[GHC] #10999: ghc: panic! (the 'impossible' happened)

[GHC]

#10999: ghc: panic! (the 'impossible' happened)
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        Reporter:  res               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash                              |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #10045            |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by thomie):

 * related:   => #10045


Comment:

 Here is a smaller test to trigger the same bug:
 {{{
 module T10999 where

 import qualified Data.Set as Set

 f :: () -> _
 f _ = Set.fromList undefined

 g = map fst $ Set.toList $ f ()
 }}}

 It is already fixed in HEAD, and seems like a duplicate of #10045.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10999#comment:1>
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