[GHC] #15867: STG scope error

[GHC]

#15867: STG scope error
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        Reporter:  csabahruska       |                Owner:  sgraf
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.7
      Resolution:                    |             Keywords:  CodeGen
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D5310
       Wiki Page:                    |
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Comment (by csabahruska):

 I've improved the scope checking:
 - allows unique name shadowing (nested scopes)
 - checks OccName duplications only for exported top-level names
 - check Unique duplications for StgRhsClosure, StgRec, DataAlt

 I've attached the improved linter patch. (StgScopeCheck2.patch). It
 requires the `nub` fix.

 Using this improvements I've got new errors:
 {{{
 buggy source: libraries/base/Data/Type/Equality.hs

 *** Stg Lint ErrMsgs: in Unarise ***
 <no location info>: warning:
      [in body of lambda with binders void_0E :: Void#,
                                      void_0E :: Void#]
     void_0E :: Void# is duplicated (Uniq)
 *** Offending Program ***

 HRefl
   :: forall k2 k2 (a :: k2) (b :: k2).
      (k2 ~# k2) -> (b ~# a) -> a :~~: b
 [GblId[DataCon],
  Arity=2,
  Caf=NoCafRefs,
  Str=<L,U><L,U>m,
  Unf=OtherCon []] =
     [] \r [void_0E void_0E] HRefl [];

 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15867#comment:9>
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