 package on Hackage.


 {{{
 {-# LANGUAGE StandaloneDeriving #-}
 module Broken where

 import Funsat.Types
 import Control.Parallel.Strategies

 deriving instance NFData AST
 }}}


 With ghc 6.12.1 on 32-bit Ubuntu, the above causes a panic:

 ghc: panic! (the 'impossible' happened)
   (GHC version 6.12.1 for i386-unknown-linux):
         genDerivBinds: bad derived class
     deepseq-1.1.0.0:Control.DeepSeq.NFData{tc rou}

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

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3886>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler