[GHC] #11370: Redundant superclass warnings being included in -Wall destroys the "3 Release Policy"

[GHC]

#11370: Redundant superclass warnings being included in -Wall destroys the "3
Release Policy"
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        Reporter:  ekmett            |                Owner:
            Type:  bug               |               Status:  new
        Priority:  highest           |            Milestone:  8.0.1
       Component:  Compiler (Type    |              Version:  7.10.3
  checker)                           |
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11369            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by gershomb):

 I definitely think it shouldn't be in the default warning set.

 I suspect making an "advisory" category is too late for 8.0. But I think
 keeping -Wredundant-constraints out of -Wall for now is the right thing.
 Any future refactors of the hierarchy will also still trip it up, so in
 the future we should probably move it into -Wall and then follow nomeata's
 suggestion of modifying the policy to be  `-Wall -Wno-redundant-
 constraints` clean.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11370#comment:5>
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