FIX: Incorrect topic tracking state count when a new category is created (#20506)

What is the problem?

We have a hidden site setting `show_category_definitions_in_topic_lists`
which is set to false by default. What this means is that category
definition topics are not shown in the topic list by default. Only the
category definition topic for the category being viewed will be shown.
However, we have a bug where we would show that a category has new
topics when a new child category along with its category definition
topic is created even though the topic list does not list the child
category's category definition topic.

What is the fix here?

This commit fixes the problem by shipping down an additional
`is_category_topic` attribute in `TopicTrackingStateItemSerializer` when
the `show_category_definitions_in_topic_lists` site setting has been set
to false. With the new attribute, we can then exclude counting child
categories' category definition topics when counting new and unread
counts for a category.

app/assets/javascripts/discourse/app/models/topic-tracking-state.js

@@ -582,6 +582,14 @@ const TopicTrackingState = EmberObject.extend({
         return false;
       }
 
+      if (
+        categoryId &&
+        topic.is_category_topic &&
+        categoryId !== topic.category_id
+      ) {
+        return false;
+      }
+
       if (tagId && !topic.tags?.includes(tagId)) {
         return false;
       }

app/models/topic_tracking_state.rb

@@ -388,6 +388,13 @@ class TopicTrackingState
         new_filter_sql
       end
 
+    category_topic_id_column_select =
+      if SiteSetting.show_category_definitions_in_topic_lists
+        ""
+      else
+        "c.topic_id AS category_topic_id,"
+      end
+
     select_sql =
       select ||
         "
@@ -398,6 +405,7 @@ class TopicTrackingState
            #{highest_post_number_column_select(whisperer)},
            last_read_post_number,
            c.id as category_id,
+           #{category_topic_id_column_select}
            tu.notification_level,
            us.first_unread_at,
            GREATEST(

app/serializers/topic_tracking_state_item_serializer.rb

@@ -6,6 +6,7 @@ class TopicTrackingStateItemSerializer < ApplicationSerializer
              :last_read_post_number,
              :created_at,
              :category_id,
+             :is_category_topic,
              :notification_level,
              :created_in_new_period,
              :treat_as_new_topic_start_date,
@@ -19,4 +20,12 @@ class TopicTrackingStateItemSerializer < ApplicationSerializer
   def include_tags?
     object.respond_to?(:tags)
   end
+
+  def is_category_topic
+    object.topic_id == object.category_topic_id
+  end
+
+  def include_is_category_topic?
+    object.respond_to?(:category_topic_id)
+  end
 end

config/site_settings.yml

@@ -2564,6 +2564,7 @@ uncategorized:
   show_category_definitions_in_topic_lists:
     default: false
     hidden: true
+    client: true
 
   create_revision_on_bulk_topic_moves:
     default: true

spec/system/page_objects/components/topic_list.rb

@@ -3,10 +3,15 @@
 module PageObjects
   module Components
     class TopicList < PageObjects::Components::Base
-      TOPIC_LIST_BODY_CLASS = ".topic-list-body"
+      TOPIC_LIST_BODY_SELECTOR = ".topic-list-body"
+      TOPIC_LIST_ITEM_SELECTOR = "#{TOPIC_LIST_BODY_SELECTOR} .topic-list-item"
 
       def topic_list
-        TOPIC_LIST_BODY_CLASS
+        TOPIC_LIST_BODY_SELECTOR
+      end
+
+      def has_topics?(count:)
+        page.has_css?(TOPIC_LIST_ITEM_SELECTOR, count: count)
       end
 
       def has_topic?(topic)
@@ -18,13 +23,13 @@ module PageObjects
       end
 
       def visit_topic_with_title(title)
-        find(".topic-list-body a", text: title).click
+        find("#{TOPIC_LIST_BODY_SELECTOR} a", text: title).click
       end
 
       private
 
       def topic_list_item_class(topic)
-        "#{TOPIC_LIST_BODY_CLASS} .topic-list-item[data-topic-id='#{topic.id}']"
+        "#{TOPIC_LIST_ITEM_SELECTOR}[data-topic-id='#{topic.id}']"
       end
     end
   end

spec/system/page_objects/pages/category.rb

@@ -58,6 +58,20 @@ module PageObjects
         find(".select-kit-collection .select-kit-row", text: template_name).click
         find(".select-category-template").click
       end
+
+      CATEGORY_NAVIGATION_NEW_NAV_ITEM_SELECTOR = ".category-navigation .nav-item_new"
+
+      def has_no_new_topics?
+        page.has_no_css?(CATEGORY_NAVIGATION_NEW_NAV_ITEM_SELECTOR)
+      end
+
+      def has_new_topics?
+        page.has_css?(CATEGORY_NAVIGATION_NEW_NAV_ITEM_SELECTOR)
+      end
+
+      def click_new
+        page.find(CATEGORY_NAVIGATION_NEW_NAV_ITEM_SELECTOR).click
+      end
     end
   end
 end

spec/system/viewing_category_spec.rb

@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+RSpec.describe "Viewing a category", type: :system, js: true do
+  fab!(:category) { Fabricate(:category) }
+  fab!(:user) { Fabricate(:user) }
+  let(:category_page) { PageObjects::Pages::Category.new }
+  let(:topic_list) { PageObjects::Components::TopicList.new }
+
+  describe "when a new child category is created with a new category topic" do
+    fab!(:child_category) { Fabricate(:category, parent_category: category) }
+
+    fab!(:child_category_topic) do
+      Fabricate(:topic, category: child_category).tap do |topic|
+        child_category.update!(topic: topic)
+      end
+    end
+
+    it "should show a new count on the parent and child category when 'show_category_definitions_in_topic_lists' is true" do
+      SiteSetting.show_category_definitions_in_topic_lists = true
+
+      sign_in(user)
+
+      category_page.visit(category)
+      category_page.click_new
+
+      expect(topic_list).to have_topics(count: 1)
+      expect(topic_list).to have_topic(child_category_topic)
+
+      category_page.visit(child_category)
+      category_page.click_new
+
+      expect(topic_list).to have_topics(count: 1)
+      expect(topic_list).to have_topic(child_category_topic)
+    end
+
+    it "should only show a new count on the child category when 'show_category_definitions_in_topic_lists' site setting is false" do
+      SiteSetting.show_category_definitions_in_topic_lists = false
+
+      sign_in(user)
+
+      category_page.visit(category)
+
+      expect(category_page).to have_no_new_topics
+
+      category_page.visit(child_category)
+
+      expect(category_page).to have_new_topics
+
+      category_page.click_new
+
+      expect(topic_list).to have_topics(count: 1)
+      expect(topic_list).to have_topic(child_category_topic)
+    end
+  end
+end