The Comments Section of the 2nd edition doesn't mention the /* */ multi-line comment syntax:

http://rust-lang.github.io/book/second-edition/ch03-04-comments.html

It even states:

In Rust, comments must start with two slashes and continue until the end of the line. For comments that extend beyond a single line, you’ll need to include // on each line, like this:

And closes with:

That’s all there is to comments. They’re not particularly complicated.

But all this conflicts with the Rust reference:

https://doc.rust-lang.org/reference/comments.html

(which btw also mentions doc comments ...)

Rust seems to support multiline comments since 7 years:

rust-lang/rust#66