[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 simonpj):

 From a GHC point of view, I think we can do whatever the Core Libraries
 Committee wants.  Eg. switch off `-Wno-redundant-constraints` for 8.0 and
 switch it on for 8.2.  Or whatever.

 But I have always felt uncomfortable with the way that warnings are being
 essentially treated like errors: you must not have any.  After all, if we
 switch it off, the exact same issue will arise the moment we switch it on!

 Maybe we need three categories:
  * **Errors**: we can't compile your program
  * **Warnings**: we can compile it but your library should probably be
 warning-free
  * **Advisories**: there's something fishy, but no expectation that a
 library will be advisory-free.  However advisories may become warnings in
 the next release, so you may want to invest a bit of effort at your
 convenience in getting rid of them.

 I see our users (embodied in the Core Libraries Committee) as being in the
 driving seat here.

 Simon

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11370#comment:3>
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