Add test_home_planet_wrap_very_lonely_traveler(), test_exo_planet_pyb…

…ind11_wrap_very_lonely_traveler()

tests/CMakeLists.txt

@@ -219,7 +219,8 @@ tests_extra_targets("test_exceptions.py;test_local_bindings.py;test_stl.py;test_
 # And add additional targets for other tests.
 tests_extra_targets("test_exceptions.py" "cross_module_interleaved_error_already_set")
 tests_extra_targets("test_gil_scoped.py" "cross_module_gil_utils")
-tests_extra_targets("test_cpp_conduit.py" "exo_planet_pybind11;exo_planet_c_api")
+tests_extra_targets("test_cpp_conduit.py"
+                    "exo_planet_pybind11;exo_planet_c_api;home_planet_very_lonely_traveler")
 
 set(PYBIND11_EIGEN_REPO
     "https://gitlab.com/libeigen/eigen.git"

tests/exo_planet_pybind11.cpp

@@ -7,4 +7,13 @@
 
 #include "test_cpp_conduit_traveler_bindings.h"
 
-PYBIND11_MODULE(exo_planet_pybind11, m) { pybind11_tests::test_cpp_conduit::wrap_traveler(m); }
+namespace pybind11_tests {
+namespace test_cpp_conduit {
+
+PYBIND11_MODULE(exo_planet_pybind11, m) {
+    wrap_traveler(m);
+    m.def("wrap_very_lonely_traveler", [m]() { wrap_very_lonely_traveler(m); });
+}
+
+} // namespace test_cpp_conduit
+} // namespace pybind11_tests

tests/home_planet_very_lonely_traveler.cpp

@@ -0,0 +1,13 @@
+// Copyright (c) 2024 The pybind Community.
+
+#include "test_cpp_conduit_traveler_bindings.h"
+
+namespace pybind11_tests {
+namespace test_cpp_conduit {
+
+PYBIND11_MODULE(home_planet_very_lonely_traveler, m) {
+    m.def("wrap_very_lonely_traveler", [m]() { wrap_very_lonely_traveler(m); });
+}
+
+} // namespace test_cpp_conduit
+} // namespace pybind11_tests

tests/test_cpp_conduit.cpp

@@ -15,6 +15,7 @@ TEST_SUBMODULE(cpp_conduit, m) {
     m.attr("cpp_type_info_capsule_int") = py::capsule(&typeid(int), typeid(std::type_info).name());
 
     wrap_traveler(m);
+    wrap_lonely_traveler(m);
 }
 
 } // namespace test_cpp_conduit

tests/test_cpp_conduit.py

@@ -4,6 +4,7 @@
 
 import exo_planet_c_api
 import exo_planet_pybind11
+import home_planet_very_lonely_traveler
 import pytest
 
 from pybind11_tests import cpp_conduit as home_planet
@@ -125,3 +126,37 @@ def test_exo_planet_c_api_premium_traveler(premium_traveler_type):
     pt = premium_traveler_type("gucci", 5)
     assert exo_planet_c_api.GetLuggage(pt) == "gucci"
     assert exo_planet_c_api.GetPoints(pt) == 5
+
+
+def test_home_planet_wrap_very_lonely_traveler():
+    # This does not exercise the cpp_conduit feature, but is here to
+    # demonstrate that the cpp_conduit feature does not solve all
+    # cross-extension interoperability issues.
+    # Here is the proof that the following works for extensions with
+    # matching `PYBIND11_INTERNALS_ID`s:
+    #     test_cpp_conduit.cpp:
+    #         py::class_<LonelyTraveler>
+    #     home_planet_very_lonely_traveler.cpp:
+    #         py::class_<VeryLonelyTraveler, LonelyTraveler>
+    # See test_exo_planet_pybind11_wrap_very_lonely_traveler() for the negative
+    # test.
+    assert home_planet.LonelyTraveler is not None  # Verify that the base class exists.
+    home_planet_very_lonely_traveler.wrap_very_lonely_traveler()
+    # Ensure that the derived class exists.
+    assert home_planet_very_lonely_traveler.VeryLonelyTraveler is not None
+
+
+def test_exo_planet_pybind11_wrap_very_lonely_traveler():
+    # See comment under test_home_planet_wrap_very_lonely_traveler() first.
+    # Here the `PYBIND11_INTERNALS_ID`s don't match between:
+    #     test_cpp_conduit.cpp:
+    #         py::class_<LonelyTraveler>
+    #     exo_planet_pybind11.cpp:
+    #         py::class_<VeryLonelyTraveler, LonelyTraveler>
+    assert home_planet.LonelyTraveler is not None  # Verify that the base class exists.
+    with pytest.raises(
+        RuntimeError,
+        match='^generic_type: type "VeryLonelyTraveler" referenced unknown base type '
+        '"pybind11_tests::test_cpp_conduit::LonelyTraveler"$',
+    ):
+        exo_planet_pybind11.wrap_very_lonely_traveler()

tests/test_cpp_conduit_traveler_bindings.h

@@ -35,5 +35,13 @@ inline void wrap_traveler(py::module_ m) {
     m.def("get_points", [](const PremiumTraveler &person) { return person.points; });
 }
 
+inline void wrap_lonely_traveler(py::module_ m) {
+    py::class_<LonelyTraveler>(m, "LonelyTraveler");
+}
+
+inline void wrap_very_lonely_traveler(py::module_ m) {
+    py::class_<VeryLonelyTraveler, LonelyTraveler>(m, "VeryLonelyTraveler");
+}
+
 } // namespace test_cpp_conduit
 } // namespace pybind11_tests

tests/test_cpp_conduit_traveler_types.h

@@ -18,5 +18,8 @@ struct PremiumTraveler : Traveler {
     int points;
 };
 
+struct LonelyTraveler {};
+struct VeryLonelyTraveler : LonelyTraveler {};
+
 } // namespace test_cpp_conduit
 } // namespace pybind11_tests