Hygiene Example Typo

[BeniReydman]

What needs to be fixed?

In the Rust book under Hygiene section for the following code:

macro_rules! foo {
    ($v:ident) => (let $v = 3);
}

fn main() {
    foo!(x);
    println!("{}", x);
}

There is missing a semi-colon at the line let $v = 3 which doesn't compile in Rust Playground

Page(s) Affected

https://doc.rust-lang.org/1.7.0/book/macros.html#hygiene

[ehuss]

That link is from the 1.7 docs, which is more than 4 years old. I believe that code was valid at the time, but was changed in #34660.

The corrected, old documentation can be found at: https://doc.rust-lang.org/1.30.0/book/first-edition/macros.html#hygiene
Hygiene was removed from the new edition (https://doc.rust-lang.org/book/ch19-06-macros.html). I would guess that is because it is an advanced topic, which is covered in the reference.

cc #44687, where there really should be a version selector, and https://internals.rust-lang.org/t/adding-outdated-notices-to-archived-versions-of-documentation/12281 for the request for a bold disclaimer to indicate you are looking at outdated documentation.