[GHC] #12489: undefined in view pattern inside pattern synonym causes GHC to panic

[GHC]

#12489: undefined in view pattern inside pattern synonym causes GHC to panic
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        Reporter:  pkmx              |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms
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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Comment (by mpickering):

 This still happens in HEAD.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12489#comment:2>
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