[GHC] #3085: warn about language extensions that are not used

[GHC]

#3085: warn about language extensions that are not used
-------------------------------------+-------------------------------------
              Reporter:              |            Owner:
  PVerswyvelen                       |           Status:  new
                  Type:  feature     |        Milestone:  7.10.1
  request                            |          Version:  6.10.1
              Priority:  normal      |         Keywords:  warnings
             Component:  Compiler    |  extensions language
            Resolution:              |     Architecture:  Unknown/Multiple
      Operating System:              |       Difficulty:  Unknown
  Unknown/Multiple                   |       Blocked By:
       Type of failure:              |  Related Tickets:  #9757
  None/Unknown                       |
             Test Case:              |
              Blocking:              |
Differential Revisions:              |
-------------------------------------+-------------------------------------
Changes (by thomie):

 * related:   => #9757


Comment:

 To cite rwbarton from #9757:
 > I think the purpose of compiler warnings should be to warn about code
 that is probably bad, not code that is probably fine that could be written
 in a (potentially) better way. (After all, we don't warn about excess
 parentheses in code either.) That is the domain of hlint, as Richard
 notes.

 Anyone disagree with a `wontfix` here as well?

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3085#comment:33>
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