Unable to save list (integer) field if 0 is used as value and field has data

In Drupal core changes are made on on 11.x (our main development branch) first, and are then back ported as needed according to the Core change policies → . Also mentioned on the version → section of the list of issue fields documentation. Thanks.

I think changing to 'readonly' could do the trick, but users will be confused why the field cannot be edited (is does not have the 'disabled' style in the end)

I was taking a look at what causes the field to be validated, is within the 'FormValidator.php' class in \Drupal\Core\Form\ namespace
if we see line 261

$is_empty_value = ($elements['#value'] === 0);

and when the field is disabled, #value contains 0 (int) while is not disabled, #value contains '0' (string)
So maybe we need to check also within that function that the field is not disabled (aka, there is no '#attributes') when the element is required within that same function...
Maybe

$is_empty_value = ($elements['#value'] === 0 && !isset($elements['#attributes']['disabled']));

But i am not core expert...

I agree with @gorkagr that using readonly does not visually indicate that the value field is non-editable, which can be confusing to users. Therefore, I updated the code as suggested in comment #5.

With this change, the value field is correctly disabled, and I am able to update the label or add a new item without encountering validation errors. I have attached screenshots demonstrating the behavior with both the readonly and disabled attributes for comparison.

abhijith s → made their first commit to this issue’s fork.