x = (let y = 6); | ^ ^ | = note: `#[warn(unused_parens)]` on by default 53/562Rust 程序设计语言 简体中文版 help: remove these parentheses | 2 - let x = (let y = 6); 2 + let x stdout ---- thread 'tests::it_sends_an_over_75_percent_warning_message' panicked at src/ lib.rs:60:53: already borrowed: BorrowMutError note: run with `RUST_BACKTRACE=1` environment variable to display