Over-zealous dup-import warning

[simonpj]

Pointed out by John Meacham [john@repetae.net]

In 6.4 the duplicate import warning seems to be 
triggered overzealously, even
when one import is qualified and the other isn't.


import qualified Data.Map 
import Data.Map(Map)

foo :: Map Int Int
foo = Data.Map.empty
             
main = do
    print foo
                    
produces:
 Foo.hs:1:0:
    Warning: `Map' is imported more than once:
               imported from Data.Map at Foo.hs:3:16-18
               imported from Data.Map at Foo.hs:2:0-24

[fergus]

Logged In: YES 
user_id=135331

Yes, this one is a pain -- it would be great if someone
would fix this.
The only work-around I have at the moment is to use "-Wall
-fno-warn-unused-imports" instead of "-Wall".
   - Fergus Henderson.

[simonpj]

Logged In: YES 
user_id=50165

OK, I've fixed this.  I've changed the message to focus on 
each import and report if it is redundant; that is, is completely 
covered by another import. (Instead of reporting on some 
overlap, in a symmetrical way.)

I hope this should be a big improvement; let me know if not.

Simon