[GHC] #11290: T6031: *** Core Lint errors : in result of Common sub-expression ***

[GHC]

#11290: T6031: *** Core Lint errors : in result of Common sub-expression ***
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        Reporter:  thomie            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler          |              Version:  7.11
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  deriving/should_compile/T6031,
                                     |  deriving/should_run/T7931 (WAY=hpc)
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 > I think it says warning, but if it stops compilation, then it's a real
 error.

 Right, the intention for the warning is to complain, but keep going, so
 this needs fixing. (I wouldn’t miss this warning if it were gone
 completely, as it cannot be complete)

 > And it should be: case expressions must have all possible alternative
 listed, or we have a potential type error.

 Not if the scrutinee diverges, as it is the case here.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11290#comment:6>
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