{"ast_node_type":"function","tokens":[{"end":88,"kind":"keyword","start":0,"text":"//"}]}
            // The closure fn is a `fn(&self, ...)`, but we want a `fn(&mut self, ...)`.
        (ty::ClosureKind::Fn, ty::ClosureKind::FnMut) => {
            // At codegen time, these are basically the same, so we can just return the closure.