#[pymethods] generated code triggers unsafe_op_in_unsafe_fn lint

[nsunderland1]

Bug Description

Functions in impl blocks annotated with pymethods trigger the unsafe_op_in_unsafe_fn lint. In a crate with #![deny(unsafe_op_in_unsafe_fn)] set, I get the following error:

error[E0133]: call to unsafe function `pyo3::impl_::pymethods::BoundRef::<'a, 'py, pyo3::PyAny>::ref_from_ptr` is unsafe and requires unsafe block
  --> src/lib.rs:10:19
   |
10 |     fn do_nothing(&self) {}
   |                   ^ call to unsafe function
   |
   = note: for more information, see issue #71668 <https://github.com/rust-lang/rust/issues/71668>
   = note: consult the function's documentation for information on how to avoid undefined behavior
note: an unsafe function restricts its caller, but its body is safe by default
  --> src/lib.rs:8:1
   |
8  | #[pymethods]
   | ^^^^^^^^^^^^
note: the lint level is defined here
  --> src/lib.rs:1:9
   |
1  | #![deny(unsafe_op_in_unsafe_fn)]
   |         ^^^^^^^^^^^^^^^^^^^^^^
   = note: this error originates in the attribute macro `pymethods` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0133`.
error: could not compile `repro_pyo3` (lib) due to 1 previous error

This points to a call to ref_from_ptr, which we can see in the expanded code:

#[doc(hidden)]
#[allow(non_snake_case)]
impl Foo {
    unsafe fn __pymethod_do_nothing__<'py>(
        py: ::pyo3::Python<'py>,
        _slf: *mut ::pyo3::ffi::PyObject,
    ) -> ::pyo3::PyResult<*mut ::pyo3::ffi::PyObject> {
        let _slf_ref = &_slf;
        let function = Foo::do_nothing;
        #[allow(clippy::let_unit_value)]
        let mut holder_0 = ::pyo3::impl_::extract_argument::FunctionArgumentHolder::INIT;
        let gil_refs_checker_0 = ::pyo3::impl_::deprecations::GilRefs::new();
        let result = {
            let ret = function(::pyo3::impl_::deprecations::inspect_type(
                ::pyo3::impl_::extract_argument::extract_pyclass_ref::<Foo>(
                    // vvv right here
                    ::pyo3::impl_::pymethods::BoundRef::ref_from_ptr(py, &_slf).0, // <<< right here
                    // ^^^ right here
                    &mut holder_0,
                )?,
                &gil_refs_checker_0,
            ));
            ::pyo3::impl_::wrap::map_result_into_ptr(
                py,
                ::pyo3::impl_::wrap::OkWrap::wrap(ret)
                    .map_err(::core::convert::Into::<::pyo3::PyErr>::into),
            )
        };
        gil_refs_checker_0.function_arg();
        result
    }
}

Steps to Reproduce

Quick method:

1. Clone this repo: https://github.com/nsunderland1/repro_pyo3/tree/main
2. Run cargo build

Alternatively:

1. Create a PyO3 project following the steps in https://github.com/PyO3/pyo3?tab=readme-ov-file#using-rust-from-python
2. Replace the contents of lib.rs with the following code:

#![deny(unsafe_op_in_unsafe_fn)]

use pyo3::prelude::*;

#[pyclass]
struct Foo;

#[pymethods]
impl Foo {
    fn do_nothing(&self) {}
}

3. Run cargo build

Backtrace

No response

Your operating system and version

macOS Sonoma

Your Python version (python --version)

Python 3.10.14

Your Rust version (rustc --version)

rustc 1.80.0 (051478957 2024-07-21)

Your PyO3 version

0.22.0

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

pyenv, using a virtual env as in the steps laid out here https://github.com/PyO3/pyo3?tab=readme-ov-file#using-rust-from-python

Additional Info

No response