[GHC] #16346: Lint error on master: Occurrence is GlobalId, but binding is LocalId

[GHC]

#16346: Lint error on master: Occurrence is GlobalId, but binding is LocalId
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        Reporter:  simonpj           |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.6.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by simonpj):

 Yes I think so.  But the real issue is this in
 `SimplEnv.refineFromInScope`:
 {{{
 refineFromInScope :: InScopeSet -> Var -> Var
 refineFromInScope in_scope v
   | isLocalId v = case lookupInScope in_scope v of
                   Just v' -> v'
                   Nothing -> WARN( True, ppr v ) v  -- This is an error!
   | otherwise = v
 }}}
 Notice that we don't look `GlobalId`s up in the in-scope set.  Yet that is
 the mechanism that ensures that in a situation like
 {{{
 let f_2dr[LclId] = blah in ...M.f_2df[GblId]...
 }}}
 (which has a local binding for a `GlobalId`), we transform to
 {{{
 let f_2dr[LclId] = blah in ...f_2df[LclId]...
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16346#comment:2>
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