rust/tests/ui/macros/macro-at-most-once-rep-2018-rpass.rs

// run-pass

#![allow(unused_mut)]

// Check that when `?` is followed by what looks like a Kleene operator (?, +, and *)
// then that `?` is not interpreted as a separator. In other words, `$(pat)?+` matches `pat +`
// or `+` but does not match `pat` or `pat ? pat`.

// edition:2018

macro_rules! foo {
    // Check for `?`.
    ($($a:ident)? ? $num:expr) => {
        foo!($($a)? ; $num);
    };
    // Check for `+`.
    ($($a:ident)? + $num:expr) => {
        foo!($($a)? ; $num);
    };
    // Check for `*`.
    ($($a:ident)? * $num:expr) => {
        foo!($($a)? ; $num);
    };
    // Check for `;`, not a kleene operator.
    ($($a:ident)? ; $num:expr) => {
        let mut x = 0;

        $(
            x += $a;
        )?

        assert_eq!(x, $num);
    };
}

pub fn main() {
    let a = 1;

    // Accept 0 repetitions.
    foo!( ; 0);
    foo!( + 0);
    foo!( * 0);
    foo!( ? 0);

    // Accept 1 repetition.
    foo!(a ; 1);
    foo!(a + 1);
    foo!(a * 1);
    foo!(a ? 1);
}