I do something similar to the unique id plugin you found, but I do it manually. What I do is that I create a text field in each row, then I create a filter for this field to make it read only. Then I generate a value for this field, I generally do this in JavaScript but it can be done using an acf/save_post filter. The main issue with doing it based on the number of rows but if I had to… assuming that new fields can be added and fields can be moved.
add_action('acf/save_post', 'repeater_unique_row_id_on_count');
function repeater_unique_row_id_on_count($post_id) {
if (have_rows('your-repeater-field')) }
// first loop over repeater to get existing IDs
$existing_ids = array();
while (have_rows('your-repeater-field')) {
the_row();
if (get_sub_field('your-id-field')) {
// note that this field should be a read only field
// you could also hide this field using custom admin CSS
$existing_ids[] = intval(get_sub_field('your-id-field');
}
} // when while have_rows
// you may need to reset rows, I don't know, next line may not be needed
reset_rows()
// second loop to set any missing IDs
$count = 1;
while (have_rows('your-repeater-field')) {
the_row();
if (!get_sub_field('your-id-field')) {
// id field is empty
while (in_array($count, $existing_ids)) {
// inc count until it does not already exist
// this will cause count to skip anything that exists
$count++;
} // end while
// record ID and update sub fiele
$existing_ids[] = $count;
update_sub_field('your-id-field', $count);
} // end if empty id
} // end while have_rows
} // end if have_rows
} // end function
