macro_rules! definitions with parenthesis breaks filtering by item path

[ElusiveMori]

Example:

// lib.rs
pub mod a;

// a.rs
macro_rules! b (
    () => {}
);

Running cargo expand whatever will dump the whole expanded crate.

If we change the macro to

macro_rules! b {
    () => {}
}

It will fail correctly with WARNING: no such item: asdasda

Having a macro like this anywhere in the crate will break the path resolution mechanism, for some reason, causing the path to be ignored all the time.

I'm not sure if macro_rules with parens has any rightful place to exist, but I just spent about half an hour trying to figure this one out ;-;

[ehuss]

This appears to be a bug in rustc's expander. It emits the following:

#![feature(prelude_import)]
#[prelude_import]
use std::prelude::v1::*;
#[macro_use]
extern crate std;
pub mod a {
    macro_rules! b(() => { })
}

Notice that it strips the semicolon.

[ehuss]

Posted rust-lang/rust#81888 with a fix.

[dtolnay]

Confirmed fixed as of nightly-2021-02-10 by rust-lang/rust#81888.