demarches-normaliennes/app/validators/expression_reguliere_validator.rb

class ExpressionReguliereValidator < ActiveModel::Validator
  def validate(record)
    if record.value.present?
      if !record.value.match?(Regexp.new(record.expression_reguliere, timeout: 5.0))
        record.errors.add(:value, :invalid_regexp)
      end
    end
  rescue Regexp::TimeoutError
    record.errors.add(:expression_reguliere, :evil_regexp)
  end
end