feat(tags): filtrer les forum enfants à partir des tags (#750)

## Description

🎸 Réduire la liste des `Forum` enfants affichés en filtrant sur leurs
tags

suite #746 

## Type de changement

🎢 Nouvelle fonctionnalité (changement non cassant qui ajoute une
fonctionnalité).

### Points d'attention

🦺 Affichage des enfants, les petits-enfants ne sont pas considérés,
qu'il possède le tag ou non

### Captures d'écran (optionnel)


![image](https://github.com/user-attachments/assets/6042fdf1-90e6-4e20-abd9-829bab8e8d0f)

lacommunaute/forum/tests/tests_views.py

@@ -670,6 +670,39 @@ def test_documentation_category_foot_content(
         assert len(add_documentation_control) == 1
         assert str(add_documentation_control[0]) == snapshot(name="documentation_category_add_file_control")
 
+    def test_filter_subforums_on_tags(self, client, db):
+        tags = [faker.word() for _ in range(3)]
+        category_forum = CategoryForumFactory(with_public_perms=True)
+        first_child = ForumFactory(parent=category_forum, with_public_perms=True, with_tags=[tags[0]])
+        second_child = ForumFactory(parent=category_forum, with_public_perms=True, with_tags=[tags[0], tags[1]])
+        third_child = ForumFactory(parent=category_forum, with_public_perms=True, with_tags=[tags[2]])
+        # forum without tags
+        ForumFactory(parent=category_forum, with_public_perms=True)
+
+        # edge case: grand_child is filtered out. No actual use case to display them in the subforum list
+        ForumFactory(parent=third_child, with_public_perms=True, with_tags=[tags[2]])
+
+        # no filter
+        response = client.get(category_forum.get_absolute_url())
+        assert response.status_code == 200
+        assert [node.obj for node in response.context_data["sub_forums"].top_nodes] == list(
+            category_forum.get_children()
+        )
+
+        # filter on first tag
+        response = client.get(category_forum.get_absolute_url() + f"?forum_tags={tags[0]}")
+        assert response.status_code == 200
+        assert set([node.obj for node in response.context_data["sub_forums"].top_nodes]) == set(
+            [first_child, second_child]
+        )
+
+        # filter on multiple tags
+        response = client.get(category_forum.get_absolute_url() + f"?forum_tags={tags[1]},{tags[2]}")
+        assert response.status_code == 200
+        assert set([node.obj for node in response.context_data["sub_forums"].top_nodes]) == set(
+            [second_child, third_child]
+        )
+
 
 @pytest.fixture(name="discussion_area_forum")
 def discussion_area_forum_fixture():

lacommunaute/forum/views.py

@@ -23,6 +23,7 @@
 logger = logging.getLogger(__name__)
 
 PermissionRequiredMixin = get_class("forum_permission.viewmixins", "PermissionRequiredMixin")
+ForumVisibilityContentTree = get_class("forum.visibility", "ForumVisibilityContentTree")
 
 
 class ForumView(BaseForumView, FilteredTopicsListViewMixin):
@@ -46,6 +47,12 @@ def will_render_documentation_category_variant(self):
     def get_queryset(self):
         return self.filter_queryset(self.get_forum().topics.optimized_for_topics_list(self.request.user.id))
 
+    def get_descendants(self):
+        forum_tags = self.request.GET.get("forum_tags")
+        if forum_tags:
+            return self.get_forum().get_descendants().filter(tags__slug__in=forum_tags.split(","))
+        return self.get_forum().get_descendants()
+
     def get_context_data(self, **kwargs):
         forum = self.get_forum()
 
@@ -75,6 +82,14 @@ def get_context_data(self, **kwargs):
         )
         context = context | self.get_topic_filter_context()
 
+        # vincentporte, overide the method to add the sub_forums, not testing permissions ^v^
+        context["sub_forums"] = ForumVisibilityContentTree.from_forums(
+            self.request.forum_permission_handler.forum_list_filter(
+                self.get_descendants(),
+                self.request.user,
+            ),
+        )
+
         if self.will_render_documentation_variant():
             context["sibling_forums"] = forum.get_siblings(include_self=True)