Memory leak with PyIterProtocol over PyErr

[Stranger6667]

Bug Description

When implementing PyIterProtocol for PyErr based on these examples from the docs, I observe a memory leak.

Other objects (e.g. usize) don't seem to cause memory leaks (though, I didn't check with #[pyclass(extends=...)].

Steps to Reproduce

use pyo3::{prelude::*, PyIterProtocol, exceptions::PyValueError};


#[pyclass]
struct Errors {
    iter: std::vec::IntoIter<PyErr>,
}

#[pyproto]
impl PyIterProtocol for Errors {
    fn __iter__(slf: PyRef<Self>) -> PyRef<Self> {
        slf
    }

    fn __next__(mut slf: PyRefMut<Self>) -> Option<PyErr> {
        slf.iter.next()
    }
}

#[pyfunction]
fn iter() -> PyResult<Errors> {
    let error = PyValueError::new_err("Failed");
    Ok(Errors {
        iter: vec![error].into_iter(),
    })
}

#[pymodule]
fn pyo3_memory_leak_example(_py: Python, module: &PyModule) -> PyResult<()> {
    module.add_wrapped(wrap_pyfunction!(iter))?;
    Ok(())
}

Memory measurement:

import tracemalloc
import pyo3_memory_leak_example


tracemalloc.start()
for _ in range(100000):
    list(pyo3_memory_leak_example.iter())

snapshot = tracemalloc.take_snapshot()
print(snapshot.statistics('lineno')[0])

It outputs the following (and the number grows with the iteration number):

/tmp/pyo3-memory-leak-example-repo/run.py:7: size=17.5 MiB, count=300081, average=61 B

Run with:

pip install maturin
maturin develop
python run.py

My expectation is that those errors are garbage collected as usual.

See the full reproduction example in this repo and the actual use case in jsonschema

Backtrace

No response

Your operating system and version

Linux archlinux 5.15.10-arch1-1 #1 SMP PREEMPT Fri, 17 Dec 2021 11:17:37 +0000 x86_64 GNU/Linux

Your Python version (python --version)

Python 3.9.9

Your Rust version (rustc --version)

rustc 1.57.0 (f1edd0429 2021-11-29)

Your PyO3 version

0.15.1

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

yay python39

Yes, I used a virtualenv.

Additional Info

No response

[davidhewitt]

Thanks for reporting. Are you willing to check with main? I suspect this might be caused by the same memory leak I found and fixed in #2026

[Stranger6667]

The issue is not happening on main :) Thank you very much