[GHC] #8470: "Fix" spurious Unused do-bind warnings

[GHC]

#8470: "Fix" spurious Unused do-bind warnings
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        Reporter:  2piix             |            Owner:
            Type:  feature request   |           Status:  new
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.6.3
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Changes (by monoidal):

 * status:  closed => new
 * resolution:  worksforme =>


Comment:

 Here's a testcase showing the incorrect warning

 {{{
 {-# LANGUAGE TypeFamilies #-}
 {-# OPTIONS_GHC -fwarn-unused-do-bind #-}

 data User
 type family MethodResult ev
 type instance MethodResult User = ()
 type EventResult a = MethodResult a

 main = do undefined :: IO (EventResult User)
           return ()
 }}}

 @2piix: Please include more information or a complete testcase when
 reporting, it was hard to reconstruct without knowing what `acidState`,
 `Brilliance.Query.AddUser` etc. are.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8470#comment:4>
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