Re: [GHC] #14125: Bogus unacceptable type in foreign declaration.

16 Aug 2017

      #14125: Bogus unacceptable type in foreign declaration.
-------------------------------------+-------------------------------------
        Reporter:  winter            |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.2.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------
Description changed by winter:

Old description:
...
I'm try to abstract FFI return type so that different errno scheme can
work together, namely i create such a class:
{{{
class Integral (IOErrno r) => IOReturn r where
    -- | The errno type associated with 'r'
    data IOErrno r :: *
    -- | Is this return value indicate an error?
    isError   :: Integral a => r a -> Bool
    -- | How can i get a errno then?
    getErrno  :: Integral a => r a -> IO (IOErrno r)
    -- | Is this errno indicate interrupted blocking call?
    isInterrupt :: IOErrno r -> Bool
    -- | Is this errno indicate no data on a non-blocking device?
    isBlock   :: IOErrno r -> Bool
    -- | OK, i want my return value if no errno.
    getReturn :: Integral a => r a -> a
    -- | Read the errno name for me.
    nameErrno :: IOErrno r -> IO String
    -- | Read the errno description for me.
    descErrno :: IOErrno r -> IO String
}}}
But when i'm try to defining instance for it, such as a standard unix
like:
{{{
newtype UnixReturn a = UnixReturn a
    deriving (Bounded, Enum, Eq, Integral, Num, Ord, Read, Real, Show,
FiniteBits, Bits, Storable)
instance IOReturn UnixReturn where
    newtype IOErrno UnixReturn = UnixErrno CInt
        deriving (Bounded, Enum, Eq, Integral, Num, Ord, Read, Real,
Show, FiniteBits, Bits, Storable)
    isError (UnixReturn r) = r == (-1)
    isInterrupt e = e == eINTR
    isBlock e = e == eAGAIN || e == eWOULDBLOCK
    getErrno _ = get_errno
    getReturn (UnixReturn r) = r
    nameErrno = return . nameUnixErrno
    descErrno e = strerror e >>= peekCString
eINTR           = UnixErrno (CONST_EINTR)
eWOULDBLOCK     = UnixErrno (CONST_EWOULDBLOCK)
...
foreign import ccall unsafe "string.h" strerror :: IOErrno UnixReturn ->
IO CString
foreign import ccall unsafe "HsBase.h __hscore_get_errno" get_errno :: IO
(IOErrno UnixReturn)
}}}
I got a error on GHC 8.2:
{{{
System/IO/Exception.hs:282:1: error:
    • Unacceptable argument type in foreign declaration:
        ‘IOErrno UnixReturn’ cannot be marshalled in a foreign call
    • When checking declaration:
        foreign import ccall unsafe "string.h" strerror
          :: IOErrno UnixReturn -> IO CString
    |
282 | foreign import ccall unsafe "string.h" strerror :: IOErrno
UnixReturn -> IO CString
    |
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
System/IO/Exception.hs:283:1: error:
    • Unacceptable result type in foreign declaration:
        ‘IOErrno UnixReturn’ cannot be marshalled in a foreign call
    • When checking declaration:
        foreign import ccall unsafe "HsBase.h __hscore_get_errno"
get_errno
          :: IO (IOErrno UnixReturn)
    |
283 | foreign import ccall unsafe "HsBase.h __hscore_get_errno" get_errno
:: IO (IOErrno UnixReturn)
    |
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
}}}
And at every place i want mark my FFI return got this error too. e.g.
following code compiles without problem on GHC < 8.2 (Note that the type
and constructor are both available):
{{{
foreign import CALLCONV unsafe "HsNet.h recv"
    c_recv :: CInt -> Ptr Word8 -> CSize -> CInt -> IO (UnixReturn
CSsize)
}}}

...
But on GHC 8.2 a `Unacceptable result type in foreign declaration` is
emitted. And I think it's a regression.
New description:

 I'm trying to abstract FFI return type so that different errno scheme can
 work together, namely i create such a class:

 {{{
 class Integral (IOErrno r) => IOReturn r where
     -- | The errno type associated with 'r'
     data IOErrno r :: *
     -- | Is this return value indicate an error?
     isError   :: Integral a => r a -> Bool
     -- | How can i get a errno then?
     getErrno  :: Integral a => r a -> IO (IOErrno r)
     -- | Is this errno indicate interrupted blocking call?
     isInterrupt :: IOErrno r -> Bool
     -- | Is this errno indicate no data on a non-blocking device?
     isBlock   :: IOErrno r -> Bool
     -- | OK, i want my return value if no errno.
     getReturn :: Integral a => r a -> a
     -- | Read the errno name for me.
     nameErrno :: IOErrno r -> IO String
     -- | Read the errno description for me.
     descErrno :: IOErrno r -> IO String
 }}}

 But when i'm try to defining instance for it, such as a standard unix
 like:

 {{{
 newtype UnixReturn a = UnixReturn a
     deriving (Bounded, Enum, Eq, Integral, Num, Ord, Read, Real, Show,
 FiniteBits, Bits, Storable)

 instance IOReturn UnixReturn where
     newtype IOErrno UnixReturn = UnixErrno CInt
         deriving (Bounded, Enum, Eq, Integral, Num, Ord, Read, Real, Show,
 FiniteBits, Bits, Storable)
     isError (UnixReturn r) = r == (-1)
     isInterrupt e = e == eINTR
     isBlock e = e == eAGAIN || e == eWOULDBLOCK
     getErrno _ = get_errno
     getReturn (UnixReturn r) = r
     nameErrno = return . nameUnixErrno
     descErrno e = strerror e >>= peekCString

 eINTR           = UnixErrno (CONST_EINTR)
 eWOULDBLOCK     = UnixErrno (CONST_EWOULDBLOCK)
 ...

 foreign import ccall unsafe "string.h" strerror :: IOErrno UnixReturn ->
 IO CString
 foreign import ccall unsafe "HsBase.h __hscore_get_errno" get_errno :: IO
 (IOErrno UnixReturn)
 }}}

 I got a error on GHC 8.2:

 {{{
 System/IO/Exception.hs:282:1: error:
     • Unacceptable argument type in foreign declaration:
         ‘IOErrno UnixReturn’ cannot be marshalled in a foreign call
     • When checking declaration:
         foreign import ccall unsafe "string.h" strerror
           :: IOErrno UnixReturn -> IO CString
     |
 282 | foreign import ccall unsafe "string.h" strerror :: IOErrno
 UnixReturn -> IO CString
     |
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 System/IO/Exception.hs:283:1: error:
     • Unacceptable result type in foreign declaration:
         ‘IOErrno UnixReturn’ cannot be marshalled in a foreign call
     • When checking declaration:
         foreign import ccall unsafe "HsBase.h __hscore_get_errno"
 get_errno
           :: IO (IOErrno UnixReturn)
     |
 283 | foreign import ccall unsafe "HsBase.h __hscore_get_errno" get_errno
 :: IO (IOErrno UnixReturn)
     |
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 }}}

 And at every place i want mark my FFI return got this error too. e.g.
 following code compiles without problem on GHC < 8.2 (Note that the type
 and constructor are both available):

 {{{

 foreign import CALLCONV unsafe "HsNet.h recv"
     c_recv :: CInt -> Ptr Word8 -> CSize -> CInt -> IO (UnixReturn CSsize)
 }}}

 But on GHC 8.2 a `Unacceptable result type in foreign declaration` is
 emitted. And I think it's a regression.

--

-- 
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14125#comment:1
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