Error

The error occurs because the 2018 edition of The Rust Programming Language is no longer distributed with Rust's documentation, and links to it now redirect to the current version or an archived copy from Rust 1.30. To access the content, use the current version of the book at https://doc.rust-lang.org/stable/book/ or the archived 2018 edition at https://doc.rust-lang.org/1.30.0/book/2018-edition/.

https://doc.rust-lang.org/stable/book/
https://doc.rust-lang.org/1.30.0/book/2018-edition/

The old version of the Rust book (2018 edition) is no longer included with new Rust installations. It's like an old software manual that was replaced by a newer one. You can still read the old version online at a special archive link, or just use the current version which has all the same concepts updated for modern Rust.