[GHC] #10505: more specific types in the generated *_stub.h files

[GHC]

#10505: more specific types in the generated *_stub.h files
-------------------------------------+-------------------------------------
        Reporter:  imz               |                   Owner:
            Type:  feature request   |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler (FFI)    |                 Version:  7.6.1
      Resolution:                    |                Keywords:
Operating System:  Linux             |            Architecture:
 Type of failure:  Other             |  Unknown/Multiple
      Blocked By:                    |               Test Case:
 Related Tickets:  #2979, #8222      |                Blocking:
                                     |  Differential Revisions:
-------------------------------------+-------------------------------------
Description changed by imz:

Old description:

> Having a declaration like:
>
> {{{#!hs
> foreign export ccall "respond" respond :: CWString -> IO CWString
> }}}
>
> all the types in the corresponding `_stub.h` are `HsPtr`.
>
> Wouldn't it be possible to write more specific types reflecting my
> expectations, i.e., `wchar_t *`?
>
> It would be nice in order to signal automatically to the C code which
> uses the Haskell functions that the types of the Haskell functions
> changed. In simple cases, one could simply include the stub.h, and get
> automatically an error if the C code doesn't match the new types.
>
> I've tried using a CTYPE pragma (cf. #2979 , #8222 ) on a newtype to get
> such results:
>
> {{{#!hs
> newtype {-# CTYPE "wchar_t *" #-} CWString' = CWString' CWString
> foreign export ccall "respond" respond :: CWString'  -> IO CWString
> }}}
>
> but that still produces `HsPtr`. (Well, I see, the CTYPE pragma was
> mostly intended for imports rather than exports.)

New description:

 Having a declaration like:

 {{{#!hs
 foreign export ccall "respond" respond :: CWString -> IO CWString
 }}}

 all the types in the corresponding `_stub.h` are `HsPtr`.

 Wouldn't it be possible to write more specific types reflecting my
 expectations, i.e., `wchar_t *`?

 It would be nice in order to signal automatically to the C code which uses
 the Haskell functions that the types of the Haskell functions changed. In
 simple cases, one could simply include the stub.h, and get automatically
 an error if the C code doesn't match the new types.

 I've tried using a CTYPE pragma (cf. #2979 , #8222 , and
 https://mail.haskell.org/pipermail/haskell/2012-February/023155.html ) on
 a newtype to get such results:

 {{{#!hs
 newtype {-# CTYPE "wchar_t *" #-} CWString' = CWString' CWString
 foreign export ccall "respond" respond :: CWString'  -> IO CWString
 }}}

 but that still produces `HsPtr`. (Well, I see, the CTYPE pragma was mostly
 intended for imports rather than exports.)

--

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10505#comment:2>
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