Jekyll liquid tag for creating atom ids for atom feeds

atom_id.rb

module Jekyll
  module AtomId
    # from http://diveintomark.org/archives/2004/05/28/howto-atom-id
    def atom_id(post)
      "#{post["date"].strftime("%Y-%m-%d")}:#{post["date"].to_i}"
    end
  end
end

Liquid::Template.register_filter(Jekyll::AtomId)

Hmm, I never considered if this would work with multiple posts on the same day...