Compile error mixing declarative macros with #[tokio::test]

[incidental-complexity]

This is reproducible in the playground:

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=fb6d73cfb878547b438d8ec49431a4d2

concrete_tests2 and concrete_tests3 compile whereas concrete_tests1 does not.

I'm producing a declarative macro that takes in an expr that is meant to be a closure, and produces a #[tokio::test] that invokes that closure. The compile error is:

error[E0618]: expected function, found `Concrete`
  --> src/lib.rs:38:32
   |
14 |             $crate::test_suite::async_test($foo_factory()).await;
   |                                                        -- call expression requires function
...
38 |     crate::use_test_suite!( || crate::Concrete::default() );
   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to previous error

The code (from the playground link above) is:

// /////////////////////////
// Define a trait Foo 
// /////////////////////////
pub trait Foo{}

// /////////////////////////
// Define a test suite suitable for any implementator of Foo
// /////////////////////////
#[macro_export]
macro_rules! use_test_suite {
    ($foo_factory:expr) => {
        #[tokio::test]
        async fn async_test() {
            $crate::test_suite::async_test($foo_factory()).await;
        }
            
        #[test]
        fn sync_test() {
            $crate::test_suite::sync_test($foo_factory());
        }
    }
}

pub mod test_suite {
    pub async fn async_test(_foo: impl crate::Foo) -> u8 { 0 }
    pub fn sync_test(_foo: impl crate::Foo) -> u8 { 0 }
}

// /////////////////////////
// Define an implementaion of Foo and test it
// /////////////////////////
#[derive(Default)]
struct Concrete;
impl Foo for Concrete {}

#[cfg(test)]
mod concrete_tests1 {
    crate::use_test_suite!( || crate::Concrete::default() );
}

#[cfg(test)]
mod concrete_tests2 {
    crate::use_test_suite!( (|| crate::Concrete::default()) );
}

#[cfg(test)]
mod concrete_tests3 {
    crate::use_test_suite!( crate::Concrete::default );
}

[Darksonn]

I strongly doubt Tokio can do anything about this. You can fix it with an extra set of parenthesises.

#[tokio::test]
async fn async_test() {
    $crate::test_suite::async_test(($foo_factory)()).await;
}

[incidental-complexity]

Cross posted with rust-lang

[carllerche]

Thoughts @taiki-e ?

[taiki-e]

Looks like this is a regression introduced in Rust 1.49.0 (it works with all versions of 1.45 to 1.48.), see rust-lang/rust#82784 (comment) for more.