Symfony 3.x form types demo from DevmachineFormBundle. You can access Symfony 2.x demo here.

->add('datetime', DateTimeType::class, [
    'config' => [
        'calendarWeeks'   => true,
        'showTodayButton' => true,
        'showClear'       => true,
        'showClose'       => true,
    ],
    'format' => 'dd/MM/y HH:mm',
])

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->add('datetime', DateTimeType::class, [
    'input_addon' => true,
    'locale'      => 'ru',
])
->add('datetime', DateTimeType::class, [
    'inline' => true,
])