A reliable hack that I used was to hook into ‘acf/pre_render_fields’ filter which allows you to modify the fields before they are rendered. There you can attach the $post_id to the field itself, then when it comes to rendering it, you can access it on the field.
Crude example
add_filter('acf/pre_render_fields', function($fields, $post_id) {
return array_map(function($field) use ($post_id) {
$field['my_post_id'] = $post_id;
return $field;
), $fields};
}, 10, 2);
add_action('acf/render_field', function($field) {
echo $field['my_post_id'];
});
Yuk, I know! You’ll have to make the function recursive if you want to get to sub fields.
