This deserves a wider audience: if you've encountered failures when
compiling FFI code with recent GHCs due to the new requirement that
newtypes be non-abstract, note that this will now be a warning, not an
error, in 7.4.1. We're deferring turning it into an error until 7.6.1.
Cheers,
Simon
-------- Original Message --------
Subject: [commit: ghc] master: Relax the restriction on using abstract
newtypes in FFI declarations. (c6b0fd6)
Date: Thu, 24 Nov 2011 06:57:21 -0800
From: Simon Marlow <marlo...@gmail.com>
To: cvs-...@haskell.org
Repository : ssh://darcs.haskell.org//srv/darcs/ghc
On branch : master
http://hackage.haskell.org/trac/ghc/changeset/c6b0fd62fc715aa6c666eb8afe09073ac7b87a83
---------------------------------------------------------------
commit c6b0fd62fc715aa6c666eb8afe09073ac7b87a83
Author: Simon Marlow <marlo...@gmail.com>
Date: Thu Nov 24 14:04:23 2011 +0000
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.
Codec/Compression/Zlib/Stream.hsc:884:1:
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
---------------------------------------------------------------
compiler/typecheck/TcForeign.lhs | 22 +++++++++++++++++-----
1 files changed, 17 insertions(+), 5 deletions(-)
diff --git a/compiler/typecheck/TcForeign.lhs
b/compiler/typecheck/TcForeign.lhs
index 886b84d..5a4bf77 100644
--- a/compiler/typecheck/TcForeign.lhs
+++ b/compiler/typecheck/TcForeign.lhs
@@ -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).
where
+
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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