[GHC] #15305: Erroneous "non-exhaustive pattern match" using nested GADT with strictness annotation

[GHC]

#15305: Erroneous "non-exhaustive pattern match" using nested GADT with strictness
annotation
-------------------------------------+-------------------------------------
        Reporter:  jkoppel           |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  Research
       Component:  Compiler (Type    |  needed
  checker)                           |              Version:  8.4.3
      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):  Phab:D5087
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Changes (by RyanGlScott):

 * status:  new => patch
 * differential:   => Phab:D5087


Comment:

 Implementing a naïve `NonVoid(ty)` solver ends up being pretty darn
 simple: just check if there is at least one inhabitation candidate for
 `ty` (as determined through `inhabitationCandidates`) such that its term
 and type constraints are satisfiable. That's sufficient to avoid warnings
 in the original program and in the program in comment:4. See Phab:D5087.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15305#comment:12>
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