Do not allow to create epic when parent reached hierarchy limit

Return error when trying to create epic as child of
another epic that has reached hierarchy limit

ee/app/models/ee/epic.rb

@@ -362,7 +362,7 @@ module EE
     private :validate_parent
 
     def level_depth_exceeded?(parent_epic)
-      hierarchy.max_descendants_depth.to_i + parent_epic.ancestors.count >= MAX_HIERARCHY_DEPTH
+      hierarchy.max_descendants_depth.to_i + parent_epic.base_and_ancestors.count >= MAX_HIERARCHY_DEPTH
     end
     private :level_depth_exceeded?
 
@@ -371,6 +371,5 @@ module EE
 
       hierarchy.base_and_ancestors(hierarchy_order: :asc)
     end
-    private :base_and_ancestors
   end
 end

ee/changelogs/unreleased/issue_38331.yml

+---
+title: Fix child epics depth validation
+merge_request: 22729
+author:
+type: fixed

ee/lib/api/epic_links.rb

@@ -84,7 +84,7 @@ module API
         if child_epic.valid?
           present child_epic, with: EE::API::Entities::LinkedEpic, user: current_user
         else
-          render_validation_error!(epic)
+          render_validation_error!(child_epic)
         end
       end
 

ee/spec/models/epic_spec.rb

@@ -128,8 +128,7 @@ describe Epic do
         epic3 = create(:epic, group: group, parent: epic2)
         epic4 = create(:epic, group: group, parent: epic3)
         epic5 = create(:epic, group: group, parent: epic4)
-        epic6 = create(:epic, group: group, parent: epic5)
-        epic.parent = epic6
+        epic.parent = epic5
 
         expect(epic.valid_parent?).to be_falsey
       end
@@ -149,8 +148,7 @@ describe Epic do
       it 'returns false when total depth after adding would exceed limit' do
         child_epic2 = create(:epic, group: group, parent: child_epic1)
         child_epic3 = create(:epic, group: group, parent: child_epic2)
-        child_epic4 = create(:epic, group: group, parent: child_epic3)
-        create(:epic, group: group, parent: child_epic4)
+        create(:epic, group: group, parent: child_epic3)
 
         epic.parent = parent_epic
 

ee/spec/requests/api/epic_links_spec.rb

@@ -135,15 +135,32 @@ describe API::EpicLinks do
       end
 
       context 'when user is developer' do
-        it 'returns 201 status' do
+        before do
           group.add_developer(user)
+        end
 
+        it 'returns 201 status' do
           subject
 
           expect(response).to have_gitlab_http_status(201)
           expect(response).to match_response_schema('public_api/v4/linked_epic', dir: 'ee')
           expect(epic.reload.children).to include(Epic.last)
         end
+
+        context 'and epic has errors' do
+          it 'returns 400 error' do
+            child_epic = Epic.new(title: 'with errors')
+            errors = ActiveModel::Errors.new(child_epic).tap { |e| e.add(:parent_id, "error message") }
+            allow(child_epic).to receive(:errors).and_return(errors)
+            allow_next_instance_of(Epics::CreateService) do |service|
+              allow(service).to receive(:execute).and_return(child_epic)
+            end
+
+            subject
+
+            expect(response).to have_gitlab_http_status(400)
+          end
+        end
       end
     end
   end