Changes and tests covering classh_type_casters try_implicit_casts.

include/pybind11/detail/classh_type_casters.h

@@ -58,7 +58,6 @@ public:
     }
 
     bool try_implicit_casts(handle src, bool convert) {
-        pybind11_fail("classh_type_casters: try_implicit_casts UNTESTED.");
         for (auto &cast : typeinfo->implicit_casts) {
             modified_type_caster_generic_load_impl sub_caster(*cast.first);
             if (sub_caster.load(src, convert)) {
@@ -68,7 +67,6 @@ public:
                 loaded_v_h = sub_caster.loaded_v_h;
                 loaded_v_h_cpptype = cast.first;
                 implicit_cast = cast.second;
-                reinterpret_cast_ok = sub_caster.reinterpret_cast_ok;
                 return true;
             }
         }
@@ -119,7 +117,6 @@ public:
             loaded_v_h = foreign_load_impl->loaded_v_h;
             loaded_v_h_cpptype = foreign_load_impl->loaded_v_h_cpptype;
             implicit_cast = foreign_load_impl->implicit_cast;
-            reinterpret_cast_ok = foreign_load_impl->reinterpret_cast_ok;
             return true;
         }
         return false;
@@ -163,7 +160,7 @@ public:
             if (bases.size() == 1 && (no_cpp_mi || bases.front()->type == typeinfo->type)) {
                 this_.load_value_and_holder(reinterpret_cast<instance *>(src.ptr())->get_value_and_holder());
                 loaded_v_h_cpptype = bases.front()->cpptype;
-                reinterpret_cast_ok = true;
+                reinterpret_cast_deemed_ok = true;
                 return true;
             }
             // Case 2b: the python type inherits from multiple C++ bases.  Check the bases to see if
@@ -175,7 +172,7 @@ public:
                     if (no_cpp_mi ? PyType_IsSubtype(base->type, typeinfo->type) : base->type == typeinfo->type) {
                         this_.load_value_and_holder(reinterpret_cast<instance *>(src.ptr())->get_value_and_holder(base));
                         loaded_v_h_cpptype = base->cpptype;
-                        reinterpret_cast_ok = true;
+                        reinterpret_cast_deemed_ok = true;
                         return true;
                     }
                 }
@@ -219,7 +216,7 @@ public:
     const std::type_info *loaded_v_h_cpptype = nullptr;
     void *(*implicit_cast)(void *) = nullptr;
     value_and_holder loaded_v_h;
-    bool reinterpret_cast_ok = false;
+    bool reinterpret_cast_deemed_ok = false;
 };
 // clang-format on
 
@@ -238,8 +235,14 @@ struct smart_holder_type_caster_load {
     }
 
     T *as_raw_ptr_unowned() {
-        if (load_impl.loaded_v_h_cpptype != nullptr && load_impl.reinterpret_cast_ok) {
-            return reinterpret_cast<T *>(loaded_smhldr_ptr->vptr.get());
+        if (load_impl.loaded_v_h_cpptype != nullptr) {
+            if (load_impl.reinterpret_cast_deemed_ok) {
+                return static_cast<T *>(loaded_smhldr_ptr->vptr.get());
+            }
+            if (load_impl.implicit_cast != nullptr) {
+                void *implicit_casted = load_impl.implicit_cast(loaded_smhldr_ptr->vptr.get());
+                return static_cast<T *>(implicit_casted);
+            }
         }
         return loaded_smhldr_ptr->as_raw_ptr_unowned<T>();
     }

tests/test_classh_inheritance.cpp

@@ -5,22 +5,45 @@
 namespace pybind11_tests {
 namespace classh_inheritance {
 
-struct base {
-    base() : base_id(100) {}
-    virtual ~base() = default;
+template <int Id>
+struct base_template {
+    base_template() : base_id(Id) {}
+    virtual ~base_template() = default;
     virtual int id() const { return base_id; }
     int base_id;
 };
 
+using base = base_template<100>;
+
 struct drvd : base {
     int id() const override { return 2 * base_id; }
 };
 
+// clang-format off
 inline drvd *make_drvd()         { return new drvd; }
 inline base *make_drvd_up_cast() { return new drvd; }
 
-inline int pass_base(const base *b) { return b->id(); }
-inline int pass_drvd(const drvd *d) { return d->id(); }
+inline int pass_base(const base *b) { return b->id() + 11; }
+inline int pass_drvd(const drvd *d) { return d->id() + 12; }
+// clang-format on
+
+using base1 = base_template<110>;
+using base2 = base_template<120>;
+
+// Not reusing base here because it would interfere with the single-inheritance test.
+struct drvd2 : base1, base2 {
+    int id() const override { return 3 * base1::base_id + 4 * base2::base_id; }
+};
+
+// clang-format off
+inline drvd2 *make_drvd2()          { return new drvd2; }
+inline base1 *make_drvd2_up_cast1() { return new drvd2; }
+inline base2 *make_drvd2_up_cast2() { return new drvd2; }
+
+inline int pass_base1(const base1 *b) { return b->id() + 21; }
+inline int pass_base2(const base2 *b) { return b->id() + 22; }
+inline int pass_drvd2(const drvd2 *d) { return d->id() + 23; }
+// clang-format on
 
 } // namespace classh_inheritance
 } // namespace pybind11_tests
@@ -28,6 +51,10 @@ inline int pass_drvd(const drvd *d) { return d->id(); }
 PYBIND11_CLASSH_TYPE_CASTERS(pybind11_tests::classh_inheritance::base)
 PYBIND11_CLASSH_TYPE_CASTERS(pybind11_tests::classh_inheritance::drvd)
 
+PYBIND11_CLASSH_TYPE_CASTERS(pybind11_tests::classh_inheritance::base1)
+PYBIND11_CLASSH_TYPE_CASTERS(pybind11_tests::classh_inheritance::base2)
+PYBIND11_CLASSH_TYPE_CASTERS(pybind11_tests::classh_inheritance::drvd2)
+
 namespace pybind11_tests {
 namespace classh_inheritance {
 
@@ -39,6 +66,17 @@ TEST_SUBMODULE(classh_inheritance, m) {
     m.def("make_drvd_up_cast", make_drvd_up_cast, py::return_value_policy::take_ownership);
     m.def("pass_base", pass_base);
     m.def("pass_drvd", pass_drvd);
+
+    py::classh<base1>(m, "base1");
+    py::classh<base2>(m, "base2");
+    py::classh<drvd2, base1, base2>(m, "drvd2");
+
+    m.def("make_drvd2", make_drvd2, py::return_value_policy::take_ownership);
+    m.def("make_drvd2_up_cast1", make_drvd2_up_cast1, py::return_value_policy::take_ownership);
+    m.def("make_drvd2_up_cast2", make_drvd2_up_cast2, py::return_value_policy::take_ownership);
+    m.def("pass_base1", pass_base1);
+    m.def("pass_base2", pass_base2);
+    m.def("pass_drvd2", pass_drvd2);
 }
 
 } // namespace classh_inheritance

tests/test_classh_inheritance.py

@@ -5,8 +5,8 @@ from pybind11_tests import classh_inheritance as m
 
 def test_make_drvd_pass_base():
     d = m.make_drvd()
-    i = m.pass_base(d)
-    assert i == 200
+    i = m.pass_base(d)  # load_impl Case 2a
+    assert i == 2 * 100 + 11
 
 
 def test_make_drvd_up_cast_pass_drvd():
@@ -14,4 +14,23 @@ def test_make_drvd_up_cast_pass_drvd():
     # the base return is down-cast immediately.
     assert b.__class__.__name__ == "drvd"
     i = m.pass_drvd(b)
-    assert i == 200
+    assert i == 2 * 100 + 12
+
+
+def test_make_drvd2_pass_bases():
+    d = m.make_drvd2()
+    i1 = m.pass_base1(d)  # load_impl Case 2c
+    assert i1 == 3 * 110 + 4 * 120 + 21
+    i2 = m.pass_base2(d)
+    assert i2 == 3 * 110 + 4 * 120 + 22
+
+
+def test_make_drvd2_up_casts_pass_drvd2():
+    b1 = m.make_drvd2_up_cast1()
+    assert b1.__class__.__name__ == "drvd2"
+    i1 = m.pass_drvd2(b1)
+    assert i1 == 3 * 110 + 4 * 120 + 23
+    b2 = m.make_drvd2_up_cast2()
+    assert b2.__class__.__name__ == "drvd2"
+    i2 = m.pass_drvd2(b2)
+    assert i2 == 3 * 110 + 4 * 120 + 23