{"ast_node_type":"variable","tokens":[{"end":100,"kind":"keyword","start":0,"text":"let"}]}
    let preamble = format!("//! Generated by `cargo xtask codegen {cg}`, do not edit by hand.\n\n");
fn add_preamble(cg: CodegenType, mut text: String) -> String {
    text.insert_str(0, &preamble);