[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
      Resolution:                    |             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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Description changed by hvr:

@@ -5,0 +5,1 @@
+ {{{
@@ -12,0 +13,1 @@
+ }}}

New description:

 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#comment:2>
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