silence deprecation warning for enum with custom __eq__ (#4692)

* silence deprecation warning for enum with custom `__eq__`

* clippy

* also support `__richcmp__`

* fix ci

---------

Co-authored-by: Icxolu <[email protected]>

newsfragments/4692.fixed.md

@@ -0,0 +1 @@
+Fix incorrect deprecation warning for `#[pyclass] enum`s with custom `__eq__` implementation.

pyo3-macros-backend/src/pyclass.rs

@@ -1908,12 +1908,7 @@ fn pyclass_richcmp_simple_enum(
     let deprecation = (options.eq_int.is_none() && options.eq.is_none())
         .then(|| {
             quote! {
-                #[deprecated(
-                    since = "0.22.0",
-                    note = "Implicit equality for simple enums is deprecated. Use `#[pyclass(eq, eq_int)]` to keep the current behavior."
-                )]
-                const DEPRECATION: () = ();
-                const _: () = DEPRECATION;
+                let _ = #pyo3_path::impl_::pyclass::DeprecationTest::<#cls>::new().autogenerated_equality();
             }
         })
         .unwrap_or_default();

pyo3-macros-backend/src/pymethod.rs

@@ -1348,13 +1348,22 @@ impl SlotDef {
         )?;
         let name = spec.name;
         let holders = holders.init_holders(ctx);
+        let dep = if method_name == "__richcmp__" {
+            quote! {
+                #[allow(unknown_lints, non_local_definitions)]
+                impl #pyo3_path::impl_::pyclass::HasCustomRichCmp for #cls {}
+            }
+        } else {
+            TokenStream::default()
+        };
         let associated_method = quote! {
             #[allow(non_snake_case)]
             unsafe fn #wrapper_ident(
                 py: #pyo3_path::Python<'_>,
                 _raw_slf: *mut #pyo3_path::ffi::PyObject,
                 #(#arg_idents: #arg_types),*
             ) -> #pyo3_path::PyResult<#ret_ty> {
+                #dep
                 let function = #cls::#name; // Shadow the method name to avoid #3017
                 let _slf = _raw_slf;
                 #holders

src/impl_/pyclass.rs

@@ -878,6 +878,8 @@ macro_rules! generate_pyclass_richcompare_slot {
                 other: *mut $crate::ffi::PyObject,
                 op: ::std::os::raw::c_int,
             ) -> *mut $crate::ffi::PyObject {
+                impl $crate::impl_::pyclass::HasCustomRichCmp for $cls {}
+
                 $crate::impl_::trampoline::richcmpfunc(slf, other, op, |py, slf, other, op| {
                     use $crate::class::basic::CompareOp;
                     use $crate::impl_::pyclass::*;
@@ -1519,6 +1521,50 @@ fn pyo3_get_value<
     Ok((unsafe { &*value }).clone().into_py(py).into_ptr())
 }
 
+/// Marker trait whether a class implemented a custom comparison. Used to
+/// silence deprecation of autogenerated `__richcmp__` for enums.
+pub trait HasCustomRichCmp {}
+
+/// Autoref specialization setup to emit deprecation warnings for autogenerated
+/// pyclass equality.
+pub struct DeprecationTest<T>(Deprecation, ::std::marker::PhantomData<T>);
+pub struct Deprecation;
+
+impl<T> DeprecationTest<T> {
+    #[inline]
+    #[allow(clippy::new_without_default)]
+    pub const fn new() -> Self {
+        DeprecationTest(Deprecation, ::std::marker::PhantomData)
+    }
+}
+
+impl<T> std::ops::Deref for DeprecationTest<T> {
+    type Target = Deprecation;
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl<T> DeprecationTest<T>
+where
+    T: HasCustomRichCmp,
+{
+    /// For `HasCustomRichCmp` types; no deprecation warning.
+    #[inline]
+    pub fn autogenerated_equality(&self) {}
+}
+
+impl Deprecation {
+    #[deprecated(
+        since = "0.22.0",
+        note = "Implicit equality for simple enums is deprecated. Use `#[pyclass(eq, eq_int)]` to keep the current behavior."
+    )]
+    /// For types which don't implement `HasCustomRichCmp`; emits deprecation warning.
+    #[inline]
+    pub fn autogenerated_equality(&self) {}
+}
+
 #[cfg(test)]
 #[cfg(feature = "macros")]
 mod tests {

tests/test_enum.rs

@@ -2,6 +2,7 @@
 
 use pyo3::prelude::*;
 use pyo3::py_run;
+use pyo3::types::PyString;
 
 #[path = "../src/tests/common.rs"]
 mod common;
@@ -357,3 +358,48 @@ mod deprecated {
         })
     }
 }
+
+#[test]
+fn custom_eq() {
+    #[pyclass(frozen)]
+    #[derive(PartialEq)]
+    pub enum CustomPyEq {
+        A,
+        B,
+    }
+
+    #[pymethods]
+    impl CustomPyEq {
+        fn __eq__(&self, other: &Bound<'_, PyAny>) -> bool {
+            if let Ok(rhs) = other.downcast::<PyString>() {
+                rhs.to_cow().map_or(false, |rhs| self.__str__() == rhs)
+            } else if let Ok(rhs) = other.downcast::<Self>() {
+                self == rhs.get()
+            } else {
+                false
+            }
+        }
+
+        fn __str__(&self) -> String {
+            match self {
+                CustomPyEq::A => "A".to_string(),
+                CustomPyEq::B => "B".to_string(),
+            }
+        }
+    }
+
+    Python::with_gil(|py| {
+        let a = Bound::new(py, CustomPyEq::A).unwrap();
+        let b = Bound::new(py, CustomPyEq::B).unwrap();
+
+        assert!(a.as_any().eq(&a).unwrap());
+        assert!(a.as_any().eq("A").unwrap());
+        assert!(a.as_any().ne(&b).unwrap());
+        assert!(a.as_any().ne("B").unwrap());
+
+        assert!(b.as_any().eq(&b).unwrap());
+        assert!(b.as_any().eq("B").unwrap());
+        assert!(b.as_any().ne(&a).unwrap());
+        assert!(b.as_any().ne("A").unwrap());
+    })
+}

tests/ui/deprecations.stderr

@@ -28,7 +28,7 @@ error: use of deprecated constant `__pyfunction_pyfunction_option_4::SIGNATURE`:
 21 | fn pyfunction_option_4(
    |    ^^^^^^^^^^^^^^^^^^^
 
-error: use of deprecated constant `SimpleEnumWithoutEq::__pyo3__generated____richcmp__::DEPRECATION`: Implicit equality for simple enums is deprecated. Use `#[pyclass(eq, eq_int)]` to keep the current behavior.
+error: use of deprecated method `pyo3::impl_::pyclass::Deprecation::autogenerated_equality`: Implicit equality for simple enums is deprecated. Use `#[pyclass(eq, eq_int)]` to keep the current behavior.
   --> tests/ui/deprecations.rs:28:1
    |
 28 | #[pyclass]

tests/ui/invalid_proto_pymethods.stderr

@@ -40,6 +40,17 @@ note: candidate #2 is defined in an impl for the type `EqAndRichcmp`
    | ^^^^^^^^^^^^
    = note: this error originates in the macro `::pyo3::impl_::pyclass::generate_pyclass_richcompare_slot` which comes from the expansion of the attribute macro `pymethods` (in Nightly builds, run with -Z macro-backtrace for more info)
 
+error[E0119]: conflicting implementations of trait `HasCustomRichCmp` for type `EqAndRichcmp`
+  --> tests/ui/invalid_proto_pymethods.rs:55:1
+   |
+55 | #[pymethods]
+   | ^^^^^^^^^^^^
+   | |
+   | first implementation here
+   | conflicting implementation for `EqAndRichcmp`
+   |
+   = note: this error originates in the macro `::pyo3::impl_::pyclass::generate_pyclass_richcompare_slot` which comes from the expansion of the attribute macro `pymethods` (in Nightly builds, run with -Z macro-backtrace for more info)
+
 error[E0592]: duplicate definitions with name `__pymethod___richcmp____`
   --> tests/ui/invalid_proto_pymethods.rs:55:1
    |

tests/ui/invalid_pyclass_args.stderr

@@ -162,6 +162,17 @@ error: The format string syntax cannot be used with enums
 171 | #[pyclass(eq, str = "Stuff...")]
     |                     ^^^^^^^^^^
 
+error[E0119]: conflicting implementations of trait `HasCustomRichCmp` for type `EqOptAndManualRichCmp`
+  --> tests/ui/invalid_pyclass_args.rs:41:1
+   |
+37 | #[pyclass(eq)]
+   | -------------- first implementation here
+...
+41 | #[pymethods]
+   | ^^^^^^^^^^^^ conflicting implementation for `EqOptAndManualRichCmp`
+   |
+   = note: this error originates in the attribute macro `pymethods` (in Nightly builds, run with -Z macro-backtrace for more info)
+
 error[E0592]: duplicate definitions with name `__pymethod___richcmp____`
   --> tests/ui/invalid_pyclass_args.rs:37:1
    |