[GHC] #11066: Inacessible branch should be warning - otherwise breaks type soundness?

[GHC]

#11066: Inacessible branch should be warning - otherwise breaks type soundness?
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        Reporter:  rrnewton          |                Owner:
            Type:  bug               |               Status:  new
        Priority:  high              |            Milestone:  7.10.3
       Component:  Compiler          |              Version:  7.10.2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  GHC rejects       |  Unknown/Multiple
  valid program                      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1454
       Wiki Page:                    |
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Comment (by simonpj):

 There was muttering on the Phab trail about details.  Not sure it's
 converged enough to commit.  I trust Richard's judgement on this.  Sadly I
 have ~zero time this week or next.

 Simon

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11066#comment:7>
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