[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                     |
       Wiki Page:                    |
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Changes (by mboes):

 * cc: mboes (added)


Comment:

 I disagree.

 Here's a data point for you to take into consideration. At Tweag I/O we've
 had at least one instance of a serious bug that shipped into production
 and several days worth of wasted effort, because a constraint maintaining
 a key invariant was mistakenly unused. -fwarn-redundant-constraints would
 of caught this bug very early and saved us all the trouble (a test would
 have worked too, but as it happens a test did exist but had
 a bug too).

 If this warning is not turned on with -Wall, then we'd have to discover
 somehow that there is this extra flag that we should pass in ''even though
 we already said -Wall'', to really get all warnings, including one that
 could be life saving.

 I think -Wall should do what it says on the tin: include all warnings.
 That many such warnings may be cause for false positives is why we have
 -Wall not turned on by default in the first place.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10635#comment:2>
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