[GHC] #15584: nonVoid is too conservative w.r.t. strict argument types

[GHC]

#15584: nonVoid is too conservative w.r.t. strict argument types
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.5
      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:  #15305            |  Differential Rev(s):  Phab:D5116
       Wiki Page:                    |
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Comment (by dfeuer):

 How clever do we want to be here? Users need to be able to predict,
 reasonably reliably, how far they should go in explaining totality to the
 compiler. We certainly wouldn't want GHC to complain about a redundant
 pattern match in

 {{{#!hs
 f :: S -> a
 f (MkS (MkV v)) = absurd v
 }}}

 because that's perfectly reasonable code.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15584#comment:2>
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