Function resolve_type_ref_in 

pub fn resolve_type_ref_in(
    r: &TypeRef,
    types: &HashMap<String, TypeDecl>,
    vars: &HashSet<String>,
) -> Option<Ty>

v0.20a: like resolve_type_ref, with a set of in-scope type parameters: a Named reference matching one resolves to Ty::Var (checked before the type-table lookup — a type parameter shadows a same-named declaration; the collision is diagnosed at the declaration).