Add template comment and package to previously empty generated kotlin proto files.

We generate a Kotlin file to correspond to each message, which left the per-file generated file blank. We would still like to generate a file to deal with edge cases where there are no messages defined in a proto file. To fix, we print the default comment about the file being generated as well as a package statement.

PiperOrigin-RevId: 486969373

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

@@ -689,6 +689,23 @@ std::string FileGenerator::GetKotlinClassname() {
   return name_resolver_->GetFileClassName(file_, immutable_api_, true);
 }
 
+void FileGenerator::GenerateKotlin(io::Printer* printer) {
+  printer->Print(
+      "// Generated by the protocol buffer compiler. DO NOT EDIT!\n"
+      "// source: $filename$\n"
+      "\n",
+      "filename", file_->name());
+  printer->Print(
+      "// Generated files should ignore deprecation warnings\n"
+      "@file:Suppress(\"DEPRECATION\")");
+  if (!java_package_.empty()) {
+    printer->Print(
+        "package $package$;\n"
+        "\n",
+        "package", EscapeKotlinKeywords(java_package_));
+  }
+}
+
 void FileGenerator::GenerateKotlinSiblings(
     const std::string& package_dir, GeneratorContext* context,
     std::vector<std::string>* file_list,

src/google/protobuf/compiler/java/file.h

@@ -82,6 +82,7 @@ class FileGenerator {
   void Generate(io::Printer* printer);
 
   std::string GetKotlinClassname();
+  void GenerateKotlin(io::Printer* printer);
   void GenerateKotlinSiblings(const std::string& package_dir,
                               GeneratorContext* generator_context,
                               std::vector<std::string>* file_list,

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

@@ -119,6 +119,8 @@ bool KotlinGenerator::Generate(const FileDescriptor* file,
       output.get(), '$',
       file_options.annotate_code ? &annotation_collector : nullptr);
 
+  file_generator->GenerateKotlin(&printer);
+
   file_generator->GenerateKotlinSiblings(package_dir, context, &all_files,
                                          &all_annotations);