[GHC] #3943: unused variable warning in view pattern is wrong

[GHC]

#3943: unused variable warning in view pattern is wrong
---------------------------------+------------------------------------------
    Reporter:  guest             |       Owner:              
        Type:  bug               |      Status:  new         
    Priority:  normal            |   Component:  Compiler    
     Version:  6.12.1            |    Keywords:              
          Os:  Unknown/Multiple  |    Testcase:              
Architecture:  Unknown/Multiple  |     Failure:  None/Unknown
---------------------------------+------------------------------------------
 {{{
 {-# OPTIONS_GHC -Wall #-}
 {-# LANGUAGE ViewPatterns #-}
 test x = let (r,(r++) -> rs) = x in rs
 }}}

 {{{
 Warning: Defined but not used: `r'
 }}}

 This seems only to happen in let (not in function clauses, or in lambdas,
 or in case).

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3943>
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