{"ast_node_type":"variable","tokens":[{"end":43,"kind":"keyword","start":0,"text":"let"}]}
    let span = cx.with_def_site_ctxt(span);
    // Generate statement `let _: assert_path<ty>;`.
    let assert_path = cx.path_all(span, true, cx.std_path(assert_path), vec![GenericArg::Type(ty)]);