Ambiguous macro call

[iluuu1994]

The guide says right here:

Error: some fatal error has occurred in the parser. For example, this happens if there are more than one pattern match, since that indicates the macro is ambiguous.

This seems not to be the case.

macro_rules! times {
    (a b) => (5000);
    ($x:ident b) => ($x * $x);
    ($x:ident $y:ident) => ($x * $y);
}

fn main() {
    dbg!(times!(a b));
}

Output: 5000

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=bf361f3a9a5ab6fd4d4d30b6d9ae2365

Rust just chooses the first pattern that matches. In fact, you can use the exact same pattern twice and the Rust compiler won't complain.

macro_rules! times {
    (a b) => (5000);
    (a b) => (10000);
}

fn main() {
    dbg!(times!(a b));
}

Output: 5000

Am I misunderstanding the description or is the description wrong?

[mark-i-m]

Hmm... I didn't realize you could do that. It seems that the check is not complete. Many of the checks on macros are not complete.