{"ast_node_type":"other","tokens":[{"end":64,"kind":"keyword","start":0,"text":"impl<'tcx>"}]}
impl<'tcx> ToTrace<'tcx> for ty::PolyExistentialTraitRef<'tcx> {
    fn to_trace(cause: &ObligationCause<'tcx>, a: Self, b: Self) -> TypeTrace<'tcx> {