Function absent_for

pub fn absent_for(
    catalog: &Catalog,
    held: &Sources,
    aside: &[SetAside],
    artist_id: Id,
) -> usize

How many records one artist has that this shelf does not.

For a page to say so at the moment somebody is looking at that artist — which is the moment they wonder. aede missing was in the help, in the README and in the manual, and still could not be found, because it was named nowhere near the question it answers. The same fault aede extract had, and the same fix.

Derived like everything else here: nothing is stored, so the number falls the day an album is added.