[GHC] #13064: Incorrect redudant imports warning

[GHC]

#13064: Incorrect redudant imports warning
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        Reporter:  phadej            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  low               |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Incorrect         |  Unknown/Multiple
  error/warning at compile-time      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #15393            |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by phadej):

 Replying to [comment:25 bgamari]:
 > **Replying to comment:24:**
 >
 > I suppose this is a possibility, although it seems to be me that we
 should rather try to introduce a mechanism to allow the user to state
 explicitly what they mean. That is: the import is known to be redundant
 but added for compatibility's sake. This could either be a general
 mechanism (e.g. wiki:Design/LocalWarningPragmas) or something more
 specifically designed to address import redundancy. (e.g. a `{-# USED #-}`
 pragma which could be attached to an import to silence the redundancy
 checker),

 We shouldn't need to go through GHC-proposal process for a bug fix. We
 should fix a bug, and then the interested people will either polish
 https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/RelaxedUnusedImports
 into a proposal, or propose some other way around (e.g. more granular
 warning toggles, then per-module).

 I'm for sure **implicitly** depend on this bug behavior for warning free
 builds, but I don't like it. For example: the tool `weeder` (to purge
 dependencies) isn't as useful now, as one might have an import which isn't
 necessary, but it retains the dependency.

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13064#comment:26>
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