[GHC] #12548: Exported pattern synonyms does not mark top-level bindings in RHS as used

[GHC]

#12548: Exported pattern synonyms does not mark top-level bindings in RHS as used
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        Reporter:  pkmx              |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
                                     |  PatternSynonyms, 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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Comment (by Simon Peyton Jones <simonpj@…>):

 In [changeset:"6305674f310633d159a4df4e2e0d033a698599d1/ghc" 6305674/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="6305674f310633d159a4df4e2e0d033a698599d1"
 Fix used-variable calculation (Trac #12548)

 The used-variable calculation for pattern synonyms is a little
 tricky, for reasons described in RnBinds
 Note [Pattern synonym builders don't yield dependencies]

 It was right semantically, but the "unused-variable warning" was
 wrong, which led to Trac #12548.
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12548#comment:2>
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