[GHC] #13708: Panic! (the "impossible" happened) bug in GHC 8.2.1 rc2

[GHC]

#13708: Panic! (the "impossible" happened) bug in GHC 8.2.1 rc2
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        Reporter:  deech             |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1-rc2
      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 deech):

 The problem is possibly being caused by some ghc options I'm using. I've
 created a self contained repo [1] that reproduces the bug on my machine
 when building with 'stack build'. It should work for 'cabal install' as
 well.

 [1] https://github.com/deech/821rc2-panic-bug

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13708#comment:4>
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