Function group_source_failure 

pub fn group_source_failure(
    field: &Value,
    path: &str,
    root: &Map<String, Value>,
) -> Option<String>

The message of the first rule that the group source of field at the declaration path breaks under the root properties, or None. The members of items are checked in declaration order, then the field, then from, the type of its field, label and then the type of its field.