Function rustc_resolve::late::lifetimes::insert_late_bound_lifetimes

fn insert_late_bound_lifetimes(
    map: &mut NamedRegionMap, 
    decl: &FnDecl<'_>, 
    generics: &Generics<'_>
)

Detects late-bound lifetimes and inserts them into map.late_bound.

A region declared on a fn is late-bound if:

• it is constrained by an argument type;
• it does not appear in a where-clause.

“Constrained” basically means that it appears in any type but not amongst the inputs to a projection. In other words, <&'a T as Trait<''b>>::Foo does not constrain 'a or 'b.