Adding unit tests: 2 x test_std_make_shared_factory

Completes unit test coverage for the changed code in smart_holder_type_casters.h.

include/pybind11/detail/smart_holder_type_casters.h

@@ -413,21 +413,20 @@ struct smart_holder_type_caster_load {
             if (std::get_deleter<shared_ptr_dec_ref_deleter>(hld.vptr) != nullptr) {
                 // This code is reachable only if there are multiple registered_instances for the
                 // same pointee.
-                // SMART_HOLDER_WIP: keep weak_ref?
+                // SMART_HOLDER_WIP: keep weak_ref
                 std::shared_ptr<void> void_shd_ptr = hld.template as_shared_ptr<void>();
                 return std::shared_ptr<T>(void_shd_ptr, type_raw_ptr);
             }
             if (!pybindit::memory::type_has_shared_from_this(type_raw_ptr)) {
-                // SMART_HOLDER_WIP: unit test coverage.
-                // SMART_HOLDER_WIP: keep weak_ref?
+                // SMART_HOLDER_WIP: keep weak_ref
                 auto self = reinterpret_cast<PyObject *>(load_impl.loaded_v_h.inst);
                 Py_INCREF(self);
                 return std::shared_ptr<T>(type_raw_ptr, shared_ptr_dec_ref_deleter{self});
             }
             if (hld.vptr_is_external_shared_ptr) {
-                // SMART_HOLDER_WIP: unit test coverage.
-                pybind11_fail("smart_holder_type_casters loaded_as_shared_ptr failure: external "
-                              "shared_ptr for type with shared_from_this.");
+                pybind11_fail("smart_holder_type_casters loaded_as_shared_ptr failure: not "
+                              "implemented: trampoline-self-life-support for external shared_ptr "
+                              "to type inheriting from std::enable_shared_from_this.");
             }
             pybind11_fail("smart_holder_type_casters: loaded_as_shared_ptr failure: internal "
                           "inconsistency.");

tests/test_class_sh_trampoline_shared_from_this.cpp

@@ -103,7 +103,10 @@ PYBIND11_SMART_HOLDER_TYPE_CASTERS(SftSharedPtrStash)
 
 TEST_SUBMODULE(class_sh_trampoline_shared_from_this, m) {
     py::classh<Sft, SftTrampoline>(m, "Sft")
-        .def(py::init<std::string>())
+        .def(py::init<const std::string &>())
+        .def(py::init([](const std::string &history, int) {
+            return std::make_shared<SftTrampoline>(history);
+        }))
         .def_readonly("history", &Sft::history)
         // This leads to multiple entries in registered_instances:
         .def(py::init([](const std::shared_ptr<Sft> &existing) { return existing; }));

tests/test_class_sh_trampoline_shared_from_this.py

@@ -171,3 +171,20 @@ def test_multiple_registered_instances_for_same_pointee():
         else:
             assert not hasattr(obj_pt, "attachment_in_dict")
         break  # Comment out for manual leak checking (use `top` command).
+
+
+def test_std_make_shared_factory():
+    class PySftMakeShared(m.Sft):
+        def __init__(self, history):
+            super(PySftMakeShared, self).__init__(history, 0)
+
+    obj = PySftMakeShared("PySftMakeShared")
+    assert obj.history == "PySftMakeShared"
+    with pytest.raises(RuntimeError) as exc_info:
+        m.pass_through_shd_ptr(obj)
+    assert (
+        str(exc_info.value)
+        == "smart_holder_type_casters loaded_as_shared_ptr failure: not implemented:"
+        " trampoline-self-life-support for external shared_ptr to type inheriting"
+        " from std::enable_shared_from_this."
+    )

tests/test_class_sh_trampoline_shared_ptr_cpp_arg.cpp

@@ -26,7 +26,10 @@ struct SpBase {
     virtual ~SpBase()      = default;
 };
 
+std::shared_ptr<SpBase> pass_through_shd_ptr(const std::shared_ptr<SpBase> &obj) { return obj; }
+
 struct PySpBase : SpBase {
+    using SpBase::SpBase;
     bool is_base_used() override { PYBIND11_OVERRIDE(bool, SpBase, is_base_used); }
 };
 
@@ -61,9 +64,12 @@ TEST_SUBMODULE(class_sh_trampoline_shared_ptr_cpp_arg, m) {
 
     py::classh<SpBase, PySpBase>(m, "SpBase")
         .def(py::init<>())
+        .def(py::init([](int) { return std::make_shared<PySpBase>(); }))
         .def("is_base_used", &SpBase::is_base_used)
         .def("has_python_instance", &SpBase::has_python_instance);
 
+    m.def("pass_through_shd_ptr", pass_through_shd_ptr);
+
     py::classh<SpBaseTester>(m, "SpBaseTester")
         .def(py::init<>())
         .def("get_object", &SpBaseTester::get_object)

tests/test_class_sh_trampoline_shared_ptr_cpp_arg.py

@@ -131,3 +131,12 @@ def test_infinite():
     while True:
         tester.set_object(m.SpBase())
         return  # Comment out for manual leak checking (use `top` command).
+
+
+def test_std_make_shared_factory():
+    class PyChild(m.SpBase):
+        def __init__(self):
+            super(PyChild, self).__init__(0)
+
+    obj = PyChild()
+    assert m.pass_through_shd_ptr(obj) is obj