{"ast_node_type":"variable","tokens":[{"end":61,"kind":"keyword","start":0,"text":"let"}]}
        let ast_id = self.source_ast_id_map.ast_id(impl_def);
    fn lower_impl(&mut self, impl_def: &ast::Impl) -> ItemTreeAstId<Impl> {
        // Note that trait impls don't get implicit `Self` unlike traits, because here they are a