{"ast_node_type":"function","tokens":[{"end":59,"kind":"keyword","start":0,"text":"pub"}]}
    pub fn fn_def(&self) -> Option<(FnDef, &GenericArgs)> {
    /// Deconstruct a function type if this is one.
        if let TyKind::RigidTy(RigidTy::FnDef(def, args)) = self {