[GHC] #4302: Impossible when deriving empty data declaration

[GHC]

#4302: Impossible when deriving empty data declaration
-------------------------------+--------------------------------------------
    Reporter:  mitar           |       Owner:              
        Type:  bug             |      Status:  new         
    Priority:  normal          |   Component:  Compiler    
     Version:  6.12.3          |    Keywords:              
    Testcase:                  |   Blockedby:              
          Os:  Linux           |    Blocking:              
Architecture:  x86_64 (amd64)  |     Failure:  None/Unknown
-------------------------------+--------------------------------------------
 When trying to load following code into GHCi I get an error:

 {{{
 ghc: panic! (the 'impossible' happened)
   (GHC version 6.12.3 for x86_64-unknown-linux):
         TcGenDeriv:mk_FunBind
 }}}

 Code is:

 {{{
 {-# LANGUAGE StandaloneDeriving, EmptyDataDecls #-}
 module Test where
 data Test
 deriving instance Show (Test)
 }}}

 Probably `Test` cannot be made instance of `Show` but still error should
 be less fatal. ;-)

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4302>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler