[GHC] #11451: Inconsistent warnings for unused binders in type and instance declarations

[GHC]

#11451: Inconsistent warnings for unused binders in type and instance declarations
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        Reporter:  simonpj           |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  7.10.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D1825
       Wiki Page:                    |
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Comment (by goldfire):

 I thought `-Wunused-type-variables` could be on with `-Wall`. But we just
 won't warn in situations where the type variable could appear in
 documentation. And then (optional extension for extra credit) we'd have a
 separate `-Wpedantic-unused-type-variables` that warned in all cases.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11451#comment:23>
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