Function resolve_impl 

pub fn resolve_impl(
    trait_ref: &TraitRef,
    ty: &Type,
    impls: &ImplTable,
) -> Option<ImplId>

Find the impl block that satisfies trait_ref for ty in impls.

Performs an exact-type lookup: the type key derived from ty must match the key stored when the impl was registered. Returns None if no impl exists for the (trait, type) pair.

To verify that supertrait obligations are also satisfied, call check_supertrait_obligations on the result.