[GHC] #13363: Wildcarn patterns and COMPLETE sets can lead to misleading redundant pattern-match warnings

[GHC]

#13363: Wildcarn patterns and COMPLETE sets can lead to misleading redundant
pattern-match warnings
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms,
                                     |  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 mpickering):

 I think this is a bug because the match is not "redundant" as removing it
 will change the semantics of the function.

 Similarly if you write

 {{{
 f T = 1
 f F = 0
 f _ = 3
 }}}

 then removing the F case leaves a complete definition but the correct
 thing to do is to remove the redundant wildcard clause.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13363#comment:4>
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