Fix bug where enums only got traits if they are used in a field.

Now they always get traits, even if unused.

PiperOrigin-RevId: 691046942

src/google/protobuf/BUILD.bazel

@@ -815,6 +815,7 @@ filegroup(
     name = "lite_test_proto_srcs",
     srcs = [
         "map_lite_unittest.proto",
+        "only_one_enum_test.proto",
         "unittest_import_lite.proto",
         "unittest_import_public_lite.proto",
         "unittest_lite.proto",

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

@@ -1546,11 +1546,11 @@ void FileGenerator::GenerateForwardDeclarations(io::Printer* p) {
     }
 
     ListAllTypesForServices(file_, &classes);
-  } else {
+  }
+
   // List all enums in this file, to declare the traits.
   google::protobuf::internal::VisitDescriptors(
       *file_, [&](const EnumDescriptor& e) { enums.push_back(&e); });
-  }
 
   // Calculate the set of files whose definitions we get through include.
   // No need to forward declare types that are defined in these.

src/google/protobuf/lite_unittest.cc

@@ -23,6 +23,7 @@
 #include "absl/strings/str_cat.h"
 #include "absl/strings/string_view.h"
 #include "google/protobuf/arena_test_util.h"
+#include "google/protobuf/generated_enum_util.h"
 #include "google/protobuf/io/coded_stream.h"
 #include "google/protobuf/io/zero_copy_stream.h"
 #include "google/protobuf/io/zero_copy_stream_impl.h"
@@ -30,6 +31,7 @@
 #include "google/protobuf/map_lite_test_util.h"
 #include "google/protobuf/map_lite_unittest.pb.h"
 #include "google/protobuf/message_lite.h"
+#include "google/protobuf/only_one_enum_test.pb.h"
 #include "google/protobuf/parse_context.h"
 #include "google/protobuf/test_util_lite.h"
 #include "google/protobuf/unittest_lite.pb.h"
@@ -1458,6 +1460,19 @@ TEST(LiteTest, DownCastMessageInvalidReferenceType) {
 }
 #endif  // GTEST_HAS_DEATH_TEST
 
+TEST(LiteTest, FileWithOnlyAnEnumGeneratesProperValidationHooks) {
+  EXPECT_TRUE(protobuf_unittest::OnlyOneEnum_IsValid(0));
+  EXPECT_TRUE(protobuf_unittest::OnlyOneEnum_IsValid(10));
+  EXPECT_FALSE(protobuf_unittest::OnlyOneEnum_IsValid(6));
+
+  // Traits also work
+  constexpr auto* data =
+      internal::EnumTraits<protobuf_unittest::OnlyOneEnum>::validation_data();
+  EXPECT_TRUE(internal::ValidateEnum(0, data));
+  EXPECT_TRUE(internal::ValidateEnum(10, data));
+  EXPECT_FALSE(internal::ValidateEnum(6, data));
+}
+
 }  // namespace
 }  // namespace protobuf
 }  // namespace google

src/google/protobuf/only_one_enum_test.proto

@@ -0,0 +1,15 @@
+edition = "2023";
+
+package protobuf_unittest;
+
+option optimize_for = LITE_RUNTIME;
+
+// A file with only a single enum, without any use of it.
+// This is useful for testing enum specific codegen that is not directly related
+// to field codegen.
+
+enum OnlyOneEnum {
+  ONLY_ONE_ENUM_DEFAULT = 0;
+  ONLY_ONE_ENUM_VALID = 10;
+}
+