Function covers 

pub fn covers(
    new_title: &str,
    new_body: &str,
    old_title: &str,
    old_body: &str,
) -> bool

Whether an existing issue already describes this one.

The title is weighed on its own, and that is the whole change from same_subject. containment normalises by the smaller token set, so a long umbrella issue, a “known issues” list, or a tracker has a large enough vocabulary that any short finding about the same module scores as covered, and the finding is then dropped without anything being written. Requiring the titles to overlap costs a genuine duplicate nothing: two people naming one defect name the same thing.