[project @ 2003-02-04 15:31:18 by simonpj]

-------------------------------------
	Fix a name-capture bug in Ext-Core
	-------------------------------------

Don't expand newtypes (even non-recursive ones) when going to External Core.
Reason: the expansion was performed *after* Tidying; the expansion performs
type substitution, which is only done right if you take account of the Uniques.
But since it's post-tidying, we got capture of occurence names.

I hope the lack of newtype expansion doesn't hurt anyone; I doubt it will.
If so, we can think again.

Thanks to Tobias Gedell for this one.

diff --git a/ghc/compiler/coreSyn/MkExternalCore.lhs b/ghc/compiler/coreSyn/MkExternalCore.lhs
index 47eb59b..a5d1751 100644 (file)
--- a/ghc/compiler/coreSyn/MkExternalCore.lhs
+++ b/ghc/compiler/coreSyn/MkExternalCore.lhs
@@ -176,13 +176,30 @@ make_lit l =
     t = make_ty (literalType l)
 
 make_ty :: Type -> C.Ty
-make_ty (TyVarTy tv) = C.Tvar (make_var_id (tyVarName tv))
-make_ty (AppTy t1 t2) = C.Tapp (make_ty t1) (make_ty t2)
-make_ty (TyConApp tc ts) = foldl C.Tapp (C.Tcon (make_con_qid (tyConName tc))) (map make_ty ts)
-make_ty (FunTy t1 t2) = make_ty (TyConApp funTyCon [t1,t2])
-make_ty (ForAllTy tv t) = C.Tforall (make_tbind tv) (make_ty t)
-make_ty (SourceTy p) = make_ty (sourceTypeRep p)
-make_ty (NoteTy _ t) = make_ty t
+make_ty (TyVarTy tv)            = C.Tvar (make_var_id (tyVarName tv))
+make_ty (AppTy t1 t2)           = C.Tapp (make_ty t1) (make_ty t2)
+make_ty (FunTy t1 t2)           = make_ty (TyConApp funTyCon [t1,t2])
+make_ty (ForAllTy tv t)         = C.Tforall (make_tbind tv) (make_ty t)
+make_ty (TyConApp tc ts)        = foldl C.Tapp (C.Tcon (make_con_qid (tyConName tc))) 
+                                        (map make_ty ts)
+-- The special case for newtypes says "do not expand newtypes".
+-- Reason: sourceTypeRep does substitution and, while substitution deals
+--        correctly with name capture, it's only correct if you see the uniques!
+--        If you just see occurrence names, name capture may occur.
+-- Example: newtype A a = A (forall b. b -> a)
+--         test :: forall q b. q -> A b
+--         test _ = undefined
+--     Here the 'a' gets substituted by 'b', which is captured.
+-- Another solution would be to expand newtypes before tidying; but that would
+-- expose the representation in interface files, which definitely isn't right.
+-- Maybe CoreTidy should know whether to expand newtypes or not?
+
+make_ty (SourceTy (NType tc ts)) = foldl C.Tapp (C.Tcon (make_con_qid (tyConName tc))) 
+                                        (map make_ty ts)
+
+make_ty (SourceTy p)            = make_ty (sourceTypeRep p)
+make_ty (NoteTy _ t)            = make_ty t
+
 
 
 make_kind :: Kind -> C.Kind