[GHC] #12026: Pattern match failure in RnNames.hs

[GHC]

#12026: Pattern match failure in RnNames.hs
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           Reporter:  davean         |             Owner:
               Type:  bug            |            Status:  new
           Priority:  high           |         Milestone:
          Component:  Compiler       |           Version:  8.0.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Compile-time
  Unknown/Multiple                   |  crash
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 When compiling dimensional-1.0.1.1 after patching numtype-dk with the
 patch at https://github.com/bjornbm/numtype-dk/issues/12 GHC does the
 "impossible":

 [ 3 of 16] Compiling Numeric.Units.Dimensional.Dimensions.TypeLevel (
 src/Numeric/Units/Dimensional/Dimensions/TypeLevel.hs, dist/dist-sandbox-
 68389a1a/build/Numeric/Units/Dimensional/Dimensions/TypeLevel.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.0.0.20160421 for x86_64-unknown-linux):
         Pattern match failure in do expression at
 compiler/rename/RnNames.hs:902:12-50

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12026>
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