[GHC] #11474: incorrect redundant-constraints warning

[GHC]

#11474: incorrect redundant-constraints warning
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        Reporter:  hvr               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  8.0.1-rc1
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Good point.  Indeed the evidence for `AllNullary` is not used, but its
 functional dependencies are.  I don't know how to reliably detect that.

 I suppose I could not warn if the class has functional dependencies.  (Or
 maybe if any of its superclasses, transititively, do?)

 Meanwhile I think we've agreed that this warning will be off by default
 for 8.0 so you won't see it anyway.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11474#comment:1>
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