[GHC] #15966: panic when using RebindableSyntax

[GHC]

#15966: panic when using RebindableSyntax
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        Reporter:  mpickering        |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.6.3
       Component:  Compiler          |              Version:  8.6.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by mpickering):

 Core lint fails as well:
 https://gist.github.com/mpickering/d72def64a6fd9df8c99e2ffe6d232dac

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15966#comment:1>
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