Cache Status#ancestors recursive query results (#2527)

app/models/status.rb

@@ -91,7 +91,7 @@ class Status < ApplicationRecord
   end
 
   def ancestors(account = nil)
-    ids      = (Status.find_by_sql(['WITH RECURSIVE search_tree(id, in_reply_to_id, path) AS (SELECT id, in_reply_to_id, ARRAY[id] FROM statuses WHERE id = ? UNION ALL SELECT statuses.id, statuses.in_reply_to_id, path || statuses.id FROM search_tree JOIN statuses ON statuses.id = search_tree.in_reply_to_id WHERE NOT statuses.id = ANY(path)) SELECT id FROM search_tree ORDER BY path DESC', id]) - [self]).pluck(:id)
+    ids      = Rails.cache.fetch("ancestors:#{id}") { (Status.find_by_sql(['WITH RECURSIVE search_tree(id, in_reply_to_id, path) AS (SELECT id, in_reply_to_id, ARRAY[id] FROM statuses WHERE id = ? UNION ALL SELECT statuses.id, statuses.in_reply_to_id, path || statuses.id FROM search_tree JOIN statuses ON statuses.id = search_tree.in_reply_to_id WHERE NOT statuses.id = ANY(path)) SELECT id FROM search_tree ORDER BY path DESC', id]) - [self]).pluck(:id) }
     statuses = Status.where(id: ids).group_by(&:id)
     results  = ids.map { |id| statuses[id].first }
     results  = results.reject { |status| filter_from_context?(status, account) }