[Rust Bug] method not found in

error[E0599]: no method named `lines` found for enum `std::result::Result<std::string::String, std::io::Error>` in the current scope
  --> src\main.rs:20:25
   |
   |                         ^^^^^ method not found in `std::result::Result<std::string::String, std::io::Error>`
error: aborting due to previous error
For more information about this error, try `rustc --explain E0599`.

你的输出或者输出，存在未处理的情况。如：

• 读文件，存在文件不可读的情况
• 转化u32, 存在不能转换的情况
• 读参数，存在参数没有的情况

加 expect 解决：

let content = std::fs::read_to_string(&args.path).expect("could not read file");
let pattern = std::env::args().nth(1).expect("no pattern given");