Weird behaviour with awaitable Rust structs and PyPy

[gi0baro]

Hi all 👋

I recently encountered some weird behaviour with PyPy and Rust structs implementing await behaviour, as tracked in this issue: emmett-framework/granian#120

To give you a bit of context, I have two Rust structs which behave as Python awaitables, in particular one implementing what in asyncio is called bare yielding, which looks like this:

#[pyclass]
pub(crate) struct PyIterAwaitable {
    result: Option<PyResult<PyObject>>
}

#[pymethods]
impl PyIterAwaitable {
    fn __await__(pyself: PyRef<'_, Self>) -> PyRef<'_, Self> {
        pyself
    }

    fn __iter__(pyself: PyRef<'_, Self>) -> PyRef<'_, Self> {
        pyself
    }

    fn __next__(&mut self, py: Python) -> PyResult<IterNextOutput<PyObject, PyObject>> {
        match self.result.take() {
            Some(res) => {
                match res {
                    Ok(v) => Ok(IterNextOutput::Return(v)),
                    Err(err) => Err(err)
                }
            },
            _ => Ok(IterNextOutput::Yield(py.None()))
        }
    }
}

and one emulating an asyncio.Future object, which looks like:

#[pyclass]
pub(crate) struct PyFutureAwaitable {
    py_block: bool,
    result: Option<PyResult<PyObject>>
}

#[pymethods]
impl PyFutureAwaitable {
    fn __await__(pyself: PyRef<'_, Self>) -> PyRef<'_, Self> {
        pyself
    }

    fn __iter__(pyself: PyRef<'_, Self>) -> PyRef<'_, Self> {
        pyself
    }

    #[getter(_asyncio_future_blocking)]
    fn get_block(&self) -> bool {
        self.py_block
    }

    #[setter(_asyncio_future_blocking)]
    fn set_block(&mut self, val: bool) {
        self.py_block = val
    }

    fn __next__(
        mut pyself: PyRefMut<'_, Self>
    ) -> PyResult<IterNextOutput<PyRefMut<'_, Self>, PyObject>> {
        match pyself.result {
            Some(_) => {
                match pyself.result.take().unwrap() {
                    Ok(v) => Ok(IterNextOutput::Return(v)),
                    Err(err) => Err(err)
                }
            },
            _ => Ok(IterNextOutput::Yield(pyself))
        }
    }
}

Now, both implementations correctly works in CPython, so the value returned with an await statement is correct. But in PyPy, the result is always None.

Has anybody experienced this? I'm not sure is a PyO3 issue, but I'm not a PyPy expert, thus I have no clues on what's going on here :/

[davidhewitt]

Hey, thanks for sharing this. I don't have a reason why PyPy should behave any differently, so it feels like a bug. I'll try to investigate later.

Might be related to #3190

[davidhewitt]

Confirmed as a bug, #3455 should fix it in the next release.