filename corruption with -osuf in ghc-7.0.3

[Evan Laforge]

I've noticed a strange behaviour with ghc's -osuf flag:

% cat >Test.hs
{-# LANGUAGE ForeignFunctionInterface #-}
module Test where
import Foreign
foreign import ccall "wrapper" c_callback :: Int -> IO (FunPtr Int)
% ghc-7.0.3 -v -c -osuf .hs.o Test.hs
% ls
Tes_stub.hs.o  Test.hs        Test_stub.c
Test.hi        Test.hs.o      Test_stub.h

Notice that the .o for the _stub.c has acquired the .hs.o suffix, but
the last 't' of 'Test' was chopped off.

I tried the same test with the latest ghc-7.4, and it doesn't generate
a Test_stub.c at all, though there is a Test_stub.h.  But I guess it
sidesteps the question of whether -osuf should apply to the _stub.c (I
feel like it shouldn't, since it's a c file compiled by cc, not by
ghc).

I'm curious about why ghc no longer seems to need _stub.c files.  I'd
test in more details, but runghc ghci for 7.4 is segfaulting
unpredictably so I think there are larger problems here.