class Cucumber::CucumberExpressions::CucumberExpression

def process_optional(expression)
  # Create non-capturing, optional capture groups from parenthesis
  expression.gsub(OPTIONAL_REGEXP) do
    g2 = $2
    # When using Parameter Types, the () characters are used to represent an optional
    # item such as (a ) which would be equivalent to (?:a )? in regex
    #
    # You cannot have optional Parameter Types i.e. ({int}) as this causes
    # problems during the conversion phase to regex. So we check for that here
    #
    # One exclusion to this rule is if you actually want the brackets i.e. you
    # want to capture (3) then we still permit this as an individual rule
    # See: https://github.com/cucumber/cucumber-ruby/issues/1337 for more info
    # look for double-escaped parentheses
    if $1 == DOUBLE_ESCAPE
      "\\(#{g2}\\)"
    else
      check_no_parameter_type(g2, PARAMETER_TYPES_CANNOT_BE_OPTIONAL)
      "(?:#{g2})?"
    end
  end
end