[GHC] #9990: Top level module identifiers shadow imported identifiers

[GHC]

#9990: Top level module identifiers shadow imported identifiers
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        Reporter:  drb226            |                   Owner:
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
 Type of failure:  None/Unknown      |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:                    |                Blocking:
                                     |  Differential Revisions:
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Comment (by alexey_r):

 Slight extension suggestion: include explicitly imported identifiers
 together with top-level identifiers. So:

 1. if an identifier is imported both explicitly and implicitly, there is
 no ambiguity;

 2. if an identifier is imported explicitly and defined at top-level, there
 is an ambiguity.

 Identifiers brought into scope by a `(..)` aren't considered explicitly
 imported for this purpose (otherwise extending a module could silently
 change meaning of an identifier).

 As a side effect, many uses of `hiding` would be no longer necessary.

 Of course, the pragma's name would have to be changed.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9990#comment:2>
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