Add operator const ProtoType&& to proto caster.

PiperOrigin-RevId: 469581055

Author: Xiaofei Wang

pybind11_protobuf/proto_caster_impl.h

@@ -269,7 +269,11 @@ struct proto_caster : public proto_caster_load_impl<ProtoType>,
     ensure_owned();
     return std::move(*owned);
   }
-
+  explicit operator const ProtoType &&() {
+    if (!value) throw pybind11::reference_cast_error();
+    ensure_owned();
+    return std::move(*owned);
+  }
 #if PYBIND11_PROTOBUF_UNSAFE
   // The following unsafe conversions are not enabled:
   explicit operator ProtoType *() { return const_cast<ProtoType *>(value); }

pybind11_protobuf/tests/pass_by_module.cc

@@ -86,6 +86,12 @@ PYBIND11_MODULE(pass_by_module, m) {
         return CheckIntMessage(&message, value);
       },
       py::arg("message"), py::arg("value"));
+  m.def(
+      "concrete_crval",
+      [](const IntMessage&& message, int value) {
+        return CheckIntMessage(&message, value);
+      },
+      py::arg("message"), py::arg("value"));
   m.def(
       "concrete_cref",
       [](const IntMessage& message, int value) {

pybind11_protobuf/tests/pass_by_test.py

@@ -53,6 +53,7 @@ def get_pass_by_params():
       'concrete_ptr_notnone',
       'concrete_ref',
       'concrete_rval',
+      'concrete_crval',
       'concrete_sptr',
       'concrete_uptr',
       'concrete_uptr_ptr',