{"ast_node_type":"other","tokens":[{"end":68,"kind":"keyword","start":0,"text":"pub"}]}
    pub arm_usefulness: Vec<(MatchArm<'p, Cx>, Usefulness<'p, Cx>)>,
    /// For each arm of the input, whether that arm is useful after the arms above it.
    /// If the match is exhaustive, this is empty. If not, this contains witnesses for the lack of