FEATURE: new site setting 'max_emojis_in_title'

lib/validators/max_emojis_validator.rb

@@ -0,0 +1,11 @@
+class MaxEmojisValidator < ActiveModel::EachValidator
+
+  def validate_each(record, attribute, value)
+    if Emoji.unicode_unescape(value).scan(/:([\w\-+]*(?::t\d)?):/).size > SiteSetting.max_emojis_in_title
+      record.errors.add(
+        attribute, :max_emojis,
+        max_emojis_count: SiteSetting.max_emojis_in_title
+      )
+    end
+  end
+end