FIX: tag topic counts wrong after adding synonyms

After adding a tag as a synonym of another tag,
both tags will have the wrong topic counts. It's
corrected within 12 hours by the EnsureDbConsistency
job. This fix ensures the topic counts are updated
much sooner.

lib/discourse_tagging.rb

@@ -424,6 +424,9 @@ module DiscourseTagging
     end
     successful = existing.select { |t| !t.errors.present? }
     TopicTag.where(tag_id: successful.map(&:id)).update_all(tag_id: target_tag.id)
+    Scheduler::Defer.later "Update tag topic counts" do
+      Tag.ensure_consistency!
+    end
     (existing - successful).presence || true
   end
 

spec/components/discourse_tagging_spec.rb

@@ -568,6 +568,8 @@ describe DiscourseTagging do
       topic = Fabricate(:topic, tags: [tag2])
       expect(DiscourseTagging.add_or_create_synonyms_by_name(tag1, [tag2.name])).to eq(true)
       expect_same_tag_names(topic.reload.tags, [tag1])
+      expect(tag1.reload.topic_count).to eq(1)
+      expect(tag2.reload.topic_count).to eq(0)
     end
   end
 end