[GHC] #12056: Too aggressive `-w` option

[GHC]

#12056: Too aggressive `-w` option
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        Reporter:  asr               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:  newcomer
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  warning at compile-time            |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Changes (by thomie):

 * keywords:   => newcomer


Comment:

 It looks like this only happens when `-w` is combined with
 `-Wunrecognised-warning-flags`. GHC seems to do the right thing when using
 `-w` and some other warning flag (make sure to use `-fforce-recomp` during
 testing).

 For a newcomer. The code to change is in `compiler/main/DynFlags.hs`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12056#comment:1>
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