{"ast_node_type":"other","tokens":[{"end":74,"kind":"keyword","start":0,"text":"//"}]}
        // shift subsequent elements down when removing the front element.
        // allocation, at the (very small) cost of (occasionally) having to
        let mut queue: SmallVec<[PredicateObligation<'tcx>; 4]> = smallvec![Obligation::new(