fix serialization warnings in generated code when compiling with Java version 18 and above

Java 18 added additional linter checks as part of
https://bugs.openjdk.java.net/browse/JDK-8274336 and
https://bugs.openjdk.java.net/browse/JDK-8274335

These additional checks cause generated protobuf code to raise the
following compiler warning: "non-transient instance field of a
serializable class declared with a non-serializable type"

This change fixes the code generation to annotate the generated fields
with the necessary suppressions to avoid false positives.

All the code generated from src/google/protobuf/*.proto now
compiles successfully without serialization warnings in Java 18.

fixes #9673

src/google/protobuf/compiler/java/enum_field.cc

@@ -680,6 +680,7 @@ void RepeatedImmutableEnumFieldGenerator::GenerateMembers(
     io::Printer* printer) const {
   printer->Print(
       variables_,
+      "@SuppressWarnings(\"serial\")\n"
       "private java.util.List<java.lang.Integer> $name$_;\n"
       "private static final "
       "com.google.protobuf.Internal.ListAdapter.Converter<\n"

src/google/protobuf/compiler/java/map_field.cc

@@ -335,6 +335,7 @@ void ImmutableMapFieldGenerator::GenerateMembers(io::Printer* printer) const {
       "              $value_default_value$);\n"
       "}\n");
   printer->Print(variables_,
+                 "@SuppressWarnings(\"serial\")\n"
                  "private com.google.protobuf.MapField<\n"
                  "    $type_parameters$> $name$_;\n"
                  "private com.google.protobuf.MapField<$type_parameters$>\n"

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

@@ -440,6 +440,7 @@ void ImmutableMessageGenerator::Generate(io::Printer* printer) {
     // oneofCase_ and oneof_
     printer->Print(vars,
                    "private int $oneof_name$Case_ = 0;\n"
+                   "@SuppressWarnings(\"serial\")\n"
                    "private java.lang.Object $oneof_name$_;\n");
     // OneofCase enum
     printer->Print(
@@ -1740,6 +1741,7 @@ void ImmutableMessageGenerator::GenerateAnyMethods(io::Printer* printer) {
       "      defaultInstance.getDescriptorForType().getFullName());\n"
       "}\n"
       "\n"
+      "@SuppressWarnings(\"serial\")\n"
       "private volatile com.google.protobuf.Message cachedUnpackValue;\n"
       "\n"
       "@java.lang.SuppressWarnings(\"unchecked\")\n"

src/google/protobuf/compiler/java/message_field.cc

@@ -910,7 +910,8 @@ void RepeatedImmutableMessageFieldGenerator::GenerateInterfaceMembers(
 
 void RepeatedImmutableMessageFieldGenerator::GenerateMembers(
     io::Printer* printer) const {
-  printer->Print(variables_, "private java.util.List<$type$> $name$_;\n");
+  printer->Print(variables_, "@SuppressWarnings(\"serial\")\n"
+                             "private java.util.List<$type$> $name$_;\n");
   PrintExtraFieldInfo(variables_, printer);
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,

src/google/protobuf/compiler/java/primitive_field.cc

@@ -715,7 +715,8 @@ void RepeatedImmutablePrimitiveFieldGenerator::GenerateInterfaceMembers(
 
 void RepeatedImmutablePrimitiveFieldGenerator::GenerateMembers(
     io::Printer* printer) const {
-  printer->Print(variables_, "private $field_list_type$ $name$_;\n");
+  printer->Print(variables_, "@SuppressWarnings(\"serial\")\n"
+                             "private $field_list_type$ $name$_;\n");
   PrintExtraFieldInfo(variables_, printer);
   WriteFieldAccessorDocComment(printer, descriptor_, LIST_GETTER);
   printer->Print(variables_,

src/google/protobuf/compiler/java/string_field.cc

@@ -218,7 +218,8 @@ void ImmutableStringFieldGenerator::GenerateInterfaceMembers(
 
 void ImmutableStringFieldGenerator::GenerateMembers(
     io::Printer* printer) const {
-  printer->Print(variables_, "private volatile java.lang.Object $name$_;\n");
+  printer->Print(variables_, "@SuppressWarnings(\"serial\")\n"
+                             "private volatile java.lang.Object $name$_;\n");
   PrintExtraFieldInfo(variables_, printer);
 
   if (HasHazzer(descriptor_)) {
@@ -801,6 +802,7 @@ void RepeatedImmutableStringFieldGenerator::GenerateInterfaceMembers(
 void RepeatedImmutableStringFieldGenerator::GenerateMembers(
     io::Printer* printer) const {
   printer->Print(variables_,
+                 "@SuppressWarnings(\"serial\")\n"
                  "private com.google.protobuf.LazyStringList $name$_;\n");
   PrintExtraFieldInfo(variables_, printer);
   WriteFieldAccessorDocComment(printer, descriptor_, LIST_GETTER);