[GHC] #10635: -fwarn-redundant-constraints should not be part of -Wall

[GHC]

#10635: -fwarn-redundant-constraints should not be part of -Wall
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        Reporter:  Lemming           |                Owner:
            Type:  feature request   |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler (Type    |              Version:  7.11
  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:  #9939, #9973,     |  Differential Rev(s):
  #10100, #10183, #11370             |
       Wiki Page:                    |
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Comment (by acfoltzer):

 Now that I'm getting some hands on 8.0.1 experience, I'm pretty quickly
 running into situations where I need to disable this warning. I'm inclined
 to agree with the suggestion to take it out of `-Wall`, but being able to
 mark certain instances and classes as exempt from the warning would work
 for my purposes.

 I also wonder if it might make sense to distinguish between certain types
 of redundancy: for example, in our code a redundancy arising from a
 superclass relationship (e.g., `(Functor f, Applicative f)`) is almost
 always something we want to fix, but unused classes are almost always an
 API design choice rather than a bug we wish to avoid.

 I'm not sure where mboes' example falls between these cases, but maybe
 distinguishing the two cases and only including the superclass redundancy
 in `-Wall` could make folks happier?

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10635#comment:15>
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