[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:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #11369, #11429    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by gershomb):

 Note that there's another silliness here. If we have both -Wcompat and
 -Wredundant-constraints in the -Wall set, then there will be cases where
 the "correct" fix to a compat warning is precisely to introduce something
 that will trigger a redundant-constraints warning! I don't think we want
 to have actively contradictory warnings in the same -Wall set -- even if
 there is a way to fix this (i.e. explicitly turn off one or the other set
 of warnings) it will send users into a flurry of confusion.

 Also, I may have missed something, but where is the discussion that
 overturned the prior resolution of this ticket? I thought we had a good
 plan of action, arrived at after a fair amount of discussion. Now I see
 that there's been a 180-degree-turn, but I don't see any discussion
 surrounding it outside of "this warning really should be in -Wall." In
 particular, if this is moved into the -Wall set a few releases down the
 line, then at a minimum users won't need a version-specific-flag to
 disable it, which was the motivation for the prior plan to begin with.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11370#comment:28>
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