foreign exports not taken into account when calculating -fwarn-unused-imports

Here we have a program that imports and uses liftM from Control.Monad, but only as a result of being used in the definition of a function that is foreign exported.

module Foo () where

import Control.Monad (liftM)

foo :: IO ()
foo = id `liftM` return ()

foreign export ccall "hs_foo"
  foo :: IO ()

GHC 6.6 and HEAD report:

foo.hs:3:0:
    Warning: Module `Control.Monad' is imported, but nothing from it is used,
               except perhaps instances visible in `Control.Monad'
             To suppress this warning, use: import Control.Monad()

So I suppose all that needs to happen is to add in foreign exports as roots when building the usage graph.

Trac metadata

Trac field	Value
Version	6.7
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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Operating system	Unknown
Architecture	Unknown