Add BoundRef::ref_from_ptr_or_opt

pyo3-macros-backend/src/pymethod.rs

@@ -572,11 +572,12 @@ pub fn impl_py_setter_def(
             _slf: *mut _pyo3::ffi::PyObject,
             _value: *mut _pyo3::ffi::PyObject,
         ) -> _pyo3::PyResult<::std::os::raw::c_int> {
-            let _value = _pyo3::Bound::from_borrowed_ptr_or_opt(py, _value)
+            use ::std::convert::Into;
+            let _value = _pyo3::impl_::pymethods::BoundRef::ref_from_ptr_or_opt(py, &_value)
                 .ok_or_else(|| {
                     _pyo3::exceptions::PyAttributeError::new_err("can't delete attribute")
                 })?;
-            let _val = _pyo3::FromPyObject::extract_bound(&_value)?;
+            let _val = _pyo3::FromPyObject::extract_bound(_value.into())?;
             #( #holders )*
             _pyo3::callback::convert(py, #setter_impl)
         }

src/impl_/pymethods.rs

@@ -483,6 +483,13 @@ impl<'a, 'py> BoundRef<'a, 'py, PyAny> {
         BoundRef(Bound::ref_from_ptr(py, ptr))
     }
 
+    pub unsafe fn ref_from_ptr_or_opt(
+        py: Python<'py>,
+        ptr: &'a *mut ffi::PyObject,
+    ) -> Option<Self> {
+        Bound::ref_from_ptr_or_opt(py, ptr).as_ref().map(BoundRef)
+    }
+
     pub unsafe fn downcast_unchecked<T>(self) -> BoundRef<'a, 'py, T> {
         BoundRef(self.0.downcast_unchecked::<T>())
     }

src/instance.rs

@@ -191,6 +191,18 @@ impl<'py> Bound<'py, PyAny> {
     ) -> &'a Self {
         &*(ptr as *const *mut ffi::PyObject).cast::<Bound<'py, PyAny>>()
     }
+
+    /// Variant of the above which returns `None` for null pointers.
+    ///
+    /// # Safety
+    /// - `ptr` must be a valid pointer to a Python object for the lifetime `'a, or null.
+    #[inline]
+    pub(crate) unsafe fn ref_from_ptr_or_opt<'a>(
+        _py: Python<'py>,
+        ptr: &'a *mut ffi::PyObject,
+    ) -> &'a Option<Self> {
+        &*(ptr as *const *mut ffi::PyObject).cast::<Option<Bound<'py, PyAny>>>()
+    }
 }
 
 impl<'py, T> Bound<'py, T>