[GHC] #3008: Strange behavior when using newtyped version of IO monad in FFI import declarations

[GHC]

#3008: Strange behavior when using newtyped version of IO monad in FFI import
declarations
-------------------+--------------------------------------------------------
Reporter:  waern   |          Owner:                
    Type:  bug     |         Status:  new           
Priority:  normal  |      Component:  Compiler      
 Version:  6.10.1  |       Severity:  normal        
Keywords:  FFI     |       Testcase:                
      Os:  Linux   |   Architecture:  x86_64 (amd64)
-------------------+--------------------------------------------------------
 Take a look at these two modules:

 A.hs:

 {{{
 module A (GL) where

 import Control.Monad
 import Control.Monad.Trans

 newtype GL a = GL (IO a) deriving (Functor, Monad, MonadIO)
 }}}

 B.hs:

 {{{
 module B where

 import A

 foreign import CALLCONV unsafe "glFlush" flush :: GL ()
 }}}

 Now, compile them with optimizations:

 {{{
 [david at alonzo temp]$ $HOME/ghc-6.10.1/bin/ghc A.hs B.hs
 -XGeneralizedNewtypeDeriving -XForeignFunctionInterface -DCALLCONV=ccall
 -XCPP -O
 compilation IS NOT required
 compilation IS NOT required
 A.o:(.text+0x8e): undefined reference to
 `mtlzm1zi1zi0zi2_ControlziMonadziTrans_ZCDMonadIO_con_info'
 A.o:(.text+0x237): undefined reference to
 `__stginit_mtlzm1zi1zi0zi2_ControlziMonadziTrans_'
 B.o:(.text+0x1e): undefined reference to `glFlush'
 /home/david/ghc-6.10.1//lib/ghc-6.10.1/libHSrts.a(Main.o): In function
 `real_main':
 Main.c:(.text+0x12): undefined reference to `__stginit_ZCMain'
 Main.c:(.text+0x26): undefined reference to `ZCMain_main_closure'
 collect2: ld returnerade avslutningsstatus 1
 }}}

 It's OK - we pass the typechecking phase.

 Now, see what happens when we compile without `-O`:

 {{{
 [david at alonzo temp]$ rm -f *.hi *.o
 [david at alonzo temp]$ $HOME/ghc-6.10.1/bin/ghc A.hs B.hs
 -XGeneralizedNewtypeDeriving -XForeignFunctionInterface -DCALLCONV=ccall
 -XCPP

 B.hs:5:0:
     Unacceptable result type in foreign declaration: GL ()
     When checking declaration:
         foreign import ccall unsafe "static  &glFlush" flush :: GL ()
 }}}

 Putting everything into one single module makes the type error go away
 completely (that is, also when compiling without `-O`).

 Something strange must be going on.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3008>
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