Fix #4125: Detect forum and comment spam.

app/models/comment.rb

@@ -2,6 +2,7 @@ class Comment < ApplicationRecord
   include Mentionable
 
   validate :validate_creator_is_not_limited, :on => :create
+  validate :validate_comment_is_not_spam, on: :create
   validates_presence_of :body, :message => "has no content"
   belongs_to :post
   belongs_to_creator
@@ -124,6 +125,10 @@ class Comment < ApplicationRecord
     end
   end
 
+  def validate_comment_is_not_spam
+    errors[:base] << "Failed to create comment" if SpamDetector.new(self).spam?
+  end
+
   def update_last_commented_at_on_create
     Post.where(:id => post_id).update_all(:last_commented_at => created_at)
     if Comment.where("post_id = ?", post_id).count <= Danbooru.config.comment_threshold && !do_not_bump_post?