Macro expansion involving identifiers in parentheses preceded by visibility is broken

[kontheocharis]

The following snippet does not expand the macro foo! correctly:

fn main() {}

macro_rules! foo {
    ($a:vis ($b:ident)) => {
        pub const X: &str = stringify!($b);
    };
}

foo!(
    pub (bar)
);

Instead of expanding to

pub const X: &str = "bar"

it expands to

pub const X: &str = "$ b"

It seems that rust-analyzer puts a space between the $ and the b before substituting the macro variables, resulting in a wrong expansion. rustc handles this expansion correctly.

rust-analyzer version: rust-analyzer version: 0.3.1641-standalone (144526c 2023-08-28) [I have also tried rust-analyzer version: 0.4.1644-standalone (3213344 2023-08-30)]
rustc version: rustc 1.74.0-nightly (84a9f4c6e 2023-08-29)

[Veykril]

The problem rather is that we parse the pub(bar) as the vis fragment (or at least more than just the pub) so we fail to match up the $b fragment. I am suprised this is allowed by rustc tbh given the ambiguity ...

[kontheocharis]

rustc seems to allow a type to appear after a visibility, and for example (bar) could be parsed as a ty, so I guess it handles it fine. Similar to above, rust-analyzer fails there too:

macro_rules! test {
    ($v:vis $x:ty, $y:expr) => {
        const X: $x = $y;
    };
}
test!(pub (usize), 0);

This emits

const X:missing =  $y;

[Veykril]

Right, given struct S(pub (usize)); is valid as well.