[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 osa1):

 I don't think the scrutinee is diverging here, I think the problem is
 something else. I tried to debug this a little bit, here's some more info
 about the error:

 {{{
 <no location info>: warning:
     [in body of lambda with binder x_aT4 :: Empty]
     No alternatives for a case scrutinee not known to diverge for sure:
 lvl_sUi
     The whole expression: case lvl_sUi of _ [Occ=Dead] { }
     Scrutinee type: Empty -> ShowS
     Expression type: String
 }}}

 Here from the type of the scrutinee we can't say it's diverging, because
 that type has inhabitants like {{{const ""}}} etc.

 One weird thing about this error message is that in the printed module
 {{{x_aT4}}} is not used at all, so I'm not sure where did the linter find
 that variable. Too bad we don't have stack traces..

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11290#comment:7>
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