[GHC] #8779: Exhaustiveness checks for pattern synonyms

[GHC]

#8779: Exhaustiveness checks for pattern synonyms
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        Reporter:  nomeata           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.8.1
  checker)                           |             Keywords:
      Resolution:                    |  PatternSynonyms
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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Changes (by mgsloan):

 * cc: mgsloan (added)


Comment:

 +1 for resolving this (though I realize it's tricky)! Stack's build on 8.0
 has this issue with ErrorCall's pattern synonym.  Due to `-fwarn-
 incomplete-uni-patterns`, `catch f (\(ErrorCall x) -> g x)` causes a non-
 exhaustive case warning.  See
 https://github.com/commercialhaskell/stack/pull/2145#issuecomment-219472907

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8779#comment:21>
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