Guessing game example does not give a warning

[vkatsikaros]

The Rust book on Guessing Game - Processing a Guess says that after compiling the example we'll get a warning. However, I didn't get one:

~/projects/rust $ cargo new guessing_game_2 --bin
     Created binary (application) `guessing_game_2` project
~/projects/rust $ cd guessing_game_2/
~/projects/rust/guessing_game_2 $ cargo build
   Compiling guessing_game_2 v0.1.0 (file:///home/vag/projects/rust/guessing_game_2)
    Finished debug [unoptimized + debuginfo] target(s) in 0.52 secs
~/projects/rust/guessing_game_2 $ cargo run
    Finished debug [unoptimized + debuginfo] target(s) in 0.0 secs
     Running `target/debug/guessing_game_2`
Hello, world!
~/projects/rust/guessing_game_2 $ cat > src/main.rs 
use std::io;

fn main() {
    println!("Guess the number!");

    println!("Please input your guess.");

    let mut guess = String::new();

    io::stdin().read_line(&mut guess)
        .expect("Failed to read line");

    println!("You guessed: {}", guess);
}

~/projects/rust/guessing_game_2 $ cargo build
   Compiling guessing_game_2 v0.1.0 (file:///home/vag/projects/rust/guessing_game_2)
    Finished debug [unoptimized + debuginfo] target(s) in 0.65 secs

According to the book I expected:

src/main.rs:10:5: 10:39 warning: unused result which must be used,
#[warn(unused_must_use)] on by default
src/main.rs:10     io::stdin().read_line(&mut guess);

I installed rust via https://rustup.rs/ and I got

$ rustc --version && cargo --version
rustc 1.12.0 (3191fbae9 2016-09-23)
cargo 0.13.0-nightly (109cb7c 2016-08-19)

I am on

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 14.04.5 LTS
Release:    14.04
Codename:   trusty

[vkatsikaros]

After playing with it a bit I got the warning with this:

fn main() {
    println!("Guess the number!");
    println!("Please input your guess.");
    let mut guess = String::new();
    io::stdin().read_line(&mut guess);
    //    .expect("Failed to read line");
    //println!("You guessed: {}", guess);
}

So maybe the wording could be a bit more explanatory?

[TimNN]

The book pretty explicitly states (emphasis mine):

If we leave off calling this method, our program will compile, but we’ll get a warning:

[vkatsikaros]

Indeed, the wording is explicit, but it could be more explanatory in case my confusion was caused by my non-native English skills.

Minor wording changes like these are quite affected by personal style, so I'd understand if you don't find this useful.

[GuillaumeGomez]

I guess it can be closed now. Don't hesitate to tell me if I'm wrong.