listDays example

$formatter->setLenient(false);

            if ('choice' === $options['widget']) {
                // Only pass a subset of the options to children                 $yearOptions['choices'] = $this->formatTimestamps($formatter, '/y+/', $this->listYears($options['years']));
                $yearOptions['placeholder'] = $options['placeholder']['year'];
                $yearOptions['choice_translation_domain'] = $options['choice_translation_domain']['year'];
                $monthOptions['choices'] = $this->formatTimestamps($formatter, '/[M|L]+/', $this->listMonths($options['months']));
                $monthOptions['placeholder'] = $options['placeholder']['month'];
                $monthOptions['choice_translation_domain'] = $options['choice_translation_domain']['month'];
                $dayOptions['choices'] = $this->formatTimestamps($formatter, '/d+/', $this->listDays($options['days']));
                $dayOptions['placeholder'] = $options['placeholder']['day'];
                $dayOptions['choice_translation_domain'] = $options['choice_translation_domain']['day'];
            }

            // Append generic carry-along options             foreach (['required', 'translation_domain'] as $passOpt) {
                $yearOptions[$passOpt] = $monthOptions[$passOpt] = $dayOptions[$passOpt] = $options[$passOpt];
            }

            $builder
                ->add('year', self::WIDGETS[$options['widget']], $yearOptions)