DEV: Add apply_modifier for SemanticTopicQuery topics list

lib/embeddings/semantic_topic_query.rb

@@ -16,12 +16,12 @@ def list_semantic_related_topics(topic)
       create_list(:semantic_related, query_opts) do |topics|
         candidate_ids = DiscourseAi::Embeddings::SemanticRelated.new.related_topic_ids_for(topic)
 
-        list =
-          topics
-            .where.not(id: topic.id)
-            .where(id: candidate_ids)
-            .order("array_position(ARRAY#{candidate_ids}, topics.id)") # array_position forces the order of the topics to be preserved
+        list = topics.where.not(id: topic.id).where(id: candidate_ids)
 
+        list = DiscoursePluginRegistry.apply_modifier(:semantic_related_topics_query, list)
+
+        # array_position forces the order of the topics to be preserved
+        list = list.order("array_position(ARRAY#{candidate_ids}, topics.id)")
         list = remove_muted(list, @user, query_opts)
       end
   end

spec/lib/modules/embeddings/semantic_topic_query_spec.rb

@@ -112,6 +112,28 @@ def stub_semantic_search_with(results)
           )
         end
       end
+
+      context "with semantic_related_topics_query modifier registered" do
+        fab!(:included_topic) { Fabricate(:topic) }
+        fab!(:excluded_topic) { Fabricate(:topic) }
+
+        before { stub_semantic_search_with([included_topic.id, excluded_topic.id]) }
+
+        let(:modifier_block) { Proc.new { |query| query.where.not(id: excluded_topic.id) } }
+
+        it "Allows modifications to default results (excluding a topic in this case)" do
+          plugin_instance = Plugin::Instance.new
+          plugin_instance.register_modifier(:semantic_related_topics_query, &modifier_block)
+
+          expect(topic_query.list_semantic_related_topics(target).topics).to eq([included_topic])
+        ensure
+          DiscoursePluginRegistry.unregister_modifier(
+            plugin_instance,
+            :semantic_related_topics_query,
+            &modifier_block
+          )
+        end
+      end
     end
   end
 end