Add PyList_GetItemRef and use it in list.get_item

newsfragments/4410.added.md

@@ -0,0 +1 @@
+Add ffi binding `PyList_GetItemRef` and `pyo3_ffi::compat::PyList_GetItemRef`

newsfragments/4410.fixed.md

@@ -0,0 +1,3 @@
+* Avoid creating temporary borrowed reference in list.get_item
+ bindings. Temporary borrowed references are unsafe in the free-threaded python
+ build if the list is shared between threads.

pyo3-ffi/src/compat.rs

@@ -12,13 +12,15 @@
 #[cfg(not(Py_3_13))]
 use crate::object::PyObject;
 #[cfg(not(Py_3_13))]
+use crate::pyport::Py_ssize_t;
+#[cfg(not(Py_3_13))]
 use std::os::raw::c_int;
 
-#[cfg_attr(docsrs, doc(cfg(all)))]
+#[cfg_attr(docsrs, doc(cfg(all())))]
 #[cfg(Py_3_13)]
 pub use crate::dictobject::PyDict_GetItemRef;
 
-#[cfg_attr(docsrs, doc(cfg(all)))]
+#[cfg_attr(docsrs, doc(cfg(all())))]
 #[cfg(not(Py_3_13))]
 pub unsafe fn PyDict_GetItemRef(
  dp: *mut PyObject,
@@ -42,3 +44,17 @@ pub unsafe fn PyDict_GetItemRef(
  -1
  }
 }
+
+#[cfg_attr(docsrs, doc(cfg(all())))]
+#[cfg(Py_3_13)]
+pub use crate::PyList_GetItemRef;
+
+#[cfg(not(Py_3_13))]
+#[cfg_attr(docsrs, doc(cfg(all())))]
+pub unsafe fn PyList_GetItemRef(arg1: *mut PyObject, arg2: Py_ssize_t) -> *mut PyObject {
+ use crate::{PyList_GetItem, Py_XINCREF};
+
+ let item: *mut PyObject = PyList_GetItem(arg1, arg2);
+ Py_XINCREF(item);
+ item
+}

pyo3-ffi/src/listobject.rs

@@ -28,6 +28,8 @@ extern "C" {
  pub fn PyList_Size(arg1: *mut PyObject) -> Py_ssize_t;
  #[cfg_attr(PyPy, link_name = "PyPyList_GetItem")]
  pub fn PyList_GetItem(arg1: *mut PyObject, arg2: Py_ssize_t) -> *mut PyObject;
+ #[cfg(Py_3_13)]
+ pub fn PyList_GetItemRef(arg1: *mut PyObject, arg2: Py_ssize_t) -> *mut PyObject;
  #[cfg_attr(PyPy, link_name = "PyPyList_SetItem")]
  pub fn PyList_SetItem(arg1: *mut PyObject, arg2: Py_ssize_t, arg3: *mut PyObject) -> c_int;
  #[cfg_attr(PyPy, link_name = "PyPyList_Insert")]

src/types/list.rs

@@ -3,7 +3,6 @@ use std::iter::FusedIterator;
 use crate::err::{self, PyResult};
 use crate::ffi::{self, Py_ssize_t};
 use crate::ffi_ptr_ext::FfiPtrExt;
-use crate::instance::Borrowed;
 use crate::internal_tricks::get_ssize_index;
 use crate::types::{PySequence, PyTuple};
 use crate::{Bound, PyAny, PyObject, Python, ToPyObject};
@@ -289,10 +288,8 @@ impl<'py> PyListMethods<'py> for Bound<'py, PyList> {
  /// ```
  fn get_item(&self, index: usize) -> PyResult<Bound<'py, PyAny>> {
  unsafe {
- // PyList_GetItem return borrowed ptr; must make owned for safety (see #890).
- ffi::PyList_GetItem(self.as_ptr(), index as Py_ssize_t)
- .assume_borrowed_or_err(self.py())
- .map(Borrowed::to_owned)
+ ffi::compat::PyList_GetItemRef(self.as_ptr(), index as Py_ssize_t)
+ .assume_owned_or_err(self.py())
  }
  }