For internal testing only (flop TGP-head 2024-25-25).

pybind11_protobuf/BUILD

@@ -25,6 +25,7 @@ pybind_library(
         ":check_unknown_fields",
         ":enum_type_caster",
         ":proto_cast_util",
+        "//net/proto:rawmessage",
         "@com_google_absl//absl/strings:string_view",
         "@com_google_protobuf//:protobuf",
     ],

pybind11_protobuf/native_proto_caster.h

@@ -18,6 +18,7 @@
 #include <type_traits>
 #include <utility>
 
+#include "net/proto/rawmessage.h"
 #include "google/protobuf/message.h"
 #include "absl/strings/string_view.h"
 #include "pybind11_protobuf/enum_type_caster.h"
@@ -80,6 +81,10 @@ namespace detail {
 //
 constexpr bool pybind11_protobuf_enable_type_caster(...) { return true; }
 
+constexpr bool pybind11_protobuf_enable_type_caster(::RawMessage *) {
+  return false;
+}
+
 // pybind11 type_caster<> specialization for c++ protocol buffer types using
 // inheritance from google::proto_caster<>.
 template <typename ProtoType>
@@ -95,13 +100,17 @@ struct type_caster<
 
 template <typename ProtoType>
 struct copyable_holder_caster_shared_ptr_with_smart_holder_support_enabled<
-    ProtoType, enable_if_t<std::is_base_of<::google::protobuf::Message, ProtoType>::value>>
-    : std::false_type {};
+    ProtoType,
+    enable_if_t<(std::is_base_of<::google::protobuf::Message, ProtoType>::value &&
+                 pybind11_protobuf_enable_type_caster(
+                     static_cast<ProtoType *>(nullptr)))>> : std::false_type {};
 
 template <typename ProtoType>
 struct move_only_holder_caster_unique_ptr_with_smart_holder_support_enabled<
-    ProtoType, enable_if_t<std::is_base_of<::google::protobuf::Message, ProtoType>::value>>
-    : std::false_type {};
+    ProtoType,
+    enable_if_t<(std::is_base_of<::google::protobuf::Message, ProtoType>::value &&
+                 pybind11_protobuf_enable_type_caster(
+                     static_cast<ProtoType *>(nullptr)))>> : std::false_type {};
 
 #endif  // PYBIND11_HAS_INTERNALS_WITH_SMART_HOLDER_SUPPORT
 

pybind11_protobuf/proto_caster_impl.h

@@ -27,6 +27,24 @@
 
 namespace pybind11_protobuf {
 
+namespace internal {
+
+template <
+    typename To, typename Proto2Message = ::google::protobuf::Message,
+    std::enable_if<std::is_polymorphic<Proto2Message>::value, int>::type = 0>
+const To *dynamic_cast_proxy(const ::google::protobuf::Message *message) {
+  return dynamic_cast<const To *>(message);
+}
+
+template <
+    typename To, typename Proto2Message = ::google::protobuf::Message,
+    std::enable_if<!std::is_polymorphic<Proto2Message>::value, int>::type = 0>
+const To *dynamic_cast_proxy(const ::google::protobuf::Message *message) {
+  return ::google::protobuf::DynamicCastToGenerated<To>(message);
+}
+
+}  // namespace internal
+
 // pybind11 constructs c++ references using the following mechanism, for
 // example:
 //
@@ -55,7 +73,7 @@ struct proto_caster_load_impl {
     const ::google::protobuf::Message *message =
         pybind11_protobuf::PyProtoGetCppMessagePointer(src);
     if (message) {
-      value = ::google::protobuf::DynamicCastToGenerated<ProtoType>(message);
+      value = internal::dynamic_cast_proxy<ProtoType>(message);
       if (value) {
         // If the capability were available, then we could probe PyProto_API and
         // allow c++ mutability based on the python reference count.

pybind11_protobuf/tests/BUILD

@@ -358,3 +358,12 @@ py_test(
         requirement("absl_py"),
     ],
 )
+
+pybind_extension(
+    name = "classh_rawmessage",
+    srcs = ["classh_rawmessage.cpp"],
+    deps = [
+        "//net/proto:rawmessage",
+        "//pybind11_protobuf:native_proto_caster",
+    ],
+)

pybind11_protobuf/tests/classh_rawmessage.cpp

@@ -0,0 +1,27 @@
+/*
+The code below compiled before https://github.com/pybind/pybind11/pull/5257
+was merged into pybind11k, but with `PYBIND11_SMART_HOLDER_TYPE_CASTERS`
+becoming a no-op, this error appears:
+
+.../pybind11/include/pybind11/detail/../cast.h:72:30: error: no member named
+'operator RawMessage *' in 'pybind11::detail::type_caster<RawMessage>' 72 |
+return std::move(caster).operator result_t(); |            ~~~~~~~~~~~~~~~~~ ^
+*/
+
+#include <pybind11/smart_holder.h>
+
+#include "net/proto/rawmessage.h"
+#include "pybind11_protobuf/native_proto_caster.h"
+
+PYBIND11_SMART_HOLDER_TYPE_CASTERS(::RawMessage)
+
+namespace py = pybind11;
+
+PYBIND11_MODULE(rawmessage, m) {
+  py::classh<::RawMessage> w_t(m, "RawMessage", py::is_final());
+  w_t.def(py::init([]() { return std::make_unique<::RawMessage>().release(); }),
+          py::return_value_policy::_clif_automatic);
+  w_t.def("as_proto2_Message", [](::RawMessage* self) {
+    return py::capsule(static_cast<void*>(self));
+  });
+}