FEATURE: allow to extend topic_eager_loads in Search (#10625)

This additional interface is required by encrypt plugin

lib/plugin/instance.rb

@@ -206,6 +206,17 @@ class Plugin::Instance
     Search.advanced_filter(trigger, &block)
   end
 
+  # Allow to eager load additional tables in Search. Useful to avoid N+1 performance problems.
+  # Example usage:
+  #   register_search_topic_eager_load do |opts|
+  #     %i(example_table)
+  #   end
+  # OR
+  #   register_search_topic_eager_load(%i(example_table))
+  def register_search_topic_eager_load(tables = nil, &block)
+    Search.custom_topic_eager_load(tables, &block)
+  end
+
   # Request a new size for topic thumbnails
   # Will respect plugin enabled setting is enabled
   # Size should be an array with two elements [max_width, max_height]

lib/search.rb

@@ -297,6 +297,14 @@ class Search
     @advanced_filters
   end
 
+  def self.custom_topic_eager_load(tables = nil, &block)
+    (@custom_topic_eager_loads ||= []) << (tables || block)
+  end
+
+  def self.custom_topic_eager_loads
+    Array.wrap(@custom_topic_eager_loads)
+  end
+
   advanced_filter(/^in:personal-direct$/) do |posts|
     if @guardian.user
       posts
@@ -1194,11 +1202,13 @@ class Search
       topic_eager_loads << :tags
     end
 
+    Search.custom_topic_eager_loads.each do |custom_loads|
+      topic_eager_loads.concat(custom_loads.is_a?(Array) ? custom_loads : custom_loads.call(search_pms: @search_pms).to_a)
+    end
+
     query.includes(topic: topic_eager_loads)
   end
 
-  private
-
   # Limited for performance reasons since `TS_HEADLINE` is slow when the text
   # document is too long.
   MAX_LENGTH_FOR_HEADLINE = 2500