FIX: Include more_topic_url in the response to /categories_and_{latest, top} (#21738)

The field more_topic_url is already included in the response preloaded in categories#index

However this field was missing if a request was subsequently made to update the page using
the end-points /categories_and_latest or /categories_and_top. This could lead the client
app to display incorrect information if it relied on this information to update the UI.

app/controllers/categories_controller.rb

@@ -327,11 +327,16 @@ class CategoriesController < ApplicationController
 
     if topics_filter == :latest
       result.topic_list = TopicQuery.new(current_user, topic_options).list_latest
+      result.topic_list.more_topics_url =
+        url_for(
+          public_send("latest_path", sort: topic_options[:order] == "created" ? :created : nil),
+        )
     elsif topics_filter == :top
       result.topic_list =
         TopicQuery.new(current_user, topic_options).list_top_for(
           SiteSetting.top_page_default_timeframe.to_sym,
         )
+      result.topic_list.more_topics_url = url_for(public_send("top_path"))
     end
 
     render_serialized(result, CategoryAndTopicListsSerializer, root: false)

spec/requests/categories_controller_spec.rb

@@ -244,6 +244,23 @@ RSpec.describe CategoriesController do
             [topic1.id, topic3.id, topic2.id],
           )
         end
+
+        it "does not include the sort parameter in more_topics_url" do
+          # we need to create more topics for more_topics_url to be serialized
+          SiteSetting.categories_topics = 5
+          Fabricate.times(
+            5,
+            :topic,
+            category: category,
+            created_at: 1.day.ago,
+            bumped_at: 1.day.ago,
+          )
+
+          get "/categories_and_latest.json"
+          expect(response.status).to eq(200)
+          expect(response.parsed_body["topic_list"]["more_topics_url"]).to start_with("/latest")
+          expect(response.parsed_body["topic_list"]["more_topics_url"]).not_to include("sort")
+        end
       end
 
       context "when order is set to created" do
@@ -258,6 +275,23 @@ RSpec.describe CategoriesController do
             [topic3.id, topic2.id, topic1.id],
           )
         end
+
+        it "includes the sort parameter in more_topics_url" do
+          # we need to create more topics for more_topics_url to be serialized
+          SiteSetting.categories_topics = 5
+          Fabricate.times(
+            5,
+            :topic,
+            category: category,
+            created_at: 1.day.ago,
+            bumped_at: 1.day.ago,
+          )
+
+          get "/categories_and_latest.json"
+          expect(response.status).to eq(200)
+          expect(response.parsed_body["topic_list"]["more_topics_url"]).to start_with("/latest")
+          expect(response.parsed_body["topic_list"]["more_topics_url"]).to include("sort=created")
+        end
       end
     end
 
@@ -885,6 +919,25 @@ RSpec.describe CategoriesController do
       ).not_to include(uncategorized.id)
     end
 
+    it "includes more_topics_url in the response to /categories_and_latest" do
+      SiteSetting.categories_topics = 5
+
+      get "/categories_and_latest.json"
+      expect(response.status).to eq(200)
+      expect(response.parsed_body["topic_list"]["more_topics_url"]).to start_with("/latest")
+    end
+
+    it "includes more_topics_url in the response to /categories_and_top" do
+      SiteSetting.categories_topics = 5
+
+      Fabricate.times(10, :topic, category: category, like_count: 1000, posts_count: 100)
+      TopTopic.refresh!
+
+      get "/categories_and_top.json"
+      expect(response.status).to eq(200)
+      expect(response.parsed_body["topic_list"]["more_topics_url"]).to start_with("/top")
+    end
+
     describe "Showing top topics from private categories" do
       it "returns the top topic from the private category when the user is a member" do
         restricted_group = Fabricate(:group)