add_index_length

# File activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb, line 194
          def add_index_length(quoted_columns, **options)
            lengths = options_for_index_columns(options[:length])
            quoted_columns.each do |name, column|
              column << "(#{lengths[name]})" if lengths[name].present?
            end
          end