Add [[deprecated]] attribute when generating enums and classes.

When the user adds `option deprecated = true` for an `enum` or `message`, we
should add the `[[deprecated]]` attribute to the generated C++ `enum` or
`class`.

PiperOrigin-RevId: 670583253

ci/Linux.bazelrc

@@ -1,4 +1,4 @@
 import common.bazelrc
 
 build --cxxopt=-std=c++14 --host_cxxopt=-std=c++14
-build --copt="-Werror" --copt="-Wno-sign-compare" --copt="-Wno-sign-conversion" --copt="-Wno-error=sign-conversion"
+build --copt="-Werror" --copt="-Wno-sign-compare" --copt="-Wno-sign-conversion" --copt="-Wno-error=sign-conversion" --copt="-Wno-deprecated-declarations"

ci/macOS.bazelrc

@@ -1,6 +1,6 @@
 import common.bazelrc
 
 build --cxxopt=-std=c++14 --host_cxxopt=-std=c++14
-build --copt="-Werror" --copt="-Wno-sign-compare" --copt="-Wno-sign-conversion" --copt="-Wno-error=sign-conversion"
+build --copt="-Werror" --copt="-Wno-sign-compare" --copt="-Wno-sign-conversion" --copt="-Wno-error=sign-conversion" --copt="-Wno-deprecated-declarations"
 common --repo_env=BAZEL_NO_APPLE_CPP_TOOLCHAIN=1
 common --xcode_version_config=@com_google_protobuf//.github:host_xcodes

src/google/protobuf/compiler/cpp/enum.cc

@@ -44,6 +44,7 @@ absl::flat_hash_map<absl::string_view, std::string> EnumVars(
     const EnumValueDescriptor* min, const EnumValueDescriptor* max) {
   auto classname = ClassName(enum_, false);
   return {
+      {"DEPRECATED", enum_->options().deprecated() ? "[[deprecated]]" : ""},
       {"Enum", std::string(enum_->name())},
       {"Enum_", ResolveKeyword(enum_->name())},
       {"Msg_Enum", classname},
@@ -162,7 +163,7 @@ void EnumGenerator::GenerateDefinition(io::Printer* p) {
            }},
       },
       R"cc(
-        enum $Msg_Enum_annotated$ : int {
+        enum $DEPRECATED $$Msg_Enum_annotated$ : int {
           $values$,
           $open_enum_sentinels$,
         };

src/google/protobuf/compiler/cpp/message.cc

@@ -501,6 +501,7 @@ std::vector<Sub> ClassVars(const Descriptor* desc, Options opts) {
       {"Msg", ClassName(desc, false)},
       {"pkg::Msg", QualifiedClassName(desc, opts)},
       {"pkg.Msg", desc->full_name()},
+      {"deprecated", desc->options().deprecated() ? "[[deprecated]]" : ""},
 
       // Old-style names, to be removed once all usages are gone in this and
       // other files.
@@ -2060,7 +2061,8 @@ void MessageGenerator::GenerateClassDefinition(io::Printer* p) {
                   )cc");
         }}},
       R"cc(
-        class $dllexport_decl $$classname$ final : public $superclass$
+        class $dllexport_decl $$deprecated $$classname$ final
+            : public $superclass$
         /* @@protoc_insertion_point(class_definition:$full_name$) */ {
          public:
           inline $classname$() : $classname$(nullptr) {}