DEV: Add preload API to CategoryList (#20778)

app/models/category_list.rb

@@ -8,6 +8,21 @@ class CategoryList
 
   attr_accessor :categories, :uncategorized
 
+  def self.on_preload(&blk)
+    (@preload ||= Set.new) << blk
+  end
+
+  def self.cancel_preload(&blk)
+    if @preload
+      @preload.delete blk
+      @preload = nil if @preload.length == 0
+    end
+  end
+
+  def self.preload(category_list)
+    @preload.each { |preload| preload.call(category_list) } if @preload
+  end
+
   def initialize(guardian = nil, options = {})
     @guardian = guardian || Guardian.new
     @options = options
@@ -111,7 +126,11 @@ class CategoryList
         :uploaded_logo_dark,
         :topic_only_relative_url,
         subcategories: [:topic_only_relative_url],
-      ).secured(@guardian)
+      )
+
+    CategoryList.preload(self)
+
+    @categories = @categories.secured(@guardian)
 
     @categories =
       @categories.where(

spec/models/category_list_spec.rb

@@ -12,6 +12,21 @@ RSpec.describe CategoryList do
   fab!(:admin) { Fabricate(:admin) }
   let(:category_list) { CategoryList.new(Guardian.new(user), include_topics: true) }
 
+  describe "preload" do
+    it "allows preloading of data" do
+      preloaded_list = nil
+      preloader = lambda { |view| preloaded_list = view }
+
+      CategoryList.on_preload(&preloader)
+
+      expect(preloaded_list).to eq(nil)
+      category_list
+      expect(preloaded_list).to eq(preloaded_list)
+
+      CategoryList.cancel_preload(&preloader)
+    end
+  end
+
   describe "security" do
     it "properly hide secure categories" do
       cat = Fabricate(:category_with_definition)