Commit c6b0fd62 authored by Simon Marlow's avatar Simon Marlow
Browse files

Relax the restriction on using abstract newtypes in FFI declarations.

Given the high impact of this change, we decided to back off and make
abstract newtypes give a warning for one release, before we make it an
error in 7.6.1.

    Warning: newtype `CInt' is used in an FFI declaration,
             but its constructor is not in scope.
             This will become an error in GHC 7.6.1.
    When checking declaration:
      foreign import ccall unsafe "static zlib.h deflate" c_deflate
        :: StreamState -> CInt -> IO CInt
parent 1eedbc6b
......@@ -121,17 +121,29 @@ normaliseFfiType' env ty0 = go [] ty0
panic "normaliseFfiType': Got more GREs than expected"
_ ->
return False
if newtypeOK
then do let nt_co = mkAxInstCo (newTyConCo tc) tys
add_co nt_co rec_nts' nt_rhs
else children_only
when (not newtypeOK) $
-- later: stop_here
addWarnTc (ptext (sLit "newtype") <+> quotes (ppr tc) <+>
ptext (sLit "is used in an FFI declaration,") $$
ptext (sLit "but its constructor is not in scope.") $$
ptext (sLit "This will become an error in GHC 7.6.1."))
let nt_co = mkAxInstCo (newTyConCo tc) tys
add_co nt_co rec_nts' nt_rhs
| isFamilyTyCon tc -- Expand open tycons
, (co, ty) <- normaliseTcApp env tc tys
, not (isReflCo co)
= add_co co rec_nts ty
| otherwise
= children_only
= return (mkReflCo ty, ty)
-- If we have reached an ordinary (non-newtype) type constructor,
-- we are done. Note that we don't need to normalise the arguments,
-- because whether an FFI type is legal or not depends only on
-- the top-level type constructor (e.g. "Ptr a" is valid for all a).
children_only = do xs <- mapM (go rec_nts) tys
let (cos, tys') = unzip xs
return (mkTyConAppCo tc cos, mkTyConApp tc tys')
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