Are semicolons optional in Rust?

Question

Since semicolons are apparently optional in Rust, why, if I do this:

fn fn1() -> i32 {    
    let a = 1
    let b = 2
    3
}

I get the

Answer 1

Semicolons are generally not optional, but there are a few situations where they are. Namely after control expressions like for, if/else, match, etc.

fn main() {
    let a: u32 = 5;
    if 5 == a {
        println!("Hello!");
    }
    if 5 == a {
        println!("Hello!");
    };
    for x in "World".chars() {
        println!("{}", x);
    }
    for x in "World".chars() {
        println!("{}", x);
    };
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=1bf94760dccae285a2bdc9c44e8f658a

(There are situations where you do need to have or not have semicolons for these statements. If you're returning the value from within you can't have a semicolon, and if you're setting a variable to be the value from within you'll need a semicolon.)