{"ast_node_type":"other","tokens":[{"end":29,"kind":"keyword","start":0,"text":"#[rustc_lint_diagnostics]"}]}
    #[rustc_lint_diagnostics]
    /// This is like [`Diag::help()`], but it's only printed once.
    pub fn help_once(&mut self, msg: impl Into<SubdiagMessage>) -> &mut Self {