fixup! review

Author: EricCousineau-TRI

include/pybind11/cast.h

@@ -92,7 +92,7 @@ public:
     static ::pybind11::handle cast(                                                               \
         T_ *src, ::pybind11::return_value_policy policy, ::pybind11::handle parent) {             \
         if (!src)                                                                                 \
-            return none().release();                                                              \
+            return ::pybind11::none().release();                                                  \
         if (policy == ::pybind11::return_value_policy::take_ownership) {                          \
             auto h = cast(std::move(*src), policy, parent);                                       \
             delete src;                                                                           \

tests/test_custom_type_casters.cpp

@@ -20,6 +20,7 @@ class ArgInspector2 {
     std::string arg = "(default arg inspector 2)";
 };
 class ArgAlwaysConverts {};
+
 namespace pybind11 {
 namespace detail {
 template <>
@@ -105,6 +106,34 @@ struct type_caster<DestructionTester> {
 } // namespace detail
 } // namespace pybind11
 
+// Define type caster outside of `pybind11::detail` and then alias it.
+namespace other_lib {
+struct MyType {};
+// Corrupt `py` shorthand alias for surrounding context.
+namespace py {}
+// Corrupt unqualified relative `pybind11` namespace.
+namespace pybind11 {}
+// Correct alias.
+namespace py_ = ::pybind11;
+// Define caster. This is effectively no-op, we only ensure it compiles and we
+// don't have any symbol collision when using macro mixin.
+struct my_caster {
+    PYBIND11_TYPE_CASTER(MyType, py_::detail::const_name("MyType"));
+    bool load(py_::handle, bool) { return true; }
+
+    static py_::handle cast(const MyType &, py_::return_value_policy, py_::handle) {
+        return py_::bool_(true).release();
+    }
+};
+} // namespace other_lib
+// Effectively "alias" it into correct namespace (via inheritance).
+namespace pybind11 {
+namespace detail {
+template <>
+struct type_caster<other_lib::MyType> : public other_lib::my_caster {};
+} // namespace detail
+} // namespace pybind11
+
 TEST_SUBMODULE(custom_type_casters, m) {
     // test_custom_type_casters
 
@@ -175,4 +204,6 @@ TEST_SUBMODULE(custom_type_casters, m) {
     m.def("destruction_tester_cstats",
           &ConstructorStats::get<DestructionTester>,
           py::return_value_policy::reference);
+
+    m.def("other_lib_type", [](other_lib::MyType x) { return x; });
 }

tests/test_custom_type_casters.py

@@ -114,3 +114,7 @@ def test_custom_caster_destruction():
 
     # Make sure we still only have the original object (from ..._no_destroy()) alive:
     assert cstats.alive() == 1
+
+
+def test_custom_caster_other_lib():
+    assert m.other_lib_type(True)