Internal change

rust/bazel/aspects.bzl

@@ -162,12 +162,15 @@ def _generate_rust_gencode(
 
     additional_args = ctx.actions.args()
 
+    annotate_code = False
+
     additional_args.add(
-        "--rust_opt=experimental-codegen=enabled,kernel={},crate_mapping={},generated_entry_point_rs_file_name={},forced_lite_runtime={}".format(
+        "--rust_opt=experimental-codegen=enabled,kernel={},crate_mapping={},generated_entry_point_rs_file_name={},forced_lite_runtime={}{}".format(
             "upb" if is_upb else "cpp",
             crate_mapping.path,
             entry_point_rs_output.basename,
             "true" if forced_lite_runtime else "false",
+            ",annotate_code=true" if annotate_code else "",
         ),
     )
 

src/google/protobuf/compiler/rust/context.cc

@@ -93,6 +93,12 @@ absl::StatusOr<Options> Options::Parse(absl::string_view param) {
     opts.force_lite_runtime = lite->second == "true";
   }
 
+  auto annotate_code = absl::c_find_if(
+      args, [](auto& arg) { return arg.first == "annotate_code"; });
+  if (annotate_code != args.end()) {
+    opts.annotate_code = annotate_code->second == "true";
+  }
+
   return opts;
 }
 

src/google/protobuf/compiler/rust/context.h

@@ -50,6 +50,7 @@ struct Options {
   std::string mapping_file_path;
   bool strip_nonfunctional_codegen = false;
   bool force_lite_runtime = false;
+  bool annotate_code = false;
 
   // The name to use for the generated entry point rs file.
   std::string generated_entry_point_rs_file_name = "generated.rs";

src/google/protobuf/compiler/rust/generator.cc

@@ -217,7 +217,14 @@ bool RustGenerator::Generate(const FileDescriptor* file,
 
   auto outfile = absl::WrapUnique(
       generator_context->Open(GetRsFile(ctx_without_printer, *file)));
-  io::Printer printer(outfile.get());
+  GeneratedCodeInfo annotations;
+  io::AnnotationProtoCollector<GeneratedCodeInfo> annotation_collector(
+      &annotations);
+  io::Printer::Options printer_options{};
+  if (opts->annotate_code) {
+    printer_options.annotation_collector = &annotation_collector;
+  }
+  io::Printer printer(outfile.get(), printer_options);
   Context ctx = ctx_without_printer.WithPrinter(&printer);
 
   // Convenience shorthands for common symbols.
@@ -327,6 +334,12 @@ bool RustGenerator::Generate(const FileDescriptor* file,
     }
   }
 
+  if (opts->annotate_code) {
+    ctx.printer().PrintRaw(absl::StrCat(
+        "// google.protobuf.GeneratedCodeInfo ",
+        absl::Base64Escape(annotations.SerializeAsString()), "\n"));
+  }
+
   return true;
 }
 

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

@@ -38,6 +38,8 @@ namespace compiler {
 namespace rust {
 namespace {
 
+using Sub = ::google::protobuf::io::Printer::Sub;
+
 void MessageNew(Context& ctx, const Descriptor& msg) {
   switch (ctx.opts().kernel) {
     case Kernel::kCpp:
@@ -409,6 +411,9 @@ void GenerateRs(Context& ctx, const Descriptor& msg, const upb::DefPool& pool) {
   upb::MessageDefPtr upb_msg = pool.FindMessageByName(msg.full_name().data());
   ctx.Emit(
       {
+          // There's also ${$/$}$-style begin and end tokens, but those might
+          // be harder to retrofit here because of the giant-template style.
+          Sub("MsgDefinition", RsSafeName(msg.name())).AnnotatedAs(&msg),
           {"Msg", RsSafeName(msg.name())},
           {"Msg::new", [&] { MessageNew(ctx, msg); }},
           {"Msg::drop", [&] { MessageDrop(ctx, msg); }},
@@ -520,7 +525,7 @@ void GenerateRs(Context& ctx, const Descriptor& msg, const upb::DefPool& pool) {
       },
       R"rs(
         #[allow(non_camel_case_types)]
-        pub struct $Msg$ {
+        pub struct $MsgDefinition$ {
           inner: $pbr$::OwnedMessageInner<$Msg$>
         }