[GHC] #12158: ghc: panic! (the 'impossible' happened) translateConPatVec: lookup

[GHC]

#12158: ghc: panic! (the 'impossible' happened)  translateConPatVec: lookup
-------------------------------------+-------------------------------------
        Reporter:  wozgonon          |                Owner:  gkaracha
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  GHCi              |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #13644            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by justus):

 I have another example of this error:

 {{{#!hs
 genExampleBenchmark :: Int -> LGCmdArgs -> [(String, Serialized)]
 genExampleBenchmark
   seed
   lgArgs@(LGCmdArgs
            { totalGraphs = total
            , language = lang
            , slowdatasource = slowDS
            , cachenum = cache
            , LG.percentages = p
            })
   = ...
 }}}

 Here I use `LG.percentages` to disambiguate between two `percentages`
 record fields that are in scope, but it still fails with the same error.
 Btw if I remove the `LG.` it does throw the appropriate error telling me
 that it is an ambiguous reference.
 Commenting out `LG.percentages` makes the panic disappear.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12158#comment:12>
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