[GHC] #7959: Panic on deriving nullary typeclass

[GHC]

#7959: Panic on deriving nullary typeclass
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Reporter:  monoidal            |          Owner:                  
    Type:  bug                 |         Status:  new             
Priority:  normal              |      Component:  Compiler        
 Version:  7.7                 |       Keywords:                  
      Os:  Unknown/Multiple    |   Architecture:  Unknown/Multiple
 Failure:  Compile-time crash  |      Blockedby:                  
Blocking:                      |        Related:                  
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 {{{
 {-# LANGUAGE NullaryTypeClasses #-}
 class C
 }}}

 Both `data A deriving C` and `deriving instance C` cause panic. Patch
 attached.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7959>
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