[GHC] #11163: New exhaustiveness checker breaks T5642

[GHC]

#11163: New exhaustiveness checker breaks T5642
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        Reporter:  bgamari           |                Owner:  gkaracha
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  performance bug                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by Ben Gamari <ben@…>):

 In [changeset:"dc33e4c65dc1587c265c698473f35f9843673cba/ghc" dc33e4c/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="dc33e4c65dc1587c265c698473f35f9843673cba"
 T5642 is broken

 This appears to be due to the new exhaustiveness checker. See #11163.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11163#comment:2>
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