[GHC] #15813: -Wredundant-constraints emits warning even if constraint is narrowing type (was: -Wredundant-constrains emits warning even if constraint is narrowing type)

[GHC]

#15813: -Wredundant-constraints emits warning even if constraint is narrowing type
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        Reporter:  jvanbruegge       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.1
      Resolution:                    |             Keywords:
Operating System:  Linux             |         Architecture:  x86_64
 Type of failure:  Incorrect         |  (amd64)
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #16154            |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by simonpj):

 * related:   => #16154


Comment:

 I have not dug into this, but I bet it's the same as #16154, which has a
 good explanation of the cause.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15813#comment:2>
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