FIX: Suggested topic links to nested replies topics (#40302)

Fixes bug reported here ->
https://meta.discourse.org/t/link-to-nested-topic-in-my-suggested-topics-doesnt-work/403743?u=markvanlan

app/serializers/suggested_topic_serializer.rb

@@ -16,6 +16,7 @@ class SuggestedTopicSerializer < ListableTopicSerializer
              :category_id,
              :featured_link,
              :featured_link_root_domain,
+             :is_nested_view,
              :op_like_count
   has_many :posters, serializer: SuggestedPosterSerializer, embed: :objects
 
@@ -38,4 +39,12 @@ class SuggestedTopicSerializer < ListableTopicSerializer
   def include_featured_link_root_domain?
     SiteSetting.topic_featured_link_enabled && object.featured_link
   end
+
+  def is_nested_view
+    true
+  end
+
+  def include_is_nested_view?
+    object.nested_view?
+  end
 end

lib/suggested_topics_builder.rb

@@ -22,6 +22,7 @@ class SuggestedTopicsBuilder
       results = results.where(category_id: @category_id)
     end
 
+    results = results.includes(:nested_topic) if SiteSetting.nested_replies_enabled
     results = results.to_a
     results.reject! { |topic| @category_topic_ids.include?(topic.id) }
 

spec/serializers/suggested_topic_serializer_spec.rb

@@ -77,4 +77,23 @@ RSpec.describe SuggestedTopicSerializer do
       expect(json[:op_like_count]).to eq(5)
     end
   end
+
+  describe "#is_nested_view" do
+    before { SiteSetting.nested_replies_enabled = true }
+
+    it "returns true when the topic uses nested replies" do
+      topic = Fabricate(:topic)
+      Fabricate(:nested_topic, topic: topic)
+
+      json = SuggestedTopicSerializer.new(topic, scope: Guardian.new(user), root: false).as_json
+      expect(json[:is_nested_view]).to eq(true)
+    end
+
+    it "omits the attribute when the topic uses the flat view" do
+      topic = Fabricate(:topic)
+
+      json = SuggestedTopicSerializer.new(topic, scope: Guardian.new(user), root: false).as_json
+      expect(json).not_to have_key(:is_nested_view)
+    end
+  end
 end