Function local_traces_to_self_field 

fn local_traces_to_self_field(
    tcx: TyCtxt<'_>,
    method: DefId,
    local: Local,
    self_local: Local,
    field_index: usize,
    seen: &mut HashSet<Local>,
) -> bool

Backward-traces local through MIR assignments to check whether its value is derived from (*self_local).field_index.