issue-92074-macro-ice.rs

pub enum En {
    A(Vec<u8>)
}

fn get_usize() -> usize {
    0
}

macro_rules! force_expr {
    ($e:expr) => { $e }
}

macro_rules! force_pat {
    ($a:expr, $b:expr) => { $a..=$b }
}

macro_rules! make_vec {
    () => { force_expr!(Vec::new()) } //~ ERROR arbitrary expressions aren't allowed
}

macro_rules! make_pat {
    () => { force_pat!(get_usize(), get_usize()) }
    //~^ ERROR arbitrary expressions aren't allowed
    //~| ERROR arbitrary expressions aren't allowed
}

#[allow(unreachable_code)]
fn f() -> Result<(), impl core::fmt::Debug> {
    let x: En = loop {};

    assert!(matches!(x, En::A(make_vec!())));
    assert!(matches!(5, make_pat!()));
    Ok::<(), &'static str>(())
}

fn main() {}