How can I change the selectable years in a date field?

Question

I have a date field, birthday, created with the Date module. By default, the selectable years are 1900-2050. This makes no sense for birthdays so I want to change it to only show years from 1900-(current year-18).

How can I do this?

There is a solution for Drupal 7 but that code does not work in Drupal 8 because form_process_date() does not exist in Drupal 8.

This is the full error:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'form_process_date' not found or invalid function name in Drupal\Core\Form\FormBuilder->doBuildForm() (line 993 of core/lib/Drupal/Core/Form/FormBuilder.php).

Here is the code I'm using:

function mymodule_form_user_register_form_alter(&$form, &$form_state, $form_id) {
  $form['account']['birthday']['#process'] = array('form_process_date', 'mymodule_fix_year_range');

Answer 1

Datelist widget accepts relative values using + or -. You can set 1950:-18 as #date_year_range. Which will create options from 1950 to 18 years before the current year.

Answer 2

@mpdonadio♦'s answer provides the explanation. Here is the actual code I used:

function mymodule_form_user_register_form_alter(&$form, &$form_state, $form_id) {
  $form['field_birthday']['widget'][0]['value']['#date_year_range'] = '1950:2005';

Answer 3

You shouldn't need to add a #process to this.

The Select List widget is based around the Datelist element.

Per the docs (and I don't know why the are on that method and not ::getInfo(). You should be able to form alter this, and change the '#date_year_range' key. This is a string value, which defaults to '1900:2050' (min-year:max-year). You would just need to have some logic to build it up in the proper format.