{"ast_node_type":"variable","tokens":[{"end":52,"kind":"keyword","start":0,"text":"let"}]}
                let var = self.table.new_type_var();
                    .map_ref(|its| its.impl_traits[idx].bounds.map_ref(|it| it.iter()));
                let var_subst = Substitution::from1(Interner, var.clone());