FIX: featured links are 'undefined' in suggested topics

app/serializers/suggested_topic_serializer.rb

@@ -7,7 +7,7 @@ class SuggestedTopicSerializer < ListableTopicSerializer
     has_one :user, serializer: BasicUserSerializer, embed: :objects
   end
 
-  attributes :archetype, :like_count, :views, :category_id, :tags, :featured_link
+  attributes :archetype, :like_count, :views, :category_id, :tags, :featured_link, :featured_link_root_domain
   has_many :posters, serializer: SuggestedPosterSerializer, embed: :objects
 
   def posters
@@ -29,4 +29,8 @@ class SuggestedTopicSerializer < ListableTopicSerializer
   def featured_link
     object.featured_link
   end
+
+  def include_featured_link_root_domain?
+    SiteSetting.topic_featured_link_enabled && object.featured_link
+  end
 end

spec/serializers/suggested_topic_serializer_spec.rb

@@ -0,0 +1,35 @@
+require 'rails_helper'
+
+describe SuggestedTopicSerializer do
+  let(:user) { Fabricate(:user) }
+
+  describe '#featured_link and #featured_link_root_domain' do
+    let(:featured_link) { 'http://meta.discourse.org' }
+    let(:topic) { Fabricate(:topic, featured_link: featured_link, category: Fabricate(:category, topic_featured_link_allowed: true)) }
+    subject(:json) { described_class.new(topic, scope: Guardian.new(user), root: false).as_json }
+
+    context 'when topic featured link is disable' do
+      before do
+        SiteSetting.topic_featured_link_enabled = true
+        topic
+        SiteSetting.topic_featured_link_enabled = false
+      end
+
+      it 'should not return featured link attrs' do
+        expect(json[:featured_link]).to eq(nil)
+        expect(json[:featured_link_root_domain]).to eq(nil)
+      end
+    end
+
+    context 'when topic featured link is enabled' do
+      before do
+        SiteSetting.topic_featured_link_enabled = true
+      end
+
+      it 'should return featured link attrs' do
+        expect(json[:featured_link]).to eq(featured_link)
+        expect(json[:featured_link_root_domain]).to eq('discourse.org')
+      end
+    end
+  end
+end