[GHC] #7672: boot file entities are sometimes invisible and are not (semantically) unified with corresponding entities in implementing module

[GHC]

#7672: boot file entities are sometimes invisible and are not (semantically)
unified with corresponding entities in implementing module
-------------------------------------+-------------------------------------
        Reporter:  skilpat           |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  7.12.1
       Component:  Compiler (Type    |                 Version:  7.4.2
  checker)                           |                Keywords:  backpack
      Resolution:                    |            Architecture:  x86_64
Operating System:  Linux             |  (amd64)
 Type of failure:  GHC rejects       |               Test Case:
  valid program                      |                Blocking:
      Blocked By:                    |  Differential Revisions:
 Related Tickets:                    |
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Comment (by ezyang):

 The reason this occurs is when we process imports in `rnImportDecl`, we
 filter out any identifiers which come from a self-boot:

 {{{
     let gbl_env = mkGlobalRdrEnv (filterOut from_this_mod gres)
 }}}

 So these identifiers never get added to the GlobalRdrEnv, and thus aren't
 brought into scope.

 I don't know what happens if you remove that `filterOut`. It comes from
 some very old code.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7672#comment:8>
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