fix rv policy inference rules (fixes issue #39)

Author: wjakob

include/nanobind/nb_cast.h

@@ -218,7 +218,9 @@ template <typename T> NB_INLINE rv_policy infer_policy(rv_policy policy) {
             policy = rv_policy::copy;
     } else {
         if (policy == rv_policy::automatic ||
-            policy == rv_policy::automatic_reference)
+            policy == rv_policy::automatic_reference ||
+            policy == rv_policy::reference ||
+            policy == rv_policy::reference_internal)
             policy = rv_policy::move;
     }
     return policy;

tests/test_enum.cpp

@@ -6,6 +6,9 @@ enum class Enum  : uint32_t { A, B, C = (uint32_t) -1 };
 enum class SEnum : int32_t { A, B, C = (int32_t) -1 };
 enum ClassicEnum { Item1, Item2 };
 
+struct EnumProperty { Enum get_enum() { return Enum::A; } };
+
+
 NB_MODULE(test_enum_ext, m) {
     nb::enum_<Enum>(m, "Enum")
         .value("A", Enum::A, "Value A")
@@ -25,4 +28,9 @@ NB_MODULE(test_enum_ext, m) {
     m.def("from_enum", [](Enum value) { return (uint32_t) value; });
     m.def("to_enum", [](uint32_t value) { return (Enum) value; });
     m.def("from_enum", [](SEnum value) { return (int32_t) value; });
+
+    // test for issue #39
+    nb::class_<EnumProperty>(m, "EnumProperty")
+        .def(nb::init<>())
+        .def_property_readonly("read_enum", &EnumProperty::get_enum);
 }

tests/test_enum.py

@@ -70,3 +70,9 @@ def test03_enum_arithmetic():
 def test04_enum_export():
     assert t.Item1 is t.ClassicEnum.Item1 and int(t.Item1) == 0
     assert t.Item2 is t.ClassicEnum.Item2 and int(t.Item2) == 1
+
+# test for issue #39
+def test05_enum_property():
+    w = t.EnumProperty()
+    assert w.read_enum == t.Enum.A
+    assert str(w.read_enum) == 'test_enum_ext.Enum.A'