From time to time I stumble upon the following error message when creating a custom field type in drupal 8: "This value should be of the correct primitive type.". It occurs when I try to enable the field on a content type and is caused by the widget ... I can't even save the widget settings form.
Each time I have to search for the error - while perfectly knowing, that I already found the solution some time before ... so that's why I'm writing it here once and for all:
When creating the field widget with drupal console it produces output like this:
public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
$element['value'] = $element + [
'#type' => 'textfield',
...
];return $element;
}
Simply remove the $element + before the returning form element to solve this issue ...
public function formElement(FieldItemListInterface $items, $delta, array $element, array &$form, FormStateInterface $form_state) {
$element['value'] = [
'#type' => 'textfield',
...
];return $element;
}