[GHC] #14059: COMPLETE sets don't work at all with data family instances

[GHC]

#14059: COMPLETE sets don't work at all with data family instances
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        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms,
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Evidently, this changed a bit from GHC 8.2 to 8.4. In 8.4, you actually
 //do// get a warning about `wobble`:

 {{{
 $ /opt/ghc/8.4.2/bin/ghci Bug.hs
 GHCi, version 8.4.2: http://www.haskell.org/ghc/  :? for help
 Loaded GHCi configuration from /home/rgscott/.ghci
 [1 of 1] Compiling Bug              ( Bug.hs, interpreted )

 Bug.hs:23:1: warning: [-Wincomplete-patterns]
     Pattern match(es) are non-exhaustive
     In an equation for ‘wibble’: Patterns not matched: SFalse
    |
 23 | wibble STrue = True
    | ^^^^^^^^^^^^^^^^^^^

 Bug.hs:26:1: warning: [-Wincomplete-patterns]
     Pattern match(es) are non-exhaustive
     In an equation for ‘wobble’: Patterns not matched: _
    |
 26 | wobble STooGoodToBeTrue = True
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 }}}

 Still, this doesn't seem quite right, as the warning says `Patterns not
 matched: _` instead of `Patterns not matched: SFalse`, like its
 counterpart `wibble`.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14059#comment:5>
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