fix `AsRef` and `Deref` impls on `Bound<T>` (#3879)

* fix `AsRef` and `Deref` of `Bound<T>` to `Bound<PyAny>`

* cleanup unnessesary `.as_any()` calls

* remove trait bound on `AsRef` impl

* add comment for `Deref` trait bound

* rename marker trait

guide/src/class/object.md

@@ -217,8 +217,8 @@ impl Number {
 
 # fn main() -> PyResult<()> {
 #     Python::with_gil(|py| {
-#         let x = &Bound::new(py, Number(4))?.into_any();
+#         let x = &Bound::new(py, Number(4))?;
-#         let y = &Bound::new(py, Number(4))?.into_any();
+#         let y = &Bound::new(py, Number(4))?;
 #         assert!(x.eq(y)?);
 #         assert!(!x.ne(y)?);
 #         Ok(())

pyo3-macros-backend/src/pyclass.rs

@@ -365,6 +365,8 @@ fn impl_class(
         const _: () = {
             use #krate as _pyo3;
 
+            impl _pyo3::types::DerefToPyAny for #cls {}
+
             #pytypeinfo_impl
 
             #py_class_impl

src/instance.rs

@@ -4,7 +4,7 @@ use crate::pycell::{PyBorrowError, PyBorrowMutError, PyCell};
 use crate::pyclass::boolean_struct::{False, True};
 use crate::type_object::HasPyGilRef;
 use crate::types::{any::PyAnyMethods, string::PyStringMethods, typeobject::PyTypeMethods};
-use crate::types::{PyDict, PyString, PyTuple};
+use crate::types::{DerefToPyAny, PyDict, PyString, PyTuple};
 use crate::{
     ffi, AsPyPointer, DowncastError, FromPyObject, IntoPy, PyAny, PyClass, PyClassInitializer,
     PyRef, PyRefMut, PyTypeInfo, Python, ToPyObject,
@@ -366,9 +366,12 @@ fn python_format(
     }
 }
 
+// The trait bound is needed to avoid running into the auto-deref recursion
+// limit (error[E0055]), because `Bound<PyAny>` would deref into itself. See:
+// https://github.com/rust-lang/rust/issues/19509
 impl<'py, T> Deref for Bound<'py, T>
 where
-    T: AsRef<PyAny>,
+    T: DerefToPyAny,
 {
     type Target = Bound<'py, PyAny>;
 
@@ -378,10 +381,7 @@ where
     }
 }
 
-impl<'py, T> AsRef<Bound<'py, PyAny>> for Bound<'py, T>
+impl<'py, T> AsRef<Bound<'py, PyAny>> for Bound<'py, T> {
-where
-    T: AsRef<PyAny>,
-{
     #[inline]
     fn as_ref(&self) -> &Bound<'py, PyAny> {
         self.as_any()

src/types/boolobject.rs

@@ -168,7 +168,7 @@ mod tests {
         Python::with_gil(|py| {
             assert!(PyBool::new_bound(py, true).is_true());
             let t = PyBool::new_bound(py, true);
-            assert!(t.as_any().extract::<bool>().unwrap());
+            assert!(t.extract::<bool>().unwrap());
             assert!(true.to_object(py).is(&*PyBool::new_bound(py, true)));
         });
     }
@@ -178,7 +178,7 @@ mod tests {
         Python::with_gil(|py| {
             assert!(!PyBool::new_bound(py, false).is_true());
             let t = PyBool::new_bound(py, false);
-            assert!(!t.as_any().extract::<bool>().unwrap());
+            assert!(!t.extract::<bool>().unwrap());
             assert!(false.to_object(py).is(&*PyBool::new_bound(py, false)));
         });
     }

src/types/mod.rs

@@ -86,6 +86,31 @@ pub mod iter {
     pub use super::tuple::{BorrowedTupleIterator, BoundTupleIterator, PyTupleIterator};
 }
 
+/// Python objects that have a base type.
+///
+/// This marks types that can be upcast into a [`PyAny`] and used in its place.
+/// This essentially includes every Python object except [`PyAny`] itself.
+///
+/// This is used to provide the [`Deref<Target = Bound<'_, PyAny>>`](std::ops::Deref)
+/// implementations for [`Bound<'_, T>`](crate::Bound).
+///
+/// Users should not need to implement this trait directly. It's implementation
+/// is provided by the [`#[pyclass]`](macro@crate::pyclass) attribute.
+///
+/// ## Note
+/// This is needed because the compiler currently tries to figure out all the
+/// types in a deref-chain before starting to look for applicable method calls.
+/// So we need to prevent [`Bound<'_, PyAny`](crate::Bound) dereferencing to
+/// itself in order to avoid running into the recursion limit. This trait is
+/// used to exclude this from our blanket implementation. See [this Rust
+/// issue][1] for more details. If the compiler limitation gets resolved, this
+/// trait will be removed.
+///
+/// [1]: https://github.com/rust-lang/rust/issues/19509
+pub trait DerefToPyAny {
+    // Empty.
+}
+
 // Implementations core to all native types
 #[doc(hidden)]
 #[macro_export]
@@ -183,6 +208,8 @@ macro_rules! pyobject_native_type_named (
                 unsafe{&*(ob as *const $name as *const $crate::PyAny)}
             }
         }
+
+        impl $crate::types::DerefToPyAny for $name {}
     };
 );
 

tests/test_buffer.rs

@@ -96,11 +96,11 @@ fn test_get_buffer_errors() {
         )
         .unwrap();
 
-        assert!(PyBuffer::<u32>::get_bound(instance.bind(py).as_any()).is_ok());
+        assert!(PyBuffer::<u32>::get_bound(instance.bind(py)).is_ok());
 
         instance.borrow_mut(py).error = Some(TestGetBufferError::NullShape);
         assert_eq!(
-            PyBuffer::<u32>::get_bound(instance.bind(py).as_any())
+            PyBuffer::<u32>::get_bound(instance.bind(py))
                 .unwrap_err()
                 .to_string(),
             "BufferError: shape is null"
@@ -108,7 +108,7 @@ fn test_get_buffer_errors() {
 
         instance.borrow_mut(py).error = Some(TestGetBufferError::NullStrides);
         assert_eq!(
-            PyBuffer::<u32>::get_bound(instance.bind(py).as_any())
+            PyBuffer::<u32>::get_bound(instance.bind(py))
                 .unwrap_err()
                 .to_string(),
             "BufferError: strides is null"
@@ -116,7 +116,7 @@ fn test_get_buffer_errors() {
 
         instance.borrow_mut(py).error = Some(TestGetBufferError::IncorrectItemSize);
         assert_eq!(
-            PyBuffer::<u32>::get_bound(instance.bind(py).as_any())
+            PyBuffer::<u32>::get_bound(instance.bind(py))
                 .unwrap_err()
                 .to_string(),
             "BufferError: buffer contents are not compatible with u32"
@@ -124,7 +124,7 @@ fn test_get_buffer_errors() {
 
         instance.borrow_mut(py).error = Some(TestGetBufferError::IncorrectFormat);
         assert_eq!(
-            PyBuffer::<u32>::get_bound(instance.bind(py).as_any())
+            PyBuffer::<u32>::get_bound(instance.bind(py))
                 .unwrap_err()
                 .to_string(),
             "BufferError: buffer contents are not compatible with u32"
@@ -132,7 +132,7 @@ fn test_get_buffer_errors() {
 
         instance.borrow_mut(py).error = Some(TestGetBufferError::IncorrectAlignment);
         assert_eq!(
-            PyBuffer::<u32>::get_bound(instance.bind(py).as_any())
+            PyBuffer::<u32>::get_bound(instance.bind(py))
                 .unwrap_err()
                 .to_string(),
             "BufferError: buffer contents are insufficiently aligned for u32"

tests/test_class_conversion.rs

@@ -146,13 +146,11 @@ fn test_pyref_as_base() {
 #[test]
 fn test_pycell_deref() {
     Python::with_gil(|py| {
-        let cell = Bound::new(py, (SubClass {}, BaseClass { value: 120 })).unwrap();
+        let obj = Bound::new(py, (SubClass {}, BaseClass { value: 120 })).unwrap();
 
         // Should be able to deref as PyAny
-        // FIXME: This deref does _not_ work
         assert_eq!(
-            cell.as_any()
+            obj.call_method0("foo")
-                .call_method0("foo")
                 .and_then(|e| e.extract::<&str>())
                 .unwrap(),
             "SubClass"

tests/test_field_cfg.rs

@@ -22,14 +22,8 @@ fn test_cfg() {
     Python::with_gil(|py| {
         let cfg = CfgClass { b: 3 };
         let py_cfg = Py::new(py, cfg).unwrap();
-        assert!(py_cfg.bind(py).as_any().getattr("a").is_err());
+        assert!(py_cfg.bind(py).getattr("a").is_err());
-        let b: u32 = py_cfg
+        let b: u32 = py_cfg.bind(py).getattr("b").unwrap().extract().unwrap();
-            .bind(py)
-            .as_any()
-            .getattr("b")
-            .unwrap()
-            .extract()
-            .unwrap();
         assert_eq!(b, 3);
     });
 }

tests/test_inheritance.rs

@@ -247,7 +247,7 @@ mod inheriting_native_type {
             let item = &py.eval_bound("object()", None, None).unwrap();
             assert_eq!(item.get_refcnt(), 1);
 
-            dict_sub.bind(py).as_any().set_item("foo", item).unwrap();
+            dict_sub.bind(py).set_item("foo", item).unwrap();
             assert_eq!(item.get_refcnt(), 2);
 
             drop(dict_sub);

tests/test_mapping.rs

@@ -123,7 +123,7 @@ fn mapping_is_not_sequence() {
 
         PyMapping::register::<Mapping>(py).unwrap();
 
-        assert!(m.bind(py).as_any().downcast::<PyMapping>().is_ok());
+        assert!(m.bind(py).downcast::<PyMapping>().is_ok());
-        assert!(m.bind(py).as_any().downcast::<PySequence>().is_err());
+        assert!(m.bind(py).downcast::<PySequence>().is_err());
     });
 }

tests/test_proto_methods.rs

@@ -81,7 +81,6 @@ fn test_getattr() {
         let example_py = make_example(py);
         assert_eq!(
             example_py
-                .as_any()
                 .getattr("value")
                 .unwrap()
                 .extract::<i32>()
@@ -90,7 +89,6 @@ fn test_getattr() {
         );
         assert_eq!(
             example_py
-                .as_any()
                 .getattr("special_custom_attr")
                 .unwrap()
                 .extract::<i32>()
@@ -98,7 +96,6 @@ fn test_getattr() {
             20,
         );
         assert!(example_py
-            .as_any()
             .getattr("other_attr")
             .unwrap_err()
             .is_instance_of::<PyAttributeError>(py));
@@ -109,13 +106,9 @@ fn test_getattr() {
 fn test_setattr() {
     Python::with_gil(|py| {
         let example_py = make_example(py);
-        example_py
+        example_py.setattr("special_custom_attr", 15).unwrap();
-            .as_any()
-            .setattr("special_custom_attr", 15)
-            .unwrap();
         assert_eq!(
             example_py
-                .as_any()
                 .getattr("special_custom_attr")
                 .unwrap()
                 .extract::<i32>()
@@ -129,12 +122,8 @@ fn test_setattr() {
 fn test_delattr() {
     Python::with_gil(|py| {
         let example_py = make_example(py);
-        example_py.as_any().delattr("special_custom_attr").unwrap();
+        example_py.delattr("special_custom_attr").unwrap();
-        assert!(example_py
+        assert!(example_py.getattr("special_custom_attr").unwrap().is_none());
-            .as_any()
-            .getattr("special_custom_attr")
-            .unwrap()
-            .is_none());
     })
 }
 
@@ -142,7 +131,7 @@ fn test_delattr() {
 fn test_str() {
     Python::with_gil(|py| {
         let example_py = make_example(py);
-        assert_eq!(example_py.as_any().str().unwrap().to_cow().unwrap(), "5");
+        assert_eq!(example_py.str().unwrap().to_cow().unwrap(), "5");
     })
 }
 
@@ -151,7 +140,7 @@ fn test_repr() {
     Python::with_gil(|py| {
         let example_py = make_example(py);
         assert_eq!(
-            example_py.as_any().repr().unwrap().to_cow().unwrap(),
+            example_py.repr().unwrap().to_cow().unwrap(),
             "ExampleClass(value=5)"
         );
     })
@@ -161,7 +150,7 @@ fn test_repr() {
 fn test_hash() {
     Python::with_gil(|py| {
         let example_py = make_example(py);
-        assert_eq!(example_py.as_any().hash().unwrap(), 5);
+        assert_eq!(example_py.hash().unwrap(), 5);
     })
 }
 
@@ -169,9 +158,9 @@ fn test_hash() {
 fn test_bool() {
     Python::with_gil(|py| {
         let example_py = make_example(py);
-        assert!(example_py.as_any().is_truthy().unwrap());
+        assert!(example_py.is_truthy().unwrap());
         example_py.borrow_mut().value = 0;
-        assert!(!example_py.as_any().is_truthy().unwrap());
+        assert!(!example_py.is_truthy().unwrap());
     })
 }
 
@@ -231,7 +220,7 @@ fn mapping() {
         )
         .unwrap();
 
-        let mapping: &Bound<'_, PyMapping> = inst.bind(py).as_any().downcast().unwrap();
+        let mapping: &Bound<'_, PyMapping> = inst.bind(py).downcast().unwrap();
 
         py_assert!(py, inst, "len(inst) == 0");
 
@@ -333,7 +322,7 @@ fn sequence() {
 
         let inst = Py::new(py, Sequence { values: vec![] }).unwrap();
 
-        let sequence: &Bound<'_, PySequence> = inst.bind(py).as_any().downcast().unwrap();
+        let sequence: &Bound<'_, PySequence> = inst.bind(py).downcast().unwrap();
 
         py_assert!(py, inst, "len(inst) == 0");
 
@@ -360,16 +349,16 @@ fn sequence() {
         // indices.
         assert!(sequence.len().is_err());
         // however regular python len() works thanks to mp_len slot
-        assert_eq!(inst.bind(py).as_any().len().unwrap(), 0);
+        assert_eq!(inst.bind(py).len().unwrap(), 0);
 
         py_run!(py, inst, "inst.append(0)");
         sequence.set_item(0, 5).unwrap();
-        assert_eq!(inst.bind(py).as_any().len().unwrap(), 1);
+        assert_eq!(inst.bind(py).len().unwrap(), 1);
 
         assert_eq!(sequence.get_item(0).unwrap().extract::<u8>().unwrap(), 5);
         sequence.del_item(0).unwrap();
 
-        assert_eq!(inst.bind(py).as_any().len().unwrap(), 0);
+        assert_eq!(inst.bind(py).len().unwrap(), 0);
     });
 }