#[tailcall] macro panics

[fosskers]

Hi there, trying to test out the library, although it seems to be panicking. Here's the code I'm testing:

use std::path::Path;

#[tailcall::tailcall]
fn recurse(n: u64) -> u64 {
    let file = Path::new("src/main.rs");
    let len = file.metadata().unwrap().len();

    if n >= 1_000_000_000 {
        n
    } else {
        recurse(len + n)
    }
}

fn main() {
    let res = recurse(1);

    println!("Done: {res}");
}

The compiler tells me:

error: custom attribute panicked
 --> src/main.rs:3:1
  |
3 | #[tailcall::tailcall]
  | ^^^^^^^^^^^^^^^^^^^^^
  |
  = help: message: expected tuple expression

Strangely, the message expected tuple expression can't be found in this repo, so is that coming from Rust itself? Thank you kindly.

[fosskers]

Hi there, any thoughts on this?

[alecdotninja]

There seems to be a bug affecting functions with only a single argument. 🙃

Until I get more time to look into this issue, you can work around the problem by adding a second dummy argument:

use std::path::Path;

#[tailcall::tailcall]
fn recurse(n: u64, _d: ()) -> u64 {
    let file = Path::new("src/main.rs");
    let len = file.metadata().unwrap().len();

    if n >= 1_000_000_000 {
        n
    } else {
        recurse(len + n, ())
    }
}


fn main() {
    let res = recurse(1, ());

    println!("Done: {res}");
}