Macros do not accept empty `vis` at the end of the token tree

[ChayimFriedman2]

I tried this code:

macro_rules! m {
    ( ($v:vis) ) => {};
}

fn main() {
    m!( () );
}

I expected to see this happen: the code compile successfully. The reference says vis is "a possibly empty Visibility qualifier", so it should match empty.

Instead, this happened: the code is rejected with:

error: no rules expected the token `)`
 --> src/main.rs:6:10
  |
1 | macro_rules! m {
  | -------------- when calling this macro
...
6 |     m!( () );
  |          ^ no rules expected this token in macro call
  |
note: while trying to match meta-variable `$v:vis`
 --> src/main.rs:2:8
  |
2 |     ( ($v:vis) ) => {};
  |        ^^^^^^

Playground.

@rustbot label +A-macros

[ehuss]

cc #71422