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

[GHC]

#7035: `deriving instance Generic (HsExpr Id)` raises panic
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    Reporter:  Daniel Schuessler  |       Owner:  dreixel           
        Type:  bug                |      Status:  new               
    Priority:  normal             |   Milestone:  7.8.1             
   Component:  Compiler           |     Version:  7.4.2             
    Keywords:                     |          Os:  Linux             
Architecture:  Unknown/Multiple   |     Failure:  Compile-time crash
  Difficulty:  Unknown            |    Testcase:                    
   Blockedby:                     |    Blocking:                    
     Related:                     |  
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Comment(by dreixel):

 Somehow I've only seen this now. I think it's fixed by now, but I'll
 check.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7035#comment:3>
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