Incorrect warnings about unqualified imports being redundant

[sciolizer]

Mixing qualified and unqualified imports can confuse the compiler.

To reproduce:

Create the file BadWarning?.hs.

module BadWarning where

import Data.Map
import qualified Data.Map as M

example = empty

Run ghci -W BadWarning.hs, and you get:

BadWarning.hs:4:1:
    Warning: The import of `Data.Map' is redundant
               except perhaps to import instances from `Data.Map'
             To import instances alone, use: import Data.Map()
Ok, modules loaded: BadWarning.

This looks similar to #3992, but that bug does not repro for me, so I think the issue is slightly different.

[batterseapower]

Isn't this warning correct? You don't use any names imported from that line. Delete it and your program will still compile!

If you added a type signature or something that uses the M. syntax e.g.

example :: M.Map Int Int

Then the warning goes away, as it should.

[sciolizer]

Doh! Yes, that's my mistake. For some reason I kept thinking the warning was referring to line 3 instead of line 4. When I deleted line 3 (as I thought the warning was suggesting), the program would not compile.

This bug report is invalid.