[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 quchen):

 I agree with Simon that things like redundant constraints are not
 "probably broken" (warnings) or broken (errors).

 I'm a big fan of compilers educating users to best practices (advisories),
 and redundant constraints fall into this category. It's as bad as trailing
 whitespace, literal tabs, or redundant parentheses.

 That said, I think we need a more strict "-Wall", I named it "-WALL" for
 the lack of a better name (-Wpedantic akin to GCC would also work, or
 -Wlint) where we enable such suggestions. This flag would be useful for
 building-and-fixing once-ish per release, and would make no compatibility
 guarantees.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11370#comment:6>
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