IDL inheritance causes runtime errors during Topic creation

Hello!

I'm experiencing the following issue with the code generated from IDL definitions that use inheritance

foo.idl

struct Parent {
    long parent1;
};

struct Child : Parent {
    long child1;
};

Generate code from IDL via idlc:

"""
  Generated by Eclipse Cyclone DDS idlc Python Backend
  Cyclone DDS IDL version: v0.11.0
  Module: 
  IDL file: foo.idl

"""

from dataclasses import dataclass
from enum import auto
from typing import TYPE_CHECKING, Optional

import cyclonedds as dds

import cyclonedds.idl as idl
import cyclonedds.idl.annotations as annotate
import cyclonedds.idl.types as types


@dataclass
@annotate.final
@annotate.autoid("sequential")
class Parent(idl.IdlStruct, typename="Parent"):
    parent1: types.int32


@dataclass
@annotate.final
@annotate.autoid("sequential")
class Child(Parent, typename="Child"):
    child1: types.int32

Parent class instead of idl.IdlStruct in Python was fixed in https://github.com/eclipse-cyclonedds/cyclonedds-python/issues/162. The change also added some additional checks for base classes. However, trying to use the code (with main branch of the core library (d6684dc96e7ef092869688358753e49e33e9bbc2) fails, for example

"""
  Generated by Eclipse Cyclone DDS idlc Python Backend
  Cyclone DDS IDL version: v0.11.0
  Module: 
  IDL file: foo.idl

"""

from dataclasses import dataclass
from enum import auto
from typing import TYPE_CHECKING, Optional

import cyclonedds as dds

import cyclonedds.idl as idl
import cyclonedds.idl.annotations as annotate
import cyclonedds.idl.types as types


@dataclass
@annotate.final
@annotate.autoid("sequential")
class Parent(idl.IdlStruct, typename="Parent"):
    parent1: types.int32


@dataclass
@annotate.final
@annotate.autoid("sequential")
class Child(Parent, typename="Child"):
    child1: types.int32


d = dds.domain.DomainParticipant(42)
t = dds.topic.Topic(d, "test_topic", Child)
w = dds.pub.DataWriter(d, t)
r = dds.sub.DataReader(d, t)
w.write(Child(parent1=1, child1=2))
print(r.read())

$ python foo.py 
Traceback (most recent call last):
  File "<...>/cyclonedds-python/a/a.py", line 35, in <module>
    t = dds.topic.Topic(d, "test_topic", Child)
  File "<...>/cyclonedds-python/.venv/lib/python3.10/site-packages/cyclonedds/topic.py", line 59, in __init__
    super().__init__(
  File "<...>/cyclonedds-python/.venv/lib/python3.10/site-packages/cyclonedds/core.py", line 181, in __init__
    raise DDSException(
cyclonedds.core.DDSException: [DDS_RETCODE_BAD_PARAMETER] Bad parameter value. Occurred upon initialisation of a cyclonedds.topic.Topic

Interestingly, if you create a different topic with the Parent class, another error occurs, seemingly because some registration happens in the native DDS:

"""
  Generated by Eclipse Cyclone DDS idlc Python Backend
  Cyclone DDS IDL version: v0.11.0
  Module: 
  IDL file: foo.idl

"""

from dataclasses import dataclass
from enum import auto
from typing import TYPE_CHECKING, Optional

import cyclonedds as dds

import cyclonedds.idl as idl
import cyclonedds.idl.annotations as annotate
import cyclonedds.idl.types as types


@dataclass
@annotate.final
@annotate.autoid("sequential")
class Parent(idl.IdlStruct, typename="Parent"):
    parent1: types.int32


@dataclass
@annotate.final
@annotate.autoid("sequential")
class Child(Parent, typename="Child"):
    child1: types.int32


d = dds.domain.DomainParticipant(42)
t_parent = dds.topic.Topic(d, "test_parent", Parent)
t = dds.topic.Topic(d, "test_topic", Child)
w = dds.pub.DataWriter(d, t)
r = dds.sub.DataReader(d, t)
w.write(Child(parent1=1, child1=2))
print(r.read())

$ python foo.py 
python: <...>/cyclonedds/src/core/ddsi/src/ddsi_typewrap.c:3112: ddsi_xt_get_typeobject_kind_impl: Assertion `xt->kind == DDSI_TYPEID_KIND_COMPLETE' failed.
Aborted (core dumped)

I've tried digging around the code and I believe I might see the issue. My understanding of the XT type encoding is practically nonexistent, but it seems that the Child class has the wrong type information in the header section, since it points to the minimal version of the Parent class instead of the complete one. The following diff makes the script above working properly:

diff --git a/cyclonedds/idl/_xt_builder.py b/cyclonedds/idl/_xt_builder.py
index 37a5453..19010c1 100644
--- a/cyclonedds/idl/_xt_builder.py
+++ b/cyclonedds/idl/_xt_builder.py
@@ -905,7 +905,7 @@ class XTBuilder:
 
     @classmethod
     def _xt_minimal_struct_header(cls, entity: Type[IdlStruct]) -> xt.MinimalStructHeader:
-        if entity.__base__ is None or entity.__base__ == IdlStruct:
+        if entity.__base__ is None or issubclass(entity.__base__, IdlStruct):
             return xt.MinimalStructHeader(
                 base_type=xt.TypeIdentifier(discriminator=xt.TK_NONE, value=None),
                 detail=cls._xt_minimal_type_detail(entity)
@@ -918,7 +918,7 @@ class XTBuilder:
 
     @classmethod
     def _xt_complete_struct_header(cls, entity: Type[IdlStruct]) -> xt.CompleteStructHeader:
-        if entity.__base__ is None or entity.__base__ == IdlStruct:
+        if entity.__base__ is None or issubclass(entity.__base__, IdlStruct):
             return xt.CompleteStructHeader(
                 base_type=xt.TypeIdentifier(discriminator=xt.TK_NONE, value=None),
                 detail=cls._xt_complete_type_detail(entity)

$ python foo.py
[Child(parent1=1, child1=2)]

Hope this might help.

Start in cyclonedds/idl/_xt_builder.py at _xt_minimal_struct_header and _xt_complete_struct_header, then reproduce the failure with the foo.idl Parent/Child example and Topic creation shown in the issue. Done means inherited IDL types can create Parent and Child topics and write/read Child instances without DDS errors or assertions.