-fwarn-unused-imports confused by hi-boot files

[George Russell]

# ghc -fwarn-unused-imports C.hs

C.hs:1:
     Warning: Module `A' is imported, but nothing from it is used
	     (except perhaps instances visible in `A')



However if I comment out the import of A I get


./B.hi-boot:3:
     tcLookup: `A.A' is not in scope
     In the type synonym declaration for `AS'

C.hs:1:
     Failed to load interface for `A':
	Bad interface file: ./A.hi
	    ./A.hi: openBinaryFile: does not exist (No such file or directory)

C.hs:1:
     Failed to find interface decl for `A.A'
     from module `A'

C.hs:1:
     Failed to find interface decl for `A.A'
     from module `A'
-------------- next part --------------
module A where

data A
-------------- next part --------------
module B where

type AS = [A.A]
-------------- next part --------------
module C where

import {-# SOURCE #-} A
import {-# SOURCE #-} B

type ASS = [AS]