fix: accept __index__ objects for unsigned integers without conversion so enum == numpy int works

include/pybind11/cast.h

@@ -259,22 +259,20 @@ struct type_caster<T, enable_if_t<std::is_arithmetic<T>::value && !is_std_char_t
             return false;
         } else {
             handle src_or_index = src;
-            // PyPy: 7.3.7's 3.8 does not implement PyLong_*'s __index__ calls.
-#if defined(PYPY_VERSION)
             object index;
-            // If not a PyLong, we need to call PyNumber_Index explicitly on PyPy.
-            // When convert is false, we only reach here if PYBIND11_INDEX_CHECK passed above.
-            if (!PYBIND11_LONG_CHECK(src.ptr())) {
+            // PyLong_AsUnsignedLong[Long] never calls __index__, so call PyNumber_Index here.
+            if (std::is_unsigned<py_type>::value && !PYBIND11_LONG_CHECK(src.ptr())
+                && PYBIND11_INDEX_CHECK(src.ptr())) {
                 index = reinterpret_steal<object>(PyNumber_Index(src.ptr()));
                 if (!index) {
                     PyErr_Clear();
-                    if (!convert)
+                    if (!convert) {
                         return false;
+                    }
                 } else {
                     src_or_index = index;
                 }
             }
-#endif
             if (std::is_unsigned<py_type>::value) {
                 py_value = as_unsigned<py_type>(src_or_index.ptr());
             } else { // signed integer:

include/pybind11/complex.h

@@ -58,7 +58,6 @@ class type_caster<std::complex<T>> {
         }
         handle src_or_index = src;
         // PyPy: 7.3.7's 3.8 does not implement PyLong_*'s __index__ calls.
-        // The same logic is used in numeric_caster for ints and floats
 #if defined(PYPY_VERSION)
         object index;
         if (PYBIND11_INDEX_CHECK(src.ptr())) {

tests/test_builtin_casters.cpp

@@ -235,6 +235,8 @@ TEST_SUBMODULE(builtin_casters, m) {
     // test_int_convert
     m.def("int_passthrough", [](int arg) { return arg; });
     m.def("int_passthrough_noconvert", [](int arg) { return arg; }, py::arg{}.noconvert());
+    m.def("uint_passthrough", [](unsigned arg) { return arg; });
+    m.def("uint_passthrough_noconvert", [](unsigned arg) { return arg; }, py::arg{}.noconvert());
 
     // test_float_convert
     m.def("float_passthrough", [](float arg) { return arg; });

tests/test_builtin_casters.py

@@ -247,7 +247,8 @@ def test_integer_casting():
     assert "incompatible function arguments" in str(excinfo.value)
 
 
-def test_int_convert(doc):
+@pytest.mark.parametrize("prefix", ["int", "uint"])
+def test_int_convert(doc, prefix):
     class Int:
         def __int__(self):
             return 42
@@ -284,13 +285,14 @@ def __index__(self):
         def __int__(self):
             return 42
 
-    convert, noconvert = m.int_passthrough, m.int_passthrough_noconvert
+    convert = getattr(m, f"{prefix}_passthrough")
+    noconvert = getattr(m, f"{prefix}_passthrough_noconvert")
 
     assert (
         doc(convert)
-        == "int_passthrough(arg0: typing.SupportsInt | typing.SupportsIndex) -> int"
+        == f"{prefix}_passthrough(arg0: typing.SupportsInt | typing.SupportsIndex) -> int"
     )
-    assert doc(noconvert) == "int_passthrough_noconvert(arg0: int) -> int"
+    assert doc(noconvert) == f"{prefix}_passthrough_noconvert(arg0: int) -> int"
 
     def requires_conversion(v):
         pytest.raises(TypeError, noconvert, v)
@@ -302,7 +304,7 @@ def cant_convert(v):
     assert noconvert(7) == 7
     cant_convert(3.14159)
     # TODO: Avoid DeprecationWarning in `PyLong_AsLong` (and similar)
-    if sys.version_info < (3, 10) and env.CPYTHON:
+    if sys.version_info < (3, 10) and env.CPYTHON and prefix == "int":
         with pytest.deprecated_call():
             assert convert(Int()) == 42
     else:
@@ -402,10 +404,12 @@ def cant_convert(v):
     cant_convert(Int())
 
 
-def test_numpy_int_convert():
+@pytest.mark.parametrize("prefix", ["int", "uint"])
+def test_numpy_int_convert(prefix):
     np = pytest.importorskip("numpy")
 
-    convert, noconvert = m.int_passthrough, m.int_passthrough_noconvert
+    convert = getattr(m, f"{prefix}_passthrough")
+    noconvert = getattr(m, f"{prefix}_passthrough_noconvert")
 
     def require_implicit(v):
         pytest.raises(TypeError, noconvert, v)
@@ -417,7 +421,7 @@ def require_implicit(v):
     # The implicit conversion from np.float32 is undesirable but currently accepted.
     # TODO: Avoid DeprecationWarning in `PyLong_AsLong` (and similar)
     # https://github.com/pybind/pybind11/issues/3408
-    if sys.version_info < (3, 10) and env.CPYTHON:
+    if sys.version_info < (3, 10) and env.CPYTHON and prefix == "int":
         with pytest.deprecated_call():
             assert convert(np.float32(3.14159)) == 3
     else:

tests/test_enum.cpp

@@ -59,6 +59,12 @@ TEST_SUBMODULE(enums, m) {
         .value("ESecondMode", ClassWithUnscopedEnum::ESecondMode)
         .export_values();
 
+    // test_scalar_comparison_with_index_object
+    enum UnscopedInt32Enum : std::int32_t { I32Three = 3 };
+    py::enum_<UnscopedInt32Enum>(m, "UnscopedInt32Enum").value("Three", I32Three);
+    enum UnscopedUInt32Enum : std::uint32_t { U32Three = 3 };
+    py::enum_<UnscopedUInt32Enum>(m, "UnscopedUInt32Enum").value("Three", U32Three);
+
     // test_enum_to_int
     m.def("test_enum_to_int", [](int) {});
     m.def("test_enum_to_uint", [](uint32_t) {});

tests/test_enum.py

@@ -230,6 +230,26 @@ def test_enum_to_int():
     m.test_enum_to_long_long(m.ScopedBoolEnum.TRUE)
 
 
+@pytest.mark.parametrize("enum_name", ["UnscopedInt32Enum", "UnscopedUInt32Enum"])
+def test_scalar_comparison_with_index_object(enum_name):
+    # An unsigned underlying type must compare like a signed one against objects
+    # that only implement __index__ (e.g. numpy integers).
+    class Index:
+        def __index__(self):
+            return 3
+
+    three = getattr(m, enum_name).Three
+    assert three == 3
+    assert three == Index()
+    assert not three != Index()
+    assert three != 4
+    np = pytest.importorskip("numpy")
+    assert three == np.int32(3)
+    assert three == np.uint64(3)
+    assert not three != np.int64(3)
+    assert three != np.int32(4)
+
+
 def test_duplicate_enum_name():
     with pytest.raises(ValueError) as excinfo:
         m.register_bad_enum()