Add an RAII namespace printer helper for C++ codegen.

This can be used to open and close namespace automatically within generated C++ code.

PiperOrigin-RevId: 618930720

src/google/protobuf/compiler/cpp/BUILD.bazel

@@ -71,6 +71,7 @@ cc_library(
         "generator.cc",
         "ifndef_guard.cc",
         "message.cc",
+        "namespace_printer.cc",
         "padding_optimizer.cc",
         "parse_function_generator.cc",
         "service.cc",
@@ -86,6 +87,7 @@ cc_library(
         "ifndef_guard.h",
         "message.h",
         "message_layout_helper.h",
+        "namespace_printer.h",
         "padding_optimizer.h",
         "parse_function_generator.h",
         "service.h",
@@ -359,6 +361,22 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "namespace_printer_unittest",
+    srcs = ["namespace_printer_unittest.cc"],
+    deps = [
+        ":cpp",
+        "//:protobuf",
+        "//src/google/protobuf/io",
+        "//src/google/protobuf/io:printer",
+        "@com_google_absl//absl/log:absl_check",
+        "@com_google_absl//absl/strings:string_view",
+        "@com_google_absl//absl/types:optional",
+        "@com_google_googletest//:gtest",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 ################################################################################
 # Distribution packaging
 ################################################################################

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

@@ -0,0 +1,37 @@
+#include "google/protobuf/compiler/cpp/namespace_printer.h"
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "absl/log/die_if_null.h"
+#include "absl/strings/substitute.h"
+#include "google/protobuf/io/printer.h"
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace cpp {
+
+NamespacePrinter::NamespacePrinter(
+    google::protobuf::io::Printer* const p, std::vector<std::string> namespace_components)
+    : p_(ABSL_DIE_IF_NULL(p)),
+      namespace_components_(std::move(namespace_components)) {
+  // Open the namespace.
+  for (const std::string& ns : namespace_components_) {
+    p_->Print(absl::Substitute("namespace $0 {\n", ns));
+  }
+  p_->Print("\n");
+}
+
+NamespacePrinter::~NamespacePrinter() {
+  // Close the namespace.
+  for (const std::string& ns : namespace_components_) {
+    p_->Print(absl::Substitute("}  // namespace $0\n", ns));
+  }
+}
+
+}  // namespace cpp
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google

src/google/protobuf/compiler/cpp/namespace_printer.h

@@ -0,0 +1,58 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2024 Google Inc.  All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file or at
+// https://developers.google.com/open-source/licenses/bsd
+
+// An RAII type for printing a namespace.
+//
+// Example:
+// {
+//   Printer printer(output_stream.get(), '$');
+//   const NamespacePrinter namespace_printer(&printer, {"a", "b", "c"});
+//   // namespace opening will be opened here
+//   ...
+//   // namespace closing will be emitted here
+// }
+//
+// By default, the filename will be converted to a macro by substituting '/' and
+// '.' characters with '_'.  If a different transformation is required, an
+// optional transformation function can be provided.
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_CPP_NAMESPACE_PRINTER_H__
+#define GOOGLE_PROTOBUF_COMPILER_CPP_NAMESPACE_PRINTER_H__
+
+#include <string>
+#include <vector>
+
+#include "google/protobuf/io/printer.h"
+
+// Must be included last.
+#include "google/protobuf/port_def.inc"
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace cpp {
+
+// An RAII type for printing a namespace.
+class PROTOC_EXPORT NamespacePrinter final {
+ public:
+  explicit NamespacePrinter(google::protobuf::io::Printer* p,
+                            std::vector<std::string> namespace_components);
+  ~NamespacePrinter();
+
+ private:
+  google::protobuf::io::Printer* const p_;
+  const std::vector<std::string> namespace_components_;
+};
+
+#include "google/protobuf/port_undef.inc"
+
+}  // namespace cpp
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
+
+#endif  // GOOGLE_PROTOBUF_COMPILER_CPP_NAMESPACE_PRINTER_H__

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

@@ -0,0 +1,78 @@
+#include "google/protobuf/compiler/cpp/namespace_printer.h"
+
+#include <string>
+
+#include <gtest/gtest.h>
+#include "absl/log/absl_check.h"
+#include "absl/strings/string_view.h"
+#include "absl/types/optional.h"
+#include "google/protobuf/io/printer.h"
+#include "google/protobuf/io/zero_copy_stream.h"
+#include "google/protobuf/io/zero_copy_stream_impl_lite.h"
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace cpp {
+
+namespace {
+
+class NamespacePrinterTest : public testing::Test {
+ protected:
+  io::ZeroCopyOutputStream* output() {
+    ABSL_CHECK(stream_.has_value());
+    return &*stream_;
+  }
+  absl::string_view written() {
+    stream_.reset();
+    return out_;
+  }
+
+  std::string out_;
+  absl::optional<io::StringOutputStream> stream_{&out_};
+};
+
+TEST_F(NamespacePrinterTest, Basic) {
+  {
+    io::Printer printer(output(), '$');
+
+    const NamespacePrinter namespace_printer(&printer, {"A", "B", "E"});
+
+    EXPECT_FALSE(printer.failed());
+  }
+
+  EXPECT_EQ(written(),
+            "namespace A {\n"
+            "namespace B {\n"
+            "namespace E {\n"
+            "\n"
+            "}  // namespace A\n"
+            "}  // namespace B\n"
+            "}  // namespace E\n");
+}
+
+TEST_F(NamespacePrinterTest, DifferentDelim) {
+  {
+    io::Printer printer(output(), '\0');
+
+    const NamespacePrinter namespace_printer(&printer, {"A", "B", "E"});
+
+    EXPECT_FALSE(printer.failed());
+  }
+
+  EXPECT_EQ(written(),
+            "namespace A {\n"
+            "namespace B {\n"
+            "namespace E {\n"
+            "\n"
+            "}  // namespace A\n"
+            "}  // namespace B\n"
+            "}  // namespace E\n");
+}
+
+}  // namespace
+
+}  // namespace cpp
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google