Cast underlying cyobject to base type and back safely instead of void *

Cython/Compiler/CypclassWrapper.py

@@ -237,12 +237,20 @@ class CypclassWrapperInjection(CythonTransform):
         return wrapper
 
     def synthesize_underlying_cyobject_attribute(self, node):
+        base_type = node.entry.type.wrapped_base_type
 
-        void_type_node = Nodes.CSimpleBaseTypeNode(
+        nesting_path = []
+        outer_scope = base_type.scope.outer_scope
+        while outer_scope and not outer_scope.is_module_scope:
+            nesting_path.append(outer_scope.name)
+            outer_scope = outer_scope.outer_scope
+        nesting_path.reverse()
+
+        base_type_node = Nodes.CSimpleBaseTypeNode(
             node.pos,
-            name = "void",
-            module_path = [],
-            is_basic_c_type = 1,
+            name = base_type.name,
+            module_path = nesting_path,
+            is_basic_c_type = 0,
             signed = 1,
             complex = 0,
             longness = 0,
@@ -251,12 +259,11 @@ class CypclassWrapperInjection(CythonTransform):
         )
 
         underlying_name_declarator = Nodes.CNameDeclaratorNode(node.pos, name=underlying_name, cname=None)
-        underlying_name_declarator = Nodes.CPtrDeclaratorNode(node.pos, base=underlying_name_declarator)
 
         underlying_cyobject = Nodes.CVarDefNode(
             pos = node.pos,
             visibility = 'private',
-            base_type = void_type_node,
+            base_type = base_type_node,
             declarators = [underlying_name_declarator],
             in_pxd = node.in_pxd,
             doc = None,
@@ -765,11 +772,14 @@ def generate_cyp_class_wrapper_definition(type, wrapper_entry, constructor_entry
 
     # initialise PyObject fields
     if is_new_return_type and type.wrapper_type:
+        chain_casted_self = "self"
+        for first_base in type.first_base_iter():
+            chain_casted_self = "static_cast<%s *>(%s)" % (first_base.empty_declaration_code(), chain_casted_self)
         objstruct_cname = type.wrapper_type.objstruct_cname
         cclass_wrapper_base = type.wrapped_base_type.wrapper_type
         code.putln("if(self) {")
         code.putln("%s * wrapper = new %s();" % (objstruct_cname, objstruct_cname))
-        code.putln("((%s *)wrapper)->nogil_cyobject = self;" % cclass_wrapper_base.objstruct_cname)
+        code.putln("((%s *)wrapper)->nogil_cyobject = %s;" % (cclass_wrapper_base.objstruct_cname, chain_casted_self))
         code.putln("PyObject * wrapper_as_py = (PyObject *) wrapper;")
         code.putln("wrapper_as_py->ob_refcnt = 0;")
         code.putln("wrapper_as_py->ob_type = %s;" % type.wrapper_type.typeptr_cname)

Cython/Compiler/ModuleNode.py

@@ -1402,7 +1402,7 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
             # internal classes (should) never need None inits, normal zeroing will do
             py_attrs = []
 
-        # cyp_class attributes should not be treated as normal cpp_class attributes
+        # unlike normal cpp_class attributes, cyp_class attributes are always held as pointers
         cpp_class_attrs = [entry for entry in scope.var_entries
                            if entry.type.is_cpp_class and not entry.type.is_cyp_class]
 
@@ -1582,7 +1582,7 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
 
         _, (py_attrs, _, memoryview_slices) = scope.get_refcounted_entries()
 
-        # cyp_class attributes should not be treated as normal cpp_class attributes
+        # unlike normal cpp_class attributes, cyp_class attributes are always held as pointers
         cpp_class_attrs = [entry for entry in scope.var_entries
                            if entry.type.is_cpp_class and not entry.type.is_cyp_class]
 

Cython/Compiler/Nodes.py

@@ -5457,13 +5457,17 @@ class CypclassWrapperDefNode(CClassDefNode):
 
         # > access the underlying cyobject from the self argument of the wrapper method
         underlying_obj = ExprNodes.AttributeNode(cfunc_method.pos, obj=self_obj, attribute=underlying_name)
-        empty_declarator = CNameDeclaratorNode(cfunc_method.pos, name="", cname=None)
-        cast_operation = ExprNodes.TypecastNode(
-            cfunc_method.pos,
-            type = self.wrapped_cypclass.entry.type,
-            operand = underlying_obj,
-            typecheck = False
-        )
+
+        # > cast the underlying object back to this type
+        underlying_type = self.wrapped_cypclass.entry.type
+        cast_operation = underlying_obj
+        for derived_type in underlying_type.first_base_rev_iter():
+            cast_operation = ExprNodes.TypecastNode(
+                cfunc_method.pos,
+                type = derived_type,
+                operand = cast_operation,
+                typecheck = False
+            )
 
         cast_underlying_obj = ExprNodes.NameNode(self_pos, name=EncodedString("cast_cyobject"))
         cast_assignment = SingleAssignmentNode(self_pos, lhs=cast_underlying_obj, rhs=cast_operation)

Cython/Compiler/PyrexTypes.py

@@ -4050,6 +4050,20 @@ class CypClassType(CppClassType):
         self._left_path_to_base[base] = path
         return path
 
+    # iterate over the chain of first wrapped bases until the oldest wrapped base is reached
+    def first_base_iter(self):
+        type_item = self
+        while type_item is not self.wrapped_base_type:
+            type_item = type_item.first_wrapped_base
+            yield type_item
+
+    # iterate down the chain of first wrapped bases until this type is reached
+    def first_base_rev_iter(self):
+        if self is not self.wrapped_base_type:
+            for t in self.first_wrapped_base.first_base_rev_iter():
+                yield t
+            yield self
+
     # allow conversion to Python only when there is a wrapper type
     def can_coerce_to_pyobject(self, env):
         return self.wrapper_type is not None