%
% (c) The University of Glasgow 2006
% (c) The AQUA Project, Glasgow University, 1998
%
\section[TcForeign]{Typechecking \tr{foreign} declarations}

A foreign declaration is used to either give an externally
implemented function a Haskell type (and calling interface) or
give a Haskell function an external calling interface. Either way,
the range of argument and result types these functions can accommodate
is restricted to what the outside world understands (read C), and this
module checks to see if a foreign declaration has got a legal type.

\begin{code}
module TcForeign 
	( 
	  tcForeignImports
        , tcForeignExports
	) where

#include "HsVersions.h"

import HsSyn

import TcRnMonad
import TcHsType
import TcExpr
import TcEnv

import ForeignCall
import ErrUtils
import Id
import Name
import TcType
import DynFlags
import Outputable
import SrcLoc
import Bag
import FastString
\end{code}

\begin{code}
-- Defines a binding
isForeignImport :: LForeignDecl name -> Bool
isForeignImport (L _ (ForeignImport _ _ _)) = True
isForeignImport _			      = False

-- Exports a binding
isForeignExport :: LForeignDecl name -> Bool
isForeignExport (L _ (ForeignExport _ _ _)) = True
isForeignExport _	  	              = False
\end{code}

%************************************************************************
%*									*
\subsection{Imports}
%*									*
%************************************************************************

\begin{code}
tcForeignImports :: [LForeignDecl Name] -> TcM ([Id], [LForeignDecl Id])
tcForeignImports decls
  = mapAndUnzipM (wrapLocSndM tcFImport) (filter isForeignImport decls)

tcFImport :: ForeignDecl Name -> TcM (Id, ForeignDecl Id)
tcFImport fo@(ForeignImport (L loc nm) hs_ty imp_decl)
 = addErrCtxt (foreignDeclCtxt fo)  $ 
   do { sig_ty <- tcHsSigType (ForSigCtxt nm) hs_ty
      ; let 
          -- Drop the foralls before inspecting the
          -- structure of the foreign type.
	    (_, t_ty)	      = tcSplitForAllTys sig_ty
	    (arg_tys, res_ty) = tcSplitFunTys t_ty
	    id  	      = mkLocalId nm sig_ty
 		-- Use a LocalId to obey the invariant that locally-defined 
		-- things are LocalIds.  However, it does not need zonking,
		-- (so TcHsSyn.zonkForeignExports ignores it).
   
      ; imp_decl' <- tcCheckFIType sig_ty arg_tys res_ty imp_decl
         -- Can't use sig_ty here because sig_ty :: Type and 
	 -- we need HsType Id hence the undefined
      ; return (id, ForeignImport (L loc id) undefined imp_decl') }
tcFImport d = pprPanic "tcFImport" (ppr d)
\end{code}


------------ Checking types for foreign import ----------------------
\begin{code}
tcCheckFIType :: Type -> [Type] -> Type -> ForeignImport -> TcM ForeignImport

tcCheckFIType sig_ty arg_tys res_ty idecl@(CImport _ safety _ (CLabel _))
  = ASSERT( null arg_tys )
    do { checkCg checkCOrAsmOrLlvmOrInterp
       ; checkSafety safety
       ; check (isFFILabelTy res_ty) (illegalForeignTyErr empty sig_ty)
       ; return idecl }	     -- NB check res_ty not sig_ty!
       	 	      	     --    In case sig_ty is (forall a. ForeignPtr a)

tcCheckFIType sig_ty arg_tys res_ty idecl@(CImport cconv safety _ CWrapper) = do
   	-- Foreign wrapper (former f.e.d.)
   	-- The type must be of the form ft -> IO (FunPtr ft), where ft is a
   	-- valid foreign type.  For legacy reasons ft -> IO (Ptr ft) as well
   	-- as ft -> IO Addr is accepted, too.  The use of the latter two forms
   	-- is DEPRECATED, though.
    checkCg checkCOrAsmOrLlvmOrInterp
    checkCConv cconv
    checkSafety safety
    case arg_tys of
        [arg1_ty] -> do checkForeignArgs isFFIExternalTy arg1_tys
                        checkForeignRes nonIOok  isFFIExportResultTy res1_ty
                        checkForeignRes mustBeIO isFFIDynResultTy    res_ty
                  where
                     (arg1_tys, res1_ty) = tcSplitFunTys arg1_ty
        _ -> addErrTc (illegalForeignTyErr empty sig_ty)
    return idecl

tcCheckFIType sig_ty arg_tys res_ty idecl@(CImport cconv safety _ (CFunction target))
  | isDynamicTarget target = do -- Foreign import dynamic
      checkCg checkCOrAsmOrLlvmOrInterp
      checkCConv cconv
      checkSafety safety
      case arg_tys of           -- The first arg must be Ptr, FunPtr, or Addr
        []                -> do
          check False (illegalForeignTyErr empty sig_ty)
          return idecl
        (arg1_ty:arg_tys) -> do
          dflags <- getDOpts
          check (isFFIDynArgumentTy arg1_ty)
                (illegalForeignTyErr argument arg1_ty)
          checkForeignArgs (isFFIArgumentTy dflags safety) arg_tys
          checkForeignRes nonIOok (isFFIImportResultTy dflags) res_ty
          return idecl
  | cconv == PrimCallConv = do
      dflags <- getDOpts
      check (xopt Opt_GHCForeignImportPrim dflags)
            (text "Use -XGHCForeignImportPrim to allow `foreign import prim'.")
      checkCg (checkCOrAsmOrLlvmOrDotNetOrInterp)
      checkCTarget target
      check (playSafe safety)
            (text "The safe/unsafe annotation should not be used with `foreign import prim'.")
      checkForeignArgs (isFFIPrimArgumentTy dflags) arg_tys
      -- prim import result is more liberal, allows (#,,#)
      checkForeignRes nonIOok (isFFIPrimResultTy dflags) res_ty
      return idecl
  | otherwise = do              -- Normal foreign import
      checkCg (checkCOrAsmOrLlvmOrDotNetOrInterp)
      checkCConv cconv
      checkSafety safety
      checkCTarget target
      dflags <- getDOpts
      checkForeignArgs (isFFIArgumentTy dflags safety) arg_tys
      checkForeignRes nonIOok (isFFIImportResultTy dflags) res_ty
      checkMissingAmpersand dflags arg_tys res_ty
      return idecl


-- This makes a convenient place to check
-- that the C identifier is valid for C
checkCTarget :: CCallTarget -> TcM ()
checkCTarget (StaticTarget str _) = do
    checkCg checkCOrAsmOrLlvmOrDotNetOrInterp
    check (isCLabelString str) (badCName str)

checkCTarget DynamicTarget = panic "checkCTarget DynamicTarget"


checkMissingAmpersand :: DynFlags -> [Type] -> Type -> TcM ()
checkMissingAmpersand dflags arg_tys res_ty
  | null arg_tys && isFunPtrTy res_ty &&
    dopt Opt_WarnDodgyForeignImports dflags
  = addWarn (ptext (sLit "possible missing & in foreign import of FunPtr"))
  | otherwise
  = return ()
\end{code}

%************************************************************************
%*									*
\subsection{Exports}
%*									*
%************************************************************************

\begin{code}
tcForeignExports :: [LForeignDecl Name] 
    		 -> TcM (LHsBinds TcId, [LForeignDecl TcId])
tcForeignExports decls
  = foldlM combine (emptyLHsBinds, []) (filter isForeignExport decls)
  where
   combine (binds, fs) fe = do
       (b, f) <- wrapLocSndM tcFExport fe
       return (b `consBag` binds, f:fs)

tcFExport :: ForeignDecl Name -> TcM (LHsBind Id, ForeignDecl Id)
tcFExport fo@(ForeignExport (L loc nm) hs_ty spec) =
   addErrCtxt (foreignDeclCtxt fo)      $ do

   sig_ty <- tcHsSigType (ForSigCtxt nm) hs_ty
   rhs <- tcPolyExpr (nlHsVar nm) sig_ty

   tcCheckFEType sig_ty spec

	  -- we're exporting a function, but at a type possibly more
	  -- constrained than its declared/inferred type. Hence the need
	  -- to create a local binding which will call the exported function
	  -- at a particular type (and, maybe, overloading).


   -- We need to give a name to the new top-level binding that
   -- is *stable* (i.e. the compiler won't change it later),
   -- because this name will be referred to by the C code stub.
   id  <- mkStableIdFromName nm sig_ty loc mkForeignExportOcc
   return (mkVarBind id rhs, ForeignExport (L loc id) undefined spec)
tcFExport d = pprPanic "tcFExport" (ppr d)
\end{code}

------------ Checking argument types for foreign export ----------------------

\begin{code}
tcCheckFEType :: Type -> ForeignExport -> TcM ()
tcCheckFEType sig_ty (CExport (CExportStatic str cconv)) = do
    checkCg checkCOrAsmOrLlvm
    check (isCLabelString str) (badCName str)
    checkCConv cconv
    checkForeignArgs isFFIExternalTy arg_tys
    checkForeignRes nonIOok isFFIExportResultTy res_ty
  where
      -- Drop the foralls before inspecting n
      -- the structure of the foreign type.
    (_, t_ty) = tcSplitForAllTys sig_ty
    (arg_tys, res_ty) = tcSplitFunTys t_ty
\end{code}



%************************************************************************
%*									*
\subsection{Miscellaneous}
%*									*
%************************************************************************

\begin{code}
------------ Checking argument types for foreign import ----------------------
checkForeignArgs :: (Type -> Bool) -> [Type] -> TcM ()
checkForeignArgs pred tys
  = mapM_ go tys
  where
    go ty = check (pred ty) (illegalForeignTyErr argument ty)

------------ Checking result types for foreign calls ----------------------
-- Check that the type has the form 
--    (IO t) or (t) , and that t satisfies the given predicate.
--
checkForeignRes :: Bool -> (Type -> Bool) -> Type -> TcM ()

nonIOok, mustBeIO :: Bool
nonIOok  = True
mustBeIO = False

checkForeignRes non_io_result_ok pred_res_ty ty
	-- (IO t) is ok, and so is any newtype wrapping thereof
  | Just (_, res_ty, _) <- tcSplitIOType_maybe ty,
    pred_res_ty res_ty
  = return ()
 
  | otherwise
  = check (non_io_result_ok && pred_res_ty ty) 
	  (illegalForeignTyErr result ty)
\end{code}

\begin{code}
checkCOrAsmOrLlvm :: HscTarget -> Maybe SDoc
checkCOrAsmOrLlvm HscC    = Nothing
checkCOrAsmOrLlvm HscAsm  = Nothing
checkCOrAsmOrLlvm HscLlvm = Nothing
checkCOrAsmOrLlvm _
   = Just (text "requires via-C, llvm (-fllvm) or native code generation (-fvia-C)")

checkCOrAsmOrLlvmOrInterp :: HscTarget -> Maybe SDoc
checkCOrAsmOrLlvmOrInterp HscC           = Nothing
checkCOrAsmOrLlvmOrInterp HscAsm         = Nothing
checkCOrAsmOrLlvmOrInterp HscLlvm        = Nothing
checkCOrAsmOrLlvmOrInterp HscInterpreted = Nothing
checkCOrAsmOrLlvmOrInterp _
   = Just (text "requires interpreted, C, Llvm or native code generation")

checkCOrAsmOrLlvmOrDotNetOrInterp :: HscTarget -> Maybe SDoc
checkCOrAsmOrLlvmOrDotNetOrInterp HscC           = Nothing
checkCOrAsmOrLlvmOrDotNetOrInterp HscAsm         = Nothing
checkCOrAsmOrLlvmOrDotNetOrInterp HscLlvm        = Nothing
checkCOrAsmOrLlvmOrDotNetOrInterp HscInterpreted = Nothing
checkCOrAsmOrLlvmOrDotNetOrInterp _
   = Just (text "requires interpreted, C, Llvm or native code generation")

checkCg :: (HscTarget -> Maybe SDoc) -> TcM ()
checkCg check = do
   dflags <- getDOpts
   let target = hscTarget dflags
   case target of
     HscNothing -> return ()
     _ ->
       case check target of
	 Nothing  -> return ()
	 Just err -> addErrTc (text "Illegal foreign declaration:" <+> err)
\end{code}
			   
Calling conventions

\begin{code}
checkCConv :: CCallConv -> TcM ()
checkCConv CCallConv  = return ()
#if i386_TARGET_ARCH
checkCConv StdCallConv = return ()
#else
-- This is a warning, not an error. see #3336
checkCConv StdCallConv = addWarnTc (text "the 'stdcall' calling convention is unsupported on this platform,"$$ text "treating as ccall")
#endif
checkCConv PrimCallConv = addErrTc (text "The `prim' calling convention can only be used with `foreign import'")
checkCConv CmmCallConv = panic "checkCConv CmmCallConv"
\end{code}

Deprecated "threadsafe" calls

\begin{code}
checkSafety :: Safety -> TcM ()
checkSafety (PlaySafe True) = addWarn (text "The `threadsafe' foreign import style is deprecated. Use `safe' instead.")
checkSafety _               = return ()
\end{code}

Warnings

\begin{code}
check :: Bool -> Message -> TcM ()
check True _	   = return ()
check _    the_err = addErrTc the_err

illegalForeignTyErr :: SDoc -> Type -> SDoc
illegalForeignTyErr arg_or_res ty
  = hang (hsep [ptext (sLit "Unacceptable"), arg_or_res, 
                ptext (sLit "type in foreign declaration:")])
       2 (hsep [ppr ty])

-- Used for 'arg_or_res' argument to illegalForeignTyErr
argument, result :: SDoc
argument = text "argument"
result   = text "result"

badCName :: CLabelString -> Message
badCName target 
   = sep [quotes (ppr target) <+> ptext (sLit "is not a valid C identifier")]

foreignDeclCtxt :: ForeignDecl Name -> SDoc
foreignDeclCtxt fo
  = hang (ptext (sLit "When checking declaration:"))
       2 (ppr fo)
\end{code}

