Function encode_def_ids 

pub(crate) fn encode_def_ids<'tcx, K: Eq + Hash + Copy>(
    genv: GlobalEnv<'_, 'tcx>,
    def_ids: impl IntoIterator<Item = DefId>,
    tables: &mut Tables<'tcx, K>,
    did_to_key: fn(DefId) -> K,
    assoc_id_to_key: fn(FluxDefId) -> FluxId<K>,
)