[gprpp] Implement down_cast - a debug-time checked down cast (#35548)

Closes #35548

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/35548 from ctiller:down_cast cd7501dadd
PiperOrigin-RevId: 599176414

CMakeLists.txt

@@ -1009,6 +1009,7 @@ if(gRPC_BUILD_TESTS)
   add_dependencies(buildtests_cxx disappearing_server_test)
   add_dependencies(buildtests_cxx dns_resolver_cooldown_test)
   add_dependencies(buildtests_cxx dns_resolver_test)
+  add_dependencies(buildtests_cxx down_cast_test)
   add_dependencies(buildtests_cxx dual_ref_counted_test)
   if(_gRPC_PLATFORM_LINUX OR _gRPC_PLATFORM_MAC OR _gRPC_PLATFORM_POSIX)
     add_dependencies(buildtests_cxx dualstack_socket_test)
@@ -11917,6 +11918,40 @@ target_link_libraries(dns_resolver_test
 )
 
 
+endif()
+if(gRPC_BUILD_TESTS)
+
+add_executable(down_cast_test
+  test/core/gprpp/down_cast_test.cc
+)
+target_compile_features(down_cast_test PUBLIC cxx_std_14)
+target_include_directories(down_cast_test
+  PRIVATE
+    ${CMAKE_CURRENT_SOURCE_DIR}
+    ${CMAKE_CURRENT_SOURCE_DIR}/include
+    ${_gRPC_ADDRESS_SORTING_INCLUDE_DIR}
+    ${_gRPC_RE2_INCLUDE_DIR}
+    ${_gRPC_SSL_INCLUDE_DIR}
+    ${_gRPC_UPB_GENERATED_DIR}
+    ${_gRPC_UPB_GRPC_GENERATED_DIR}
+    ${_gRPC_UPB_INCLUDE_DIR}
+    ${_gRPC_XXHASH_INCLUDE_DIR}
+    ${_gRPC_ZLIB_INCLUDE_DIR}
+    third_party/googletest/googletest/include
+    third_party/googletest/googletest
+    third_party/googletest/googlemock/include
+    third_party/googletest/googlemock
+    ${_gRPC_PROTO_GENS_DIR}
+)
+
+target_link_libraries(down_cast_test
+  ${_gRPC_ALLTARGETS_LIBRARIES}
+  gtest
+  absl::config
+  gpr
+)
+
+
 endif()
 if(gRPC_BUILD_TESTS)
 

build_autogenerated.yaml

@@ -7990,6 +7990,19 @@ targets:
   deps:
   - gtest
   - grpc_test_util
+- name: down_cast_test
+  gtest: true
+  build: test
+  language: c++
+  headers:
+  - src/core/lib/gprpp/down_cast.h
+  src:
+  - test/core/gprpp/down_cast_test.cc
+  deps:
+  - gtest
+  - absl/base:config
+  - gpr
+  uses_polling: false
 - name: dual_ref_counted_test
   gtest: true
   build: test

src/core/BUILD

@@ -5085,6 +5085,13 @@ grpc_cc_library(
     ],
 )
 
+grpc_cc_library(
+    name = "down_cast",
+    hdrs = ["lib/gprpp/down_cast.h"],
+    external_deps = ["absl/base:config"],
+    deps = ["//:gpr"],
+)
+
 grpc_cc_library(
     name = "status_conversion",
     srcs = ["lib/transport/status_conversion.cc"],

src/core/lib/gprpp/down_cast.h

@@ -0,0 +1,49 @@
+// Copyright 2024 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef GRPC_SRC_CORE_LIB_GPRPP_DOWN_CAST_H
+#define GRPC_SRC_CORE_LIB_GPRPP_DOWN_CAST_H
+
+#include <grpc/support/port_platform.h>
+
+#include <type_traits>
+
+#include "absl/base/config.h"
+
+#include <grpc/support/log.h>
+
+namespace grpc_core {
+
+template <typename To, typename From>
+inline To down_cast(From* f) {
+  static_assert(
+      std::is_base_of<From, typename std::remove_pointer<To>::type>::value,
+      "down_cast requires a base-to-derived relationship");
+// If we have RTTI & we're in debug, assert that the cast is legal.
+#if ABSL_INTERNAL_HAS_RTTI
+#ifndef NDEBUG
+  if (f != nullptr) GPR_ASSERT(dynamic_cast<To>(f) != nullptr);
+#endif
+#endif
+  return static_cast<To>(f);
+}
+
+template <typename To, typename From>
+inline To down_cast(From& f) {
+  return *down_cast<typename std::remove_reference<To>::type*>(&f);
+}
+
+}  // namespace grpc_core
+
+#endif  // GRPC_SRC_CORE_LIB_GPRPP_DOWN_CAST_H

test/core/gprpp/BUILD

@@ -135,6 +135,18 @@ grpc_cc_test(
     ],
 )
 
+grpc_cc_test(
+    name = "down_cast_test",
+    srcs = ["down_cast_test.cc"],
+    external_deps = ["gtest"],
+    language = "C++",
+    uses_event_engine = False,
+    uses_polling = False,
+    deps = [
+        "//src/core:down_cast",
+    ],
+)
+
 grpc_cc_test(
     name = "table_test",
     srcs = ["table_test.cc"],

test/core/gprpp/down_cast_test.cc

@@ -0,0 +1,45 @@
+// Copyright 2024 gRPC authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "src/core/lib/gprpp/down_cast.h"
+
+#include "gtest/gtest.h"
+
+namespace grpc_core {
+namespace {
+
+class Base {
+ public:
+  virtual ~Base() = default;
+};
+
+class Derived : public Base {
+ public:
+  int i = 3;
+};
+
+TEST(DownCastTest, DownCast) {
+  Derived d;
+  Base* b = &d;
+  EXPECT_EQ(down_cast<Derived*>(b)->i, 3);
+  EXPECT_EQ(down_cast<Derived&>(*b).i, 3);
+}
+
+}  // namespace
+}  // namespace grpc_core
+
+int main(int argc, char** argv) {
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}

tools/distrib/fix_build_deps.py

@@ -44,6 +44,7 @@ EXTERNAL_DEPS = {
     "absl/algorithm/container.h": "absl/algorithm:container",
     "absl/base/attributes.h": "absl/base:core_headers",
     "absl/base/call_once.h": "absl/base",
+    "absl/base/config.h": "absl/base:config",
     # TODO(ctiller) remove this
     "absl/base/internal/endian.h": "absl/base:endian",
     "absl/base/thread_annotations.h": "absl/base:core_headers",

tools/run_tests/generated/tests.json

@@ -2899,6 +2899,30 @@
     ],
     "uses_polling": true
   },
+  {
+    "args": [],
+    "benchmark": false,
+    "ci_platforms": [
+      "linux",
+      "mac",
+      "posix",
+      "windows"
+    ],
+    "cpu_cost": 1.0,
+    "exclude_configs": [],
+    "exclude_iomgrs": [],
+    "flaky": false,
+    "gtest": true,
+    "language": "c++",
+    "name": "down_cast_test",
+    "platforms": [
+      "linux",
+      "mac",
+      "posix",
+      "windows"
+    ],
+    "uses_polling": false
+  },
   {
     "args": [],
     "benchmark": false,