Add a (failing test) for issue PyO3#1064

RichComparisonToSelf expects to compare itself with objects of the same type,
but they we shouldn't raise TypeError but return NotImplemented.

Cargo.toml

@@ -41,6 +41,8 @@ macros = ["ctor", "indoc", "inventory", "paste", "pyo3cls", "unindent"]
 # Optimizes PyObject to Vec conversion and so on.
 nightly = []
 
+no-return-notimplemented = []
+
 # this is no longer needed internally, but setuptools-rust assumes this feature
 python3 = []
 

tests/test_arithmetics.rs

@@ -423,3 +423,65 @@ fn rich_comparisons_python_3_type_error() {
     py_expect_exception!(py, c2, "c2 >= 1", PyTypeError);
     py_expect_exception!(py, c2, "1 >= c2", PyTypeError);
 }
+
+#[cfg(not(feature = "no-return-notimplemented"))]
+#[cfg(test)]
+mod not_implemented {
+    use super::*;
+
+    #[pyclass]
+    struct RichComparisonToSelf {}
+
+    #[pyproto]
+    impl<'p> PyObjectProtocol<'p> for RichComparisonToSelf {
+        fn __repr__(&self) -> &'static str {
+            "RC_Self"
+        }
+
+        fn __richcmp__(&self, other: PyRef<'p, Self>, _op: CompareOp) -> PyObject {
+            other.py().None()
+        }
+    }
+
+    macro_rules! not_implemented_test {
+        ($dunder: ident, $operator: literal) => {
+            #[test]
+            fn $dunder() {
+                let gil = Python::acquire_gil();
+                let py = gil.python();
+                let c2 = PyCell::new(py, RichComparisonToSelf {}).unwrap();
+                py_run!(
+                    py,
+                    c2,
+                    &format!(
+                        "\
+class Other:
+    def __{}__(self, other):
+        return True
+assert c2 {} Other()",
+                        stringify!($dunder), $operator
+                    )
+                );
+                py_expect_exception!(
+                    py,
+                    c2,
+                    &format!("class Other: pass; assert c2 {} Other()", $operator),
+                    PyTypeError
+                );
+            }
+        };
+
+        [$( ($dunder: ident, $operator: literal) ),*] => {
+			$(not_implemented_test!{$dunder, $operator})*
+		};
+    }
+
+    not_implemented_test![
+        (eq, "=="),
+        (ne, "!="),
+        (lt, "<"),
+        (le, "<="),
+        (gt, ">"),
+        (ge, ">=")
+    ];
+}