🐛(backend) compute ancestor_links in get_abilities if needed

The refactor made in the tree view caching the ancestors_links to not
compute them again in the document.get_abilities method lead to a bug.
If the get_abilities method is called without ancestors_links, then they
are computed on all the ancestors but not from the highest readable
ancestor for the current user. We have to compute them with this
constraint.

CHANGELOG.md

@@ -16,6 +16,10 @@ and this project adheres to
 
 - ♻️(frontend) Integrate UI kit #783
 
+## Fixed
+
+- 🐛(backend) compute ancestor_links in get_abilities if needed #725
+
 ## [2.6.0] - 2025-03-21
 
 ## Added

src/backend/core/api/viewsets.py

@@ -846,14 +846,15 @@ class DocumentViewSet(
         )
 
         # Get the highest readable ancestor
-        highest_readable = ancestors.readable_per_se(request.user).only("depth").first()
+        highest_readable = (
+            ancestors.readable_per_se(request.user).only("depth", "path").first()
+        )
         if highest_readable is None:
             raise (
                 drf.exceptions.PermissionDenied()
                 if request.user.is_authenticated
                 else drf.exceptions.NotAuthenticated()
             )
-
         paths_links_mapping = {}
         ancestors_links = []
         children_clause = db.Q()
@@ -876,6 +877,17 @@ class DocumentViewSet(
 
         queryset = ancestors.filter(depth__gte=highest_readable.depth) | children
         queryset = queryset.order_by("path")
+        # Annotate if the current document is the highest ancestor for the user
+        queryset = queryset.annotate(
+            is_highest_ancestor_for_user=db.Case(
+                db.When(
+                    path=db.Value(highest_readable.path),
+                    then=db.Value(True),
+                ),
+                default=db.Value(False),
+                output_field=db.BooleanField(),
+            )
+        )
         queryset = self.annotate_user_roles(queryset)
         queryset = self.annotate_is_favorite(queryset)
 

src/backend/core/models.py

@@ -754,6 +754,32 @@ class Document(MP_Node, BaseModel):
 
         return dict(links_definitions)  # Convert defaultdict back to a normal dict
 
+    def compute_ancestors_links(self, user):
+        """
+        Compute the ancestors links for the current document up to the highest readable ancestor.
+        """
+        ancestors = (
+            (self.get_ancestors() | self._meta.model.objects.filter(pk=self.pk))
+            .filter(ancestors_deleted_at__isnull=True)
+            .order_by("path")
+        )
+        highest_readable = ancestors.readable_per_se(user).only("depth").first()
+
+        if highest_readable is None:
+            return []
+
+        ancestors_links = []
+        paths_links_mapping = {}
+        for ancestor in ancestors.filter(depth__gte=highest_readable.depth):
+            ancestors_links.append(
+                {"link_reach": ancestor.link_reach, "link_role": ancestor.link_role}
+            )
+            paths_links_mapping[ancestor.path] = ancestors_links.copy()
+
+        ancestors_links = paths_links_mapping.get(self.path[: -self.steplen], [])
+
+        return ancestors_links
+
     def get_abilities(self, user, ancestors_links=None):
         """
         Compute and return abilities for a given user on the document.
@@ -761,7 +787,7 @@ class Document(MP_Node, BaseModel):
         if self.depth <= 1 or getattr(self, "is_highest_ancestor_for_user", False):
             ancestors_links = []
         elif ancestors_links is None:
-            ancestors_links = self.get_ancestors().values("link_reach", "link_role")
+            ancestors_links = self.compute_ancestors_links(user=user)
 
         roles = set(
             self.get_roles(user)

src/backend/core/tests/documents/test_api_documents_retrieve.py

@@ -789,7 +789,7 @@ def test_api_documents_retrieve_user_roles(django_assert_max_num_queries):
     )
     expected_roles = {access.role for access in accesses}
 
-    with django_assert_max_num_queries(12):
+    with django_assert_max_num_queries(14):
         response = client.get(f"/api/v1.0/documents/{document.id!s}/")
 
     assert response.status_code == 200

src/backend/core/tests/test_models_documents.py

@@ -1305,3 +1305,47 @@ def test_models_documents_restore_complex_bis(django_assert_num_queries):
 def test_models_documents_get_select_options(ancestors_links, select_options):
     """Validate that the "get_select_options" method operates as expected."""
     assert models.LinkReachChoices.get_select_options(ancestors_links) == select_options
+
+
+def test_models_documents_compute_ancestors_links_no_highest_readable():
+    """Test the compute_ancestors_links method."""
+    document = factories.DocumentFactory(link_reach="public")
+    assert document.compute_ancestors_links(user=AnonymousUser()) == []
+
+
+def test_models_documents_compute_ancestors_links_highest_readable(
+    django_assert_num_queries,
+):
+    """Test the compute_ancestors_links method."""
+    user = factories.UserFactory()
+    other_user = factories.UserFactory()
+    root = factories.DocumentFactory(
+        link_reach="restricted", link_role="reader", users=[user]
+    )
+
+    factories.DocumentFactory(
+        parent=root, link_reach="public", link_role="reader", users=[user]
+    )
+    child2 = factories.DocumentFactory(
+        parent=root,
+        link_reach="authenticated",
+        link_role="editor",
+        users=[user, other_user],
+    )
+    child3 = factories.DocumentFactory(
+        parent=child2,
+        link_reach="authenticated",
+        link_role="reader",
+        users=[user, other_user],
+    )
+
+    with django_assert_num_queries(2):
+        assert child3.compute_ancestors_links(user=user) == [
+            {"link_reach": root.link_reach, "link_role": root.link_role},
+            {"link_reach": child2.link_reach, "link_role": child2.link_role},
+        ]
+
+    with django_assert_num_queries(2):
+        assert child3.compute_ancestors_links(user=other_user) == [
+            {"link_reach": child2.link_reach, "link_role": child2.link_role},
+        ]