[GHC] #13089: GHC panic

[GHC]

#13089: GHC panic
-------------------------------------+-------------------------------------
           Reporter:  cbaatz         |             Owner:
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:  x86_64         |   Type of failure:  None/Unknown
  (amd64)                            |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 I stumbled upon a GHC panic for some reason. Not sure how to debug
 this/get more details on it so attaching the error message:

 ```
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.1 for x86_64-apple-darwin):
         filterImports/combine
   (Array,
    Array{Array, AByteString, ACursored, ADelayed, AForeignPtr,
 AInterleave, ASmall, APart, AUnboxed, AUndefined, AVector, cursoredExtent,
 loadCursor, makeCursor, shiftCursor},
    Nothing)
   (Array,
    Source{Source, Array, deepSeqArray, extent, index, linearIndex,
 unsafeIndex, unsafeLinearIndex},
    Nothing)
 ```

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13089>
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