[GHC] #10890: Incorrect redundant import warning for type classes

[GHC]

#10890: Incorrect redundant import warning for type classes
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        Reporter:  quchen            |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:  8.0.1
       Component:  Compiler          |                 Version:  7.10.2
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Comment (by osa1):

 Not sure how much this helps with debugging this, but I found out that
 when compiling this slightly modified program:

 {{{#!haskell
 module Main where

 import Base (AClass (has))
 import Extends (BClass (has))

 data Bar = Bar

 instance AClass Bar where
   has = Bar

 instance BClass Bar where
   has = Bar
 }}}

 GHC prints this:

 {{{
 Main.hs:3:1: warning:
     The import of ‘Base.has’ from module ‘Base’ is redundant

 Main.hs:4:1: warning:
     The import of ‘Extends.has’ from module ‘Extends’ is redundant
 Linking Main ...
 }}}

 This is a test case I generated while trying to figure out if GHC thinks
 both `has` are coming from the same module.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10890#comment:4>
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