Async pymethod with receiver can not pass any other arguments

[reswqa]

Bug Description

When I tried to introduce argument other than receiver(i.e. &self/&mut self) to async method, I found that the code(see Steps to Reproduce) would not compile(see the Backtrace part), even though the parameter was actually Send + 'static itself.

I'm not sure if this is by design, but it looks strange to me.

---

I'm new to the PyO3's code base, but I took a closer look.

FnType::Fn(SelfType::Receiver { mutable: false, .. }) => {
         quote! {{
           let __guard = #pyo3_path::impl_::coroutine::RefGuard::<#cls>::new(&#pyo3_path::impl_::pymethods::BoundRef::ref_from_ptr(py, &_slf))?;
           async move { function(&__guard, #(#args),*).await }
        }}
}

The expanded code for the async block is:

async move { function(&__guard, ::pyo3::impl_::deprecations::inspect_type(::pyo3::impl_::extract_argument::extract_argument(&::pyo3::impl_::extract_argument::unwrap_required_argument(output[0usize]), &mut holder_0, "v")?, &gil_refs_checker_0)).await }

This move the output(Option<pyo3::Borrowed<', ', pyo3::PyAny>> here) to async block and therefore does not satisfy the requirements of Send.

I think we should evaluate the arg before move it, like:

let arg = ::pyo3::impl_::deprecations::inspect_type(::pyo3::impl_::extract_argument::extract_argument(&::pyo3::impl_::extract_argument::unwrap_required_argument(output[0usize]), &mut holder_0, "a")?, &gil_refs_checker_0)
async move { function(&__guard, arg).await }

If this idea make sense, I can come up with a PR then.

Steps to Reproduce

#[test]
fn test_async_receiver_with_args() {
    #[pyclass]
    struct Foo;
    #[pymethods]
    impl Foo {
        async fn bar(&self, v: i32) -> PyResult<()>{
            // do nothing
            Ok(())
        }
    }
}

Backtrace

317 |     #[pymethods]
    |     ^^^^^^^^^^^^ future created by async block is not `Send`
    |
    = help: within `{async block@tests/test_foo.rs:317:5: 317:17}`, the trait `std::marker::Send` is not implemented for `NonNull<pyo3::ffi::PyObject>`
note: captured value is not `Send`
   --> tests/test_foo.rs:317:5
    |
317 |     #[pymethods]
    |     ^^^^^^^^^^^^ has type `[Option<pyo3::Borrowed<'_, '_, pyo3::PyAny>>; 1]` which is not `Send`
note: required by a bound in `new_coroutine`
   --> xxx/pyo3/src/impl_/coroutine.rs:22:40
    |
15  | pub fn new_coroutine<F, T, E>(
    |        ------------- required by a bound in this function
...
22  |     F: Future<Output = Result<T, E>> + Send + 'static,
    |                                        ^^^^ required by this bound in `new_coroutine`
    = note: this error originates in the attribute macro `pymethods` (in Nightly builds, run with -Z macro-backtrace for more info)

Your operating system and version

MacOs 14.3.1

Your Python version (python --version)

3.11

Your Rust version (rustc --version)

rustc 1.76.0 (07dca489a 2024-02-04)

Your PyO3 version

0.21.0

How did you install python? Did you use a virtualenv?

By virtualenv

Additional Info

No response

[davidhewitt]

Hi, thanks for the report. Your analysis that this is a bug, and the proposed fix, looks correct to me! A PR would be greatly appreciated 🙏

[reswqa]

Thank you for your confirmation. I will come up with a fix recently.