{"ast_node_type":"variable","tokens":[{"end":89,"kind":"keyword","start":0,"text":"let"}]}
        let parent_subst = parent_subst.unwrap_or_else(|| Substitution::empty(Interner));
    ) -> Self {
        Self { data, vec: SmallVec::with_capacity(param_kinds.len()), param_kinds, parent_subst }