Fix topic inheritance for translated documents

This commit addresses issues with topic handling for translated documents:

1. Adds signal handler to automatically propagate topic changes from parent
   documents to their translations, ensuring database consistency

2. Improves query filtering in facets.py to include translated documents
   based on their parent's topics, providing correct results even before
   database synchronization occurs

These changes ensure that topics are consistently applied across all
translations of a document, both at the database level and in query results.

Author: smithellis

kitsune/wiki/apps.py

@@ -6,6 +6,8 @@ class WikiConfig(AppConfig):
     default_auto_field = "django.db.models.AutoField"
 
     def ready(self):
+        # Import signals to register them
+        from kitsune.wiki import signals  # noqa: F401 - import for signal registration
         from kitsune.wiki.badges import register_signals
 
         # register signals for badges

kitsune/wiki/facets.py

@@ -112,7 +112,9 @@ def _documents_for(user, locale, topics=None, products=None):
     if topics:
         topic_ids = [t.id for t in topics]
         # we need to filter against parent topics for localized articles
-        qs = qs.filter(Q(topics__in=topic_ids) | Q(parent__topics__in=topic_ids))
+        qs = qs.filter(
+            Q(topics__in=topic_ids) | Q(parent__isnull=False, parent__topics__in=topic_ids)
+        )
     for product in products or []:
         # we need to filter against parent products for localized articles
         qs = qs.filter(Q(products=product) | Q(parent__products=product))

kitsune/wiki/models.py

@@ -797,6 +797,18 @@ def is_linked_in_product(self):
             locale__in=("", self.locale), target__contains=f"kb/{self.slug}"
         ).exists()
 
+    def propagate_topics_to_translations(self):
+        """Propagate topic changes from a parent document to its translations."""
+        if self.locale != settings.WIKI_DEFAULT_LANGUAGE:
+            # Only operate on parent documents
+            return
+
+        parent_topics = list(self.topics.all())
+        for translated_doc in self.translations.all():
+            # Clear existing topics and add parent's topics
+            translated_doc.topics.clear()
+            translated_doc.topics.add(*parent_topics)
+
 
 class AbstractRevision(models.Model):
     # **%(class)s** is being used because it will allow  a unique reverse name for the field

kitsune/wiki/signals.py

@@ -0,0 +1,11 @@
+from django.db.models.signals import m2m_changed
+from django.dispatch import receiver
+
+from kitsune.wiki.models import Document
+
+
+@receiver(m2m_changed, sender=Document.topics.through)
+def handle_document_topics_change(sender, instance, action, **kwargs):
+    """When a document's topics change, propagate to translations if needed."""
+    if action in ("post_add", "post_remove", "post_clear"):
+        instance.propagate_topics_to_translations()