[GHC] #14813: EmptyCase thinks pattern match involving type family is not exhaustive, when it actually is

[GHC]

#14813: EmptyCase thinks pattern match involving type family is not exhaustive,
when it actually is
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.2
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Replying to [comment:3 simonpj]:
 > Why do you think the typechecker "isn't giving the correct type"

 Like I said in comment:2, what I meant by "correct type" is
 "insufficiently type-family–free type".

 > and would would be consequences of that be?

 The consequences are this very ticket! As explained in comment:1, `F False
 a` and `Void` can produce different results in the pattern-match coverage
 checker, so it's critical that we use the latter whenever possible.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14813#comment:4>
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