{"ast_node_type":"function","tokens":[{"end":68,"kind":"keyword","start":0,"text":"fn"}]}
fn opt_trait_item(tcx: TyCtxt<'_>, def_id: DefId) -> Option<DefId> {
/// If the provided DefId is a method in a trait impl, return the DefId of the method prototype.
    let impl_item = tcx.opt_associated_item(def_id)?;