[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 svenpanne):

 Just a word of warning from a library maintainer's point of view:
 Including new flags into `-Wall` puts some non-trivial burden onto
 maintainers wanting a warning-free build. Simply adding a new pragma is
 not enough: Old GHCs don't know that pragma, so you have to put that into
 some ugly `#ifdef`s, which in turn oftern implies adding another
 (language) pragma to allow the preprocessor plus perhaps some changes in
 the `.cabal` file. So including `-fwarn-redundant-constraints` in `-Wall`
 is far from free for real-world code.

 I'm not saying that this shouldn't be done, but at least I want to bring
 up the maintenance issue. From my personal experience, Haskell code is
 becoming more and more cluttered with CPP stuff because of seemingly
 innocent changes like this. Of course this isn't a problem if you only
 consider the latest and greatest GHC, but this isn't an option for most
 maintainers.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10635#comment:29>
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