[GHC] #10746: No non-exhaustive pattern match warning given for empty case analysis

[GHC]

#10746: No non-exhaustive pattern match warning given for empty case analysis
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        Reporter:  bgamari           |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
                                     |  PatternMatchWarnings
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #7669, #11806     |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by dfeuer):

 I don't actually understand most of this code, but it *looks* like the
 problem is probably in the `checkMatches'` function in
 `compiler/deSugar/Check.hs`. Specifically, there's a guard

 {{{#!hs
  | null matches = return ([], [], [])
 }}}

 that looks fishy. I don't have things set up properly to build GHC at the
 moment, but my guess is that simply removing this clause and going
 straight to the `otherwise` will fix the bug.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10746#comment:9>
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