Fix #303 as per Lisandro's idea

Cython/Compiler/Nodes.py

@@ -793,10 +793,17 @@ class CVarDefNode(StatNode):
             dest_scope = env
         self.dest_scope = dest_scope
         base_type = self.base_type.analyse(env)
-        if (dest_scope.is_c_class_scope
-                and self.visibility == 'public' 
+
+        # If the field is an external typedef, we cannot be sure about the type,
+        # so do conversion ourself rather than rely on the CPython mechanism (through
+        # a property; made in AnalyseDeclarationsTransform).
+        # Also, if the type is an extension type, then the CPython mechanism does
+        # not do enough type-checking for us.
+        if (dest_scope.is_c_class_scope and
+               ((self.visibility == 'public' 
                  and base_type.is_pyobject 
-                and (base_type.is_builtin_type or base_type.is_extension_type)):
+                 and (base_type.is_builtin_type or base_type.is_extension_type)
+                or (base_type.is_typedef and base_type.typedef_is_external)))):
             self.need_properties = []
             need_property = True
             visibility = 'private'

Cython/Compiler/PyrexTypes.py

@@ -161,12 +161,15 @@ class CTypedefType(BaseType):
     #  qualified_name      string
     #  typedef_cname       string
     #  typedef_base_type   PyrexType
+    #  typedef_is_external bool
     
     is_typedef = 1
+    typedef_is_external = 0
     
-    def __init__(self, cname, base_type):
+    def __init__(self, cname, base_type, is_external=0):
         self.typedef_cname = cname
         self.typedef_base_type = base_type
+        self.typedef_is_external = is_external
     
     def resolve(self):
         return self.typedef_base_type.resolve()

Cython/Compiler/Symtab.py

@@ -347,7 +347,7 @@ class Scope(object):
                 cname = name
             else:
                 cname = self.mangle(Naming.type_prefix, name)
-        type = PyrexTypes.CTypedefType(cname, base_type)
+        type = PyrexTypes.CTypedefType(cname, base_type, (visibility == 'extern'))
         entry = self.declare_type(name, type, pos, cname, visibility)
         type.qualified_name = entry.qualified_name
         return entry