{"ast_node_type":"function","tokens":[{"end":67,"kind":"keyword","start":0,"text":"r#\"fn"}]}
            r#"fn f(x: &mut Vec<$0impl Iterator<Item = i32>>) {}"#,
            introduce_named_type_parameter,
            r#"fn f<$0I: Iterator<Item = i32>>(x: &mut Vec<I>) {}"#,