[GHC] #11806: GHC does not warn for mistakenly empty case

[GHC]

#11806: GHC does not warn for mistakenly empty case
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        Reporter:  dfeuer            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC accepts       |  Unknown/Multiple
  invalid program                    |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * cc: gkaracha (added)


Comment:

 Yes that is odd. If you have
 {{{
 module T11806 where

 f1 :: Int -> Int
 f1 x = case x of { 1 -> 2 }

 f2 :: Bool -> Int
 f2 x = case x of { True -> 2 }
 }}}
 you get (with 8.0)
 {{{
 T11806.hs:7:8: warning: [-Wincomplete-patterns]
     Pattern match(es) are non-exhaustive
     In a case alternative:
         Patterns not matched: p where p is not one of {1}

 T11806.hs:10:8: warning: [-Wincomplete-patterns]
     Pattern match(es) are non-exhaustive
     In a case alternative: Patterns not matched: False
 }}}
 but if you remove all the branches, you get no warnings at all!

 I'm adding George (who is responsible for pattern match overlap checks) in
 cc.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11806#comment:1>
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