Function check_refs 

pub fn check_refs(
    wanted: &BTreeMap<String, String>,
    held: &BTreeMap<String, String>,
) -> RefCheck

Compares the refs a view names for one repository (wanted) with the refs a copy of it holds (held), both refname -> oid.

One direction, on purpose: every wanted ref must be held at its oid, and a held ref nobody wanted is counted in RefCheck::ahead rather than refused.