deprecate the use of `PyCell` in favor of `Bound` and `Py` (#3916)

* deprecate the use of `PyCell` in favor of `Bound` and `Py`

* update `FromPyObject` for `T: PyClass + Clone` impl

* move `PyCell` deprecation to the `gil-refs` feature gate and add a migration note

guide/src/class.md

@@ -1230,6 +1230,7 @@ struct MyClass {
 
 impl pyo3::types::DerefToPyAny for MyClass {}
 
+# #[allow(deprecated)]
 unsafe impl pyo3::type_object::HasPyGilRef for MyClass {
     type AsRefTarget = pyo3::PyCell<Self>;
 }

guide/src/types.md

@@ -96,6 +96,7 @@ For a `&PyAny` object reference `any` where the underlying object is a `#[pyclas
 let obj: &PyAny = Py::new(py, MyClass {})?.into_ref(py);
 
 // To &PyCell<MyClass> with PyAny::downcast
+# #[allow(deprecated)]
 let _: &PyCell<MyClass> = obj.downcast()?;
 
 // To Py<PyAny> (aka PyObject) with .into()

pyo3-macros-backend/src/pyclass.rs

@@ -1281,6 +1281,7 @@ fn impl_pytypeinfo(
     };
 
     quote! {
+        #[allow(deprecated)]
         unsafe impl _pyo3::type_object::HasPyGilRef for #cls {
             type AsRefTarget = _pyo3::PyCell<Self>;
         }

src/conversion.rs

@@ -6,9 +6,7 @@ use crate::pyclass::boolean_struct::False;
 use crate::type_object::PyTypeInfo;
 use crate::types::any::PyAnyMethods;
 use crate::types::PyTuple;
-use crate::{
+use crate::{ffi, gil, Bound, Py, PyAny, PyClass, PyNativeType, PyObject, PyRef, PyRefMut, Python};
-    ffi, gil, Bound, Py, PyAny, PyCell, PyClass, PyNativeType, PyObject, PyRef, PyRefMut, Python,
-};
 use std::ptr::NonNull;
 
 /// Returns a borrowed pointer to a Python object.
@@ -265,7 +263,8 @@ where
     }
 }
 
-impl<'py, T> FromPyObject<'py> for &'py PyCell<T>
+#[allow(deprecated)]
+impl<'py, T> FromPyObject<'py> for &'py crate::PyCell<T>
 where
     T: PyClass,
 {
@@ -278,9 +277,9 @@ impl<T> FromPyObject<'_> for T
 where
     T: PyClass + Clone,
 {
-    fn extract(obj: &PyAny) -> PyResult<Self> {
+    fn extract_bound(obj: &Bound<'_, PyAny>) -> PyResult<Self> {
-        let cell: &PyCell<Self> = obj.downcast()?;
+        let bound = obj.downcast::<Self>()?;
-        Ok(unsafe { cell.try_borrow_unguarded()?.clone() })
+        Ok(bound.try_borrow()?.clone())
     }
 }
 
@@ -389,7 +388,7 @@ mod implementations {
         }
     }
 
-    impl<'v, T> PyTryFrom<'v> for PyCell<T>
+    impl<'v, T> PyTryFrom<'v> for crate::PyCell<T>
     where
         T: 'v + PyClass,
     {

src/conversions/std/array.rs

@@ -240,7 +240,7 @@ mod tests {
             let array: [Foo; 8] = [Foo, Foo, Foo, Foo, Foo, Foo, Foo, Foo];
             let pyobject = array.into_py(py);
             let list = pyobject.downcast_bound::<PyList>(py).unwrap();
-            let _cell: &crate::PyCell<Foo> = list.get_item(4).unwrap().extract().unwrap();
+            let _bound = list.get_item(4).unwrap().downcast::<Foo>().unwrap();
         });
     }
 

src/impl_/pymethods.rs

@@ -7,8 +7,8 @@ use crate::pycell::{PyBorrowError, PyBorrowMutError};
 use crate::pyclass::boolean_struct::False;
 use crate::types::{any::PyAnyMethods, PyModule, PyType};
 use crate::{
-    ffi, Borrowed, Bound, DowncastError, Py, PyAny, PyCell, PyClass, PyClassInitializer, PyErr,
+    ffi, Borrowed, Bound, DowncastError, Py, PyAny, PyClass, PyClassInitializer, PyErr, PyObject,
-    PyObject, PyRef, PyRefMut, PyResult, PyTraverseError, PyTypeCheck, PyVisit, Python,
+    PyRef, PyRefMut, PyResult, PyTraverseError, PyTypeCheck, PyVisit, Python,
 };
 use std::borrow::Cow;
 use std::ffi::CStr;
@@ -518,7 +518,8 @@ impl<'a> From<BoundRef<'a, 'a, PyModule>> for &'a PyModule {
     }
 }
 
-impl<'a, 'py, T: PyClass> From<BoundRef<'a, 'py, T>> for &'a PyCell<T> {
+#[allow(deprecated)]
+impl<'a, 'py, T: PyClass> From<BoundRef<'a, 'py, T>> for &'a crate::PyCell<T> {
     #[inline]
     fn from(bound: BoundRef<'a, 'py, T>) -> Self {
         bound.0.as_gil_ref()

src/instance.rs

@@ -1,6 +1,6 @@
 use crate::err::{self, PyDowncastError, PyErr, PyResult};
 use crate::impl_::pycell::PyClassObject;
-use crate::pycell::{PyBorrowError, PyBorrowMutError, PyCell};
+use crate::pycell::{PyBorrowError, PyBorrowMutError};
 use crate::pyclass::boolean_struct::{False, True};
 use crate::type_object::HasPyGilRef;
 use crate::types::{any::PyAnyMethods, string::PyStringMethods, typeobject::PyTypeMethods};
@@ -1698,11 +1698,12 @@ impl<T> std::convert::From<Bound<'_, T>> for Py<T> {
 }
 
 // `&PyCell<T>` can be converted to `Py<T>`
-impl<T> std::convert::From<&PyCell<T>> for Py<T>
+#[allow(deprecated)]
+impl<T> std::convert::From<&crate::PyCell<T>> for Py<T>
 where
     T: PyClass,
 {
-    fn from(cell: &PyCell<T>) -> Self {
+    fn from(cell: &crate::PyCell<T>) -> Self {
         cell.as_borrowed().to_owned().unbind()
     }
 }

src/lib.rs

@@ -315,7 +315,9 @@ pub use crate::gil::GILPool;
 pub use crate::gil::{prepare_freethreaded_python, with_embedded_python_interpreter};
 pub use crate::instance::{Borrowed, Bound, Py, PyNativeType, PyObject};
 pub use crate::marker::Python;
-pub use crate::pycell::{PyCell, PyRef, PyRefMut};
+#[allow(deprecated)]
+pub use crate::pycell::PyCell;
+pub use crate::pycell::{PyRef, PyRefMut};
 pub use crate::pyclass::PyClass;
 pub use crate::pyclass_init::PyClassInitializer;
 pub use crate::type_object::{PyTypeCheck, PyTypeInfo};

src/prelude.rs

@@ -14,7 +14,9 @@ pub use crate::conversion::{PyTryFrom, PyTryInto};
 pub use crate::err::{PyErr, PyResult};
 pub use crate::instance::{Borrowed, Bound, Py, PyObject};
 pub use crate::marker::Python;
-pub use crate::pycell::{PyCell, PyRef, PyRefMut};
+#[allow(deprecated)]
+pub use crate::pycell::PyCell;
+pub use crate::pycell::{PyRef, PyRefMut};
 pub use crate::pyclass_init::PyClassInitializer;
 pub use crate::types::{PyAny, PyModule};
 pub use crate::PyNativeType;

src/pycell.rs

@@ -154,6 +154,7 @@
 //! # pub struct Number {
 //! #     inner: u32,
 //! # }
+//! # #[allow(deprecated)]
 //! #[pyfunction]
 //! fn swap_numbers(a: &PyCell<Number>, b: &PyCell<Number>) {
 //!     // Check that the pointers are unequal
@@ -250,13 +251,22 @@ use self::impl_::{PyClassObject, PyClassObjectLayout};
 /// ```
 /// For more information on how, when and why (not) to use `PyCell` please see the
 /// [module-level documentation](self).
+#[cfg_attr(
+    not(feature = "gil-refs"),
+    deprecated(
+        since = "0.21.0",
+        note = "`PyCell` was merged into `Bound`, use that instead; see the migration guide for more info"
+    )
+)]
 #[repr(transparent)]
 pub struct PyCell<T: PyClassImpl>(PyClassObject<T>);
 
+#[allow(deprecated)]
 unsafe impl<T: PyClass> PyNativeType for PyCell<T> {
     type AsRefSource = T;
 }
 
+#[allow(deprecated)]
 impl<T: PyClass> PyCell<T> {
     /// Makes a new `PyCell` on the Python heap and return the reference to it.
     ///
@@ -478,9 +488,12 @@ impl<T: PyClass> PyCell<T> {
     }
 }
 
+#[allow(deprecated)]
 unsafe impl<T: PyClassImpl> PyLayout<T> for PyCell<T> {}
+#[allow(deprecated)]
 impl<T: PyClass> PySizedLayout<T> for PyCell<T> {}
 
+#[allow(deprecated)]
 impl<T> PyTypeCheck for PyCell<T>
 where
     T: PyClass,
@@ -492,18 +505,21 @@ where
     }
 }
 
+#[allow(deprecated)]
 unsafe impl<T: PyClass> AsPyPointer for PyCell<T> {
     fn as_ptr(&self) -> *mut ffi::PyObject {
         (self as *const _) as *mut _
     }
 }
 
+#[allow(deprecated)]
 impl<T: PyClass> ToPyObject for &PyCell<T> {
     fn to_object(&self, py: Python<'_>) -> PyObject {
         unsafe { PyObject::from_borrowed_ptr(py, self.as_ptr()) }
     }
 }
 
+#[allow(deprecated)]
 impl<T: PyClass> AsRef<PyAny> for PyCell<T> {
     fn as_ref(&self) -> &PyAny {
         #[allow(deprecated)]
@@ -513,6 +529,7 @@ impl<T: PyClass> AsRef<PyAny> for PyCell<T> {
     }
 }
 
+#[allow(deprecated)]
 impl<T: PyClass> Deref for PyCell<T> {
     type Target = PyAny;
 
@@ -524,6 +541,7 @@ impl<T: PyClass> Deref for PyCell<T> {
     }
 }
 
+#[allow(deprecated)]
 impl<T: PyClass + fmt::Debug> fmt::Debug for PyCell<T> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         match self.try_borrow() {
@@ -748,6 +766,7 @@ impl<T: PyClass> IntoPy<PyObject> for &'_ PyRef<'_, T> {
     }
 }
 
+#[allow(deprecated)]
 impl<'a, T: PyClass> std::convert::TryFrom<&'a PyCell<T>> for crate::PyRef<'a, T> {
     type Error = PyBorrowError;
     fn try_from(cell: &'a crate::PyCell<T>) -> Result<Self, Self::Error> {
@@ -905,6 +924,7 @@ unsafe impl<'a, T: PyClass<Frozen = False>> AsPyPointer for PyRefMut<'a, T> {
     }
 }
 
+#[allow(deprecated)]
 impl<'a, T: PyClass<Frozen = False>> std::convert::TryFrom<&'a PyCell<T>>
     for crate::PyRefMut<'a, T>
 {

src/pyclass.rs

@@ -1,7 +1,7 @@
 //! `PyClass` and related traits.
 use crate::{
-    callback::IntoPyCallbackOutput, ffi, impl_::pyclass::PyClassImpl, IntoPy, PyCell, PyObject,
+    callback::IntoPyCallbackOutput, ffi, impl_::pyclass::PyClassImpl, IntoPy, PyObject, PyResult,
-    PyResult, PyTypeInfo, Python,
+    PyTypeInfo, Python,
 };
 use std::{cmp::Ordering, os::raw::c_int};
 
@@ -15,7 +15,8 @@ pub use self::gc::{PyTraverseError, PyVisit};
 ///
 /// The `#[pyclass]` attribute implements this trait for your Rust struct -
 /// you shouldn't implement this trait directly.
-pub trait PyClass: PyTypeInfo<AsRefTarget = PyCell<Self>> + PyClassImpl {
+#[allow(deprecated)]
+pub trait PyClass: PyTypeInfo<AsRefTarget = crate::PyCell<Self>> + PyClassImpl {
     /// Whether the pyclass is frozen.
     ///
     /// This can be enabled via `#[pyclass(frozen)]`.

src/types/pysuper.rs

@@ -62,7 +62,7 @@ impl PySuper {
     ///         (SubClass {}, BaseClass::new())
     ///     }
     ///
-    ///     fn method(self_: &PyCell<Self>) -> PyResult<&PyAny> {
+    ///     fn method<'py>(self_: &Bound<'py, Self>) -> PyResult<Bound<'py, PyAny>> {
     ///         let super_ = self_.py_super()?;
     ///         super_.call_method("method", (), None)
     ///     }

tests/test_buffer_protocol.rs

@@ -24,11 +24,11 @@ struct TestBufferClass {
 #[pymethods]
 impl TestBufferClass {
     unsafe fn __getbuffer__(
-        slf: &PyCell<Self>,
+        slf: Bound<'_, Self>,
         view: *mut ffi::Py_buffer,
         flags: c_int,
     ) -> PyResult<()> {
-        fill_view_from_readonly_data(view, flags, &slf.borrow().vec, slf)
+        fill_view_from_readonly_data(view, flags, &slf.borrow().vec, slf.into_any())
     }
 
     unsafe fn __releasebuffer__(&self, view: *mut ffi::Py_buffer) {
@@ -105,12 +105,12 @@ fn test_releasebuffer_unraisable_error() {
     #[pymethods]
     impl ReleaseBufferError {
         unsafe fn __getbuffer__(
-            slf: &PyCell<Self>,
+            slf: Bound<'_, Self>,
             view: *mut ffi::Py_buffer,
             flags: c_int,
         ) -> PyResult<()> {
             static BUF_BYTES: &[u8] = b"hello world";
-            fill_view_from_readonly_data(view, flags, BUF_BYTES, slf)
+            fill_view_from_readonly_data(view, flags, BUF_BYTES, slf.into_any())
         }
 
         unsafe fn __releasebuffer__(&self, _view: *mut ffi::Py_buffer) -> PyResult<()> {
@@ -145,7 +145,7 @@ unsafe fn fill_view_from_readonly_data(
     view: *mut ffi::Py_buffer,
     flags: c_int,
     data: &[u8],
-    owner: &PyAny,
+    owner: Bound<'_, PyAny>,
 ) -> PyResult<()> {
     if view.is_null() {
         return Err(PyBufferError::new_err("View is null"));

tests/test_class_new.rs

@@ -23,7 +23,7 @@ fn empty_class_with_new() {
         assert!(typeobj
             .call((), None)
             .unwrap()
-            .downcast::<PyCell<EmptyClassWithNew>>()
+            .downcast::<EmptyClassWithNew>()
             .is_ok());
 
         // Calling with arbitrary args or kwargs is not ok
@@ -52,7 +52,7 @@ fn unit_class_with_new() {
         assert!(typeobj
             .call((), None)
             .unwrap()
-            .downcast::<PyCell<UnitClassWithNew>>()
+            .downcast::<UnitClassWithNew>()
             .is_ok());
     });
 }

tests/test_pyself.rs

@@ -18,15 +18,18 @@ struct Reader {
 
 #[pymethods]
 impl Reader {
-    fn clone_ref(slf: &PyCell<Self>) -> &PyCell<Self> {
+    fn clone_ref<'a, 'py>(slf: &'a Bound<'py, Self>) -> &'a Bound<'py, Self> {
         slf
     }
-    fn clone_ref_with_py<'py>(slf: &'py PyCell<Self>, _py: Python<'py>) -> &'py PyCell<Self> {
+    fn clone_ref_with_py<'a, 'py>(
+        slf: &'a Bound<'py, Self>,
+        _py: Python<'py>,
+    ) -> &'a Bound<'py, Self> {
         slf
     }
-    fn get_iter(slf: &PyCell<Self>, keys: Py<PyBytes>) -> Iter {
+    fn get_iter(slf: &Bound<'_, Self>, keys: Py<PyBytes>) -> Iter {
         Iter {
-            reader: slf.into(),
+            reader: slf.clone().unbind(),
             keys,
             idx: 0,
         }

tests/test_super.rs

@@ -29,14 +29,14 @@ impl SubClass {
         (SubClass {}, BaseClass::new())
     }
 
-    fn method(self_: &PyCell<Self>) -> PyResult<&PyAny> {
+    fn method<'py>(self_: &Bound<'py, Self>) -> PyResult<Bound<'py, PyAny>> {
         let super_ = self_.py_super()?;
         super_.call_method("method", (), None)
     }
 
-    fn method_super_new(self_: &PyCell<Self>) -> PyResult<&PyAny> {
+    fn method_super_new<'py>(self_: &Bound<'py, Self>) -> PyResult<Bound<'py, PyAny>> {
         #[cfg_attr(not(feature = "gil-refs"), allow(deprecated))]
-        let super_ = PySuper::new(self_.get_type(), self_)?;
+        let super_ = PySuper::new_bound(&self_.get_type(), self_)?;
         super_.call_method("method", (), None)
     }
 }

tests/test_text_signature.rs

@@ -367,7 +367,7 @@ fn test_methods() {
             let _ = a;
         }
         #[pyo3(text_signature = "($self, b)")]
-        fn pyself_method(_this: &PyCell<Self>, b: i32) {
+        fn pyself_method(_this: &Bound<'_, Self>, b: i32) {
             let _ = b;
         }
         #[classmethod]

tests/test_various.rs

@@ -124,7 +124,7 @@ impl PickleSupport {
     }
 
     pub fn __reduce__<'py>(
-        slf: &'py PyCell<Self>,
+        slf: &Bound<'py, Self>,
         py: Python<'py>,
     ) -> PyResult<(PyObject, Bound<'py, PyTuple>, PyObject)> {
         let cls = slf.to_object(py).getattr(py, "__class__")?;

tests/ui/invalid_frozen_pyclass_borrow.rs

@@ -29,7 +29,7 @@ fn py_get_of_mutable_class_fails(class: Py<MutableBase>) {
     class.get();
 }
 
-fn pyclass_get_of_mutable_class_fails(class: &PyCell<MutableBase>) {
+fn pyclass_get_of_mutable_class_fails(class: &Bound<'_, MutableBase>) {
     class.get();
 }
 

tests/ui/invalid_frozen_pyclass_borrow.stderr

@@ -67,11 +67,11 @@ error[E0271]: type mismatch resolving `<MutableBase as PyClass>::Frozen == True`
 33 |     class.get();
    |           ^^^ expected `True`, found `False`
    |
-note: required by a bound in `pyo3::PyCell::<T>::get`
+note: required by a bound in `pyo3::Bound::<'py, T>::get`
-  --> src/pycell.rs
+  --> src/instance.rs
    |
    |     pub fn get(&self) -> &T
    |            --- required by a bound in this associated function
    |     where
    |         T: PyClass<Frozen = True> + Sync,
-   |                    ^^^^^^^^^^^^^ required by this bound in `PyCell::<T>::get`
+   |                    ^^^^^^^^^^^^^ required by this bound in `Bound::<'py, T>::get`

tests/ui/pyclass_send.rs

@@ -8,15 +8,15 @@ struct NotThreadSafe {
 
 fn main() {
     let obj = Python::with_gil(|py| {
-        PyCell::new(py, NotThreadSafe { data: Rc::new(5) })
+        Bound::new(py, NotThreadSafe { data: Rc::new(5) })
             .unwrap()
-            .to_object(py)
+            .unbind(py)
     });
 
     std::thread::spawn(move || {
         Python::with_gil(|py| {
             // Uh oh, moved Rc to a new thread!
-            let c: &PyCell<NotThreadSafe> = obj.as_ref(py).downcast().unwrap();
+            let c = obj.bind(py).downcast::<NotThreadSafe>().unwrap();
 
             assert_eq!(*c.borrow().data, 5);
         })