Emulate Python MRO by adding virtual methods in derived cypclasses forwarding to correct method

Cython/Compiler/ExprNodes.py

@@ -7581,8 +7581,6 @@ class AttributeNode(ExprNode):
             if obj.type.is_cpp_class and self.entry and self.entry.is_cfunction:
                 # the entry might have been resolved to an overladed alternative in the meantime
                 self.member = self.entry.cname
-            if obj.type.is_cyp_class and self.entry and self.entry.from_type:
-                self.member = "%s::%s" % (self.entry.from_type.empty_declaration_code(), self.member)
             return "%s%s%s" % (obj_code, self.op, self.member)
 
     def generate_result_code(self, code):

Cython/Compiler/ModuleNode.py

@@ -1066,6 +1066,7 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
                 constructor = scope.lookup_here("<constructor>")
                 for constructor_alternative in constructor.all_alternatives():
                     code.putln("static %s;" % constructor_alternative.type.declaration_code(constructor_alternative.cname))
+                self.generate_cyp_class_mro_method_resolution(scope, code)
             elif constructor or py_attrs:
                 if constructor:
                     for constructor_alternative in constructor.all_alternatives():
@@ -1155,6 +1156,47 @@ class ModuleNode(Nodes.Node, Nodes.BlockNode):
             code.globalstate.use_utility_code(
                 UtilityCode.load("CyObjects", "CyObjects.cpp", proto_block="utility_code_proto_before_types"))
 
+    def generate_cyp_class_mro_method_resolution(self, scope, code):
+        """
+            Generate overriding methods in derived cypclasses to forward calls to the correct method according
+            to the MRO, regardless of the type of the pointer to the object through which the call is made.
+            In other words: emulate Python MRO lookup rules using only C++ virtual methods.
+        """
+        inherited_methods = [
+            e for entry in scope.entries.values() for e in entry.all_alternatives()
+            if e.is_cfunction
+            and e.from_type
+            and e.mro_index > 0
+            and not e.type.is_static_method # avoid dealing with static methods for now
+            and e.name not in ("<init>", "<del>")
+            and not e.type.has_varargs # avoid dealing with varargs for now (is this ever required anyway ?)
+        ]
+        if inherited_methods:
+            code.putln("")
+            code.putln("/* make all inherited (non overriden) methods resolve correctly according to the MRO */")
+        for e in inherited_methods:
+            modifiers = code.build_function_modifiers(e.func_modifiers)
+
+            arg_decls = [arg.declaration_code() for arg in e.type.args]
+            arg_names = [arg.cname for arg in e.type.args]
+            if e.type.optional_arg_count:
+                opt_name = Naming.optional_args_cname
+                arg_decls.append(e.type.op_arg_struct.declaration_code(opt_name))
+                arg_names.append(opt_name)
+
+            header = e.type.function_header_code(e.cname, ", ".join(arg_decls))
+            if not e.name.startswith("operator "):
+                header = e.type.return_type.declaration_code(header)
+
+            return_code = "" if e.type.return_type.is_void else "return "
+            resolution = e.from_type.empty_declaration_code()
+
+            body = "%s%s::%s(%s);" % (return_code, resolution, e.cname, ", ".join(arg_names))
+
+            code.putln("virtual %s%s {%s}" % (modifiers, header, body))
+        if inherited_methods:
+            code.putln("")
+
     def generate_cyp_class_attrs_destructor_definition(self, entry, code):
         scope = entry.type.scope
         cypclass_attrs = [e for e in scope.var_entries

Cython/Compiler/PyrexTypes.py

@@ -2951,10 +2951,10 @@ class CFuncType(CType):
             return 0
         return 1
 
-    def compatible_signature_with(self, other_type, as_cmethod = 0):
-        return self.compatible_signature_with_resolved_type(other_type.resolve(), as_cmethod)
+    def compatible_signature_with(self, other_type, as_cmethod = 0, ignore_return_type=0):
+        return self.compatible_signature_with_resolved_type(other_type.resolve(), as_cmethod, ignore_return_type)
 
-    def compatible_signature_with_resolved_type(self, other_type, as_cmethod):
+    def compatible_signature_with_resolved_type(self, other_type, as_cmethod, ignore_return_type=0):
         #print "CFuncType.same_c_signature_as_resolved_type:", \
         #    self, other_type, "as_cmethod =", as_cmethod ###
         if other_type is error_type:
@@ -2977,6 +2977,7 @@ class CFuncType(CType):
                 return 0
         if self.has_varargs != other_type.has_varargs:
             return 0
+        if not ignore_return_type:
             if not self.return_type.subtype_of_resolved_type(other_type.return_type):
                 return 0
         if not self.same_calling_convention_as(other_type):

Cython/Compiler/Symtab.py

@@ -534,7 +534,12 @@ class Scope(object):
             if type.is_cfunction and old_entry.type.is_cfunction and self.is_cpp():
                 cpp_override_allowed = True
                 for index, alt_entry in enumerate(old_entry.all_alternatives()):
-                    if type.compatible_signature_with(alt_entry.type):
+                    # in a cypclass, a method can hide a method inherited from a different class
+                    # regardless of their return types
+                    ignore_return_type = (self.is_cyp_class_scope
+                                          and alt_entry.is_inherited
+                                          and alt_entry.from_type is not from_type)
+                    if type.compatible_signature_with(alt_entry.type, ignore_return_type=ignore_return_type):
 
                         cpp_override_allowed = False
 
@@ -3033,7 +3038,6 @@ class CppClassScope(Scope):
             entry.is_cfunction = base_entry.is_cfunction
             if entry.is_cfunction:
                 entry.func_cname = base_entry.func_cname
-            self.inherited_var_entries.append(entry)
 
         for base_entry in base_scope.type_entries:
             if base_entry.name not in base_templates:
@@ -3041,7 +3045,6 @@ class CppClassScope(Scope):
                                           base_entry.pos, base_entry.cname,
                                           base_entry.visibility, defining=0)
                 entry.is_inherited = 1
-                self.inherited_type_entries.append(entry)
 
     def specialize(self, values, type_entry):
         scope = CppClassScope(self.name, self.outer_scope)