Down-integrate from internal code base.

author: Feng Xiao <xfxyjwf@gmail.com> 2014-11-10 17:34:54 -0800
committer: Feng Xiao <xfxyjwf@gmail.com> 2014-11-10 17:34:54 -0800
commit: 6ef984af4b0c63c1c33127a12dcfc8e6359f0c9e (patch)
tree: d17c61ff9f3ae28224fbddac6d26bfc59e2cf755 /src/google/protobuf/compiler
parent: baca1a8a1aa180c42de6278d3b8286c4496c6a10 (diff)
53 files changed, 3990 insertions, 1361 deletions
diff --git a/src/google/protobuf/compiler/command_line_interface.cc b/src/google/protobuf/compiler/command_line_interface.cc
index f9f27bd8..fc7df414 100644
--- a/src/google/protobuf/compiler/command_line_interface.cc
+++ b/src/google/protobuf/compiler/command_line_interface.cc
@@ -50,6 +50,9 @@
 
 #include <google/protobuf/stubs/hash.h>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/stubs/stringprintf.h>
diff --git a/src/google/protobuf/compiler/command_line_interface_unittest.cc b/src/google/protobuf/compiler/command_line_interface_unittest.cc
index 5bc1fea9..6e1a204d 100644
--- a/src/google/protobuf/compiler/command_line_interface_unittest.cc
+++ b/src/google/protobuf/compiler/command_line_interface_unittest.cc
@@ -41,6 +41,9 @@
 #include <unistd.h>
 #endif
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <vector>
 
 #include <google/protobuf/descriptor.pb.h>
@@ -48,6 +51,7 @@
 #include <google/protobuf/io/zero_copy_stream.h>
 #include <google/protobuf/compiler/command_line_interface.h>
 #include <google/protobuf/compiler/code_generator.h>
+#include <google/protobuf/testing/file.h>
 #include <google/protobuf/compiler/mock_code_generator.h>
 #include <google/protobuf/compiler/subprocess.h>
 #include <google/protobuf/io/printer.h>
@@ -59,6 +63,7 @@
 #include <google/protobuf/testing/googletest.h>
 #include <gtest/gtest.h>
 
+
 namespace google {
 namespace protobuf {
 namespace compiler {
@@ -77,6 +82,10 @@ namespace compiler {
 
 namespace {
 
+bool FileExists(const string& path) {
+  return File::Exists(path);
+}
+
 class CommandLineInterfaceTest : public testing::Test {
  protected:
   virtual void SetUp();
@@ -226,7 +235,7 @@ void CommandLineInterfaceTest::SetUp() {
 
   // If the temp directory already exists, it must be left over from a
   // previous run.  Delete it.
-  if (File::Exists(temp_directory_)) {
+  if (FileExists(temp_directory_)) {
     File::DeleteRecursively(temp_directory_, NULL, NULL);
   }
 
@@ -335,7 +344,7 @@ void CommandLineInterfaceTest::CreateTempFile(
   string::size_type slash_pos = name.find_last_of('/');
   if (slash_pos != string::npos) {
     string dir = name.substr(0, slash_pos);
-    if (!File::Exists(temp_directory_ + "/" + dir)) {
+    if (!FileExists(temp_directory_ + "/" + dir)) {
       GOOGLE_CHECK_OK(File::RecursivelyCreateDir(temp_directory_ + "/" + dir,
                                           0777));
     }
diff --git a/src/google/protobuf/compiler/cpp/cpp_enum.cc b/src/google/protobuf/compiler/cpp/cpp_enum.cc
index c31cb5b3..32d5516e 100644
--- a/src/google/protobuf/compiler/cpp/cpp_enum.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_enum.cc
@@ -101,6 +101,15 @@ void EnumGenerator::GenerateDefinition(io::Printer* printer) {
     }
   }
 
+  if (HasPreservingUnknownEnumSemantics(descriptor_->file())) {
+    // For new enum semantics: generate min and max sentinel values equal to
+    // INT32_MIN and INT32_MAX
+    if (descriptor_->value_count() > 0) printer->Print(",\n");
+    printer->Print(vars,
+        "$classname$_$prefix$INT_MIN_SENTINEL_DO_NOT_USE_ = INT32_MIN,\n"
+        "$classname$_$prefix$INT_MAX_SENTINEL_DO_NOT_USE_ = INT32_MAX");
+  }
+
   printer->Outdent();
   printer->Print("\n};\n");
 
diff --git a/src/google/protobuf/compiler/cpp/cpp_enum_field.cc b/src/google/protobuf/compiler/cpp/cpp_enum_field.cc
index 20b18ade..17926135 100644
--- a/src/google/protobuf/compiler/cpp/cpp_enum_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_enum_field.cc
@@ -87,9 +87,13 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  return static_cast< $type$ >($name$_);\n"
     "}\n"
-    "inline void $classname$::set_$name$($type$ value) {\n"
-    "  assert($type$_IsValid(value));\n"
-    "  set_has_$name$();\n"
+    "inline void $classname$::set_$name$($type$ value) {\n");
+  if (!HasPreservingUnknownEnumSemantics(descriptor_->file())) {
+    printer->Print(variables_,
+    "  assert($type$_IsValid(value));\n");
+  }
+  printer->Print(variables_,
+    "  $set_hasbit$\n"
     "  $name$_ = value;\n"
     "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "}\n");
@@ -121,21 +125,27 @@ GenerateMergeFromCodedStream(io::Printer* printer) const {
     "int value;\n"
     "DO_((::google::protobuf::internal::WireFormatLite::ReadPrimitive<\n"
     "         int, ::google::protobuf::internal::WireFormatLite::TYPE_ENUM>(\n"
-    "       input, &value)));\n"
-    "if ($type$_IsValid(value)) {\n"
-    "  set_$name$(static_cast< $type$ >(value));\n");
-  if (UseUnknownFieldSet(descriptor_->file())) {
+    "       input, &value)));\n");
+  if (HasPreservingUnknownEnumSemantics(descriptor_->file())) {
     printer->Print(variables_,
-      "} else {\n"
-      "  mutable_unknown_fields()->AddVarint($number$, value);\n");
+      "set_$name$(static_cast< $type$ >(value));\n");
   } else {
-    printer->Print(
-      "} else {\n"
-      "  unknown_fields_stream.WriteVarint32(tag);\n"
-      "  unknown_fields_stream.WriteVarint32(value);\n");
+    printer->Print(variables_,
+      "if ($type$_IsValid(value)) {\n"
+      "  set_$name$(static_cast< $type$ >(value));\n");
+    if (UseUnknownFieldSet(descriptor_->file())) {
+      printer->Print(variables_,
+        "} else {\n"
+        "  mutable_unknown_fields()->AddVarint($number$, value);\n");
+    } else {
+      printer->Print(
+        "} else {\n"
+        "  unknown_fields_stream.WriteVarint32(tag);\n"
+        "  unknown_fields_stream.WriteVarint32(value);\n");
+    }
+    printer->Print(variables_,
+      "}\n");
   }
-  printer->Print(variables_,
-    "}\n");
 }
 
 void EnumFieldGenerator::
@@ -174,18 +184,24 @@ void EnumOneofFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
     "inline $type$ $classname$::$name$() const {\n"
+    "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  if (has_$name$()) {\n"
     "    return static_cast< $type$ >($oneof_prefix$$name$_);\n"
     "  }\n"
     "  return static_cast< $type$ >($default$);\n"
     "}\n"
-    "inline void $classname$::set_$name$($type$ value) {\n"
-    "  assert($type$_IsValid(value));\n"
+    "inline void $classname$::set_$name$($type$ value) {\n");
+  if (!HasPreservingUnknownEnumSemantics(descriptor_->file())) {
+    printer->Print(variables_,
+    "  assert($type$_IsValid(value));\n");
+  }
+  printer->Print(variables_,
     "  if (!has_$name$()) {\n"
     "    clear_$oneof_name$();\n"
     "    set_has_$name$();\n"
     "  }\n"
     "  $oneof_prefix$$name$_ = value;\n"
+    "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "}\n");
 }
 
@@ -245,13 +261,21 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  return static_cast< $type$ >($name$_.Get(index));\n"
     "}\n"
-    "inline void $classname$::set_$name$(int index, $type$ value) {\n"
-    "  assert($type$_IsValid(value));\n"
+    "inline void $classname$::set_$name$(int index, $type$ value) {\n");
+  if (!HasPreservingUnknownEnumSemantics(descriptor_->file())) {
+    printer->Print(variables_,
+    "  assert($type$_IsValid(value));\n");
+  }
+  printer->Print(variables_,
     "  $name$_.Set(index, value);\n"
     "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "}\n"
-    "inline void $classname$::add_$name$($type$ value) {\n"
-    "  assert($type$_IsValid(value));\n"
+    "inline void $classname$::add_$name$($type$ value) {\n");
+  if (!HasPreservingUnknownEnumSemantics(descriptor_->file())) {
+    printer->Print(variables_,
+    "  assert($type$_IsValid(value));\n");
+  }
+  printer->Print(variables_,
     "  $name$_.Add(value);\n"
     "  // @@protoc_insertion_point(field_add:$full_name$)\n"
     "}\n");
@@ -280,7 +304,7 @@ GenerateMergingCode(io::Printer* printer) const {
 
 void RepeatedEnumFieldGenerator::
 GenerateSwappingCode(io::Printer* printer) const {
-  printer->Print(variables_, "$name$_.Swap(&other->$name$_);\n");
+  printer->Print(variables_, "$name$_.UnsafeArenaSwap(&other->$name$_);\n");
 }
 
 void RepeatedEnumFieldGenerator::
@@ -295,20 +319,26 @@ GenerateMergeFromCodedStream(io::Printer* printer) const {
     "int value;\n"
     "DO_((::google::protobuf::internal::WireFormatLite::ReadPrimitive<\n"
     "         int, ::google::protobuf::internal::WireFormatLite::TYPE_ENUM>(\n"
-    "       input, &value)));\n"
-    "if ($type$_IsValid(value)) {\n"
-    "  add_$name$(static_cast< $type$ >(value));\n");
-  if (UseUnknownFieldSet(descriptor_->file())) {
+    "       input, &value)));\n");
+  if (HasPreservingUnknownEnumSemantics(descriptor_->file())) {
     printer->Print(variables_,
-      "} else {\n"
-      "  mutable_unknown_fields()->AddVarint($number$, value);\n");
+      "add_$name$(static_cast< $type$ >(value));\n");
   } else {
-    printer->Print(
-      "} else {\n"
-      "  unknown_fields_stream.WriteVarint32(tag);\n"
-      "  unknown_fields_stream.WriteVarint32(value);\n");
+    printer->Print(variables_,
+      "if ($type$_IsValid(value)) {\n"
+      "  add_$name$(static_cast< $type$ >(value));\n");
+    if (UseUnknownFieldSet(descriptor_->file())) {
+      printer->Print(variables_,
+        "} else {\n"
+        "  mutable_unknown_fields()->AddVarint($number$, value);\n");
+    } else {
+      printer->Print(
+        "} else {\n"
+        "  unknown_fields_stream.WriteVarint32(tag);\n"
+        "  unknown_fields_stream.WriteVarint32(value);\n");
+    }
+    printer->Print("}\n");
   }
-  printer->Print("}\n");
 }
 
 void RepeatedEnumFieldGenerator::
@@ -318,8 +348,15 @@ GenerateMergeFromCodedStreamWithPacking(io::Printer* printer) const {
     // rarely be executed.
     printer->Print(variables_,
       "DO_((::google::protobuf::internal::WireFormatLite::ReadPackedEnumNoInline(\n"
-      "       input,\n"
-      "       &$type$_IsValid,\n"
+      "       input,\n");
+    if (HasPreservingUnknownEnumSemantics(descriptor_->file())) {
+      printer->Print(variables_,
+      "       NULL,\n");
+    } else {
+      printer->Print(variables_,
+      "       &$type$_IsValid,\n");
+    }
+    printer->Print(variables_,
       "       this->mutable_$name$())));\n");
   } else {
     printer->Print(variables_,
@@ -331,10 +368,17 @@ GenerateMergeFromCodedStreamWithPacking(io::Printer* printer) const {
       "  int value;\n"
       "  DO_((::google::protobuf::internal::WireFormatLite::ReadPrimitive<\n"
       "         int, ::google::protobuf::internal::WireFormatLite::TYPE_ENUM>(\n"
-      "       input, &value)));\n"
+      "       input, &value)));\n");
+    if (HasPreservingUnknownEnumSemantics(descriptor_->file())) {
+      printer->Print(variables_,
+      "  add_$name$(static_cast< $type$ >(value));\n");
+    } else {
+      printer->Print(variables_,
       "  if ($type$_IsValid(value)) {\n"
       "    add_$name$(static_cast< $type$ >(value));\n"
-      "  }\n"
+      "  }\n");
+    }
+    printer->Print(variables_,
       "}\n"
       "input->PopLimit(limit);\n");
   }
diff --git a/src/google/protobuf/compiler/cpp/cpp_field.cc b/src/google/protobuf/compiler/cpp/cpp_field.cc
index 1e9a40ac..85838ac3 100644
--- a/src/google/protobuf/compiler/cpp/cpp_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_field.cc
@@ -34,6 +34,9 @@
 
 #include <google/protobuf/compiler/cpp/cpp_field.h>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/compiler/cpp/cpp_helpers.h>
 #include <google/protobuf/compiler/cpp/cpp_primitive_field.h>
@@ -68,6 +71,20 @@ void SetCommonFieldVariables(const FieldDescriptor* descriptor,
       ? " PROTOBUF_DEPRECATED" : "";
 
   (*variables)["cppget"] = "Get";
+
+  if (HasFieldPresence(descriptor->file())) {
+    (*variables)["set_hasbit"] =
+        "set_has_" + FieldName(descriptor) + "();";
+    (*variables)["clear_hasbit"] =
+        "clear_has_" + FieldName(descriptor) + "();";
+  } else {
+    (*variables)["set_hasbit"] = "";
+    (*variables)["clear_hasbit"] = "";
+  }
+
+  // By default, empty string, so that generic code used for both oneofs and
+  // singular fields can be written.
+  (*variables)["oneof_prefix"] = "";
 }
 
 void SetCommonOneofFieldVariables(const FieldDescriptor* descriptor,
diff --git a/src/google/protobuf/compiler/cpp/cpp_field.h b/src/google/protobuf/compiler/cpp/cpp_field.h
index 0342c35e..088e5063 100644
--- a/src/google/protobuf/compiler/cpp/cpp_field.h
+++ b/src/google/protobuf/compiler/cpp/cpp_field.h
@@ -37,6 +37,9 @@
 
 #include <map>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <string>
 
 #include <google/protobuf/descriptor.h>
@@ -124,6 +127,16 @@ class FieldGenerator {
   // Most field types don't need this, so the default implementation is empty.
   virtual void GenerateDestructorCode(io::Printer* /*printer*/) const {}
 
+  // Generate a manual destructor invocation for use when the message is on an
+  // arena. The code that this method generates will be executed inside a
+  // shared-for-the-whole-message-class method registered with OwnDestructor().
+  // The method should return |true| if it generated any code that requires a
+  // call; this allows the message generator to eliminate the OwnDestructor()
+  // registration if no fields require it.
+  virtual bool GenerateArenaDestructorCode(io::Printer* printer) const {
+    return false;
+  }
+
   // Generate code that allocates the fields's default instance.
   virtual void GenerateDefaultInstanceAllocator(io::Printer* /*printer*/)
       const {}
diff --git a/src/google/protobuf/compiler/cpp/cpp_file.cc b/src/google/protobuf/compiler/cpp/cpp_file.cc
index fa194273..dc8bf613 100644
--- a/src/google/protobuf/compiler/cpp/cpp_file.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_file.cc
@@ -34,6 +34,9 @@
 
 #include <google/protobuf/compiler/cpp/cpp_file.h>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <set>
 
 #include <google/protobuf/compiler/cpp/cpp_enum.h>
@@ -102,6 +105,7 @@ void FileGenerator::GenerateHeader(io::Printer* printer) {
     "#define PROTOBUF_$filename_identifier$__INCLUDED\n"
     "\n"
     "#include <string>\n"
+    "#include <stdint.h>\n"  // INT32_MIN, INT32_MAX
     "\n",
     "filename", file_->name(),
     "filename_identifier", filename_identifier);
@@ -131,7 +135,10 @@ void FileGenerator::GenerateHeader(io::Printer* printer) {
 
   // OK, it's now safe to #include other files.
   printer->Print(
-    "#include <google/protobuf/generated_message_util.h>\n");
+    "#include <google/protobuf/arena.h>\n"
+    "#include <google/protobuf/arenastring.h>\n"
+    "#include <google/protobuf/generated_message_util.h>\n"
+    "#include <google/protobuf/metadata.h>\n");
   if (file_->message_type_count() > 0) {
     if (HasDescriptorMethods(file_)) {
       printer->Print(
@@ -181,6 +188,7 @@ void FileGenerator::GenerateHeader(io::Printer* printer) {
     "// @@protoc_insertion_point(includes)\n");
 
 
+
   // Open namespace.
   GenerateNamespaceOpeners(printer);
 
@@ -189,9 +197,10 @@ void FileGenerator::GenerateHeader(io::Printer* printer) {
   printer->Print(
     "\n"
     "// Internal implementation detail -- do not call these.\n"
-    "void $dllexport_decl$ $adddescriptorsname$();\n",
+    "void $dllexport_decl$$adddescriptorsname$();\n",
     "adddescriptorsname", GlobalAddDescriptorsName(file_->name()),
-    "dllexport_decl", options_.dllexport_decl);
+    "dllexport_decl",
+    options_.dllexport_decl.empty() ? "" : options_.dllexport_decl + " ");
 
   printer->Print(
     // Note that we don't put dllexport_decl on these because they are only
@@ -295,7 +304,7 @@ void FileGenerator::GenerateHeader(io::Printer* printer) {
     }
     printer->Print(
         "\n"
-        "}  // namespace google\n}  // namespace protobuf\n"
+        "}  // namespace protobuf\n}  // namespace google\n"
         "#endif  // SWIG\n");
   }
 
diff --git a/src/google/protobuf/compiler/cpp/cpp_file.h b/src/google/protobuf/compiler/cpp/cpp_file.h
index 4e4d8b6a..13d06f98 100644
--- a/src/google/protobuf/compiler/cpp/cpp_file.h
+++ b/src/google/protobuf/compiler/cpp/cpp_file.h
@@ -36,6 +36,9 @@
 #define GOOGLE_PROTOBUF_COMPILER_CPP_FILE_H__
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <string>
 #include <vector>
 #include <google/protobuf/stubs/common.h>
diff --git a/src/google/protobuf/compiler/cpp/cpp_generator.cc b/src/google/protobuf/compiler/cpp/cpp_generator.cc
index 75d558ea..a2fb7162 100644
--- a/src/google/protobuf/compiler/cpp/cpp_generator.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_generator.cc
@@ -36,6 +36,9 @@
 
 #include <vector>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <utility>
 
 #include <google/protobuf/compiler/cpp/cpp_file.h>
diff --git a/src/google/protobuf/compiler/cpp/cpp_helpers.cc b/src/google/protobuf/compiler/cpp/cpp_helpers.cc
index b7a47acb..63b0265e 100644
--- a/src/google/protobuf/compiler/cpp/cpp_helpers.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_helpers.cc
@@ -60,16 +60,17 @@ string DotsToColons(const string& name) {
 }
 
 const char* const kKeywordList[] = {
-  "and", "and_eq", "asm", "auto", "bitand", "bitor", "bool", "break", "case",
-  "catch", "char", "class", "compl", "const", "const_cast", "continue",
-  "default", "delete", "do", "double", "dynamic_cast", "else", "enum",
-  "explicit", "extern", "false", "float", "for", "friend", "goto", "if",
-  "inline", "int", "long", "mutable", "namespace", "new", "not", "not_eq",
-  "operator", "or", "or_eq", "private", "protected", "public", "register",
-  "reinterpret_cast", "return", "short", "signed", "sizeof", "static",
-  "static_cast", "struct", "switch", "template", "this", "throw", "true", "try",
-  "typedef", "typeid", "typename", "union", "unsigned", "using", "virtual",
-  "void", "volatile", "wchar_t", "while", "xor", "xor_eq"
+  "alignas", "alignof", "and", "and_eq", "asm", "auto", "bitand", "bitor",
+  "bool", "break", "case", "catch", "char", "class", "compl", "const",
+  "constexpr", "const_cast", "continue", "decltype", "default", "delete", "do",
+  "double", "dynamic_cast", "else", "enum", "explicit", "extern", "false",
+  "float", "for", "friend", "goto", "if", "inline", "int", "long", "mutable",
+  "namespace", "new", "noexcept", "not", "not_eq", "nullptr", "operator", "or",
+  "or_eq", "private", "protected", "public", "register", "reinterpret_cast",
+  "return", "short", "signed", "sizeof", "static", "static_assert",
+  "static_cast", "struct", "switch", "template", "this", "thread_local",
+  "throw", "true", "try", "typedef", "typeid", "typename", "union", "unsigned",
+  "using", "virtual", "void", "volatile", "wchar_t", "while", "xor", "xor_eq"
 };
 
 hash_set<string> MakeKeywordsMap() {
diff --git a/src/google/protobuf/compiler/cpp/cpp_helpers.h b/src/google/protobuf/compiler/cpp/cpp_helpers.h
index 5d30240c..1cff17c8 100644
--- a/src/google/protobuf/compiler/cpp/cpp_helpers.h
+++ b/src/google/protobuf/compiler/cpp/cpp_helpers.h
@@ -135,8 +135,15 @@ string SafeFunctionName(const Descriptor* descriptor,
                         const FieldDescriptor* field,
                         const string& prefix);
 
-// Do message classes in this file use UnknownFieldSet?
-// Otherwise, messages will store unknown fields in a string
+// Returns true if unknown fields are preseved after parsing.
+inline bool PreserveUnknownFields(const Descriptor* message) {
+  return message->file()->syntax() != FileDescriptor::SYNTAX_PROTO3;
+}
+
+// If PreserveUnknownFields() is true, determines whether unknown
+// fields will be stored in an UnknownFieldSet or a string.
+// If PreserveUnknownFields() is false, this method will not be
+// used.
 inline bool UseUnknownFieldSet(const FileDescriptor* file) {
   return file->options().optimize_for() != FileOptions::LITE_RUNTIME;
 }
@@ -198,6 +205,28 @@ bool IsStringOrMessage(const FieldDescriptor* field);
 
 string UnderscoresToCamelCase(const string& input, bool cap_next_letter);
 
+inline bool HasFieldPresence(const FileDescriptor* file) {
+  return file->syntax() != FileDescriptor::SYNTAX_PROTO3;
+}
+
+// Returns true if 'enum' semantics are such that unknown values are preserved
+// in the enum field itself, rather than going to the UnknownFieldSet.
+inline bool HasPreservingUnknownEnumSemantics(const FileDescriptor* file) {
+  return file->syntax() == FileDescriptor::SYNTAX_PROTO3;
+}
+
+inline bool SupportsArenas(const FileDescriptor* file) {
+  return true;
+}
+
+inline bool SupportsArenas(const Descriptor* desc) {
+  return SupportsArenas(desc->file());
+}
+
+inline bool SupportsArenas(const FieldDescriptor* field) {
+  return SupportsArenas(field->file());
+}
+
 }  // namespace cpp
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/cpp/cpp_message.cc b/src/google/protobuf/compiler/cpp/cpp_message.cc
index 3a9d2639..54a92ae4 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_message.cc
@@ -36,6 +36,9 @@
 #include <google/protobuf/stubs/hash.h>
 #include <map>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <set>
 #include <utility>
 #include <vector>
@@ -281,8 +284,67 @@ string MessageTypeProtoName(const FieldDescriptor* field) {
   return field->message_type()->full_name();
 }
 
+// Emits an if-statement with a condition that evaluates to true if |field| is
+// considered non-default (will be sent over the wire), for message types
+// without true field presence. Should only be called if
+// !HasFieldPresence(message_descriptor).
+bool EmitFieldNonDefaultCondition(io::Printer* printer,
+                                  const string& prefix,
+                                  const FieldDescriptor* field) {
+  // Merge and serialize semantics: primitive fields are merged/serialized only
+  // if non-zero (numeric) or non-empty (string).
+  if (!field->is_repeated() && !field->containing_oneof()) {
+    if (field->cpp_type() == FieldDescriptor::CPPTYPE_STRING) {
+      printer->Print(
+          "if ($prefix$$name$().size() > 0) {\n",
+          "prefix", prefix,
+          "name", FieldName(field));
+    } else if (field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
+      // Message fields still have has_$name$() methods.
+      printer->Print(
+          "if ($prefix$has_$name$()) {\n",
+          "prefix", prefix,
+          "name", FieldName(field));
+    } else {
+      printer->Print(
+          "if ($prefix$$name$() != 0) {\n",
+          "prefix", prefix,
+          "name", FieldName(field));
+    }
+    printer->Indent();
+    return true;
+  } else if (field->containing_oneof()) {
+    printer->Print(
+        "if (has_$name$()) {\n",
+        "name", FieldName(field));
+    printer->Indent();
+    return true;
+  }
+  return false;
+}
+
+// Does the given field have a has_$name$() method?
+bool HasHasMethod(const FieldDescriptor* field) {
+  if (HasFieldPresence(field->file())) {
+    // In proto1/proto2, every field has a has_$name$() method.
+    return true;
+  }
+  // For message types without true field presence, only fields with a message
+  // type have a has_$name$() method.
+  return field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE;
 }
 
+// Does the given field have a private (internal helper only) has_$name$()
+// method?
+bool HasPrivateHasMethod(const FieldDescriptor* field) {
+  // Only for oneofs in message types with no field presence. has_$name$(),
+  // based on the oneof case, is still useful internally for generated code.
+  return (!HasFieldPresence(field->file()) &&
+          field->containing_oneof() != NULL);
+}
+
+}  // anonymous namespace
+
 // ===================================================================
 
 MessageGenerator::MessageGenerator(const Descriptor* descriptor,
@@ -312,6 +374,13 @@ MessageGenerator::MessageGenerator(const Descriptor* descriptor,
     extension_generators_[i].reset(
       new ExtensionGenerator(descriptor->extension(i), options));
   }
+
+  num_required_fields_ = 0;
+  for (int i = 0; i < descriptor->field_count(); i++) {
+    if (descriptor->field(i)->is_required()) {
+      ++num_required_fields_;
+    }
+  }
 }
 
 MessageGenerator::~MessageGenerator() {}
@@ -360,8 +429,13 @@ GenerateFieldAccessorDeclarations(io::Printer* printer) {
 
     if (field->is_repeated()) {
       printer->Print(vars, "inline int $name$_size() const$deprecation$;\n");
-    } else {
+    } else if (HasHasMethod(field)) {
       printer->Print(vars, "inline bool has_$name$() const$deprecation$;\n");
+    } else if (HasPrivateHasMethod(field)) {
+      printer->Print(vars,
+          "private:\n"
+          "inline bool has_$name$() const$deprecation$;\n"
+          "public:\n");
     }
 
     printer->Print(vars, "inline void clear_$name$()$deprecation$;\n");
@@ -410,32 +484,59 @@ GenerateFieldAccessorDefinitions(io::Printer* printer) {
         "}\n");
     } else if (field->containing_oneof()) {
       // Singular field in a oneof
+      // N.B.: Without field presence, we do not use has-bits or generate
+      // has_$name$() methods, but oneofs still have set_has_$name$().
+      // Oneofs also have has_$name$() but only as a private helper
+      // method, so that generated code is slightly cleaner (vs.  comparing
+      // _oneof_case_[index] against a constant everywhere).
       vars["field_name"] = UnderscoresToCamelCase(field->name(), true);
       vars["oneof_name"] = field->containing_oneof()->name();
       vars["oneof_index"] = SimpleItoa(field->containing_oneof()->index());
       printer->Print(vars,
         "inline bool $classname$::has_$name$() const {\n"
         "  return $oneof_name$_case() == k$field_name$;\n"
-        "}\n"
+        "}\n");
+      printer->Print(vars,
         "inline void $classname$::set_has_$name$() {\n"
         "  _oneof_case_[$oneof_index$] = k$field_name$;\n"
         "}\n");
     } else {
       // Singular field.
-      char buffer[kFastToBufferSize];
-      vars["has_array_index"] = SimpleItoa(field->index() / 32);
-      vars["has_mask"] = FastHex32ToBuffer(1u << (field->index() % 32), buffer);
-      printer->Print(vars,
-        "inline bool $classname$::has_$name$() const {\n"
-        "  return (_has_bits_[$has_array_index$] & 0x$has_mask$u) != 0;\n"
-        "}\n"
-        "inline void $classname$::set_has_$name$() {\n"
-        "  _has_bits_[$has_array_index$] |= 0x$has_mask$u;\n"
-        "}\n"
-        "inline void $classname$::clear_has_$name$() {\n"
-        "  _has_bits_[$has_array_index$] &= ~0x$has_mask$u;\n"
-        "}\n"
-        );
+      if (HasFieldPresence(descriptor_->file())) {
+        // N.B.: without field presence, we do not use has-bits or generate
+        // has_$name$() methods.
+        char buffer[kFastToBufferSize];
+        vars["has_array_index"] = SimpleItoa(field->index() / 32);
+        vars["has_mask"] = FastHex32ToBuffer(1u << (field->index() % 32),
+                                             buffer);
+        printer->Print(vars,
+          "inline bool $classname$::has_$name$() const {\n"
+          "  return (_has_bits_[$has_array_index$] & 0x$has_mask$u) != 0;\n"
+          "}\n"
+          "inline void $classname$::set_has_$name$() {\n"
+          "  _has_bits_[$has_array_index$] |= 0x$has_mask$u;\n"
+          "}\n"
+          "inline void $classname$::clear_has_$name$() {\n"
+          "  _has_bits_[$has_array_index$] &= ~0x$has_mask$u;\n"
+          "}\n"
+          );
+      } else {
+        // Message fields have a has_$name$() method.
+        if (field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE) {
+          bool is_lazy = false;
+          if (is_lazy) {
+            printer->Print(vars,
+              "inline bool $classname$::has_$name$() const {\n"
+              "  return !$name$_.IsCleared();\n"
+              "}\n");
+          } else {
+            printer->Print(vars,
+              "inline bool $classname$::has_$name$() const {\n"
+              "  return $name$_ != NULL;\n"
+              "}\n");
+          }
+        }
+      }
     }
 
     // Generate clear_$name$()
@@ -457,9 +558,11 @@ GenerateFieldAccessorDefinitions(io::Printer* printer) {
       printer->Print("}\n");
     } else {
       field_generators_.get(field).GenerateClearingCode(printer);
-      if (!field->is_repeated()) {
-        printer->Print(vars,
-                       "clear_has_$name$();\n");
+      if (HasFieldPresence(descriptor_->file())) {
+        if (!field->is_repeated()) {
+          printer->Print(vars,
+                         "clear_has_$name$();\n");
+        }
       }
     }
 
@@ -553,26 +656,41 @@ GenerateClassDefinition(io::Printer* printer) {
     "}\n"
     "\n");
 
-  if (UseUnknownFieldSet(descriptor_->file())) {
-    printer->Print(
-      "inline const ::google::protobuf::UnknownFieldSet& unknown_fields() const {\n"
-      "  return _unknown_fields_;\n"
-      "}\n"
-      "\n"
-      "inline ::google::protobuf::UnknownFieldSet* mutable_unknown_fields() {\n"
-      "  return &_unknown_fields_;\n"
-      "}\n"
-      "\n");
-  } else {
+  if (PreserveUnknownFields(descriptor_)) {
+    if (UseUnknownFieldSet(descriptor_->file())) {
+      printer->Print(
+        "inline const ::google::protobuf::UnknownFieldSet& unknown_fields() const {\n"
+        "  return _internal_metadata_.unknown_fields();\n"
+        "}\n"
+        "\n"
+        "inline ::google::protobuf::UnknownFieldSet* mutable_unknown_fields() {\n"
+        "  return _internal_metadata_.mutable_unknown_fields();\n"
+        "}\n"
+        "\n");
+    } else {
+      printer->Print(
+        "inline const ::std::string& unknown_fields() const {\n"
+        "  return _unknown_fields_;\n"
+        "}\n"
+        "\n"
+        "inline ::std::string* mutable_unknown_fields() {\n"
+        "  return &_unknown_fields_;\n"
+        "}\n"
+        "\n");
+    }
+  }
+
+  // N.B.: We exclude GetArena() when arena support is disabled, falling back on
+  // MessageLite's implementation which returns NULL rather than generating our
+  // own method which returns NULL, in order to reduce code size.
+  if (SupportsArenas(descriptor_)) {
+    // virtual method version of GetArenaNoVirtual(), required for generic dispatch given a
+    // MessageLite* (e.g., in RepeatedField::AddAllocated()).
     printer->Print(
-      "inline const ::std::string& unknown_fields() const {\n"
-      "  return _unknown_fields_;\n"
-      "}\n"
-      "\n"
-      "inline ::std::string* mutable_unknown_fields() {\n"
-      "  return &_unknown_fields_;\n"
-      "}\n"
-      "\n");
+        "inline ::google::protobuf::Arena* GetArena() const { return GetArenaNoVirtual(); }\n"
+        "inline void* GetMaybeArenaPointer() const {\n"
+        "  return MaybeArenaPtr();\n"
+        "}\n");
   }
 
   // Only generate this member if it's not disabled.
@@ -628,12 +746,18 @@ GenerateClassDefinition(io::Printer* printer) {
   }
 
 
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(vars,
+      "void UnsafeArenaSwap($classname$* other);\n");
+  }
   printer->Print(vars,
     "void Swap($classname$* other);\n"
     "\n"
     "// implements Message ----------------------------------------------\n"
     "\n"
-    "$classname$* New() const;\n");
+    "inline $classname$* New() const { return New(NULL); }\n"
+    "\n"
+    "$classname$* New(::google::protobuf::Arena* arena) const;\n");
 
   if (HasGeneratedMethods(descriptor_->file())) {
     if (HasDescriptorMethods(descriptor_->file())) {
@@ -699,7 +823,41 @@ GenerateClassDefinition(io::Printer* printer) {
     "void SharedCtor();\n"
     "void SharedDtor();\n"
     "void SetCachedSize(int size) const;\n"
-    "public:\n");
+    "void InternalSwap($classname$* other);\n",
+    "classname", classname_);
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(
+      "protected:\n"
+      "explicit $classname$(::google::protobuf::Arena* arena);\n"
+      "private:\n"
+      "static void ArenaDtor(void* object);\n"
+      "inline void RegisterArenaDtor(::google::protobuf::Arena* arena);\n",
+      "classname", classname_);
+  }
+
+  if (UseUnknownFieldSet(descriptor_->file())) {
+    printer->Print(
+      "private:\n"
+      "inline ::google::protobuf::Arena* GetArenaNoVirtual() const {\n"
+      "  return _internal_metadata_.arena();\n"
+      "}\n"
+      "inline void* MaybeArenaPtr() const {\n"
+      "  return _internal_metadata_.raw_arena_ptr();\n"
+      "}\n"
+      "public:\n"
+      "\n");
+  } else {
+    printer->Print(
+      "private:\n"
+      "inline ::google::protobuf::Arena* GetArenaNoVirtual() const {\n"
+      "  return _arena_ptr_;\n"
+      "}\n"
+      "inline ::google::protobuf::Arena* MaybeArenaPtr() const {\n"
+      "  return _arena_ptr_;\n"
+      "}\n"
+      "public:\n"
+      "\n");
+  }
 
   if (HasDescriptorMethods(descriptor_->file())) {
     printer->Print(
@@ -759,10 +917,18 @@ GenerateClassDefinition(io::Printer* printer) {
 
   for (int i = 0; i < descriptor_->field_count(); i++) {
     if (!descriptor_->field(i)->is_repeated()) {
-      printer->Print(
-        "inline void set_has_$name$();\n",
-        "name", FieldName(descriptor_->field(i)));
-      if (!descriptor_->field(i)->containing_oneof()) {
+      // set_has_***() generated in all proto1/2 code and in oneofs (only) for
+      // messages without true field presence.
+      if (HasFieldPresence(descriptor_->file()) ||
+          descriptor_->field(i)->containing_oneof()) {
+        printer->Print(
+          "inline void set_has_$name$();\n",
+          "name", FieldName(descriptor_->field(i)));
+      }
+      // clear_has_***() generated only for non-oneof fields
+      // in proto1/2.
+      if (!descriptor_->field(i)->containing_oneof() &&
+          HasFieldPresence(descriptor_->file())) {
         printer->Print(
           "inline void clear_has_$name$();\n",
           "name", FieldName(descriptor_->field(i)));
@@ -780,6 +946,14 @@ GenerateClassDefinition(io::Printer* printer) {
         "oneof_name", descriptor_->oneof_decl(i)->name());
   }
 
+  if (HasGeneratedMethods(descriptor_->file()) &&
+      !descriptor_->options().message_set_wire_format() &&
+      num_required_fields_ > 1) {
+    printer->Print(
+        "// helper for ByteSize()\n"
+        "int RequiredFieldsByteSizeFallback() const;\n\n");
+  }
+
   // Prepare decls for _cached_size_ and _has_bits_.  Their position in the
   // output will be determined later.
 
@@ -816,23 +990,32 @@ GenerateClassDefinition(io::Printer* printer) {
 
   if (UseUnknownFieldSet(descriptor_->file())) {
     printer->Print(
-      "::google::protobuf::UnknownFieldSet _unknown_fields_;\n"
-      "\n");
+      "::google::protobuf::internal::InternalMetadataWithArena _internal_metadata_;\n");
   } else {
     printer->Print(
       "::std::string _unknown_fields_;\n"
+      "::google::protobuf::Arena* _arena_ptr_;\n"
       "\n");
   }
 
-  // _has_bits_ is frequently accessed, so to reduce code size and improve
-  // speed, it should be close to the start of the object.  But, try not to
-  // waste space:_has_bits_ by itself always makes sense if its size is a
-  // multiple of 8, but, otherwise, maybe _has_bits_ and cached_size_ together
-  // will work well.
-  printer->Print(has_bits_decl.c_str());
-  if ((sizeof_has_bits % 8) != 0) {
-    printer->Print(cached_size_decl.c_str());
-    need_to_emit_cached_size = false;
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(
+      "friend class ::google::protobuf::Arena;\n"
+      "typedef void InternalArenaConstructable_;\n"
+      "typedef void DestructorSkippable_;\n");
+  }
+
+  if (HasFieldPresence(descriptor_->file())) {
+    // _has_bits_ is frequently accessed, so to reduce code size and improve
+    // speed, it should be close to the start of the object.  But, try not to
+    // waste space:_has_bits_ by itself always makes sense if its size is a
+    // multiple of 8, but, otherwise, maybe _has_bits_ and cached_size_ together
+    // will work well.
+    printer->Print(has_bits_decl.c_str());
+    if ((sizeof_has_bits % 8) != 0) {
+      printer->Print(cached_size_decl.c_str());
+      need_to_emit_cached_size = false;
+    }
   }
 
   // Field members:
@@ -871,7 +1054,10 @@ GenerateClassDefinition(io::Printer* printer) {
   // For each oneof generate a union
   for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
     printer->Print(
-        "union $camel_oneof_name$Union {\n",
+        "union $camel_oneof_name$Union {\n"
+        // explicit empty constructor is needed when union contains
+        // ArenaStringPtr members for string fields.
+        "  $camel_oneof_name$Union() {}\n",
         "camel_oneof_name",
         UnderscoresToCamelCase(descriptor_->oneof_decl(i)->name(), true));
     printer->Indent();
@@ -1029,10 +1215,28 @@ GenerateDescriptorInitializer(io::Printer* printer, int index) {
     "  new ::google::protobuf::internal::GeneratedMessageReflection(\n"
     "    $classname$_descriptor_,\n"
     "    $classname$::default_instance_,\n"
-    "    $classname$_offsets_,\n"
-    "    GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET($classname$, _has_bits_[0]),\n"
+    "    $classname$_offsets_,\n");
+  if (!HasFieldPresence(descriptor_->file())) {
+    // If we don't have field presence, then _has_bits_ does not exist.
+    printer->Print(vars,
+    "    -1,\n");
+  } else {
+    printer->Print(vars,
+    "    GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET($classname$, _has_bits_[0]),\n");
+  }
+
+  // Unknown field offset: either points to the unknown field set if embedded
+  // directly, or indicates that the unknown field set is stored as part of the
+  // internal metadata if not.
+  if (UseUnknownFieldSet(descriptor_->file())) {
+    printer->Print(vars,
+    "    -1,\n");
+  } else {
+    printer->Print(vars,
     "    GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET("
       "$classname$, _unknown_fields_),\n");
+  }
+
   if (descriptor_->extension_range_count() > 0) {
     printer->Print(vars,
       "    GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET("
@@ -1054,8 +1258,23 @@ GenerateDescriptorInitializer(io::Printer* printer, int index) {
     "    ::google::protobuf::DescriptorPool::generated_pool(),\n");
   printer->Print(vars,
     "    ::google::protobuf::MessageFactory::generated_factory(),\n");
+
   printer->Print(vars,
-    "    sizeof($classname$));\n");
+    "    sizeof($classname$),\n");
+
+  // Arena offset: either an offset to the metadata struct that contains the
+  // arena pointer and unknown field set (in a space-efficient way) if we use
+  // that implementation strategy, or an offset directly to the arena pointer if
+  // not (because e.g. we don't have an unknown field set).
+  if (UseUnknownFieldSet(descriptor_->file())) {
+    printer->Print(vars,
+    "    GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET("
+    "$classname$, _internal_metadata_));\n");
+  } else {
+    printer->Print(vars,
+    "    GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET("
+    "$classname$, _arena_));\n");
+  }
 
   // Handle nested types.
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
@@ -1100,7 +1319,7 @@ GenerateDefaultInstanceAllocator(io::Printer* printer) {
   if ((descriptor_->oneof_decl_count() > 0) &&
       HasDescriptorMethods(descriptor_->file())) {
     printer->Print(
-    "$classname$_default_oneof_instance_ = new $classname$OneofInstance;\n",
+    "$classname$_default_oneof_instance_ = new $classname$OneofInstance();\n",
     "classname", classname_);
   }
 
@@ -1312,8 +1531,10 @@ GenerateSharedConstructorCode(io::Printer* printer) {
     }
   }
 
-  printer->Print(
-    "::memset(_has_bits_, 0, sizeof(_has_bits_));\n");
+  if (HasFieldPresence(descriptor_->file())) {
+    printer->Print(
+      "::memset(_has_bits_, 0, sizeof(_has_bits_));\n");
+  }
 
   for (int i = 0; i < descriptor_->oneof_decl_count(); i++) {
     printer->Print(
@@ -1331,6 +1552,14 @@ GenerateSharedDestructorCode(io::Printer* printer) {
     "void $classname$::SharedDtor() {\n",
     "classname", classname_);
   printer->Indent();
+  if (SupportsArenas(descriptor_)) {
+    // Do nothing when the message is allocated in an arena.
+    printer->Print(
+      "if (GetArenaNoVirtual() != NULL) {\n"
+      "  return;\n"
+      "}\n"
+      "\n");
+  }
   // Write the destructors for each field except oneof members.
   for (int i = 0; i < descriptor_->field_count(); i++) {
     if (!descriptor_->field(i)->containing_oneof()) {
@@ -1381,19 +1610,107 @@ GenerateSharedDestructorCode(io::Printer* printer) {
 }
 
 void MessageGenerator::
+GenerateArenaDestructorCode(io::Printer* printer) {
+  // Generate the ArenaDtor() method. Track whether any fields actually produced
+  // code that needs to be called.
+  printer->Print(
+      "void $classname$::ArenaDtor(void* object) {\n",
+      "classname", classname_);
+  printer->Indent();
+
+  // This code is placed inside a static method, rather than an ordinary one,
+  // since that simplifies Arena's destructor list (ordinary function pointers
+  // rather than member function pointers). _this is the object being
+  // destructed.
+  printer->Print(
+      "$classname$* _this = reinterpret_cast< $classname$* >(object);\n"
+      // avoid an "unused variable" warning in case no fields have dtor code.
+      "(void)_this;\n",
+      "classname", classname_);
+
+  bool need_registration = false;
+  for (int i = 0; i < descriptor_->field_count(); i++) {
+    if (field_generators_.get(descriptor_->field(i))
+                         .GenerateArenaDestructorCode(printer)) {
+      need_registration = true;
+    }
+  }
+  printer->Outdent();
+  printer->Print(
+      "}\n");
+
+  if (need_registration) {
+    printer->Print(
+        "inline void $classname$::RegisterArenaDtor(::google::protobuf::Arena* arena) {\n"
+        "  if (arena != NULL) {"
+        "    arena->OwnCustomDestructor(this, &$classname$::ArenaDtor);\n"
+        "  }\n"
+        "}\n",
+        "classname", classname_);
+  } else {
+    printer->Print(
+        "void $classname$::RegisterArenaDtor(::google::protobuf::Arena* arena) {\n"
+        "}\n",
+        "classname", classname_);
+  }
+}
+
+void MessageGenerator::
 GenerateStructors(io::Printer* printer) {
   string superclass = SuperClassName(descriptor_);
+  string initializer_with_arena;
+  if (UseUnknownFieldSet(descriptor_->file())) {
+    initializer_with_arena = "_internal_metadata_(arena)";
+  } else {
+    initializer_with_arena = "_arena_ptr_(arena)";
+  }
+  if (descriptor_->extension_range_count() > 0) {
+      initializer_with_arena  = string("\n  _extensions_(arena)") +
+        (!initializer_with_arena.empty() ?  ", " : "") + initializer_with_arena;
+  } else {
+    initializer_with_arena  = "\n  " + initializer_with_arena;
+  }
+
+  // Initialize member variables with arena constructor.
+  for (int i = 0; i < descriptor_->field_count(); i++) {
+    bool has_arena_constructor = descriptor_->field(i)->is_repeated();
+    if (has_arena_constructor) {
+      initializer_with_arena += string(",\n  ") +
+          FieldName(descriptor_->field(i)) + string("_(arena)");
+    }
+  }
+  initializer_with_arena = superclass + "()" +
+      (!initializer_with_arena.empty() ?  "," : " ") + initializer_with_arena;
+
+  string initializer_null;
+  initializer_null = (UseUnknownFieldSet(descriptor_->file()) ?
+    ", _internal_metadata_(NULL) " : ", _arena_ptr_(NULL)");
 
-  // Generate the default constructor.
   printer->Print(
-    "$classname$::$classname$()\n"
-    "  : $superclass$() {\n"
-    "  SharedCtor();\n"
-    "  // @@protoc_insertion_point(constructor:$full_name$)\n"
-    "}\n",
-    "classname", classname_,
-    "superclass", superclass,
-    "full_name", descriptor_->full_name());
+      "$classname$::$classname$()\n"
+      "  : $superclass$() $initializer$ {\n"
+      "  SharedCtor();\n"
+      "  // @@protoc_insertion_point(constructor:$full_name$)\n"
+      "}\n",
+      "classname", classname_,
+      "superclass", superclass,
+      "full_name", descriptor_->full_name(),
+      "initializer", initializer_null);
+
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(
+        "\n"
+        "$classname$::$classname$(::google::protobuf::Arena* arena)\n"
+        "  : $initializer$ {\n"
+        "  SharedCtor();\n"
+        "  RegisterArenaDtor(arena);\n"
+        "  // @@protoc_insertion_point(arena_constructor:$full_name$)\n"
+        "}\n",
+        "initializer", initializer_with_arena,
+        "classname", classname_,
+        "superclass", superclass,
+        "full_name", descriptor_->full_name());
+  }
 
   printer->Print(
     "\n"
@@ -1441,7 +1758,17 @@ GenerateStructors(io::Printer* printer) {
   // Generate the copy constructor.
   printer->Print(
     "$classname$::$classname$(const $classname$& from)\n"
-    "  : $superclass$() {\n"
+    "  : $superclass$()",
+    "classname", classname_,
+    "superclass", superclass,
+    "full_name", descriptor_->full_name());
+  if (UseUnknownFieldSet(descriptor_->file())) {
+    printer->Print(
+        ",\n    _internal_metadata_(NULL) {\n");
+  } else if (!UseUnknownFieldSet(descriptor_->file())) {
+    printer->Print(",\n    _arena_ptr_(NULL) {\n");
+  }
+  printer->Print(
     "  SharedCtor();\n"
     "  MergeFrom(from);\n"
     "  // @@protoc_insertion_point(copy_constructor:$full_name$)\n"
@@ -1467,6 +1794,11 @@ GenerateStructors(io::Printer* printer) {
   // Generate the shared destructor code.
   GenerateSharedDestructorCode(printer);
 
+  // Generate the arena-specific destructor code.
+  if (SupportsArenas(descriptor_)) {
+    GenerateArenaDestructorCode(printer);
+  }
+
   // Generate SetCachedSize.
   printer->Print(
     "void $classname$::SetCachedSize(int size) const {\n"
@@ -1512,11 +1844,23 @@ GenerateStructors(io::Printer* printer) {
     "\n",
     "classname", classname_);
 
-  printer->Print(
-    "$classname$* $classname$::New() const {\n"
-    "  return new $classname$;\n"
-    "}\n",
-    "classname", classname_);
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(
+      "$classname$* $classname$::New(::google::protobuf::Arena* arena) const {\n"
+      "  return ::google::protobuf::Arena::CreateMessage<$classname$>(arena);\n"
+      "}\n",
+      "classname", classname_);
+  } else {
+    printer->Print(
+      "$classname$* $classname$::New(::google::protobuf::Arena* arena) const {\n"
+      "  $classname$* n = new $classname$;\n"
+      "  if (arena != NULL) {\n"
+      "    arena->Own(n);\n"
+      "  }\n"
+      "  return n;\n"
+      "}\n",
+      "classname", classname_);
+  }
 
 }
 
@@ -1616,16 +1960,19 @@ GenerateClear(io::Printer* printer) {
       const string& memsets = memsets_for_chunk[i / 8];
       uint32 mask = fields_mask_for_chunk[i / 8];
       int count = popcnt(mask);
+      GOOGLE_DCHECK_GE(count, 1);
       if (count == 1 ||
           (count <= 4 && count == memset_field_count_for_chunk[i / 8])) {
         // No "if" here because the chunk is trivial.
       } else {
-        printer->Print(
-          "if (_has_bits_[$index$ / 32] & $mask$) {\n",
-          "index", SimpleItoa(i / 8 * 8),
-          "mask", SimpleItoa(mask));
-        printer->Indent();
-        chunk_block_in_progress = true;
+        if (HasFieldPresence(descriptor_->file())) {
+          printer->Print(
+            "if (_has_bits_[$index$ / 32] & $mask$) {\n",
+            "index", SimpleItoa(i / 8 * 8),
+            "mask", SimpleItoa(mask));
+          printer->Indent();
+          chunk_block_in_progress = true;
+        }
       }
       printer->Print(memsets.c_str());
     }
@@ -1639,14 +1986,18 @@ GenerateClear(io::Printer* printer) {
       field->cpp_type() == FieldDescriptor::CPPTYPE_MESSAGE ||
       field->cpp_type() == FieldDescriptor::CPPTYPE_STRING;
 
-    if (should_check_bit) {
+    bool have_enclosing_if = false;
+    if (should_check_bit &&
+        // If no field presence, then always clear strings/messages as well.
+        HasFieldPresence(descriptor_->file())) {
       printer->Print("if (has_$name$()) {\n", "name", fieldname);
       printer->Indent();
+      have_enclosing_if = true;
     }
 
     field_generators_.get(field).GenerateClearingCode(printer);
 
-    if (should_check_bit) {
+    if (have_enclosing_if) {
       printer->Outdent();
       printer->Print("}\n");
     }
@@ -1678,16 +2029,22 @@ GenerateClear(io::Printer* printer) {
         "oneof_name", descriptor_->oneof_decl(i)->name());
   }
 
-  // Step 5: Everything else.
-  printer->Print(
-    "::memset(_has_bits_, 0, sizeof(_has_bits_));\n");
-
-  if (UseUnknownFieldSet(descriptor_->file())) {
+  if (HasFieldPresence(descriptor_->file())) {
+    // Step 5: Everything else.
     printer->Print(
-      "mutable_unknown_fields()->Clear();\n");
-  } else {
-    printer->Print(
-      "mutable_unknown_fields()->clear();\n");
+      "::memset(_has_bits_, 0, sizeof(_has_bits_));\n");
+  }
+
+  if (PreserveUnknownFields(descriptor_)) {
+    if (UseUnknownFieldSet(descriptor_->file())) {
+      printer->Print(
+        "if (_internal_metadata_.have_unknown_fields()) {\n"
+        "  mutable_unknown_fields()->Clear();\n"
+        "}\n");
+    } else {
+      printer->Print(
+        "mutable_unknown_fields()->clear();\n");
+    }
   }
 
   printer->Outdent();
@@ -1748,12 +2105,42 @@ GenerateOneofClear(io::Printer* printer) {
 
 void MessageGenerator::
 GenerateSwap(io::Printer* printer) {
-  // Generate the Swap member function.
-  printer->Print("void $classname$::Swap($classname$* other) {\n",
+  if (SupportsArenas(descriptor_)) {
+    // Generate the Swap member function. This is a lightweight wrapper around
+    // UnsafeArenaSwap() / MergeFrom() with temporaries, depending on the memory
+    // ownership situation: swapping across arenas or between an arena and a
+    // heap requires copying.
+    printer->Print(
+        "void $classname$::Swap($classname$* other) {\n"
+        "  if (other == this) return;\n"
+        "  if (GetArenaNoVirtual() == other->GetArenaNoVirtual()) {\n"
+        "    InternalSwap(other);\n"
+        "  } else {\n"
+        "    $classname$ temp;\n"
+        "    temp.MergeFrom(*this);\n"
+        "    CopyFrom(*other);\n"
+        "    other->CopyFrom(temp);\n"
+        "  }\n"
+        "}\n"
+        "void $classname$::UnsafeArenaSwap($classname$* other) {\n"
+        "  if (other == this) return;\n"
+        "  GOOGLE_DCHECK(GetArenaNoVirtual() == other->GetArenaNoVirtual());\n"
+        "  InternalSwap(other);\n"
+        "}\n",
+        "classname", classname_);
+  } else {
+    printer->Print(
+        "void $classname$::Swap($classname$* other) {\n"
+        "  if (other == this) return;\n"
+        "  InternalSwap(other);\n"
+        "}\n",
+        "classname", classname_);
+  }
+
+  // Generate the UnsafeArenaSwap member function.
+  printer->Print("void $classname$::InternalSwap($classname$* other) {\n",
                  "classname", classname_);
   printer->Indent();
-  printer->Print("if (other != this) {\n");
-  printer->Indent();
 
   if (HasGeneratedMethods(descriptor_->file())) {
     for (int i = 0; i < descriptor_->field_count(); i++) {
@@ -1769,15 +2156,25 @@ GenerateSwap(io::Printer* printer) {
         "i", SimpleItoa(i));
     }
 
-    for (int i = 0; i < (descriptor_->field_count() + 31) / 32; ++i) {
-      printer->Print("std::swap(_has_bits_[$i$], other->_has_bits_[$i$]);\n",
-                     "i", SimpleItoa(i));
+    if (HasFieldPresence(descriptor_->file())) {
+      for (int i = 0; i < (descriptor_->field_count() + 31) / 32; ++i) {
+        printer->Print("std::swap(_has_bits_[$i$], other->_has_bits_[$i$]);\n",
+                       "i", SimpleItoa(i));
+      }
     }
 
-    if (UseUnknownFieldSet(descriptor_->file())) {
-      printer->Print("_unknown_fields_.Swap(&other->_unknown_fields_);\n");
+    if (PreserveUnknownFields(descriptor_)) {
+      if (UseUnknownFieldSet(descriptor_->file())) {
+        printer->Print(
+          "_internal_metadata_.Swap(&other->_internal_metadata_);\n");
+      } else {
+        printer->Print("_unknown_fields_.swap(other->_unknown_fields_);\n");
+      }
     } else {
-      printer->Print("_unknown_fields_.swap(other->_unknown_fields_);\n");
+      // Still swap internal_metadata as it may contain more than just
+      // unknown fields.
+      printer->Print(
+        "_internal_metadata_.Swap(&other->_internal_metadata_);\n");
     }
     printer->Print("std::swap(_cached_size_, other->_cached_size_);\n");
     if (descriptor_->extension_range_count() > 0) {
@@ -1789,8 +2186,6 @@ GenerateSwap(io::Printer* printer) {
 
   printer->Outdent();
   printer->Print("}\n");
-  printer->Outdent();
-  printer->Print("}\n");
 }
 
 void MessageGenerator::
@@ -1886,33 +2281,48 @@ GenerateMergeFrom(io::Printer* printer) {
     const FieldDescriptor* field = descriptor_->field(i);
 
     if (!field->is_repeated() && !field->containing_oneof()) {
-      // See above in GenerateClear for an explanation of this.
-      if (i / 8 != last_index / 8 || last_index < 0) {
-        if (last_index >= 0) {
-          printer->Outdent();
-          printer->Print("}\n");
+      if (HasFieldPresence(descriptor_->file())) {
+        // See above in GenerateClear for an explanation of this.
+        if (i / 8 != last_index / 8 || last_index < 0) {
+          if (last_index >= 0) {
+            printer->Outdent();
+            printer->Print("}\n");
+          }
+          printer->Print(
+            "if (from._has_bits_[$index$ / 32] & "
+            "(0xffu << ($index$ % 32))) {\n",
+            "index", SimpleItoa(field->index()));
+          printer->Indent();
         }
-        printer->Print(
-          "if (from._has_bits_[$index$ / 32] & (0xffu << ($index$ % 32))) {\n",
-          "index", SimpleItoa(field->index()));
-        printer->Indent();
       }
 
       last_index = i;
 
-      printer->Print(
-        "if (from.has_$name$()) {\n",
-        "name", FieldName(field));
-      printer->Indent();
+      bool have_enclosing_if = false;
+      if (HasFieldPresence(descriptor_->file())) {
+        printer->Print(
+          "if (from.has_$name$()) {\n",
+          "name", FieldName(field));
+        printer->Indent();
+        have_enclosing_if = true;
+      } else {
+        // Merge semantics without true field presence: primitive fields are
+        // merged only if non-zero (numeric) or non-empty (string).
+        have_enclosing_if = EmitFieldNonDefaultCondition(
+            printer, "from.", field);
+      }
 
       field_generators_.get(field).GenerateMergingCode(printer);
 
-      printer->Outdent();
-      printer->Print("}\n");
+      if (have_enclosing_if) {
+        printer->Outdent();
+        printer->Print("}\n");
+      }
     }
   }
 
-  if (last_index >= 0) {
+  if (HasFieldPresence(descriptor_->file()) &&
+      last_index >= 0) {
     printer->Outdent();
     printer->Print("}\n");
   }
@@ -1921,12 +2331,16 @@ GenerateMergeFrom(io::Printer* printer) {
     printer->Print("_extensions_.MergeFrom(from._extensions_);\n");
   }
 
-  if (UseUnknownFieldSet(descriptor_->file())) {
-    printer->Print(
-      "mutable_unknown_fields()->MergeFrom(from.unknown_fields());\n");
-  } else {
-    printer->Print(
-      "mutable_unknown_fields()->append(from.unknown_fields());\n");
+  if (PreserveUnknownFields(descriptor_)) {
+    if (UseUnknownFieldSet(descriptor_->file())) {
+      printer->Print(
+        "if (from._internal_metadata_.have_unknown_fields()) {\n"
+        "  mutable_unknown_fields()->MergeFrom(from.unknown_fields());\n"
+        "}\n");
+    } else {
+      printer->Print(
+        "mutable_unknown_fields()->append(from.unknown_fields());\n");
+    }
   }
 
   printer->Outdent();
@@ -2171,24 +2585,33 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
       }
     }
     printer->Print(") {\n");
-    if (UseUnknownFieldSet(descriptor_->file())) {
-      PrintHandlingOptionalStaticInitializers(
-        descriptor_->file(), printer,
-        // With static initializers.
-        "  DO_(_extensions_.ParseField(tag, input, default_instance_,\n"
-        "                              mutable_unknown_fields()));\n",
-        // Without.
-        "  DO_(_extensions_.ParseField(tag, input, &default_instance(),\n"
-        "                              mutable_unknown_fields()));\n");
+    if (PreserveUnknownFields(descriptor_)) {
+      if (UseUnknownFieldSet(descriptor_->file())) {
+        PrintHandlingOptionalStaticInitializers(
+          descriptor_->file(), printer,
+          // With static initializers.
+          "  DO_(_extensions_.ParseField(tag, input, default_instance_,\n"
+          "                              mutable_unknown_fields()));\n",
+          // Without.
+          "  DO_(_extensions_.ParseField(tag, input, &default_instance(),\n"
+          "                              mutable_unknown_fields()));\n");
+      } else {
+        PrintHandlingOptionalStaticInitializers(
+          descriptor_->file(), printer,
+          // With static initializers.
+          "  DO_(_extensions_.ParseField(tag, input, default_instance_,\n"
+          "                              &unknown_fields_stream));\n",
+          // Without.
+          "  DO_(_extensions_.ParseField(tag, input, &default_instance(),\n"
+          "                              &unknown_fields_stream));\n");
+      }
     } else {
       PrintHandlingOptionalStaticInitializers(
         descriptor_->file(), printer,
         // With static initializers.
-        "  DO_(_extensions_.ParseField(tag, input, default_instance_,\n"
-        "                              &unknown_fields_stream));\n",
+        "  DO_(_extensions_.ParseField(tag, input, default_instance_);\n",
         // Without.
-        "  DO_(_extensions_.ParseField(tag, input, &default_instance(),\n"
-        "                              &unknown_fields_stream));\n");
+        "  DO_(_extensions_.ParseField(tag, input, &default_instance());\n");
     }
     printer->Print(
       "  continue;\n"
@@ -2196,14 +2619,19 @@ GenerateMergeFromCodedStream(io::Printer* printer) {
   }
 
   // We really don't recognize this tag.  Skip it.
-  if (UseUnknownFieldSet(descriptor_->file())) {
-    printer->Print(
-      "DO_(::google::protobuf::internal::WireFormat::SkipField(\n"
-      "      input, tag, mutable_unknown_fields()));\n");
+  if (PreserveUnknownFields(descriptor_)) {
+    if (UseUnknownFieldSet(descriptor_->file())) {
+      printer->Print(
+        "DO_(::google::protobuf::internal::WireFormat::SkipField(\n"
+        "      input, tag, mutable_unknown_fields()));\n");
+    } else {
+      printer->Print(
+        "DO_(::google::protobuf::internal::WireFormatLite::SkipField(\n"
+        "    input, tag, &unknown_fields_stream));\n");
+    }
   } else {
     printer->Print(
-      "DO_(::google::protobuf::internal::WireFormatLite::SkipField(\n"
-      "    input, tag, &unknown_fields_stream));\n");
+      "DO_(::google::protobuf::internal::WireFormatLite::SkipField(input, tag));\n");
   }
 
   if (descriptor_->field_count() > 0) {
@@ -2232,11 +2660,15 @@ void MessageGenerator::GenerateSerializeOneField(
     io::Printer* printer, const FieldDescriptor* field, bool to_array) {
   PrintFieldComment(printer, field);
 
-  if (!field->is_repeated()) {
+  bool have_enclosing_if = false;
+  if (!field->is_repeated() && HasFieldPresence(descriptor_->file())) {
     printer->Print(
       "if (has_$name$()) {\n",
       "name", FieldName(field));
     printer->Indent();
+    have_enclosing_if = true;
+  } else if (!HasFieldPresence(descriptor_->file())) {
+    have_enclosing_if = EmitFieldNonDefaultCondition(printer, "this->", field);
   }
 
   if (to_array) {
@@ -2246,7 +2678,7 @@ void MessageGenerator::GenerateSerializeOneField(
     field_generators_.get(field).GenerateSerializeWithCachedSizes(printer);
   }
 
-  if (!field->is_repeated()) {
+  if (have_enclosing_if) {
     printer->Outdent();
     printer->Print("}\n");
   }
@@ -2386,28 +2818,69 @@ GenerateSerializeWithCachedSizesBody(io::Printer* printer, bool to_array) {
     }
   }
 
-  if (UseUnknownFieldSet(descriptor_->file())) {
-    printer->Print("if (!unknown_fields().empty()) {\n");
-    printer->Indent();
-    if (to_array) {
+  if (PreserveUnknownFields(descriptor_)) {
+    if (UseUnknownFieldSet(descriptor_->file())) {
+      printer->Print("if (_internal_metadata_.have_unknown_fields()) {\n");
+      printer->Indent();
+      if (to_array) {
+        printer->Print(
+          "target = "
+              "::google::protobuf::internal::WireFormat::SerializeUnknownFieldsToArray(\n"
+          "    unknown_fields(), target);\n");
+      } else {
+        printer->Print(
+          "::google::protobuf::internal::WireFormat::SerializeUnknownFields(\n"
+          "    unknown_fields(), output);\n");
+      }
+      printer->Outdent();
+
       printer->Print(
-        "target = "
-            "::google::protobuf::internal::WireFormat::SerializeUnknownFieldsToArray(\n"
-        "    unknown_fields(), target);\n");
+        "}\n");
     } else {
       printer->Print(
-        "::google::protobuf::internal::WireFormat::SerializeUnknownFields(\n"
-        "    unknown_fields(), output);\n");
+        "output->WriteRaw(unknown_fields().data(),\n"
+        "                 unknown_fields().size());\n");
     }
-    printer->Outdent();
+  }
+}
 
-    printer->Print(
-      "}\n");
-  } else {
-    printer->Print(
-      "output->WriteRaw(unknown_fields().data(),\n"
-      "                 unknown_fields().size());\n");
+static vector<uint32> RequiredFieldsBitMask(const Descriptor* desc) {
+  vector<uint32> result;
+  uint32 mask = 0;
+  for (int i = 0; i < desc->field_count(); i++) {
+    if (i > 0 && i % 32 == 0) {
+      result.push_back(mask);
+      mask = 0;
+    }
+    if (desc->field(i)->is_required()) {
+      mask |= (1 << (i & 31));
+    }
+  }
+  if (mask != 0) {
+    result.push_back(mask);
   }
+  return result;
+}
+
+// Create an expression that evaluates to
+//  "for all i, (_has_bits_[i] & masks[i]) == masks[i]"
+// masks is allowed to be shorter than _has_bits_, but at least one element of
+// masks must be non-zero.
+static string ConditionalToCheckBitmasks(const vector<uint32>& masks) {
+  vector<string> parts;
+  for (int i = 0; i < masks.size(); i++) {
+    if (masks[i] == 0) continue;
+    char buffer[kFastToBufferSize];
+    FastHex32ToBuffer(masks[i], buffer);
+    string m = StrCat("0x", buffer);
+    // Each xor evaluates to 0 if the expected bits are present.
+    parts.push_back(StrCat("((_has_bits_[", i, "] & ", m, ") ^ ", m, ")"));
+  }
+  GOOGLE_CHECK(!parts.empty());
+  // If we have multiple parts, each expected to be 0, then bitwise-or them.
+  string result = parts.size() == 1 ? parts[0] :
+      StrCat("(", Join(parts, "\n       | "), ")");
+  return result + " == 0";
 }
 
 void MessageGenerator::
@@ -2420,8 +2893,10 @@ GenerateByteSize(io::Printer* printer) {
       "classname", classname_);
     GOOGLE_CHECK(UseUnknownFieldSet(descriptor_->file()));
     printer->Print(
+      "if (_internal_metadata_.have_unknown_fields()) {\n"
       "  total_size += ::google::protobuf::internal::WireFormat::\n"
-      "      ComputeUnknownMessageSetItemsSize(unknown_fields());\n");
+      "      ComputeUnknownMessageSetItemsSize(unknown_fields());\n"
+      "}\n");
     printer->Print(
       "  GOOGLE_SAFE_CONCURRENT_WRITES_BEGIN();\n"
       "  _cached_size_ = total_size;\n"
@@ -2431,6 +2906,33 @@ GenerateByteSize(io::Printer* printer) {
     return;
   }
 
+  if (num_required_fields_ > 1 && HasFieldPresence(descriptor_->file())) {
+    // Emit a function (rarely used, we hope) that handles the required fields
+    // by checking for each one individually.
+    printer->Print(
+        "int $classname$::RequiredFieldsByteSizeFallback() const {\n",
+        "classname", classname_);
+    printer->Indent();
+    printer->Print("int total_size = 0;\n");
+    for (int i = 0; i < descriptor_->field_count(); i++) {
+      const FieldDescriptor* field = descriptor_->field(i);
+      if (field->is_required()) {
+        printer->Print("\n"
+                       "if (has_$name$()) {\n",
+                       "name", FieldName(field));
+        printer->Indent();
+        PrintFieldComment(printer, field);
+        field_generators_.get(field).GenerateByteSize(printer);
+        printer->Outdent();
+        printer->Print("}\n");
+      }
+    }
+    printer->Print("\n"
+                   "return total_size;\n");
+    printer->Outdent();
+    printer->Print("}\n");
+  }
+
   printer->Print(
     "int $classname$::ByteSize() const {\n",
     "classname", classname_);
@@ -2439,45 +2941,121 @@ GenerateByteSize(io::Printer* printer) {
     "int total_size = 0;\n"
     "\n");
 
-  int last_index = -1;
+  // Handle required fields (if any).  We expect all of them to be
+  // present, so emit one conditional that checks for that.  If they are all
+  // present then the fast path executes; otherwise the slow path executes.
+  if (num_required_fields_ > 1 && HasFieldPresence(descriptor_->file())) {
+    // The fast path works if all required fields are present.
+    vector<uint32> masks_for_has_bits = RequiredFieldsBitMask(descriptor_);
+    printer->Print((string("if (") +
+                    ConditionalToCheckBitmasks(masks_for_has_bits) +
+                    ") {  // All required fields are present.\n").c_str());
+    printer->Indent();
+    for (int i = 0; i < descriptor_->field_count(); i++) {
+      const FieldDescriptor* field = descriptor_->field(i);
+      if (!field->is_required()) continue;
+      PrintFieldComment(printer, field);
+      field_generators_.get(field).GenerateByteSize(printer);
+      printer->Print("\n");
+    }
+    printer->Outdent();
+    printer->Print("} else {\n"  // the slow path
+                   "  total_size += RequiredFieldsByteSizeFallback();\n"
+                   "}\n");
+  } else {
+    // num_required_fields_ <= 1: no need to be tricky
+    for (int i = 0; i < descriptor_->field_count(); i++) {
+      const FieldDescriptor* field = descriptor_->field(i);
+      if (!field->is_required()) continue;
+      PrintFieldComment(printer, field);
+      printer->Print("if (has_$name$()) {\n",
+                     "name", FieldName(field));
+      printer->Indent();
+      field_generators_.get(field).GenerateByteSize(printer);
+      printer->Outdent();
+      printer->Print("}\n");
+    }
+  }
 
+  // Handle optional fields (worry below about repeateds, oneofs, etc.).
+  // These are handled in chunks of 8.  The first chunk is
+  // the non-requireds-non-repeateds-non-unions-non-extensions in
+  //  descriptor_->field(0), descriptor_->field(1), ... descriptor_->field(7),
+  // and the second chunk is the same for
+  //  descriptor_->field(8), descriptor_->field(9), ... descriptor_->field(15),
+  // etc.
+  hash_map<int, uint32> fields_mask_for_chunk;
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = descriptor_->field(i);
+    if (!field->is_required() && !field->is_repeated() &&
+        !field->containing_oneof()) {
+      fields_mask_for_chunk[i / 8] |= static_cast<uint32>(1) << (i % 32);
+    }
+  }
 
-    if (!field->is_repeated() && !field->containing_oneof()) {
+  int last_index = -1;
+  bool chunk_block_in_progress = false;
+  for (int i = 0; i < descriptor_->field_count(); i++) {
+    const FieldDescriptor* field = descriptor_->field(i);
+    if (!field->is_required() && !field->is_repeated() &&
+        !field->containing_oneof()) {
       // See above in GenerateClear for an explanation of this.
       // TODO(kenton):  Share code?  Unclear how to do so without
       //   over-engineering.
-      if ((i / 8) != (last_index / 8) ||
-          last_index < 0) {
-        if (last_index >= 0) {
+      if (i / 8 != last_index / 8 || last_index < 0) {
+        // End previous chunk, if there was one.
+        if (chunk_block_in_progress) {
           printer->Outdent();
           printer->Print("}\n");
+          chunk_block_in_progress = false;
+        }
+        // Start chunk.
+        uint32 mask = fields_mask_for_chunk[i / 8];
+        int count = popcnt(mask);
+        GOOGLE_DCHECK_GE(count, 1);
+        if (count == 1) {
+          // No "if" here because the chunk is trivial.
+        } else {
+          if (HasFieldPresence(descriptor_->file())) {
+            printer->Print(
+              "if (_has_bits_[$index$ / 32] & $mask$) {\n",
+              "index", SimpleItoa(i),
+              "mask", SimpleItoa(mask));
+            printer->Indent();
+            chunk_block_in_progress = true;
+          }
         }
-        printer->Print(
-          "if (_has_bits_[$index$ / 32] & (0xffu << ($index$ % 32))) {\n",
-          "index", SimpleItoa(field->index()));
-        printer->Indent();
       }
       last_index = i;
 
       PrintFieldComment(printer, field);
 
-      printer->Print(
-        "if (has_$name$()) {\n",
-        "name", FieldName(field));
-      printer->Indent();
+      bool have_enclosing_if = false;
+      if (HasFieldPresence(descriptor_->file())) {
+        printer->Print(
+          "if (has_$name$()) {\n",
+          "name", FieldName(field));
+        printer->Indent();
+        have_enclosing_if = true;
+      } else {
+        // Without field presence: field is serialized only if it has a
+        // non-default value.
+        have_enclosing_if = EmitFieldNonDefaultCondition(
+            printer, "this->", field);
+      }
 
       field_generators_.get(field).GenerateByteSize(printer);
 
-      printer->Outdent();
-      printer->Print(
-        "}\n"
-        "\n");
+      if (have_enclosing_if) {
+        printer->Outdent();
+        printer->Print(
+          "}\n"
+          "\n");
+      }
     }
   }
 
-  if (last_index >= 0) {
+  if (chunk_block_in_progress) {
     printer->Outdent();
     printer->Print("}\n");
   }
@@ -2532,19 +3110,19 @@ GenerateByteSize(io::Printer* printer) {
       "\n");
   }
 
-  if (UseUnknownFieldSet(descriptor_->file())) {
-    printer->Print("if (!unknown_fields().empty()) {\n");
-    printer->Indent();
-    printer->Print(
-      "total_size +=\n"
-      "  ::google::protobuf::internal::WireFormat::ComputeUnknownFieldsSize(\n"
-      "    unknown_fields());\n");
-    printer->Outdent();
-    printer->Print("}\n");
-  } else {
-    printer->Print(
-      "total_size += unknown_fields().size();\n"
-      "\n");
+  if (PreserveUnknownFields(descriptor_)) {
+    if (UseUnknownFieldSet(descriptor_->file())) {
+      printer->Print(
+        "if (_internal_metadata_.have_unknown_fields()) {\n"
+        "  total_size +=\n"
+        "    ::google::protobuf::internal::WireFormat::ComputeUnknownFieldsSize(\n"
+        "      unknown_fields());\n"
+        "}\n");
+    } else {
+      printer->Print(
+        "total_size += unknown_fields().size();\n"
+        "\n");
+    }
   }
 
   // We update _cached_size_ even though this is a const method.  In theory,
@@ -2569,27 +3147,29 @@ GenerateIsInitialized(io::Printer* printer) {
     "classname", classname_);
   printer->Indent();
 
-  // Check that all required fields in this message are set.  We can do this
-  // most efficiently by checking 32 "has bits" at a time.
-  int has_bits_array_size = (descriptor_->field_count() + 31) / 32;
-  for (int i = 0; i < has_bits_array_size; i++) {
-    uint32 mask = 0;
-    for (int bit = 0; bit < 32; bit++) {
-      int index = i * 32 + bit;
-      if (index >= descriptor_->field_count()) break;
-      const FieldDescriptor* field = descriptor_->field(index);
-
-      if (field->is_required()) {
-        mask |= 1 << bit;
+  if (HasFieldPresence(descriptor_->file())) {
+    // Check that all required fields in this message are set.  We can do this
+    // most efficiently by checking 32 "has bits" at a time.
+    int has_bits_array_size = (descriptor_->field_count() + 31) / 32;
+    for (int i = 0; i < has_bits_array_size; i++) {
+      uint32 mask = 0;
+      for (int bit = 0; bit < 32; bit++) {
+        int index = i * 32 + bit;
+        if (index >= descriptor_->field_count()) break;
+        const FieldDescriptor* field = descriptor_->field(index);
+
+        if (field->is_required()) {
+          mask |= 1 << bit;
+        }
       }
-    }
 
-    if (mask != 0) {
-      char buffer[kFastToBufferSize];
-      printer->Print(
-        "if ((_has_bits_[$i$] & 0x$mask$) != 0x$mask$) return false;\n",
-        "i", SimpleItoa(i),
-        "mask", FastHex32ToBuffer(mask, buffer));
+      if (mask != 0) {
+        char buffer[kFastToBufferSize];
+        printer->Print(
+          "if ((_has_bits_[$i$] & 0x$mask$) != 0x$mask$) return false;\n",
+          "i", SimpleItoa(i),
+          "mask", FastHex32ToBuffer(mask, buffer));
+      }
     }
   }
 
@@ -2607,7 +3187,7 @@ GenerateIsInitialized(io::Printer* printer) {
           "name", FieldName(field));
       } else {
         if (field->options().weak()) {
-          // For weak fields, use the data member (google::protobuf::Message*) instead
+          // For weak fields, use the data member (::google::protobuf::Message*) instead
           // of the getter to avoid a link dependency on the weak message type
           // which is only forward declared.
           printer->Print(
diff --git a/src/google/protobuf/compiler/cpp/cpp_message.h b/src/google/protobuf/compiler/cpp/cpp_message.h
index bfd3cec1..a781c234 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message.h
+++ b/src/google/protobuf/compiler/cpp/cpp_message.h
@@ -36,6 +36,9 @@
 #define GOOGLE_PROTOBUF_COMPILER_CPP_MESSAGE_H__
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <string>
 #include <vector>
 #include <google/protobuf/compiler/cpp/cpp_field.h>
@@ -58,8 +61,7 @@ class ExtensionGenerator;      // extension.h
 class MessageGenerator {
  public:
   // See generator.cc for the meaning of dllexport_decl.
-  explicit MessageGenerator(const Descriptor* descriptor,
-                            const Options& options);
+  MessageGenerator(const Descriptor* descriptor, const Options& options);
   ~MessageGenerator();
 
   // Header stuff.
@@ -130,6 +132,8 @@ class MessageGenerator {
   void GenerateSharedConstructorCode(io::Printer* printer);
   // Generate the shared destructor code.
   void GenerateSharedDestructorCode(io::Printer* printer);
+  // Generate the arena-specific destructor code.
+  void GenerateArenaDestructorCode(io::Printer* printer);
 
   // Generate standard Message methods.
   void GenerateClear(io::Printer* printer);
@@ -162,6 +166,7 @@ class MessageGenerator {
   scoped_array<scoped_ptr<MessageGenerator> > nested_generators_;
   scoped_array<scoped_ptr<EnumGenerator> > enum_generators_;
   scoped_array<scoped_ptr<ExtensionGenerator> > extension_generators_;
+  int num_required_fields_;
   bool uses_string_;
 
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(MessageGenerator);
diff --git a/src/google/protobuf/compiler/cpp/cpp_message_field.cc b/src/google/protobuf/compiler/cpp/cpp_message_field.cc
index 6ac15a5a..da1ec60b 100644
--- a/src/google/protobuf/compiler/cpp/cpp_message_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_message_field.cc
@@ -86,6 +86,12 @@ GenerateAccessorDeclarations(io::Printer* printer) const {
     "inline $type$* mutable_$name$()$deprecation$;\n"
     "inline $type$* $release_name$()$deprecation$;\n"
     "inline void set_allocated_$name$($type$* $name$)$deprecation$;\n");
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(variables_,
+      "inline $type$* unsafe_arena_release_$name$()$deprecation$;\n"
+      "inline void unsafe_arena_set_allocated_$name$(\n"
+      "    $type$* $name$)$deprecation$;\n");
+  }
 }
 
 void MessageFieldGenerator::
@@ -101,36 +107,157 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     // Without.
     "  return $name$_ != NULL ? *$name$_ : *default_instance().$name$_;\n");
 
-  printer->Print(variables_,
-    "}\n"
-    "inline $type$* $classname$::mutable_$name$() {\n"
-    "  set_has_$name$();\n"
-    "  if ($name$_ == NULL) $name$_ = new $type$;\n"
-    "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
-    "  return $name$_;\n"
-    "}\n"
-    "inline $type$* $classname$::$release_name$() {\n"
-    "  clear_has_$name$();\n"
-    "  $type$* temp = $name$_;\n"
-    "  $name$_ = NULL;\n"
-    "  return temp;\n"
-    "}\n"
-    "inline void $classname$::set_allocated_$name$($type$* $name$) {\n"
-    "  delete $name$_;\n"
-    "  $name$_ = $name$;\n"
-    "  if ($name$) {\n"
-    "    set_has_$name$();\n"
-    "  } else {\n"
-    "    clear_has_$name$();\n"
-    "  }\n"
-    "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
-    "}\n");
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(variables_,
+      "}\n"
+      "inline $type$* $classname$::mutable_$name$() {\n"
+      "  $set_hasbit$\n"
+      "  if ($name$_ == NULL) {\n");
+    if (SupportsArenas(descriptor_->message_type())) {
+      printer->Print(variables_,
+      "    $name$_ = ::google::protobuf::Arena::CreateMessage< $type$ >(\n"
+      "        GetArenaNoVirtual());\n");
+    } else {
+      printer->Print(variables_,
+       "    $name$_ = ::google::protobuf::Arena::Create< $type$ >(\n"
+       "        GetArenaNoVirtual());\n");
+    }
+    printer->Print(variables_, "  }\n"
+      "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
+      "  return $name$_;\n"
+      "}\n"
+      "inline $type$* $classname$::$release_name$() {\n"
+      "  $clear_hasbit$\n"
+      "  if (GetArenaNoVirtual() != NULL) {\n"
+      "    if ($name$_ == NULL) {\n"
+      "      return NULL;\n"
+      "    } else {\n"
+      "      $type$* temp = new $type$;\n"
+      "      temp->MergeFrom(*$name$_);\n"
+      "      $name$_ = NULL;\n"
+      "      return temp;\n"
+      "    }\n"
+      "  } else {\n"
+      "    $type$* temp = $name$_;\n"
+      "    $name$_ = NULL;\n"
+      "    return temp;\n"
+      "  }\n"
+      "}\n"
+      "inline $type$* $classname$::unsafe_arena_release_$name$() {\n"
+      "  $clear_hasbit$\n"
+      "  $type$* temp = $name$_;\n"
+      "  $name$_ = NULL;\n"
+      "  return temp;\n"
+      "}\n"
+      "inline void $classname$::set_allocated_$name$($type$* $name$) {\n"
+      "  if (GetArenaNoVirtual() == NULL) {\n"
+      "    delete $name$_;\n"
+      "  }\n"
+      "  if ($name$ != NULL) {\n");
+    if (SupportsArenas(descriptor_->message_type())) {
+      // If we're on an arena and the incoming message is not, simply Own() it
+      // rather than copy to the arena -- either way we need a heap dealloc,
+      // so we might as well defer it. Otherwise, if incoming message is on a
+      // different ownership domain (specific arena, or the heap) than we are,
+      // copy to our arena (or heap, as the case may be).
+      printer->Print(variables_,
+        "    if (GetArenaNoVirtual() != NULL && \n"
+        "        ::google::protobuf::Arena::GetArena($name$) == NULL) {\n"
+        "      GetArenaNoVirtual()->Own($name$);\n"
+        "    } else if (GetArenaNoVirtual() !=\n"
+        "               ::google::protobuf::Arena::GetArena($name$)) {\n"
+        "      $type$* new_$name$ = \n"
+        "            ::google::protobuf::Arena::CreateMessage< $type$ >(\n"
+        "            GetArenaNoVirtual());\n"
+        "      new_$name$->CopyFrom(*$name$);\n"
+        "      $name$ = new_$name$;\n"
+        "    }\n");
+    } else {
+      printer->Print(variables_,
+        "    if (GetArenaNoVirtual() != NULL) {\n"
+        "      GetArenaNoVirtual()->Own($name$);\n"
+        "    }\n");
+    }
+
+    printer->Print(variables_,
+      "  }\n"
+      "  $name$_ = $name$;\n"
+      "  if ($name$) {\n"
+      "    $set_hasbit$\n"
+      "  } else {\n"
+      "    $clear_hasbit$\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
+      "}\n"
+      "inline void $classname$::unsafe_arena_set_allocated_$name$(\n"
+      "    $type$* $name$) {\n"
+      // If we're not on an arena, free whatever we were holding before.
+      // (If we are on arena, we can just forget the earlier pointer.)
+      "  if (GetArenaNoVirtual() == NULL) {\n"
+      "    delete $name$_;\n"
+      "  }\n"
+      "  $name$_ = $name$;\n"
+      "  if ($name$) {\n"
+      "    $set_hasbit$\n"
+      "  } else {\n"
+      "    $clear_hasbit$\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_unsafe_arena_set_allocated"
+      ":$full_name$)\n"
+      "}\n");
+  } else {
+    printer->Print(variables_,
+      "}\n"
+      "inline $type$* $classname$::mutable_$name$() {\n"
+      "  $set_hasbit$\n"
+      "  if ($name$_ == NULL) {\n"
+      "    $name$_ = new $type$;\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
+      "  return $name$_;\n"
+      "}\n"
+      "inline $type$* $classname$::$release_name$() {\n"
+      "  $clear_hasbit$\n"
+      "  $type$* temp = $name$_;\n"
+      "  $name$_ = NULL;\n"
+      "  return temp;\n"
+      "}\n"
+      "inline void $classname$::set_allocated_$name$($type$* $name$) {\n"
+      "  delete $name$_;\n");
+
+    if (SupportsArenas(descriptor_->message_type())) {
+      printer->Print(variables_,
+      "  if ($name$ != NULL && $name$->GetArena() != NULL) {\n"
+      "    $type$* new_$name$ = new $type$;\n"
+      "    new_$name$->CopyFrom(*$name$);\n"
+      "    $name$ = new_$name$;\n"
+      "  }\n");
+    }
+
+    printer->Print(variables_,
+      "  $name$_ = $name$;\n"
+      "  if ($name$) {\n"
+      "    $set_hasbit$\n"
+      "  } else {\n"
+      "    $clear_hasbit$\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
+      "}\n");
+  }
 }
 
 void MessageFieldGenerator::
 GenerateClearingCode(io::Printer* printer) const {
-  printer->Print(variables_,
-    "if ($name$_ != NULL) $name$_->$type$::Clear();\n");
+  if (!HasFieldPresence(descriptor_->file())) {
+    // If we don't have has-bits, message presence is indicated only by ptr !=
+    // NULL. Thus on clear, we need to delete the object.
+    printer->Print(variables_,
+      "if ($name$_ != NULL) delete $name$_;\n"
+      "$name$_ = NULL;\n");
+  } else {
+    printer->Print(variables_,
+      "if ($name$_ != NULL) $name$_->$type$::Clear();\n");
+  }
 }
 
 void MessageFieldGenerator::
@@ -198,43 +325,165 @@ MessageOneofFieldGenerator::~MessageOneofFieldGenerator() {}
 
 void MessageOneofFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
-  printer->Print(variables_,
-    "inline const $type$& $classname$::$name$() const {\n"
-    "  return has_$name$() ? *$oneof_prefix$$name$_\n"
-    "                      : $type$::default_instance();\n"
-    "}\n"
-    "inline $type$* $classname$::mutable_$name$() {\n"
-    "  if (!has_$name$()) {\n"
-    "    clear_$oneof_name$();\n"
-    "    set_has_$name$();\n"
-    "    $oneof_prefix$$name$_ = new $type$;\n"
-    "  }\n"
-    "  return $oneof_prefix$$name$_;\n"
-    "}\n"
-    "inline $type$* $classname$::$release_name$() {\n"
-    "  if (has_$name$()) {\n"
-    "    clear_has_$oneof_name$();\n"
-    "    $type$* temp = $oneof_prefix$$name$_;\n"
-    "    $oneof_prefix$$name$_ = NULL;\n"
-    "    return temp;\n"
-    "  } else {\n"
-    "    return NULL;\n"
-    "  }\n"
-    "}\n"
-    "inline void $classname$::set_allocated_$name$($type$* $name$) {\n"
-    "  clear_$oneof_name$();\n"
-    "  if ($name$) {\n"
-    "    set_has_$name$();\n"
-    "    $oneof_prefix$$name$_ = $name$;\n"
-    "  }\n"
-    "}\n");
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(variables_,
+      "inline const $type$& $classname$::$name$() const {\n"
+      "  // @@protoc_insertion_point(field_get:$full_name$)\n"
+      "  return has_$name$() ? *$oneof_prefix$$name$_\n"
+      "                      : $type$::default_instance();\n"
+      "}\n"
+      "inline $type$* $classname$::mutable_$name$() {\n"
+      "  if (!has_$name$()) {\n"
+      "    clear_$oneof_name$();\n"
+      "    set_has_$name$();\n");
+    if (SupportsArenas(descriptor_->message_type())) {
+      printer->Print(variables_,
+         "    $oneof_prefix$$name$_ = \n"
+         "      ::google::protobuf::Arena::CreateMessage< $type$ >(\n"
+         "      GetArenaNoVirtual());\n");
+    } else {
+      printer->Print(variables_,
+         "    $oneof_prefix$$name$_ = \n"
+         "      ::google::protobuf::Arena::Create< $type$ >(\n"
+         "      GetArenaNoVirtual());\n");
+    }
+    printer->Print(variables_,
+      "  }\n"
+      "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
+      "  return $oneof_prefix$$name$_;\n"
+      "}\n"
+      "inline $type$* $classname$::$release_name$() {\n"
+      "  if (has_$name$()) {\n"
+      "    clear_has_$oneof_name$();\n"
+      "    if (GetArenaNoVirtual() != NULL) {\n"
+      // N.B.: safe to use the underlying field pointer here because we are sure
+      // that it is non-NULL (because has_$name$() returned true).
+      "      $type$* temp = new $type$;\n"
+      "      temp->MergeFrom(*$oneof_prefix$$name$_);\n"
+      "      $oneof_prefix$$name$_ = NULL;\n"
+      "      return temp;\n"
+      "    } else {\n"
+      "      $type$* temp = $oneof_prefix$$name$_;\n"
+      "      $oneof_prefix$$name$_ = NULL;\n"
+      "      return temp;\n"
+      "    }\n"
+      "  } else {\n"
+      "    return NULL;\n"
+      "  }\n"
+      "}\n"
+      "inline $type$* $classname$::unsafe_arena_release_$name$() {\n"
+      "  if (has_$name$()) {\n"
+      "    clear_has_$oneof_name$();\n"
+      "    $type$* temp = $oneof_prefix$$name$_;\n"
+      "    $oneof_prefix$$name$_ = NULL;\n"
+      "    return temp;\n"
+      "  } else {\n"
+      "    return NULL;\n"
+      "  }\n"
+      "}\n"
+      "inline void $classname$::set_allocated_$name$($type$* $name$) {\n"
+      "  clear_$oneof_name$();\n"
+      "  if ($name$) {\n");
+
+    if (SupportsArenas(descriptor_->message_type())) {
+      printer->Print(variables_,
+        // If incoming message is on the heap and we are on an arena, just Own()
+        // it (see above). If it's on a different arena than we are or one of us
+        // is on the heap, we make a copy to our arena/heap.
+        "    if (GetArenaNoVirtual() != NULL &&\n"
+        "        ::google::protobuf::Arena::GetArena($name$) == NULL) {\n"
+        "      GetArenaNoVirtual()->Own($name$);\n"
+        "    } else if (GetArenaNoVirtual() !=\n"
+        "               ::google::protobuf::Arena::GetArena($name$)) {\n"
+        "      $type$* new_$name$ = \n"
+        "          ::google::protobuf::Arena::CreateMessage< $type$ >(\n"
+        "          GetArenaNoVirtual());\n"
+        "      new_$name$->CopyFrom(*$name$);\n"
+        "      $name$ = new_$name$;\n"
+        "    }\n");
+    } else {
+      printer->Print(variables_,
+        "    if (GetArenaNoVirtual() != NULL) {\n"
+        "      GetArenaNoVirtual()->Own($name$);\n"
+        "    }\n");
+    }
+
+    printer->Print(variables_,
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_ = $name$;\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
+      "}\n"
+      "inline void $classname$::unsafe_arena_set_allocated_$name$("
+      "$type$* $name$) {\n"
+      // We rely on the oneof clear method to free the earlier contents of this
+      // oneof. We can directly use the pointer we're given to set the new
+      // value.
+      "  clear_$oneof_name$();\n"
+      "  if ($name$) {\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_ = $name$;\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_unsafe_arena_set_allocated:"
+      "$full_name$)\n"
+      "}\n");
+  } else {
+    printer->Print(variables_,
+      "inline const $type$& $classname$::$name$() const {\n"
+      "  // @@protoc_insertion_point(field_get:$full_name$)\n"
+      "  return has_$name$() ? *$oneof_prefix$$name$_\n"
+      "                      : $type$::default_instance();\n"
+      "}\n"
+      "inline $type$* $classname$::mutable_$name$() {\n"
+      "  if (!has_$name$()) {\n"
+      "    clear_$oneof_name$();\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_ = new $type$;\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
+      "  return $oneof_prefix$$name$_;\n"
+      "}\n"
+      "inline $type$* $classname$::$release_name$() {\n"
+      "  if (has_$name$()) {\n"
+      "    clear_has_$oneof_name$();\n"
+      "    $type$* temp = $oneof_prefix$$name$_;\n"
+      "    $oneof_prefix$$name$_ = NULL;\n"
+      "    return temp;\n"
+      "  } else {\n"
+      "    return NULL;\n"
+      "  }\n"
+      "}\n"
+      "inline void $classname$::set_allocated_$name$($type$* $name$) {\n"
+      "  clear_$oneof_name$();\n"
+      "  if ($name$) {\n");
+    if (SupportsArenas(descriptor_->message_type())) {
+      printer->Print(variables_,
+        "    if ($name$->GetArena() != NULL) {\n"
+        "      $type$* new_$name$ = new $type$;\n"
+        "      new_$name$->CopyFrom(*$name$);\n"
+        "      $name$ = new_$name$;\n"
+        "    }\n");
+    }
+    printer->Print(variables_,
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_ = $name$;\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
+      "}\n");
+  }
 }
 
 void MessageOneofFieldGenerator::
 GenerateClearingCode(io::Printer* printer) const {
-  // if it is the active field, it cannot be NULL.
-  printer->Print(variables_,
-    "delete $oneof_prefix$$name$_;\n");
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(variables_,
+      "if (GetArenaNoVirtual() == NULL) {\n"
+      "  delete $oneof_prefix$$name$_;\n"
+      "}\n");
+  } else {
+    printer->Print(variables_,
+      "delete $oneof_prefix$$name$_;\n");
+  }
 }
 
 void MessageOneofFieldGenerator::
@@ -318,7 +567,7 @@ GenerateMergingCode(io::Printer* printer) const {
 
 void RepeatedMessageFieldGenerator::
 GenerateSwappingCode(io::Printer* printer) const {
-  printer->Print(variables_, "$name$_.Swap(&other->$name$_);\n");
+  printer->Print(variables_, "$name$_.UnsafeArenaSwap(&other->$name$_);\n");
 }
 
 void RepeatedMessageFieldGenerator::
diff --git a/src/google/protobuf/compiler/cpp/cpp_plugin_unittest.cc b/src/google/protobuf/compiler/cpp/cpp_plugin_unittest.cc
index 2dbf14ce..26cefb2e 100644
--- a/src/google/protobuf/compiler/cpp/cpp_plugin_unittest.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_plugin_unittest.cc
@@ -35,6 +35,9 @@
 //   worth.
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/compiler/cpp/cpp_generator.h>
 #include <google/protobuf/compiler/command_line_interface.h>
@@ -69,6 +72,100 @@ class TestGenerator : public CodeGenerator {
     TryInsert("test.pb.cc", "includes", context);
     TryInsert("test.pb.cc", "namespace_scope", context);
     TryInsert("test.pb.cc", "global_scope", context);
+
+    // Check field accessors for an optional int32:
+    TryInsert("test.pb.h", "field_get:foo.Bar.optInt", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.optInt", context);
+
+    // Check field accessors for a repeated int32:
+    TryInsert("test.pb.h", "field_get:foo.Bar.repeatedInt", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.repeatedInt", context);
+
+    // Check field accessors for a required string:
+    TryInsert("test.pb.h", "field_get:foo.Bar.requiredString", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.requiredString", context);
+    TryInsert("test.pb.h", "field_set_char:foo.Bar.requiredString", context);
+    TryInsert("test.pb.h", "field_set_pointer:foo.Bar.requiredString", context);
+    TryInsert("test.pb.h", "field_mutable:foo.Bar.requiredString", context);
+    TryInsert("test.pb.h", "field_set_allocated:foo.Bar.requiredString",
+              context);
+    TryInsert("test.pb.h", "field_set_char:foo.Bar.requiredString", context);
+    TryInsert("test.pb.h", "field_set_pointer:foo.Bar.requiredString", context);
+
+    // Check field accessors for a repeated string:
+    TryInsert("test.pb.h", "field_get:foo.Bar.repeatedString", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.repeatedString", context);
+    TryInsert("test.pb.h", "field_set_char:foo.Bar.repeatedString", context);
+    TryInsert("test.pb.h", "field_set_pointer:foo.Bar.repeatedString", context);
+    TryInsert("test.pb.h", "field_mutable:foo.Bar.repeatedString", context);
+    TryInsert("test.pb.h", "field_set_char:foo.Bar.repeatedString", context);
+    TryInsert("test.pb.h", "field_set_pointer:foo.Bar.repeatedString", context);
+
+    // Check field accessors for an int inside oneof{}:
+    TryInsert("test.pb.h", "field_get:foo.Bar.oneOfInt", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.oneOfInt", context);
+
+    // Check field accessors for a string inside oneof{}:
+    TryInsert("test.pb.h", "field_get:foo.Bar.oneOfString", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.oneOfString", context);
+    TryInsert("test.pb.h", "field_set_char:foo.Bar.oneOfString", context);
+    TryInsert("test.pb.h", "field_set_pointer:foo.Bar.oneOfString", context);
+    TryInsert("test.pb.h", "field_mutable:foo.Bar.oneOfString", context);
+    TryInsert("test.pb.h", "field_set_allocated:foo.Bar.oneOfString", context);
+    TryInsert("test.pb.h", "field_set_char:foo.Bar.oneOfString", context);
+    TryInsert("test.pb.h", "field_set_pointer:foo.Bar.oneOfString", context);
+
+    // Check field accessors for an optional message:
+    TryInsert("test.pb.h", "field_get:foo.Bar.optMessage", context);
+    TryInsert("test.pb.h", "field_mutable:foo.Bar.optMessage", context);
+    TryInsert("test.pb.h", "field_set_allocated:foo.Bar.optMessage", context);
+
+    // Check field accessors for a repeated message:
+    TryInsert("test.pb.h", "field_add:foo.Bar.repeatedMessage", context);
+    TryInsert("test.pb.h", "field_get:foo.Bar.repeatedMessage", context);
+    TryInsert("test.pb.h", "field_list:foo.Bar.repeatedMessage", context);
+    TryInsert("test.pb.h", "field_mutable:foo.Bar.repeatedMessage", context);
+    TryInsert("test.pb.h", "field_mutable_list:foo.Bar.repeatedMessage",
+              context);
+
+    // Check field accessors for a message inside oneof{}:
+    TryInsert("test.pb.h", "field_get:foo.Bar.oneOfMessage", context);
+    TryInsert("test.pb.h", "field_mutable:foo.Bar.oneOfMessage", context);
+    TryInsert("test.pb.h", "field_set_allocated:foo.Bar.oneOfMessage", context);
+
+    // Check field accessors for an optional enum:
+    TryInsert("test.pb.h", "field_get:foo.Bar.optEnum", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.optEnum", context);
+
+    // Check field accessors for a repeated enum:
+    TryInsert("test.pb.h", "field_get:foo.Bar.repeatedEnum", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.repeatedEnum", context);
+    TryInsert("test.pb.h", "field_add:foo.Bar.repeatedEnum", context);
+    TryInsert("test.pb.h", "field_list:foo.Bar.repeatedEnum", context);
+    TryInsert("test.pb.h", "field_mutable_list:foo.Bar.repeatedEnum", context);
+
+    // Check field accessors for an enum inside oneof{}:
+    TryInsert("test.pb.h", "field_get:foo.Bar.oneOfEnum", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.oneOfEnum", context);
+
+    // Check field accessors for a required cord:
+    TryInsert("test.pb.h", "field_get:foo.Bar.requiredCord", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.requiredCord", context);
+    TryInsert("test.pb.h", "field_mutable:foo.Bar.requiredCord", context);
+
+    // Check field accessors for a repeated cord:
+    TryInsert("test.pb.h", "field_get:foo.Bar.repeatedCord", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.repeatedCord", context);
+    TryInsert("test.pb.h", "field_add:foo.Bar.repeatedCord", context);
+    TryInsert("test.pb.h", "field_list:foo.Bar.repeatedCord", context);
+    TryInsert("test.pb.h", "field_mutable:foo.Bar.repeatedCord", context);
+    TryInsert("test.pb.h", "field_mutable_list:foo.Bar.repeatedCord", context);
+
+    // Check field accessors for a cord inside oneof{}:
+    TryInsert("test.pb.h", "field_get:foo.Bar.oneOfCord", context);
+    TryInsert("test.pb.h", "field_set:foo.Bar.oneOfCord", context);
+    TryInsert("test.pb.h", "field_mutable:foo.Bar.oneOfCord", context);
+
     return true;
   }
 
@@ -88,8 +185,39 @@ TEST(CppPluginTest, PluginTest) {
   GOOGLE_CHECK_OK(File::SetContents(TestTempDir() + "/test.proto",
                              "syntax = \"proto2\";\n"
                              "package foo;\n"
+                             "\n"
+                             "enum Thud { VALUE = 0; }\n"
+                             "\n"
                              "message Bar {\n"
                              "  message Baz {}\n"
+                             "  optional int32 optInt = 1;\n"
+                             "  repeated int32 repeatedInt = 2;\n"
+                             "\n"
+                             "  required string requiredString = 3;\n"
+                             "  repeated string repeatedString = 4;\n"
+                             "\n"
+                             "  optional Baz optMessage = 6;\n"
+                             "  repeated Baz repeatedMessage = 7;\n"
+                             "\n"
+                             "  optional Thud optEnum = 8;\n"
+                             "  repeated Thud repeatedEnum = 9;\n"
+                             "\n"
+                             "  required string requiredCord = 10 [\n"
+                             "    ctype = CORD\n"
+                             "  ];\n"
+                             "  repeated string repeatedCord = 11 [\n"
+                             "    ctype = CORD\n"
+                             "  ];\n"
+                             "\n"
+                             "  oneof Qux {\n"
+                             "    int64 oneOfInt = 20;\n"
+                             "    string oneOfString = 21;\n"
+                             "    Baz oneOfMessage = 22;\n"
+                             "    Thud oneOfEnum = 23;"
+                             "    string oneOfCord = 24 [\n"
+                             "      ctype = CORD\n"
+                             "    ];\n"
+                             "  }\n"
                              "}\n",
                              true));
 
diff --git a/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc b/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc
index 44290a31..9a2c930e 100644
--- a/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_primitive_field.cc
@@ -129,7 +129,7 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     "  return $name$_;\n"
     "}\n"
     "inline void $classname$::set_$name$($type$ value) {\n"
-    "  set_has_$name$();\n"
+    "  $set_hasbit$\n"
     "  $name$_ = value;\n"
     "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "}\n");
@@ -161,7 +161,7 @@ GenerateMergeFromCodedStream(io::Printer* printer) const {
     "DO_((::google::protobuf::internal::WireFormatLite::ReadPrimitive<\n"
     "         $type$, $wire_format_field_type$>(\n"
     "       input, &$name$_)));\n"
-    "set_has_$name$();\n");
+    "$set_hasbit$\n");
 }
 
 void PrimitiveFieldGenerator::
@@ -207,6 +207,7 @@ void PrimitiveOneofFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
   printer->Print(variables_,
     "inline $type$ $classname$::$name$() const {\n"
+    "  // @@protoc_insertion_point(field_get:$full_name$)\n"
     "  if (has_$name$()) {\n"
     "    return $oneof_prefix$$name$_;\n"
     "  }\n"
@@ -218,6 +219,7 @@ GenerateInlineAccessorDefinitions(io::Printer* printer) const {
     "    set_has_$name$();\n"
     "  }\n"
     "  $oneof_prefix$$name$_ = value;\n"
+    "  // @@protoc_insertion_point(field_set:$full_name$)\n"
     "}\n");
 }
 
@@ -330,7 +332,7 @@ GenerateMergingCode(io::Printer* printer) const {
 
 void RepeatedPrimitiveFieldGenerator::
 GenerateSwappingCode(io::Printer* printer) const {
-  printer->Print(variables_, "$name$_.Swap(&other->$name$_);\n");
+  printer->Print(variables_, "$name$_.UnsafeArenaSwap(&other->$name$_);\n");
 }
 
 void RepeatedPrimitiveFieldGenerator::
diff --git a/src/google/protobuf/compiler/cpp/cpp_string_field.cc b/src/google/protobuf/compiler/cpp/cpp_string_field.cc
index 180d236b..a2a8c81c 100644
--- a/src/google/protobuf/compiler/cpp/cpp_string_field.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_string_field.cc
@@ -52,9 +52,14 @@ void SetStringVariables(const FieldDescriptor* descriptor,
   (*variables)["default"] = DefaultValue(descriptor);
   (*variables)["default_length"] =
       SimpleItoa(descriptor->default_value_string().length());
-  (*variables)["default_variable"] = descriptor->default_value_string().empty()
-      ? "&::google::protobuf::internal::GetEmptyStringAlreadyInited()"
-      : "_default_" + FieldName(descriptor) + "_";
+  string default_variable_string =
+      descriptor->default_value_string().empty()
+          ? "&::google::protobuf::internal::GetEmptyStringAlreadyInited()"
+          : "_default_" + FieldName(descriptor) + "_";
+  (*variables)["default_variable"] = default_variable_string;
+  (*variables)["default_value_init"] =
+      descriptor->default_value_string().empty()
+      ? "" : "*" + default_variable_string;
   (*variables)["pointer_type"] =
       descriptor->type() == FieldDescriptor::TYPE_BYTES ? "void" : "char";
   // NOTE: Escaped here to unblock proto1->proto2 migration.
@@ -63,6 +68,8 @@ void SetStringVariables(const FieldDescriptor* descriptor,
       SafeFunctionName(descriptor->containing_type(),
                        descriptor, "release_");
   (*variables)["full_name"] = descriptor->full_name();
+
+  (*variables)["string_piece"] = "::std::string";
 }
 
 }  // namespace
@@ -80,7 +87,19 @@ StringFieldGenerator::~StringFieldGenerator() {}
 
 void StringFieldGenerator::
 GeneratePrivateMembers(io::Printer* printer) const {
-  printer->Print(variables_, "::std::string* $name$_;\n");
+  // N.B. that we continue to use |ArenaStringPtr| instead of |string*| for
+  // string fields, even when SupportArenas(descriptor_) == false. Why?
+  // The simple answer is to avoid unmaintainable complexity. The reflection
+  // code assumes ArenaStringPtrs. These are *almost* in-memory-compatible with
+  // string*, except for the pointer tags and related ownership semantics. We
+  // could modify the runtime code to use string* for the not-supporting-arenas
+  // case, but this would require a way to detect which type of class was
+  // generated (adding overhead and complexity to GeneratedMessageReflection)
+  // and littering the runtime code paths with conditionals. It's simpler to
+  // stick with this but use lightweight accessors that assume arena == NULL.
+  // There should be very little overhead anyway because it's just a tagged
+  // pointer in-memory.
+  printer->Print(variables_, "::google::protobuf::internal::ArenaStringPtr $name$_;\n");
 }
 
 void StringFieldGenerator::
@@ -125,6 +144,12 @@ GenerateAccessorDeclarations(io::Printer* printer) const {
     "inline ::std::string* mutable_$name$()$deprecation$;\n"
     "inline ::std::string* $release_name$()$deprecation$;\n"
     "inline void set_allocated_$name$(::std::string* $name$)$deprecation$;\n");
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(variables_,
+      "inline ::std::string* unsafe_arena_release_$name$()$deprecation$;\n"
+      "inline void unsafe_arena_set_allocated_$name$(\n"
+      "    ::std::string* $name$)$deprecation$;\n");
+  }
 
 
   if (descriptor_->options().ctype() != FieldOptions::STRING) {
@@ -136,74 +161,113 @@ GenerateAccessorDeclarations(io::Printer* printer) const {
 
 void StringFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
-  printer->Print(variables_,
-    "inline const ::std::string& $classname$::$name$() const {\n"
-    "  // @@protoc_insertion_point(field_get:$full_name$)\n"
-    "  return *$name$_;\n"
-    "}\n"
-    "inline void $classname$::set_$name$(const ::std::string& value) {\n"
-    "  set_has_$name$();\n"
-    "  if ($name$_ == $default_variable$) {\n"
-    "    $name$_ = new ::std::string;\n"
-    "  }\n"
-    "  $name$_->assign(value);\n"
-    "  // @@protoc_insertion_point(field_set:$full_name$)\n"
-    "}\n"
-    "inline void $classname$::set_$name$(const char* value) {\n"
-    "  set_has_$name$();\n"
-    "  if ($name$_ == $default_variable$) {\n"
-    "    $name$_ = new ::std::string;\n"
-    "  }\n"
-    "  $name$_->assign(value);\n"
-    "  // @@protoc_insertion_point(field_set_char:$full_name$)\n"
-    "}\n"
-    "inline "
-    "void $classname$::set_$name$(const $pointer_type$* value, size_t size) {\n"
-    "  set_has_$name$();\n"
-    "  if ($name$_ == $default_variable$) {\n"
-    "    $name$_ = new ::std::string;\n"
-    "  }\n"
-    "  $name$_->assign(reinterpret_cast<const char*>(value), size);\n"
-    "  // @@protoc_insertion_point(field_set_pointer:$full_name$)\n"
-    "}\n"
-    "inline ::std::string* $classname$::mutable_$name$() {\n"
-    "  set_has_$name$();\n"
-    "  if ($name$_ == $default_variable$) {\n");
-  if (descriptor_->default_value_string().empty()) {
+  if (SupportsArenas(descriptor_)) {
     printer->Print(variables_,
-      "    $name$_ = new ::std::string;\n");
+      "inline const ::std::string& $classname$::$name$() const {\n"
+      "  // @@protoc_insertion_point(field_get:$full_name$)\n"
+      "  return $name$_.Get($default_variable$);\n"
+      "}\n"
+      "inline void $classname$::set_$name$(const ::std::string& value) {\n"
+      "  $set_hasbit$\n"
+      "  $name$_.Set($default_variable$, value, GetArenaNoVirtual());\n"
+      "  // @@protoc_insertion_point(field_set:$full_name$)\n"
+      "}\n"
+      "inline void $classname$::set_$name$(const char* value) {\n"
+      "  $set_hasbit$\n"
+      "  $name$_.Set($default_variable$, $string_piece$(value),\n"
+      "              GetArenaNoVirtual());\n"
+      "  // @@protoc_insertion_point(field_set_char:$full_name$)\n"
+      "}\n"
+      "inline "
+      "void $classname$::set_$name$(const $pointer_type$* value,\n"
+      "    size_t size) {\n"
+      "  $set_hasbit$\n"
+      "  $name$_.Set($default_variable$, $string_piece$(\n"
+      "      reinterpret_cast<const char*>(value), size), GetArenaNoVirtual());\n"
+      "  // @@protoc_insertion_point(field_set_pointer:$full_name$)\n"
+      "}\n"
+      "inline ::std::string* $classname$::mutable_$name$() {\n"
+      "  $set_hasbit$\n"
+      "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
+      "  return $name$_.Mutable($default_variable$, GetArenaNoVirtual());\n"
+      "}\n"
+      "inline ::std::string* $classname$::$release_name$() {\n"
+      "  $clear_hasbit$\n"
+      "  return $name$_.Release($default_variable$, GetArenaNoVirtual());\n"
+      "}\n"
+      "inline ::std::string* $classname$::unsafe_arena_release_$name$() {\n"
+      "  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);\n"
+      "  $clear_hasbit$\n"
+      "  return $name$_.UnsafeArenaRelease($default_variable$,\n"
+      "      GetArenaNoVirtual());\n"
+      "}\n"
+      "inline void $classname$::set_allocated_$name$(::std::string* $name$) {\n"
+      "  if ($name$ != NULL) {\n"
+      "    $set_hasbit$\n"
+      "  } else {\n"
+      "    $clear_hasbit$\n"
+      "  }\n"
+      "  $name$_.SetAllocated($default_variable$, $name$,\n"
+      "      GetArenaNoVirtual());\n"
+      "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
+      "}\n"
+      "inline void $classname$::unsafe_arena_set_allocated_$name$(\n"
+      "    ::std::string* $name$) {\n"
+      "  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);\n"
+      "  if ($name$ != NULL) {\n"
+      "    $set_hasbit$\n"
+      "  } else {\n"
+      "    $clear_hasbit$\n"
+      "  }\n"
+      "  $set_hasbit$\n"
+      "  $name$_.UnsafeArenaSetAllocated($default_variable$,\n"
+      "      $name$, GetArenaNoVirtual());\n"
+      "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
+      "}\n");
   } else {
+    // No-arena case.
     printer->Print(variables_,
-      "    $name$_ = new ::std::string(*$default_variable$);\n");
+      "inline const ::std::string& $classname$::$name$() const {\n"
+      "  // @@protoc_insertion_point(field_get:$full_name$)\n"
+      "  return $name$_.GetNoArena($default_variable$);\n"
+      "}\n"
+      "inline void $classname$::set_$name$(const ::std::string& value) {\n"
+      "  $set_hasbit$\n"
+      "  $name$_.SetNoArena($default_variable$, value);\n"
+      "  // @@protoc_insertion_point(field_set:$full_name$)\n"
+      "}\n"
+      "inline void $classname$::set_$name$(const char* value) {\n"
+      "  $set_hasbit$\n"
+      "  $name$_.SetNoArena($default_variable$, $string_piece$(value));\n"
+      "  // @@protoc_insertion_point(field_set_char:$full_name$)\n"
+      "}\n"
+      "inline "
+      "void $classname$::set_$name$(const $pointer_type$* value, "
+      "size_t size) {\n"
+      "  $set_hasbit$\n"
+      "  $name$_.SetNoArena($default_variable$,\n"
+      "      $string_piece$(reinterpret_cast<const char*>(value), size));\n"
+      "  // @@protoc_insertion_point(field_set_pointer:$full_name$)\n"
+      "}\n"
+      "inline ::std::string* $classname$::mutable_$name$() {\n"
+      "  $set_hasbit$\n"
+      "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
+      "  return $name$_.MutableNoArena($default_variable$);\n"
+      "}\n"
+      "inline ::std::string* $classname$::$release_name$() {\n"
+      "  $clear_hasbit$\n"
+      "  return $name$_.ReleaseNoArena($default_variable$);\n"
+      "}\n"
+      "inline void $classname$::set_allocated_$name$(::std::string* $name$) {\n"
+      "  if ($name$ != NULL) {\n"
+      "    $set_hasbit$\n"
+      "  } else {\n"
+      "    $clear_hasbit$\n"
+      "  }\n"
+      "  $name$_.SetAllocatedNoArena($default_variable$, $name$);\n"
+      "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
+      "}\n");
   }
-  printer->Print(variables_,
-    "  }\n"
-    "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
-    "  return $name$_;\n"
-    "}\n"
-    "inline ::std::string* $classname$::$release_name$() {\n"
-    "  clear_has_$name$();\n"
-    "  if ($name$_ == $default_variable$) {\n"
-    "    return NULL;\n"
-    "  } else {\n"
-    "    ::std::string* temp = $name$_;\n"
-    "    $name$_ = const_cast< ::std::string*>($default_variable$);\n"
-    "    return temp;\n"
-    "  }\n"
-    "}\n"
-    "inline void $classname$::set_allocated_$name$(::std::string* $name$) {\n"
-    "  if ($name$_ != $default_variable$) {\n"
-    "    delete $name$_;\n"
-    "  }\n"
-    "  if ($name$) {\n"
-    "    set_has_$name$();\n"
-    "    $name$_ = $name$;\n"
-    "  } else {\n"
-    "    clear_has_$name$();\n"
-    "    $name$_ = const_cast< ::std::string*>($default_variable$);\n"
-    "  }\n"
-    "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
-    "}\n");
 }
 
 void StringFieldGenerator::
@@ -217,16 +281,26 @@ GenerateNonInlineAccessorDefinitions(io::Printer* printer) const {
 
 void StringFieldGenerator::
 GenerateClearingCode(io::Printer* printer) const {
-  if (descriptor_->default_value_string().empty()) {
-    printer->Print(variables_,
-      "if ($name$_ != $default_variable$) {\n"
-      "  $name$_->clear();\n"
-      "}\n");
+  // Two-dimension specialization here: supporting arenas or not, and default
+  // value is the empty string or not. Complexity here ensures the minimal
+  // number of branches / amount of extraneous code at runtime (given that the
+  // below methods are inlined one-liners)!
+  if (SupportsArenas(descriptor_)) {
+    if (descriptor_->default_value_string().empty()) {
+      printer->Print(variables_,
+        "$name$_.ClearToEmpty($default_variable$, GetArenaNoVirtual());\n");
+    } else {
+      printer->Print(variables_,
+        "$name$_.ClearToDefault($default_variable$, GetArenaNoVirtual());\n");
+    }
   } else {
-    printer->Print(variables_,
-      "if ($name$_ != $default_variable$) {\n"
-      "  $name$_->assign(*$default_variable$);\n"
-      "}\n");
+    if (descriptor_->default_value_string().empty()) {
+      printer->Print(variables_,
+        "$name$_.ClearToEmptyNoArena($default_variable$);\n");
+    } else {
+      printer->Print(variables_,
+        "$name$_.ClearToDefaultNoArena($default_variable$);\n");
+    }
   }
 }
 
@@ -237,21 +311,24 @@ GenerateMergingCode(io::Printer* printer) const {
 
 void StringFieldGenerator::
 GenerateSwappingCode(io::Printer* printer) const {
-  printer->Print(variables_, "std::swap($name$_, other->$name$_);\n");
+  printer->Print(variables_, "$name$_.Swap(&other->$name$_);\n");
 }
 
 void StringFieldGenerator::
 GenerateConstructorCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "$name$_ = const_cast< ::std::string*>($default_variable$);\n");
+      "$name$_.UnsafeSetDefault($default_variable$);\n");
 }
 
 void StringFieldGenerator::
 GenerateDestructorCode(io::Printer* printer) const {
-  printer->Print(variables_,
-    "if ($name$_ != $default_variable$) {\n"
-    "  delete $name$_;\n"
-    "}\n");
+  if (SupportsArenas(descriptor_)) {
+    printer->Print(variables_,
+      "$name$_.Destroy($default_variable$, GetArenaNoVirtual());\n");
+  } else {
+    printer->Print(variables_,
+      "$name$_.DestroyNoArena($default_variable$);\n");
+  }
 }
 
 void StringFieldGenerator::
@@ -276,13 +353,14 @@ GenerateMergeFromCodedStream(io::Printer* printer) const {
   printer->Print(variables_,
     "DO_(::google::protobuf::internal::WireFormatLite::Read$declared_type$(\n"
     "      input, this->mutable_$name$()));\n");
+
   if (HasUtf8Verification(descriptor_->file()) &&
       descriptor_->type() == FieldDescriptor::TYPE_STRING) {
     printer->Print(variables_,
       "::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "  this->$name$().data(), this->$name$().length(),\n"
       "  ::google::protobuf::internal::WireFormat::PARSE,\n"
-      "  \"$name$\");\n");
+      "  \"$full_name$\");\n");
   }
 }
 
@@ -294,7 +372,7 @@ GenerateSerializeWithCachedSizes(io::Printer* printer) const {
       "::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "  this->$name$().data(), this->$name$().length(),\n"
       "  ::google::protobuf::internal::WireFormat::SERIALIZE,\n"
-      "  \"$name$\");\n");
+      "  \"$full_name$\");\n");
   }
   printer->Print(variables_,
     "::google::protobuf::internal::WireFormatLite::Write$declared_type$MaybeAliased(\n"
@@ -309,7 +387,7 @@ GenerateSerializeWithCachedSizesToArray(io::Printer* printer) const {
       "::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "  this->$name$().data(), this->$name$().length(),\n"
       "  ::google::protobuf::internal::WireFormat::SERIALIZE,\n"
-      "  \"$name$\");\n");
+      "  \"$full_name$\");\n");
   }
   printer->Print(variables_,
     "target =\n"
@@ -338,84 +416,186 @@ StringOneofFieldGenerator::~StringOneofFieldGenerator() {}
 
 void StringOneofFieldGenerator::
 GenerateInlineAccessorDefinitions(io::Printer* printer) const {
-  printer->Print(variables_,
-    "inline const ::std::string& $classname$::$name$() const {\n"
-    "  if (has_$name$()) {\n"
-    "    return *$oneof_prefix$$name$_;\n"
-    "  }\n");
-  if (descriptor_->default_value_string().empty()) {
-    printer->Print(variables_,
-      "  return ::google::protobuf::internal::GetEmptyStringAlreadyInited();\n");
-  } else {
-    printer->Print(variables_,
-      "  return *$default_variable$;\n");
-  }
-  printer->Print(variables_,
-    "}\n"
-    "inline void $classname$::set_$name$(const ::std::string& value) {\n"
-    "  if (!has_$name$()) {\n"
-    "    clear_$oneof_name$();\n"
-    "    set_has_$name$();\n"
-    "    $oneof_prefix$$name$_ = new ::std::string;\n"
-    "  }\n"
-    "  $oneof_prefix$$name$_->assign(value);\n"
-    "}\n"
-    "inline void $classname$::set_$name$(const char* value) {\n"
-    "  if (!has_$name$()) {\n"
-    "    clear_$oneof_name$();\n"
-    "    set_has_$name$();\n"
-    "    $oneof_prefix$$name$_ = new ::std::string;\n"
-    "  }\n"
-    "  $oneof_prefix$$name$_->assign(value);\n"
-    "}\n"
-    "inline "
-    "void $classname$::set_$name$(const $pointer_type$* value, size_t size) {\n"
-    "  if (!has_$name$()) {\n"
-    "    clear_$oneof_name$();\n"
-    "    set_has_$name$();\n"
-    "    $oneof_prefix$$name$_ = new ::std::string;\n"
-    "  }\n"
-    "  $oneof_prefix$$name$_->assign(\n"
-    "      reinterpret_cast<const char*>(value), size);\n"
-    "}\n"
-    "inline ::std::string* $classname$::mutable_$name$() {\n"
-    "  if (!has_$name$()) {\n"
-    "    clear_$oneof_name$();\n"
-    "    set_has_$name$();\n");
-  if (descriptor_->default_value_string().empty()) {
+  if (SupportsArenas(descriptor_)) {
     printer->Print(variables_,
-      "    $oneof_prefix$$name$_ = new ::std::string;\n");
+      "inline const ::std::string& $classname$::$name$() const {\n"
+      "  // @@protoc_insertion_point(field_get:$full_name$)\n"
+      "  if (has_$name$()) {\n"
+      "    return $oneof_prefix$$name$_.Get($default_variable$);\n"
+      "  }\n"
+      "  return *$default_variable$;\n"
+      "}\n"
+      "inline void $classname$::set_$name$(const ::std::string& value) {\n"
+      "  if (!has_$name$()) {\n"
+      "    clear_$oneof_name$();\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  $oneof_prefix$$name$_.Set($default_variable$, value,\n"
+      "      GetArenaNoVirtual());\n"
+      "  // @@protoc_insertion_point(field_set:$full_name$)\n"
+      "}\n"
+      "inline void $classname$::set_$name$(const char* value) {\n"
+      "  if (!has_$name$()) {\n"
+      "    clear_$oneof_name$();\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  $oneof_prefix$$name$_.Set($default_variable$,\n"
+      "      $string_piece$(value), GetArenaNoVirtual());\n"
+      "  // @@protoc_insertion_point(field_set_char:$full_name$)\n"
+      "}\n"
+      "inline "
+      "void $classname$::set_$name$(const $pointer_type$* value,\n"
+      "                             size_t size) {\n"
+      "  if (!has_$name$()) {\n"
+      "    clear_$oneof_name$();\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  $oneof_prefix$$name$_.Set($default_variable$, $string_piece$(\n"
+      "      reinterpret_cast<const char*>(value), size),\n"
+      "      GetArenaNoVirtual());\n"
+      "  // @@protoc_insertion_point(field_set_pointer:$full_name$)\n"
+      "}\n"
+      "inline ::std::string* $classname$::mutable_$name$() {\n"
+      "  if (!has_$name$()) {\n"
+      "    clear_$oneof_name$();\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  return $oneof_prefix$$name$_.Mutable($default_variable$,\n"
+      "      GetArenaNoVirtual());\n"
+      "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
+      "}\n"
+      "inline ::std::string* $classname$::$release_name$() {\n"
+      "  if (has_$name$()) {\n"
+      "    clear_has_$oneof_name$();\n"
+      "    return $oneof_prefix$$name$_.Release($default_variable$,\n"
+      "        GetArenaNoVirtual());\n"
+      "  } else {\n"
+      "    return NULL;\n"
+      "  }\n"
+      "}\n"
+      "inline ::std::string* $classname$::unsafe_arena_release_$name$() {\n"
+      "  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);\n"
+      "  if (has_$name$()) {\n"
+      "    clear_has_$oneof_name$();\n"
+      "    return $oneof_prefix$$name$_.UnsafeArenaRelease(\n"
+      "        $default_variable$, GetArenaNoVirtual());\n"
+      "  } else {\n"
+      "    return NULL;\n"
+      "  }\n"
+      "}\n"
+      "inline void $classname$::set_allocated_$name$(::std::string* $name$) {\n"
+      "  if (!has_$name$()) {\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  clear_$oneof_name$();\n"
+      "  if ($name$ != NULL) {\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.SetAllocated($default_variable$, $name$,\n"
+      "        GetArenaNoVirtual());\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
+      "}\n"
+      "inline void $classname$::unsafe_arena_set_allocated_$name$("
+      "::std::string* $name$) {\n"
+      "  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);\n"
+      "  if (!has_$name$()) {\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  clear_$oneof_name$();\n"
+      "  if ($name$) {\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.UnsafeArenaSetAllocated($default_variable$, "
+      "$name$, GetArenaNoVirtual());\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
+      "}\n");
   } else {
+    // No-arena case.
     printer->Print(variables_,
-      "    $oneof_prefix$$name$_ = new ::std::string(*$default_variable$);\n");
+      "inline const ::std::string& $classname$::$name$() const {\n"
+      "  // @@protoc_insertion_point(field_get:$full_name$)\n"
+      "  if (has_$name$()) {\n"
+      "    return $oneof_prefix$$name$_.GetNoArena($default_variable$);\n"
+      "  }\n"
+      "  return *$default_variable$;\n"
+      "}\n"
+      "inline void $classname$::set_$name$(const ::std::string& value) {\n"
+      "  // @@protoc_insertion_point(field_set:$full_name$)\n"
+      "  if (!has_$name$()) {\n"
+      "    clear_$oneof_name$();\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  $oneof_prefix$$name$_.SetNoArena($default_variable$, value);\n"
+      "  // @@protoc_insertion_point(field_set:$full_name$)\n"
+      "}\n"
+      "inline void $classname$::set_$name$(const char* value) {\n"
+      "  if (!has_$name$()) {\n"
+      "    clear_$oneof_name$();\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  $oneof_prefix$$name$_.SetNoArena($default_variable$,\n"
+      "      $string_piece$(value));\n"
+      "  // @@protoc_insertion_point(field_set_char:$full_name$)\n"
+      "}\n"
+      "inline "
+      "void $classname$::set_$name$(const $pointer_type$* value, size_t size) {\n"
+      "  if (!has_$name$()) {\n"
+      "    clear_$oneof_name$();\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  $oneof_prefix$$name$_.SetNoArena($default_variable$, $string_piece$(\n"
+      "      reinterpret_cast<const char*>(value), size));\n"
+      "  // @@protoc_insertion_point(field_set_pointer:$full_name$)\n"
+      "}\n"
+      "inline ::std::string* $classname$::mutable_$name$() {\n"
+      "  if (!has_$name$()) {\n"
+      "    clear_$oneof_name$();\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_mutable:$full_name$)\n"
+      "  return $oneof_prefix$$name$_.MutableNoArena($default_variable$);\n"
+      "}\n"
+      "inline ::std::string* $classname$::$release_name$() {\n"
+      "  if (has_$name$()) {\n"
+      "    clear_has_$oneof_name$();\n"
+      "    return $oneof_prefix$$name$_.ReleaseNoArena($default_variable$);\n"
+      "  } else {\n"
+      "    return NULL;\n"
+      "  }\n"
+      "}\n"
+      "inline void $classname$::set_allocated_$name$(::std::string* $name$) {\n"
+      "  if (!has_$name$()) {\n"
+      "    $oneof_prefix$$name$_.UnsafeSetDefault($default_variable$);\n"
+      "  }\n"
+      "  clear_$oneof_name$();\n"
+      "  if ($name$ != NULL) {\n"
+      "    set_has_$name$();\n"
+      "    $oneof_prefix$$name$_.SetAllocatedNoArena($default_variable$,\n"
+      "        $name$);\n"
+      "  }\n"
+      "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
+      "}\n");
   }
-  printer->Print(variables_,
-    "  }\n"
-    "  return $oneof_prefix$$name$_;\n"
-    "}\n"
-    "inline ::std::string* $classname$::$release_name$() {\n"
-    "  if (has_$name$()) {\n"
-    "    clear_has_$oneof_name$();\n"
-    "    ::std::string* temp = $oneof_prefix$$name$_;\n"
-    "    $oneof_prefix$$name$_ = NULL;\n"
-    "    return temp;\n"
-    "  } else {\n"
-    "    return NULL;\n"
-    "  }\n"
-    "}\n"
-    "inline void $classname$::set_allocated_$name$(::std::string* $name$) {\n"
-    "  clear_$oneof_name$();\n"
-    "  if ($name$) {\n"
-    "    set_has_$name$();\n"
-    "    $oneof_prefix$$name$_ = $name$;\n"
-    "  }\n"
-    "}\n");
 }
 
 void StringOneofFieldGenerator::
 GenerateClearingCode(io::Printer* printer) const {
+  if (SupportsArenas(descriptor_)) {
     printer->Print(variables_,
-      "delete $oneof_prefix$$name$_;\n");
+      "$oneof_prefix$$name$_.Destroy($default_variable$,\n"
+      "    GetArenaNoVirtual());\n");
+  } else {
+    printer->Print(variables_,
+      "$oneof_prefix$$name$_.DestroyNoArena($default_variable$);\n");
+  }
 }
 
 void StringOneofFieldGenerator::
@@ -425,25 +605,45 @@ GenerateSwappingCode(io::Printer* printer) const {
 
 void StringOneofFieldGenerator::
 GenerateConstructorCode(io::Printer* printer) const {
-  if (!descriptor_->default_value_string().empty()) {
+  printer->Print(variables_,
+    "  const_cast< ::google::protobuf::internal::ArenaStringPtr*>("
+    "&$classname$_default_oneof_instance_->$name$_)->UnsafeSetDefault("
+    "$default_variable$);\n");
+}
+
+void StringOneofFieldGenerator::
+GenerateDestructorCode(io::Printer* printer) const {
+  if (SupportsArenas(descriptor_)) {
     printer->Print(variables_,
-      "  $classname$_default_oneof_instance_->$name$_ = "
-      "$classname$::$default_variable$;\n");
+      "if (has_$name$()) {\n"
+      "  $oneof_prefix$$name$_.Destroy($default_variable$,\n"
+      "      GetArenaNoVirtual());\n"
+      "}\n");
   } else {
     printer->Print(variables_,
-      "  $classname$_default_oneof_instance_->$name$_ = "
-      "$default_variable$;\n");
+      "if (has_$name$()) {\n"
+      "  $oneof_prefix$$name$_.DestroyNoArena($default_variable$);\n"
+      "}\n");
   }
 }
 
 void StringOneofFieldGenerator::
-GenerateDestructorCode(io::Printer* printer) const {
-  printer->Print(variables_,
-    "if (has_$name$()) {\n"
-    "  delete $oneof_prefix$$name$_;\n"
-    "}\n");
+GenerateMergeFromCodedStream(io::Printer* printer) const {
+    printer->Print(variables_,
+      "DO_(::google::protobuf::internal::WireFormatLite::Read$declared_type$(\n"
+      "      input, this->mutable_$name$()));\n");
+
+  if (HasUtf8Verification(descriptor_->file()) &&
+      descriptor_->type() == FieldDescriptor::TYPE_STRING) {
+    printer->Print(variables_,
+      "::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
+      "  this->$name$().data(), this->$name$().length(),\n"
+      "  ::google::protobuf::internal::WireFormat::PARSE,\n"
+      "  \"$full_name$\");\n");
+  }
 }
 
+
 // ===================================================================
 
 RepeatedStringFieldGenerator::
@@ -566,7 +766,7 @@ GenerateMergingCode(io::Printer* printer) const {
 
 void RepeatedStringFieldGenerator::
 GenerateSwappingCode(io::Printer* printer) const {
-  printer->Print(variables_, "$name$_.Swap(&other->$name$_);\n");
+  printer->Print(variables_, "$name$_.UnsafeArenaSwap(&other->$name$_);\n");
 }
 
 void RepeatedStringFieldGenerator::
@@ -586,7 +786,7 @@ GenerateMergeFromCodedStream(io::Printer* printer) const {
       "  this->$name$(this->$name$_size() - 1).data(),\n"
       "  this->$name$(this->$name$_size() - 1).length(),\n"
       "  ::google::protobuf::internal::WireFormat::PARSE,\n"
-      "  \"$name$\");\n");
+      "  \"$full_name$\");\n");
   }
 }
 
@@ -600,7 +800,7 @@ GenerateSerializeWithCachedSizes(io::Printer* printer) const {
       "::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "  this->$name$(i).data(), this->$name$(i).length(),\n"
       "  ::google::protobuf::internal::WireFormat::SERIALIZE,\n"
-      "  \"$name$\");\n");
+      "  \"$full_name$\");\n");
   }
   printer->Print(variables_,
     "  ::google::protobuf::internal::WireFormatLite::Write$declared_type$(\n"
@@ -618,7 +818,7 @@ GenerateSerializeWithCachedSizesToArray(io::Printer* printer) const {
       "  ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(\n"
       "    this->$name$(i).data(), this->$name$(i).length(),\n"
       "    ::google::protobuf::internal::WireFormat::SERIALIZE,\n"
-      "    \"$name$\");\n");
+      "    \"$full_name$\");\n");
   }
   printer->Print(variables_,
     "  target = ::google::protobuf::internal::WireFormatLite::\n"
diff --git a/src/google/protobuf/compiler/cpp/cpp_string_field.h b/src/google/protobuf/compiler/cpp/cpp_string_field.h
index 86da38f2..0a5ca440 100644
--- a/src/google/protobuf/compiler/cpp/cpp_string_field.h
+++ b/src/google/protobuf/compiler/cpp/cpp_string_field.h
@@ -88,6 +88,7 @@ class StringOneofFieldGenerator : public StringFieldGenerator {
   void GenerateSwappingCode(io::Printer* printer) const;
   void GenerateConstructorCode(io::Printer* printer) const;
   void GenerateDestructorCode(io::Printer* printer) const;
+  void GenerateMergeFromCodedStream(io::Printer* printer) const;
 
  private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StringOneofFieldGenerator);
diff --git a/src/google/protobuf/compiler/cpp/cpp_test_bad_identifiers.proto b/src/google/protobuf/compiler/cpp/cpp_test_bad_identifiers.proto
index 6b7f8308..4fa3c144 100644
--- a/src/google/protobuf/compiler/cpp/cpp_test_bad_identifiers.proto
+++ b/src/google/protobuf/compiler/cpp/cpp_test_bad_identifiers.proto
@@ -35,6 +35,7 @@
 // This file tests that various identifiers work as field and type names even
 // though the same identifiers are used internally by the C++ code generator.
 
+syntax = "proto2";
 
 // Some generic_services option(s) added automatically.
 // See:  http://go/proto2-generic-services-default
@@ -58,7 +59,7 @@ message TestConflictingSymbolNames {
   optional int32 total_size = 6;
   optional int32 tag = 7;
 
-  enum TestEnum { FOO = 1; }
+  enum TestEnum { FOO = 0; }
   message Data1 { repeated int32 data = 1; }
   message Data2 { repeated TestEnum data = 1; }
   message Data3 { repeated string data = 1; }
@@ -99,6 +100,8 @@ message TestConflictingSymbolNames {
   optional uint32 int = 30;
   optional uint32 friend = 31;
   optional uint32 class = 37;
+  optional uint32 typedecl = 39;
+  optional uint32 auto = 40;
 
   // The generator used to #define a macro called "DO" inside the .cc file.
   message DO {}
@@ -116,15 +119,18 @@ message TestConflictingSymbolNames {
   // names.
   optional DO release_do = 36;
 
-  extensions 1000 to max;
-}
+  // For clashing local variables in Serialize and ByteSize calculation.
+  optional string target = 38;
 
-message TestConflictingSymbolNamesExtension {
-  extend TestConflictingSymbolNames {
-    repeated int32 repeated_int32_ext = 20423638 [packed=true];
-  }
+  extensions 1000 to max;  // NO_PROTO3
 }
 
+message TestConflictingSymbolNamesExtension {                    // NO_PROTO3
+  extend TestConflictingSymbolNames {                            // NO_PROTO3
+    repeated int32 repeated_int32_ext = 20423638 [packed=true];  // NO_PROTO3
+  }                                                              // NO_PROTO3
+}                                                                // NO_PROTO3
+
 message DummyMessage {}
 
 service TestConflictingMethodNames {
diff --git a/src/google/protobuf/compiler/cpp/cpp_unittest.cc b/src/google/protobuf/compiler/cpp/cpp_unittest.cc
index 93e1c3f1..c509a6a9 100644
--- a/src/google/protobuf/compiler/cpp/cpp_unittest.cc
+++ b/src/google/protobuf/compiler/cpp/cpp_unittest.cc
@@ -47,6 +47,9 @@
 #include <google/protobuf/compiler/cpp/cpp_unittest.h>
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <vector>
 
 #include <google/protobuf/unittest.pb.h>
diff --git a/src/google/protobuf/compiler/importer.cc b/src/google/protobuf/compiler/importer.cc
index e6c446af..678823cd 100644
--- a/src/google/protobuf/compiler/importer.cc
+++ b/src/google/protobuf/compiler/importer.cc
@@ -44,6 +44,9 @@
 
 #include <algorithm>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/compiler/importer.h>
 
diff --git a/src/google/protobuf/compiler/importer_unittest.cc b/src/google/protobuf/compiler/importer_unittest.cc
index 8cc5d882..81c636c6 100644
--- a/src/google/protobuf/compiler/importer_unittest.cc
+++ b/src/google/protobuf/compiler/importer_unittest.cc
@@ -34,9 +34,13 @@
 
 #include <google/protobuf/stubs/hash.h>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/compiler/importer.h>
 #include <google/protobuf/descriptor.h>
+#include <google/protobuf/testing/file.h>
 #include <google/protobuf/io/zero_copy_stream_impl.h>
 
 #include <google/protobuf/stubs/map_util.h>
@@ -53,6 +57,10 @@ namespace compiler {
 
 namespace {
 
+bool FileExists(const string& path) {
+  return File::Exists(path);
+}
+
 #define EXPECT_SUBSTRING(needle, haystack) \
   EXPECT_PRED_FORMAT2(testing::IsSubstring, (needle), (haystack))
 
@@ -215,120 +223,6 @@ TEST_F(ImporterTest, RecursiveImport) {
     error_collector_.text_);
 }
 
-// TODO(sanjay): The MapField tests below more properly belong in
-// descriptor_unittest, but are more convenient to test here.
-TEST_F(ImporterTest, MapFieldValid) {
-  AddFile(
-      "map.proto",
-      "syntax = \"proto2\";\n"
-      "message Item {\n"
-      "  required string key = 1;\n"
-      "}\n"
-      "message Map {\n"
-      "  repeated Item items = 1 [experimental_map_key = \"key\"];\n"
-      "}\n"
-      );
-  const FileDescriptor* file = importer_.Import("map.proto");
-  ASSERT_TRUE(file != NULL) << error_collector_.text_;
-  EXPECT_EQ("", error_collector_.text_);
-
-  // Check that Map::items points to Item::key
-  const Descriptor* item_type = file->FindMessageTypeByName("Item");
-  ASSERT_TRUE(item_type != NULL);
-  const Descriptor* map_type = file->FindMessageTypeByName("Map");
-  ASSERT_TRUE(map_type != NULL);
-  const FieldDescriptor* key_field = item_type->FindFieldByName("key");
-  ASSERT_TRUE(key_field != NULL);
-  const FieldDescriptor* items_field = map_type->FindFieldByName("items");
-  ASSERT_TRUE(items_field != NULL);
-  EXPECT_EQ(items_field->experimental_map_key(), key_field);
-}
-
-TEST_F(ImporterTest, MapFieldNotRepeated) {
-  AddFile(
-      "map.proto",
-      "syntax = \"proto2\";\n"
-      "message Item {\n"
-      "  required string key = 1;\n"
-      "}\n"
-      "message Map {\n"
-      "  required Item items = 1 [experimental_map_key = \"key\"];\n"
-      "}\n"
-      );
-  EXPECT_TRUE(importer_.Import("map.proto") == NULL);
-  EXPECT_SUBSTRING("only allowed for repeated fields", error());
-}
-
-TEST_F(ImporterTest, MapFieldNotMessageType) {
-  AddFile(
-      "map.proto",
-      "syntax = \"proto2\";\n"
-      "message Map {\n"
-      "  repeated int32 items = 1 [experimental_map_key = \"key\"];\n"
-      "}\n"
-      );
-  EXPECT_TRUE(importer_.Import("map.proto") == NULL);
-  EXPECT_SUBSTRING("only allowed for fields with a message type", error());
-}
-
-TEST_F(ImporterTest, MapFieldTypeNotFound) {
-  AddFile(
-      "map.proto",
-      "syntax = \"proto2\";\n"
-      "message Map {\n"
-      "  repeated Unknown items = 1 [experimental_map_key = \"key\"];\n"
-      "}\n"
-      );
-  EXPECT_TRUE(importer_.Import("map.proto") == NULL);
-  EXPECT_SUBSTRING("not defined", error());
-}
-
-TEST_F(ImporterTest, MapFieldKeyNotFound) {
-  AddFile(
-      "map.proto",
-      "syntax = \"proto2\";\n"
-      "message Item {\n"
-      "  required string key = 1;\n"
-      "}\n"
-      "message Map {\n"
-      "  repeated Item items = 1 [experimental_map_key = \"badkey\"];\n"
-      "}\n"
-      );
-  EXPECT_TRUE(importer_.Import("map.proto") == NULL);
-  EXPECT_SUBSTRING("Could not find field", error());
-}
-
-TEST_F(ImporterTest, MapFieldKeyRepeated) {
-  AddFile(
-      "map.proto",
-      "syntax = \"proto2\";\n"
-      "message Item {\n"
-      "  repeated string key = 1;\n"
-      "}\n"
-      "message Map {\n"
-      "  repeated Item items = 1 [experimental_map_key = \"key\"];\n"
-      "}\n"
-      );
-  EXPECT_TRUE(importer_.Import("map.proto") == NULL);
-  EXPECT_SUBSTRING("must not name a repeated field", error());
-}
-
-TEST_F(ImporterTest, MapFieldKeyNotScalar) {
-  AddFile(
-      "map.proto",
-      "syntax = \"proto2\";\n"
-      "message ItemKey { }\n"
-      "message Item {\n"
-      "  required ItemKey key = 1;\n"
-      "}\n"
-      "message Map {\n"
-      "  repeated Item items = 1 [experimental_map_key = \"key\"];\n"
-      "}\n"
-      );
-  EXPECT_TRUE(importer_.Import("map.proto") == NULL);
-  EXPECT_SUBSTRING("must name a scalar or string", error());
-}
-
 
 // ===================================================================
 
@@ -339,7 +233,7 @@ class DiskSourceTreeTest : public testing::Test {
     dirnames_.push_back(TestTempDir() + "/test_proto2_import_path_2");
 
     for (int i = 0; i < dirnames_.size(); i++) {
-      if (File::Exists(dirnames_[i])) {
+      if (FileExists(dirnames_[i])) {
         File::DeleteRecursively(dirnames_[i], NULL, NULL);
       }
       GOOGLE_CHECK_OK(File::CreateDir(dirnames_[i], 0777));
diff --git a/src/google/protobuf/compiler/java/java_context.h b/src/google/protobuf/compiler/java/java_context.h
index 57914450..7f1ce1f9 100644
--- a/src/google/protobuf/compiler/java/java_context.h
+++ b/src/google/protobuf/compiler/java/java_context.h
@@ -33,6 +33,9 @@
 
 #include <map>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <vector>
 
 #include <google/protobuf/stubs/common.h>
diff --git a/src/google/protobuf/compiler/java/java_enum.cc b/src/google/protobuf/compiler/java/java_enum.cc
index 668377a3..0353b607 100644
--- a/src/google/protobuf/compiler/java/java_enum.cc
+++ b/src/google/protobuf/compiler/java/java_enum.cc
@@ -111,6 +111,10 @@ void EnumGenerator::Generate(io::Printer* printer) {
       "$name$($index$, $number$),\n");
   }
 
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    printer->Print("UNRECOGNIZED(-1, -1),\n");
+  }
+
   printer->Print(
     ";\n"
     "\n");
@@ -141,7 +145,17 @@ void EnumGenerator::Generate(io::Printer* printer) {
 
   printer->Print(
     "\n"
-    "public final int getNumber() { return value; }\n"
+    "public final int getNumber() {\n");
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    printer->Print(
+      "  if (index == -1) {\n"
+      "    throw new java.lang.IllegalArgumentException(\n"
+      "        \"Can't get the number of an unknown enum value.\");\n"
+      "  }\n");
+  }
+  printer->Print(
+    "  return value;\n"
+    "}\n"
     "\n"
     "public static $classname$ valueOf(int value) {\n"
     "  switch (value) {\n",
@@ -231,11 +245,12 @@ void EnumGenerator::Generate(io::Printer* printer) {
             "index", SimpleItoa(descriptor_->index()));
         }
         printer->Print(
-          "return $immutable_package$.$descriptor_class$.getDescriptor()\n"
+          "return $immutable_package$.$descriptor_class$.$descriptor$\n"
           "    .getEnumTypes().get($index$);\n",
           "immutable_package", FileJavaPackage(descriptor_->file(), true),
           "descriptor_class",
           name_resolver_->GetDescriptorClassName(descriptor_->file()),
+          "descriptor", "getDescriptor()",
           "index", SimpleItoa(descriptor_->index()));
         printer->Outdent();
       }
@@ -283,11 +298,18 @@ void EnumGenerator::Generate(io::Printer* printer) {
       "  if (desc.getType() != getDescriptor()) {\n"
       "    throw new java.lang.IllegalArgumentException(\n"
       "      \"EnumValueDescriptor is not for this type.\");\n"
-      "  }\n"
+      "  }\n",
+      "classname", descriptor_->name());
+    if (SupportUnknownEnumValue(descriptor_->file())) {
+      printer->Print(
+        "  if (desc.getIndex() == -1) {\n"
+        "    return UNRECOGNIZED;\n"
+        "  }\n");
+    }
+    printer->Print(
       "  return VALUES[desc.getIndex()];\n"
       "}\n"
-      "\n",
-      "classname", descriptor_->name());
+      "\n");
 
     // index is only used for reflection; lite implementation does not need it
     printer->Print("private final int index;\n");
diff --git a/src/google/protobuf/compiler/java/java_enum_field.cc b/src/google/protobuf/compiler/java/java_enum_field.cc
index 1f0c4af0..71a2ba4b 100644
--- a/src/google/protobuf/compiler/java/java_enum_field.cc
+++ b/src/google/protobuf/compiler/java/java_enum_field.cc
@@ -65,6 +65,8 @@ void SetEnumVariables(const FieldDescriptor* descriptor,
   (*variables)["mutable_type"] =
       name_resolver->GetMutableClassName(descriptor->enum_type());
   (*variables)["default"] = ImmutableDefaultValue(descriptor, name_resolver);
+  (*variables)["default_number"] = SimpleItoa(
+      descriptor->default_value_enum()->number());
   (*variables)["tag"] = SimpleItoa(internal::WireFormat::MakeTag(descriptor));
   (*variables)["tag_size"] = SimpleItoa(
       internal::WireFormat::TagSize(descriptor->number(), GetType(descriptor)));
@@ -95,7 +97,8 @@ void SetEnumVariables(const FieldDescriptor* descriptor,
     (*variables)["clear_has_field_bit_builder"] = "";
 
     (*variables)["is_field_present_message"] =
-          (*variables)["name"] + "_ != " + (*variables)["default"];
+        (*variables)["name"] + "_ != " +
+        (*variables)["default"] + ".getNumber()";
   }
 
   // For repated builders, one bit is used for whether the array is immutable.
@@ -114,6 +117,12 @@ void SetEnumVariables(const FieldDescriptor* descriptor,
       GenerateGetBitFromLocal(builderBitIndex);
   (*variables)["set_has_field_bit_to_local"] =
       GenerateSetBitToLocal(messageBitIndex);
+
+  if (SupportUnknownEnumValue(descriptor->file())) {
+    (*variables)["unknown"] = (*variables)["type"] + ".UNRECOGNIZED";
+  } else {
+    (*variables)["unknown"] = (*variables)["default"];
+  }
 }
 
 }  // namespace
@@ -150,6 +159,11 @@ GenerateInterfaceMembers(io::Printer* printer) const {
     printer->Print(variables_,
       "$deprecation$boolean has$capitalized_name$();\n");
   }
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$int get$capitalized_name$Value();\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$$type$ get$capitalized_name$();\n");
@@ -158,7 +172,7 @@ GenerateInterfaceMembers(io::Printer* printer) const {
 void ImmutableEnumFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
-    "private $type$ $name$_;\n");
+    "private int $name$_;\n");
   PrintExtraFieldInfo(variables_, printer);
   if (SupportFieldPresence(descriptor_->file())) {
     WriteFieldDocComment(printer, descriptor_);
@@ -167,17 +181,25 @@ GenerateMembers(io::Printer* printer) const {
       "  return $get_has_field_bit_message$;\n"
       "}\n");
   }
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public int get$capitalized_name$Value() {\n"
+      "  return $name$_;\n"
+      "}\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public $type$ get$capitalized_name$() {\n"
-    "  return $name$_;\n"
+    "  $type$ result = $type$.valueOf($name$_);\n"
+    "  return result == null ? $unknown$ : result;\n"
     "}\n");
 }
 
 void ImmutableEnumFieldGenerator::
 GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
-    "private $type$ $name$_ = $default$;\n");
+    "private int $name$_ = $default_number$;\n");
   if (SupportFieldPresence(descriptor_->file())) {
     WriteFieldDocComment(printer, descriptor_);
     printer->Print(variables_,
@@ -185,10 +207,25 @@ GenerateBuilderMembers(io::Printer* printer) const {
       "  return $get_has_field_bit_builder$;\n"
       "}\n");
   }
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public int get$capitalized_name$Value() {\n"
+      "  return $name$_;\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public Builder set$capitalized_name$Value(int value) {\n"
+      "  $name$_ = value;\n"
+      "  $on_changed$\n"
+      "  return this;\n"
+      "}\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public $type$ get$capitalized_name$() {\n"
-    "  return $name$_;\n"
+    "  $type$ result = $type$.valueOf($name$_);\n"
+    "  return result == null ? $unknown$ : result;\n"
     "}\n");
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
@@ -197,7 +234,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "    throw new NullPointerException();\n"
     "  }\n"
     "  $set_has_field_bit_builder$\n"
-    "  $name$_ = value;\n"
+    "  $name$_ = value.getNumber();\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
@@ -205,7 +242,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
   printer->Print(variables_,
     "$deprecation$public Builder clear$capitalized_name$() {\n"
     "  $clear_has_field_bit_builder$\n"
-    "  $name$_ = $default$;\n"
+    "  $name$_ = $default_number$;\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
@@ -218,13 +255,13 @@ GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
 
 void ImmutableEnumFieldGenerator::
 GenerateInitializationCode(io::Printer* printer) const {
-  printer->Print(variables_, "$name$_ = $default$;\n");
+  printer->Print(variables_, "$name$_ = $default_number$;\n");
 }
 
 void ImmutableEnumFieldGenerator::
 GenerateBuilderClearCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "$name$_ = $default$;\n"
+    "$name$_ = $default_number$;\n"
     "$clear_has_field_bit_builder$\n");
 }
 
@@ -235,11 +272,13 @@ GenerateMergingCode(io::Printer* printer) const {
       "if (other.has$capitalized_name$()) {\n"
       "  set$capitalized_name$(other.get$capitalized_name$());\n"
       "}\n");
-  } else {
+  } else if (SupportUnknownEnumValue(descriptor_->file())) {
     printer->Print(variables_,
-      "if (other.get$capitalized_name$() != $default$) {\n"
-      "  set$capitalized_name$(other.get$capitalized_name$());\n"
+      "if (other.$name$_ != $default_number$) {\n"
+      "  set$capitalized_name$Value(other.get$capitalized_name$Value());\n"
       "}\n");
+  } else {
+    GOOGLE_LOG(FATAL) << "Can't reach here.";
   }
 }
 
@@ -257,23 +296,26 @@ GenerateBuildingCode(io::Printer* printer) const {
 
 void ImmutableEnumFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
-  printer->Print(variables_,
-    "int rawValue = input.readEnum();\n"
-    "$type$ value = $type$.valueOf(rawValue);\n"
-    "if (value == null) {\n");
-  if (UseUnknownFieldSet(descriptor_->containing_type())) {
+  if (SupportUnknownEnumValue(descriptor_->file())) {
     printer->Print(variables_,
-      "  unknownFields.mergeVarintField($number$, rawValue);\n");
+      "int rawValue = input.readEnum();\n"
+      "$set_has_field_bit_message$\n"
+      "$name$_ = rawValue;\n");
   } else {
     printer->Print(variables_,
-      "  unknownFieldsCodedOutput.writeRawVarint32(tag);\n"
-      "  unknownFieldsCodedOutput.writeRawVarint32(rawValue);\n");
+      "int rawValue = input.readEnum();\n"
+      "$type$ value = $type$.valueOf(rawValue);\n"
+      "if (value == null) {\n");
+    if (PreserveUnknownFields(descriptor_->containing_type())) {
+      printer->Print(variables_,
+        "  unknownFields.mergeVarintField($number$, rawValue);\n");
+    }
+    printer->Print(variables_,
+      "} else {\n"
+      "  $set_has_field_bit_message$\n"
+      "  $name$_ = rawValue;\n"
+      "}\n");
   }
-  printer->Print(variables_,
-    "} else {\n"
-    "  $set_has_field_bit_message$\n"
-    "  $name$_ = value;\n"
-    "}\n");
 }
 
 void ImmutableEnumFieldGenerator::
@@ -285,7 +327,7 @@ void ImmutableEnumFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if ($is_field_present_message$) {\n"
-    "  output.writeEnum($number$, $name$_.getNumber());\n"
+    "  output.writeEnum($number$, $name$_);\n"
     "}\n");
 }
 
@@ -294,23 +336,21 @@ GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if ($is_field_present_message$) {\n"
     "  size += com.google.protobuf.CodedOutputStream\n"
-    "    .computeEnumSize($number$, $name$_.getNumber());\n"
+    "    .computeEnumSize($number$, $name$_);\n"
     "}\n");
 }
 
 void ImmutableEnumFieldGenerator::
 GenerateEqualsCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "result = result &&\n"
-    "    (get$capitalized_name$() == other.get$capitalized_name$());\n");
+    "result = result && $name$_ == other.$name$_;\n");
 }
 
 void ImmutableEnumFieldGenerator::
 GenerateHashCode(io::Printer* printer) const {
   printer->Print(variables_,
     "hash = (37 * hash) + $constant_name$;\n"
-    "hash = (53 * hash) + com.google.protobuf.Internal.hashEnum(\n"
-    "    get$capitalized_name$());\n");
+    "hash = (53 * hash) + $name$_;\n");
 }
 
 string ImmutableEnumFieldGenerator::GetBoxedType() const {
@@ -344,11 +384,22 @@ GenerateMembers(io::Printer* printer) const {
       "  return $has_oneof_case_message$;\n"
       "}\n");
   }
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public int get$capitalized_name$Value() {\n"
+      "  if ($has_oneof_case_message$) {\n"
+      "    return (java.lang.Integer) $oneof_name$_;\n"
+      "  }\n"
+      "  return $default_number$;\n"
+      "}\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public $type$ get$capitalized_name$() {\n"
     "  if ($has_oneof_case_message$) {\n"
-    "    return ($type$) $oneof_name$_;\n"
+    "    $type$ result =  $type$.valueOf((java.lang.Integer) $oneof_name$_);\n"
+    "    return result == null ? $unknown$ : result;\n"
     "  }\n"
     "  return $default$;\n"
     "}\n");
@@ -363,11 +414,30 @@ GenerateBuilderMembers(io::Printer* printer) const {
       "  return $has_oneof_case_message$;\n"
       "}\n");
   }
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public int get$capitalized_name$Value() {\n"
+      "  if ($has_oneof_case_message$) {\n"
+      "    return ((java.lang.Integer) $oneof_name$_).intValue();\n"
+      "  }\n"
+      "  return $default_number$;\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public Builder set$capitalized_name$Value(int value) {\n"
+      "  $set_oneof_case_message$;\n"
+      "  $oneof_name$_ = value;\n"
+      "  $on_changed$\n"
+      "  return this;\n"
+      "}\n");
+  }
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public $type$ get$capitalized_name$() {\n"
     "  if ($has_oneof_case_message$) {\n"
-    "    return ($type$) $oneof_name$_;\n"
+    "    $type$ result =  $type$.valueOf((java.lang.Integer) $oneof_name$_);\n"
+    "    return result == null ? $unknown$ : result;\n"
     "  }\n"
     "  return $default$;\n"
     "}\n");
@@ -378,7 +448,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "    throw new NullPointerException();\n"
     "  }\n"
     "  $set_oneof_case_message$;\n"
-    "  $oneof_name$_ = value;\n"
+    "  $oneof_name$_ = value.getNumber();\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
@@ -404,36 +474,44 @@ GenerateBuildingCode(io::Printer* printer) const {
 
 void ImmutableEnumOneofFieldGenerator::
 GenerateMergingCode(io::Printer* printer) const {
-  printer->Print(variables_,
-    "set$capitalized_name$(other.get$capitalized_name$());\n");
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    printer->Print(variables_,
+      "set$capitalized_name$Value(other.get$capitalized_name$Value());\n");
+  } else {
+    printer->Print(variables_,
+      "set$capitalized_name$(other.get$capitalized_name$());\n");
+  }
 }
 
 void ImmutableEnumOneofFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
-  printer->Print(variables_,
-    "int rawValue = input.readEnum();\n"
-    "$type$ value = $type$.valueOf(rawValue);\n"
-    "if (value == null) {\n");
-  if (UseUnknownFieldSet(descriptor_->containing_type())) {
+  if (SupportUnknownEnumValue(descriptor_->file())) {
     printer->Print(variables_,
-      "  unknownFields.mergeVarintField($number$, rawValue);\n");
+      "int rawValue = input.readEnum();\n"
+      "$set_oneof_case_message$;\n"
+      "$oneof_name$_ = rawValue;\n");
   } else {
     printer->Print(variables_,
-      "  unknownFieldsCodedOutput.writeRawVarint32(tag);\n"
-      "  unknownFieldsCodedOutput.writeRawVarint32(rawValue);\n");
+      "int rawValue = input.readEnum();\n"
+      "$type$ value = $type$.valueOf(rawValue);\n"
+      "if (value == null) {\n");
+    if (PreserveUnknownFields(descriptor_->containing_type())) {
+      printer->Print(variables_,
+        "  unknownFields.mergeVarintField($number$, rawValue);\n");
+    }
+    printer->Print(variables_,
+      "} else {\n"
+      "  $set_oneof_case_message$;\n"
+      "  $oneof_name$_ = rawValue;\n"
+      "}\n");
   }
-  printer->Print(variables_,
-    "} else {\n"
-    "  $set_oneof_case_message$;\n"
-    "  $oneof_name$_ = value;\n"
-    "}\n");
 }
 
 void ImmutableEnumOneofFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if ($has_oneof_case_message$) {\n"
-    "  output.writeEnum($number$, (($type$) $oneof_name$_).getNumber());\n"
+    "  output.writeEnum($number$, ((java.lang.Integer) $oneof_name$_));\n"
     "}\n");
 }
 
@@ -442,10 +520,36 @@ GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if ($has_oneof_case_message$) {\n"
     "  size += com.google.protobuf.CodedOutputStream\n"
-    "    .computeEnumSize($number$, (($type$) $oneof_name$_).getNumber());\n"
+    "    .computeEnumSize($number$, ((java.lang.Integer) $oneof_name$_));\n"
     "}\n");
 }
 
+void ImmutableEnumOneofFieldGenerator::
+GenerateEqualsCode(io::Printer* printer) const {
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    printer->Print(variables_,
+      "result = result && get$capitalized_name$Value()\n"
+      "    == other.get$capitalized_name$Value();\n");
+  } else {
+    printer->Print(variables_,
+      "result = result && get$capitalized_name$()\n"
+      "    .equals(other.get$capitalized_name$());\n");
+  }
+}
+
+void ImmutableEnumOneofFieldGenerator::
+GenerateHashCode(io::Printer* printer) const {
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    printer->Print(variables_,
+      "hash = (37 * hash) + $constant_name$;\n"
+      "hash = (53 * hash) + get$capitalized_name$Value();\n");
+  } else {
+    printer->Print(variables_,
+      "hash = (37 * hash) + $constant_name$;\n"
+      "hash = (53 * hash) + get$capitalized_name$().getNumber();\n");
+  }
+}
+
 // ===================================================================
 
 RepeatedImmutableEnumFieldGenerator::
@@ -482,17 +586,36 @@ GenerateInterfaceMembers(io::Printer* printer) const {
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$$type$ get$capitalized_name$(int index);\n");
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$java.util.List<java.lang.Integer>\n"
+      "get$capitalized_name$ValueList();\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$int get$capitalized_name$Value(int index);\n");
+  }
 }
 
 void RepeatedImmutableEnumFieldGenerator::
 GenerateMembers(io::Printer* printer) const {
   printer->Print(variables_,
-    "private java.util.List<$type$> $name$_;\n");
+    "private java.util.List<java.lang.Integer> $name$_;\n"
+    "private static final com.google.protobuf.Internal.ListAdapter.Converter<\n"
+    "    java.lang.Integer, $type$> $name$_converter_ =\n"
+    "        new com.google.protobuf.Internal.ListAdapter.Converter<\n"
+    "            java.lang.Integer, $type$>() {\n"
+    "          public $type$ convert(java.lang.Integer from) {\n"
+    "            $type$ result = $type$.valueOf(from);\n"
+    "            return result == null ? $unknown$ : result;\n"
+    "          }\n"
+    "        };\n");
   PrintExtraFieldInfo(variables_, printer);
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public java.util.List<$type$> get$capitalized_name$List() {\n"
-    "  return $name$_;\n"   // note:  unmodifiable list
+    "  return new com.google.protobuf.Internal.ListAdapter<\n"
+    "      java.lang.Integer, $type$>($name$_, $name$_converter_);\n"
     "}\n");
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
@@ -502,8 +625,21 @@ GenerateMembers(io::Printer* printer) const {
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public $type$ get$capitalized_name$(int index) {\n"
-    "  return $name$_.get(index);\n"
+    "  return $name$_converter_.convert($name$_.get(index));\n"
     "}\n");
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public java.util.List<java.lang.Integer>\n"
+      "get$capitalized_name$ValueList() {\n"
+      "  return $name$_;\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public int get$capitalized_name$Value(int index) {\n"
+      "  return $name$_.get(index);\n"
+      "}\n");
+  }
 
   if (descriptor_->options().packed() &&
       HasGeneratedMethods(descriptor_->containing_type())) {
@@ -524,12 +660,12 @@ GenerateBuilderMembers(io::Printer* printer) const {
     // memory allocations. Note, immutable is a strong guarantee here -- not
     // just that the list cannot be modified via the reference but that the
     // list can never be modified.
-    "private java.util.List<$type$> $name$_ =\n"
+    "private java.util.List<java.lang.Integer> $name$_ =\n"
     "  java.util.Collections.emptyList();\n"
 
     "private void ensure$capitalized_name$IsMutable() {\n"
     "  if (!$get_mutable_bit_builder$) {\n"
-    "    $name$_ = new java.util.ArrayList<$type$>($name$_);\n"
+    "    $name$_ = new java.util.ArrayList<java.lang.Integer>($name$_);\n"
     "    $set_mutable_bit_builder$;\n"
     "  }\n"
     "}\n");
@@ -541,7 +677,8 @@ GenerateBuilderMembers(io::Printer* printer) const {
     //   has been built, thus mutating the message which is supposed to be
     //   immutable.
     "$deprecation$public java.util.List<$type$> get$capitalized_name$List() {\n"
-    "  return java.util.Collections.unmodifiableList($name$_);\n"
+    "  return new com.google.protobuf.Internal.ListAdapter<\n"
+    "      java.lang.Integer, $type$>($name$_, $name$_converter_);\n"
     "}\n");
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
@@ -551,7 +688,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
     "$deprecation$public $type$ get$capitalized_name$(int index) {\n"
-    "  return $name$_.get(index);\n"
+    "  return $name$_converter_.convert($name$_.get(index));\n"
     "}\n");
   WriteFieldDocComment(printer, descriptor_);
   printer->Print(variables_,
@@ -561,7 +698,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "    throw new NullPointerException();\n"
     "  }\n"
     "  ensure$capitalized_name$IsMutable();\n"
-    "  $name$_.set(index, value);\n"
+    "  $name$_.set(index, value.getNumber());\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
@@ -572,7 +709,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "    throw new NullPointerException();\n"
     "  }\n"
     "  ensure$capitalized_name$IsMutable();\n"
-    "  $name$_.add(value);\n"
+    "  $name$_.add(value.getNumber());\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
@@ -581,8 +718,9 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "$deprecation$public Builder addAll$capitalized_name$(\n"
     "    java.lang.Iterable<? extends $type$> values) {\n"
     "  ensure$capitalized_name$IsMutable();\n"
-    "  com.google.protobuf.AbstractMessageLite.Builder.addAll(\n"
-    "      values, $name$_);\n"
+    "  for ($type$ value : values) {\n"
+    "    $name$_.add(value.getNumber());\n"
+    "  }\n"
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
@@ -594,6 +732,48 @@ GenerateBuilderMembers(io::Printer* printer) const {
     "  $on_changed$\n"
     "  return this;\n"
     "}\n");
+
+  if (SupportUnknownEnumValue(descriptor_->file())) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public java.util.List<java.lang.Integer>\n"
+      "get$capitalized_name$ValueList() {\n"
+      "  return java.util.Collections.unmodifiableList($name$_);\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public int get$capitalized_name$Value(int index) {\n"
+      "  return $name$_.get(index);\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public Builder set$capitalized_name$Value(\n"
+      "    int index, int value) {\n"
+      "  ensure$capitalized_name$IsMutable();\n"
+      "  $name$_.set(index, value);\n"
+      "  $on_changed$\n"
+      "  return this;\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public Builder add$capitalized_name$Value(int value) {\n"
+      "  ensure$capitalized_name$IsMutable();\n"
+      "  $name$_.add(value);\n"
+      "  $on_changed$\n"
+      "  return this;\n"
+      "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(variables_,
+      "$deprecation$public Builder addAll$capitalized_name$Value(\n"
+      "    java.lang.Iterable<java.lang.Integer> values) {\n"
+      "  ensure$capitalized_name$IsMutable();\n"
+      "  for (int value : values) {\n"
+      "    $name$_.add(value);\n"
+      "  }\n"
+      "  $on_changed$\n"
+      "  return this;\n"
+      "}\n");
+  }
 }
 
 void RepeatedImmutableEnumFieldGenerator::
@@ -648,26 +828,32 @@ GenerateBuildingCode(io::Printer* printer) const {
 void RepeatedImmutableEnumFieldGenerator::
 GenerateParsingCode(io::Printer* printer) const {
   // Read and store the enum
-  printer->Print(variables_,
-    "int rawValue = input.readEnum();\n"
-    "$type$ value = $type$.valueOf(rawValue);\n"
-    "if (value == null) {\n");
-  if (UseUnknownFieldSet(descriptor_->containing_type())) {
+  if (SupportUnknownEnumValue(descriptor_->file())) {
     printer->Print(variables_,
-      "  unknownFields.mergeVarintField($number$, rawValue);\n");
+      "int rawValue = input.readEnum();\n"
+      "if (!$get_mutable_bit_parser$) {\n"
+      "  $name$_ = new java.util.ArrayList<java.lang.Integer>();\n"
+      "  $set_mutable_bit_parser$;\n"
+      "}\n"
+      "$name$_.add(rawValue);\n");
   } else {
     printer->Print(variables_,
-      "  unknownFieldsCodedOutput.writeRawVarint32(tag);\n"
-      "  unknownFieldsCodedOutput.writeRawVarint32(rawValue);\n");
+      "int rawValue = input.readEnum();\n"
+      "$type$ value = $type$.valueOf(rawValue);\n"
+        "if (value == null) {\n");
+    if (PreserveUnknownFields(descriptor_->containing_type())) {
+      printer->Print(variables_,
+        "  unknownFields.mergeVarintField($number$, rawValue);\n");
+    }
+    printer->Print(variables_,
+      "} else {\n"
+      "  if (!$get_mutable_bit_parser$) {\n"
+      "    $name$_ = new java.util.ArrayList<java.lang.Integer>();\n"
+      "    $set_mutable_bit_parser$;\n"
+      "  }\n"
+      "  $name$_.add(rawValue);\n"
+      "}\n");
   }
-  printer->Print(variables_,
-    "  } else {\n"
-    "  if (!$get_mutable_bit_parser$) {\n"
-    "    $name$_ = new java.util.ArrayList<$type$>();\n"
-    "    $set_mutable_bit_parser$;\n"
-    "  }\n"
-    "  $name$_.add(value);\n"
-    "}\n");
 }
 
 void RepeatedImmutableEnumFieldGenerator::
@@ -705,12 +891,12 @@ GenerateSerializationCode(io::Printer* printer) const {
       "  output.writeRawVarint32($name$MemoizedSerializedSize);\n"
       "}\n"
       "for (int i = 0; i < $name$_.size(); i++) {\n"
-      "  output.writeEnumNoTag($name$_.get(i).getNumber());\n"
+      "  output.writeEnumNoTag($name$_.get(i));\n"
       "}\n");
   } else {
     printer->Print(variables_,
       "for (int i = 0; i < $name$_.size(); i++) {\n"
-      "  output.writeEnum($number$, $name$_.get(i).getNumber());\n"
+      "  output.writeEnum($number$, $name$_.get(i));\n"
       "}\n");
   }
 }
@@ -725,7 +911,7 @@ GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
     "for (int i = 0; i < $name$_.size(); i++) {\n"
     "  dataSize += com.google.protobuf.CodedOutputStream\n"
-    "    .computeEnumSizeNoTag($name$_.get(i).getNumber());\n"
+    "    .computeEnumSizeNoTag($name$_.get(i));\n"
     "}\n");
   printer->Print(
     "size += dataSize;\n");
@@ -754,8 +940,7 @@ GenerateSerializedSizeCode(io::Printer* printer) const {
 void RepeatedImmutableEnumFieldGenerator::
 GenerateEqualsCode(io::Printer* printer) const {
   printer->Print(variables_,
-    "result = result && get$capitalized_name$List()\n"
-    "    .equals(other.get$capitalized_name$List());\n");
+    "result = result && $name$_.equals(other.$name$_);\n");
 }
 
 void RepeatedImmutableEnumFieldGenerator::
@@ -763,8 +948,7 @@ GenerateHashCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if (get$capitalized_name$Count() > 0) {\n"
     "  hash = (37 * hash) + $constant_name$;\n"
-    "  hash = (53 * hash) + com.google.protobuf.Internal.hashEnumList(\n"
-    "      get$capitalized_name$List());\n"
+    "  hash = (53 * hash) + $name$_.hashCode();\n"
     "}\n");
 }
 
diff --git a/src/google/protobuf/compiler/java/java_enum_field.h b/src/google/protobuf/compiler/java/java_enum_field.h
index 6a9535aa..b8ff7343 100644
--- a/src/google/protobuf/compiler/java/java_enum_field.h
+++ b/src/google/protobuf/compiler/java/java_enum_field.h
@@ -106,6 +106,8 @@ class ImmutableEnumOneofFieldGenerator : public ImmutableEnumFieldGenerator {
   void GenerateParsingCode(io::Printer* printer) const;
   void GenerateSerializationCode(io::Printer* printer) const;
   void GenerateSerializedSizeCode(io::Printer* printer) const;
+  void GenerateEqualsCode(io::Printer* printer) const;
+  void GenerateHashCode(io::Printer* printer) const;
 
  private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ImmutableEnumOneofFieldGenerator);
diff --git a/src/google/protobuf/compiler/java/java_field.cc b/src/google/protobuf/compiler/java/java_field.cc
index d7b0f3fc..49635bb4 100644
--- a/src/google/protobuf/compiler/java/java_field.cc
+++ b/src/google/protobuf/compiler/java/java_field.cc
@@ -35,12 +35,16 @@
 #include <google/protobuf/compiler/java/java_field.h>
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/compiler/java/java_context.h>
 #include <google/protobuf/compiler/java/java_enum_field.h>
 #include <google/protobuf/compiler/java/java_helpers.h>
 #include <google/protobuf/compiler/java/java_lazy_message_field.h>
+#include <google/protobuf/compiler/java/java_map_field.h>
 #include <google/protobuf/compiler/java/java_message_field.h>
 #include <google/protobuf/compiler/java/java_primitive_field.h>
 #include <google/protobuf/compiler/java/java_string_field.h>
@@ -48,6 +52,7 @@
 #include <google/protobuf/stubs/strutil.h>
 #include <google/protobuf/stubs/substitute.h>
 
+
 namespace google {
 namespace protobuf {
 namespace compiler {
@@ -61,12 +66,17 @@ ImmutableFieldGenerator* MakeImmutableGenerator(
   if (field->is_repeated()) {
     switch (GetJavaType(field)) {
       case JAVATYPE_MESSAGE:
-        if (IsLazy(field)) {
-          return new RepeatedImmutableLazyMessageFieldGenerator(
+        if (IsMapEntry(field->message_type())) {
+          return new ImmutableMapFieldGenerator(
               field, messageBitIndex, builderBitIndex, context);
         } else {
-          return new RepeatedImmutableMessageFieldGenerator(
-              field, messageBitIndex, builderBitIndex, context);
+          if (IsLazy(field)) {
+            return new RepeatedImmutableLazyMessageFieldGenerator(
+                field, messageBitIndex, builderBitIndex, context);
+          } else {
+            return new RepeatedImmutableMessageFieldGenerator(
+                field, messageBitIndex, builderBitIndex, context);
+          }
         }
       case JAVATYPE_ENUM:
         return new RepeatedImmutableEnumFieldGenerator(
diff --git a/src/google/protobuf/compiler/java/java_field.h b/src/google/protobuf/compiler/java/java_field.h
index db339d5b..5bc5634e 100644
--- a/src/google/protobuf/compiler/java/java_field.h
+++ b/src/google/protobuf/compiler/java/java_field.h
@@ -37,6 +37,9 @@
 
 #include <map>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <string>
 
 #include <google/protobuf/stubs/common.h>
diff --git a/src/google/protobuf/compiler/java/java_file.cc b/src/google/protobuf/compiler/java/java_file.cc
index 231b1445..1ac945cd 100644
--- a/src/google/protobuf/compiler/java/java_file.cc
+++ b/src/google/protobuf/compiler/java/java_file.cc
@@ -35,6 +35,9 @@
 #include <google/protobuf/compiler/java/java_file.h>
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/compiler/java/java_context.h>
 #include <google/protobuf/compiler/java/java_enum.h>
@@ -180,29 +183,6 @@ bool FileGenerator::Validate(string* error) {
       "option to specify a different outer class name for the .proto file.");
     return false;
   }
-  // If java_outer_classname option is not set and the default outer class name
-  // conflicts with a type defined in the message, we will append a suffix to
-  // avoid the conflict. This allows proto1 API protos to be dual-compiled into
-  // proto2 API without code change. When this happens we'd like to issue an
-  // warning to let the user know that the outer class name has been changed.
-  // Although we only do this automatic naming fix for immutable API, mutable
-  // outer class name will also be affected as it's contructed from immutable
-  // outer class name with an additional "Mutable" prefix. Since the naming
-  // change in mutable API is not caused by a naming conflict, we generate the
-  // warning for immutable API only.
-  if (immutable_api_ && !file_->options().has_java_outer_classname()) {
-    string default_classname =
-        name_resolver_->GetFileDefaultImmutableClassName(file_);
-    if (default_classname != classname_) {
-      GOOGLE_LOG(WARNING) << file_->name() << ": The default outer class name, \""
-                   << default_classname << "\", conflicts with a type "
-                   << "declared in the proto file and an alternative outer "
-                   << "class name is used: \"" << classname_ << "\". To avoid "
-                   << "this warning, please use the java_outer_classname "
-                   << "option to specify a different outer class name for "
-                   << "the .proto file.";
-    }
-  }
   return true;
 }
 
@@ -323,6 +303,7 @@ void FileGenerator::GenerateDescriptorInitializationCodeForImmutable(
   SharedCodeGenerator shared_code_generator(file_);
   shared_code_generator.GenerateDescriptors(printer);
 
+
   for (int i = 0; i < file_->message_type_count(); i++) {
     message_generators_[i]->GenerateStaticVariableInitializers(printer);
   }
diff --git a/src/google/protobuf/compiler/java/java_file.h b/src/google/protobuf/compiler/java/java_file.h
index c805b9a6..0b2230a0 100644
--- a/src/google/protobuf/compiler/java/java_file.h
+++ b/src/google/protobuf/compiler/java/java_file.h
@@ -36,6 +36,9 @@
 #define GOOGLE_PROTOBUF_COMPILER_JAVA_FILE_H__
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <string>
 #include <vector>
 #include <google/protobuf/stubs/common.h>
diff --git a/src/google/protobuf/compiler/java/java_generator.cc b/src/google/protobuf/compiler/java/java_generator.cc
index c3a47e3e..a743ce22 100644
--- a/src/google/protobuf/compiler/java/java_generator.cc
+++ b/src/google/protobuf/compiler/java/java_generator.cc
@@ -35,6 +35,9 @@
 #include <google/protobuf/compiler/java/java_generator.h>
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/compiler/java/java_file.h>
 #include <google/protobuf/compiler/java/java_generator_factory.h>
@@ -99,10 +102,14 @@ bool JavaGenerator::Generate(const FileDescriptor* file,
 
   vector<string> all_files;
 
+
   vector<FileGenerator*> file_generators;
   if (generate_immutable_code) {
     file_generators.push_back(new FileGenerator(file, /* immutable = */ true));
   }
+  if (generate_mutable_code) {
+    file_generators.push_back(new FileGenerator(file, /* mutable = */ false));
+  }
   for (int i = 0; i < file_generators.size(); ++i) {
     if (!file_generators[i]->Validate(error)) {
       for (int j = 0; j < file_generators.size(); ++j) {
diff --git a/src/google/protobuf/compiler/java/java_helpers.cc b/src/google/protobuf/compiler/java/java_helpers.cc
index 3efd7edb..23685385 100644
--- a/src/google/protobuf/compiler/java/java_helpers.cc
+++ b/src/google/protobuf/compiler/java/java_helpers.cc
@@ -306,6 +306,26 @@ JavaType GetJavaType(const FieldDescriptor* field) {
   return JAVATYPE_INT;
 }
 
+const char* PrimitiveTypeName(JavaType type) {
+  switch (type) {
+    case JAVATYPE_INT    : return "int";
+    case JAVATYPE_LONG   : return "long";
+    case JAVATYPE_FLOAT  : return "float";
+    case JAVATYPE_DOUBLE : return "double";
+    case JAVATYPE_BOOLEAN: return "boolean";
+    case JAVATYPE_STRING : return "java.lang.String";
+    case JAVATYPE_BYTES  : return "com.google.protobuf.ByteString";
+    case JAVATYPE_ENUM   : return NULL;
+    case JAVATYPE_MESSAGE: return NULL;
+
+    // No default because we want the compiler to complain if any new
+    // JavaTypes are added.
+  }
+
+  GOOGLE_LOG(FATAL) << "Can't get here.";
+  return NULL;
+}
+
 const char* BoxedPrimitiveTypeName(JavaType type) {
   switch (type) {
     case JAVATYPE_INT    : return "java.lang.Integer";
diff --git a/src/google/protobuf/compiler/java/java_helpers.h b/src/google/protobuf/compiler/java/java_helpers.h
index 93f23a93..2707fa0a 100644
--- a/src/google/protobuf/compiler/java/java_helpers.h
+++ b/src/google/protobuf/compiler/java/java_helpers.h
@@ -149,6 +149,8 @@ enum JavaType {
 
 JavaType GetJavaType(const FieldDescriptor* field);
 
+const char* PrimitiveTypeName(JavaType type);
+
 // Get the fully-qualified class name for a boxed primitive type, e.g.
 // "java.lang.Integer" for JAVATYPE_INT.  Returns NULL for enum and message
 // types.
@@ -168,13 +170,6 @@ inline string ImmutableDefaultValue(const FieldDescriptor* field,
 }
 bool IsDefaultValueJavaDefault(const FieldDescriptor* field);
 
-// Does this message class use UnknownFieldSet?
-// Otherwise, unknown fields will be stored in a ByteString object
-inline bool UseUnknownFieldSet(const Descriptor* descriptor) {
-  return descriptor->file()->options().optimize_for() !=
-           FileOptions::LITE_RUNTIME;
-}
-
 // Does this message class have generated parsing, serialization, and other
 // standard methods for which reflection-based fallback implementations exist?
 inline bool HasGeneratedMethods(const Descriptor* descriptor) {
@@ -308,12 +303,27 @@ bool HasRequiredFields(const Descriptor* descriptor);
 
 // Whether a .proto file supports field presence test for non-message types.
 inline bool SupportFieldPresence(const FileDescriptor* descriptor) {
-  return true;
+  return descriptor->syntax() != FileDescriptor::SYNTAX_PROTO3;
+}
+
+// Whether unknown enum values are kept (i.e., not stored in UnknownFieldSet
+// but in the message and can be queried using additional getters that return
+// ints.
+inline bool SupportUnknownEnumValue(const FileDescriptor* descriptor) {
+  return descriptor->syntax() == FileDescriptor::SYNTAX_PROTO3;
 }
 
 // Check whether a mesasge has repeated fields.
 bool HasRepeatedFields(const Descriptor* descriptor);
 
+inline bool IsMapEntry(const Descriptor* descriptor) {
+  return descriptor->options().map_entry();
+}
+
+inline bool PreserveUnknownFields(const Descriptor* descriptor) {
+  return descriptor->file()->syntax() != FileDescriptor::SYNTAX_PROTO3;
+}
+
 }  // namespace java
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/java/java_map_field.cc b/src/google/protobuf/compiler/java/java_map_field.cc
new file mode 100644
index 00000000..2986f51f
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_map_field.cc
@@ -0,0 +1,455 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include <google/protobuf/compiler/java/java_map_field.h>
+
+#include <google/protobuf/compiler/java/java_context.h>
+#include <google/protobuf/compiler/java/java_doc_comment.h>
+#include <google/protobuf/compiler/java/java_helpers.h>
+#include <google/protobuf/compiler/java/java_name_resolver.h>
+#include <google/protobuf/io/printer.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+namespace {
+
+const FieldDescriptor* KeyField(const FieldDescriptor* descriptor) {
+  GOOGLE_CHECK_EQ(FieldDescriptor::TYPE_MESSAGE, descriptor->type());
+  const Descriptor* message = descriptor->message_type();
+  GOOGLE_CHECK(message->options().map_entry());
+  return message->FindFieldByName("key");
+}
+
+const FieldDescriptor* ValueField(const FieldDescriptor* descriptor) {
+  GOOGLE_CHECK_EQ(FieldDescriptor::TYPE_MESSAGE, descriptor->type());
+  const Descriptor* message = descriptor->message_type();
+  GOOGLE_CHECK(message->options().map_entry());
+  return message->FindFieldByName("value");
+}
+
+string TypeName(const FieldDescriptor* field,
+                ClassNameResolver* name_resolver,
+                bool boxed) {
+  if (GetJavaType(field) == JAVATYPE_MESSAGE) {
+    return name_resolver->GetImmutableClassName(field->message_type());
+  } else if (GetJavaType(field) == JAVATYPE_ENUM) {
+    return name_resolver->GetImmutableClassName(field->enum_type());
+  } else {
+    return boxed ? BoxedPrimitiveTypeName(GetJavaType(field))
+                 : PrimitiveTypeName(GetJavaType(field));
+  }
+}
+
+string WireType(const FieldDescriptor* field) {
+  return "com.google.protobuf.WireFormat.FieldType." +
+      string(FieldTypeName(field->type()));
+}
+
+void SetMessageVariables(const FieldDescriptor* descriptor,
+                         int messageBitIndex,
+                         int builderBitIndex,
+                         const FieldGeneratorInfo* info,
+                         ClassNameResolver* name_resolver,
+                         map<string, string>* variables) {
+  SetCommonFieldVariables(descriptor, info, variables);
+
+  (*variables)["type"] =
+      name_resolver->GetImmutableClassName(descriptor->message_type());
+  const FieldDescriptor* key = KeyField(descriptor);
+  const FieldDescriptor* value = ValueField(descriptor);
+  (*variables)["key_type"] = TypeName(key, name_resolver, false);
+  (*variables)["boxed_key_type"] = TypeName(key, name_resolver, true);
+  (*variables)["key_wire_type"] = WireType(key);
+  (*variables)["key_default_value"] = DefaultValue(key, true, name_resolver);
+  if (GetJavaType(value) == JAVATYPE_ENUM) {
+    // We store enums as Integers internally.
+    (*variables)["value_type"] = "int";
+    (*variables)["boxed_value_type"] = "java.lang.Integer";
+    (*variables)["value_wire_type"] = WireType(value);
+    (*variables)["value_default_value"] =
+        DefaultValue(value, true, name_resolver) + ".getNumber()";
+
+    (*variables)["value_enum_type"] = TypeName(value, name_resolver, false);
+
+    if (SupportUnknownEnumValue(descriptor->file())) {
+      // Map unknown values to a special UNRECOGNIZED value if supported.
+      (*variables)["unrecognized_value"] =
+          (*variables)["value_enum_type"] + ".UNRECOGNIZED";
+    } else {
+      // Map unknown values to the default value if we don't have UNRECOGNIZED.
+      (*variables)["unrecognized_value"] =
+          DefaultValue(value, true, name_resolver);
+    }
+  } else {
+    (*variables)["value_type"] = TypeName(value, name_resolver, false);
+    (*variables)["boxed_value_type"] = TypeName(value, name_resolver, true);
+    (*variables)["value_wire_type"] = WireType(value);
+    (*variables)["value_default_value"] =
+        DefaultValue(value, true, name_resolver);
+  }
+  (*variables)["type_parameters"] =
+      (*variables)["boxed_key_type"] + ", " + (*variables)["boxed_value_type"];
+  // TODO(birdo): Add @deprecated javadoc when generating javadoc is supported
+  // by the proto compiler
+  (*variables)["deprecation"] = descriptor->options().deprecated()
+      ? "@java.lang.Deprecated " : "";
+  (*variables)["on_changed"] =
+      HasDescriptorMethods(descriptor->containing_type()) ? "onChanged();" : "";
+
+  // For repeated fields, one bit is used for whether the array is immutable
+  // in the parsing constructor.
+  (*variables)["get_mutable_bit_parser"] =
+      GenerateGetBitMutableLocal(builderBitIndex);
+  (*variables)["set_mutable_bit_parser"] =
+      GenerateSetBitMutableLocal(builderBitIndex);
+
+  if (HasDescriptorMethods(descriptor->file())) {
+    (*variables)["lite"] = "";
+    (*variables)["map_field_parameter"] = (*variables)["name"] + "DefaultEntry";
+    (*variables)["descriptor"] =
+        name_resolver->GetImmutableClassName(descriptor->file()) +
+        ".internal_" + UniqueFileScopeIdentifier(descriptor->message_type()) +
+        "_descriptor, ";
+  } else {
+    (*variables)["lite"] = "Lite";
+    (*variables)["map_field_parameter"] = "";
+    (*variables)["descriptor"] = "";
+  }
+}
+
+}  // namespace
+
+ImmutableMapFieldGenerator::
+ImmutableMapFieldGenerator(const FieldDescriptor* descriptor,
+                                       int messageBitIndex,
+                                       int builderBitIndex,
+                                       Context* context)
+  : descriptor_(descriptor), messageBitIndex_(messageBitIndex),
+    builderBitIndex_(builderBitIndex), context_(context),
+    name_resolver_(context->GetNameResolver())  {
+  SetMessageVariables(descriptor, messageBitIndex, builderBitIndex,
+                      context->GetFieldGeneratorInfo(descriptor),
+                      name_resolver_, &variables_);
+}
+
+ImmutableMapFieldGenerator::
+~ImmutableMapFieldGenerator() {}
+
+int ImmutableMapFieldGenerator::GetNumBitsForMessage() const {
+  return 0;
+}
+
+int ImmutableMapFieldGenerator::GetNumBitsForBuilder() const {
+  return 1;
+}
+
+void ImmutableMapFieldGenerator::
+GenerateInterfaceMembers(io::Printer* printer) const {
+  if (GetJavaType(ValueField(descriptor_)) == JAVATYPE_ENUM) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(
+        variables_,
+        "$deprecation$java.util.Map<$boxed_key_type$, $value_enum_type$>\n"
+        "get$capitalized_name$();\n");
+    if (SupportUnknownEnumValue(descriptor_->file())) {
+      WriteFieldDocComment(printer, descriptor_);
+      printer->Print(
+          variables_,
+          "$deprecation$java.util.Map<$type_parameters$>\n"
+          "get$capitalized_name$Value();\n");
+    }
+  } else {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(
+        variables_,
+        "$deprecation$java.util.Map<$type_parameters$>\n"
+        "get$capitalized_name$();\n");
+  }
+}
+
+void ImmutableMapFieldGenerator::
+GenerateMembers(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      "private static final com.google.protobuf.MapEntry$lite$<\n"
+      "    $type_parameters$> $name$DefaultEntry =\n"
+      "        com.google.protobuf.MapEntry$lite$\n"
+      "        .<$type_parameters$>newDefaultInstance(\n"
+      "            $descriptor$\n"
+      "            $key_wire_type$,\n"
+      "            $key_default_value$,\n"
+      "            $value_wire_type$,\n"
+      "            $value_default_value$);\n");
+  printer->Print(
+      variables_,
+      "private com.google.protobuf.MapField$lite$<\n"
+      "    $type_parameters$> $name$_ =\n"
+      "        com.google.protobuf.MapField$lite$.emptyMapField(\n"
+      "            $map_field_parameter$);\n"
+      "\n");
+  if (GetJavaType(ValueField(descriptor_)) == JAVATYPE_ENUM) {
+    printer->Print(
+        variables_,
+        "private static final\n"
+        "com.google.protobuf.Internal.MapAdapter.Converter<\n"
+        "    java.lang.Integer, $value_enum_type$> $name$ValueConverter =\n"
+        "        com.google.protobuf.Internal.MapAdapter.newEnumConverter(\n"
+        "            $value_enum_type$.internalGetValueMap(),\n"
+        "            $unrecognized_value$);\n");
+    if (SupportUnknownEnumValue(descriptor_->file())) {
+      WriteFieldDocComment(printer, descriptor_);
+      printer->Print(
+          variables_,
+          "$deprecation$\n"
+          "public java.util.Map<$boxed_key_type$, $boxed_value_type$>\n"
+          "get$capitalized_name$Value() {\n"
+          "  return $name$_.getMap();\n"
+          "}\n");
+    }
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(
+        variables_,
+        "$deprecation$\n"
+        "public java.util.Map<$boxed_key_type$, $value_enum_type$>\n"
+        "get$capitalized_name$() {\n"
+        "  return new com.google.protobuf.Internal.MapAdapter<\n"
+        "      $boxed_key_type$, $value_enum_type$, java.lang.Integer>(\n"
+        "          $name$_.getMap(), $name$ValueConverter);\n"
+        "}\n");
+  } else {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(
+        variables_,
+        "$deprecation$\n"
+        "public java.util.Map<$type_parameters$> get$capitalized_name$() {\n"
+        "  return $name$_.getMap();\n"
+        "}\n");
+  }
+}
+
+void ImmutableMapFieldGenerator::
+GenerateBuilderMembers(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      "private com.google.protobuf.MapField$lite$<\n"
+      "    $type_parameters$> $name$_ =\n"
+      "        com.google.protobuf.MapField$lite$.newMapField(\n"
+      "            $map_field_parameter$);\n"
+      "\n");
+  if (GetJavaType(ValueField(descriptor_)) == JAVATYPE_ENUM) {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(
+        variables_,
+        "$deprecation$\n"
+        "public java.util.Map<$boxed_key_type$, $value_enum_type$>\n"
+        "get$capitalized_name$() {\n"
+        "  return new com.google.protobuf.Internal.MapAdapter<\n"
+        "      $boxed_key_type$, $value_enum_type$, java.lang.Integer>(\n"
+        "          $name$_.getMap(), $name$ValueConverter);\n"
+        "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(
+        variables_,
+        "$deprecation$\n"
+        "public java.util.Map<$boxed_key_type$, $value_enum_type$>\n"
+        "getMutable$capitalized_name$() {\n"
+        "  $on_changed$\n"
+        "  return new com.google.protobuf.Internal.MapAdapter<\n"
+        "      $boxed_key_type$, $value_enum_type$, java.lang.Integer>(\n"
+        "          $name$_.getMutableMap(), $name$ValueConverter);\n"
+        "}\n");
+    if (SupportUnknownEnumValue(descriptor_->file())) {
+      WriteFieldDocComment(printer, descriptor_);
+      printer->Print(
+          variables_,
+          "$deprecation$\n"
+          "public java.util.Map<$boxed_key_type$, $boxed_value_type$>\n"
+          "get$capitalized_name$Value() {\n"
+          "  return $name$_.getMap();\n"
+          "}\n");
+      WriteFieldDocComment(printer, descriptor_);
+      printer->Print(
+          variables_,
+          "$deprecation$\n"
+          "public java.util.Map<$boxed_key_type$, $boxed_value_type$>\n"
+          "getMutable$capitalized_name$Value() {\n"
+          "  $on_changed$\n"
+          "  return $name$_.getMutableMap();\n"
+          "}\n");
+    }
+  } else {
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(
+        variables_,
+        "public java.util.Map<$type_parameters$> get$capitalized_name$() {\n"
+        "  return $name$_.getMap();\n"
+        "}\n");
+    WriteFieldDocComment(printer, descriptor_);
+    printer->Print(
+        variables_,
+        "public java.util.Map<$type_parameters$>\n"
+        "getMutable$capitalized_name$() {\n"
+        "  $on_changed$\n"
+        "  return $name$_.getMutableMap();\n"
+        "}\n");
+  }
+}
+
+void ImmutableMapFieldGenerator::
+GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
+  // Nothing to initialize.
+}
+
+void ImmutableMapFieldGenerator::
+GenerateInitializationCode(io::Printer* printer) const {
+  // Nothing to initialize.
+}
+
+void ImmutableMapFieldGenerator::
+GenerateBuilderClearCode(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      "$name$_.clear();\n");
+}
+
+void ImmutableMapFieldGenerator::
+GenerateMergingCode(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      "$name$_.mergeFrom(other.$name$_);\n");
+}
+
+void ImmutableMapFieldGenerator::
+GenerateBuildingCode(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      // We do a copy of the map field to ensure that the built result is
+      // immutable. Implementation of this copy() method can do copy-on-write
+      // to defer this copy until further modifications are made on the field.
+      "result.$name$_ = $name$_.copy();\n");
+}
+
+void ImmutableMapFieldGenerator::
+GenerateParsingCode(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      "if (!$get_mutable_bit_parser$) {\n"
+      "  $name$_ = com.google.protobuf.MapField$lite$.newMapField(\n"
+      "      $map_field_parameter$);\n"
+      "  $set_mutable_bit_parser$;\n"
+      "}\n");
+  if (!SupportUnknownEnumValue(descriptor_->file()) &&
+      GetJavaType(ValueField(descriptor_)) == JAVATYPE_ENUM) {
+    printer->Print(
+        variables_,
+        "com.google.protobuf.ByteString bytes = input.readBytes();\n"
+        "com.google.protobuf.MapEntry$lite$<$type_parameters$>\n"
+        "$name$ = $name$DefaultEntry.getParserForType().parseFrom(bytes);\n");
+    printer->Print(
+        variables_,
+        "if ($value_enum_type$.valueOf($name$.getValue()) == null) {\n"
+        "  unknownFields.mergeLengthDelimitedField($number$, bytes);\n"
+        "} else {\n"
+        "  $name$_.getMutableMap().put($name$.getKey(), $name$.getValue());\n"
+        "}\n");
+  } else {
+    printer->Print(
+        variables_,
+        "com.google.protobuf.MapEntry$lite$<$type_parameters$>\n"
+        "$name$ = input.readMessage(\n"
+        "    $name$DefaultEntry.getParserForType(), extensionRegistry);\n"
+        "$name$_.getMutableMap().put($name$.getKey(), $name$.getValue());\n");
+  }
+}
+
+void ImmutableMapFieldGenerator::
+GenerateParsingDoneCode(io::Printer* printer) const {
+  // Nothing to do here.
+}
+
+void ImmutableMapFieldGenerator::
+GenerateSerializationCode(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      "for (java.util.Map.Entry<$type_parameters$> entry\n"
+      "     : $name$_.getMap().entrySet()) {\n"
+      "  com.google.protobuf.MapEntry$lite$<$type_parameters$>\n"
+      "  $name$ = $name$DefaultEntry.newBuilderForType()\n"
+      "      .setKey(entry.getKey())\n"
+      "      .setValue(entry.getValue())\n"
+      "      .build();\n"
+      "  output.writeMessage($number$, $name$);\n"
+      "}\n");
+}
+
+void ImmutableMapFieldGenerator::
+GenerateSerializedSizeCode(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      "for (java.util.Map.Entry<$type_parameters$> entry\n"
+      "     : $name$_.getMap().entrySet()) {\n"
+      "  com.google.protobuf.MapEntry$lite$<$type_parameters$>\n"
+      "  $name$ = $name$DefaultEntry.newBuilderForType()\n"
+      "      .setKey(entry.getKey())\n"
+      "      .setValue(entry.getValue())\n"
+      "      .build();\n"
+      "  size += com.google.protobuf.CodedOutputStream\n"
+      "      .computeMessageSize($number$, $name$);\n"
+      "}\n");
+}
+
+void ImmutableMapFieldGenerator::
+GenerateEqualsCode(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      "result = result && $name$_.equals(other.$name$_);\n");
+}
+
+void ImmutableMapFieldGenerator::
+GenerateHashCode(io::Printer* printer) const {
+  printer->Print(
+      variables_,
+      "if (!$name$_.getMap().isEmpty()) {\n"
+      "  hash = (37 * hash) + $constant_name$;\n"
+      "  hash = (53 * hash) + $name$_.hashCode();\n"
+      "}\n");
+}
+
+string ImmutableMapFieldGenerator::GetBoxedType() const {
+  return name_resolver_->GetImmutableClassName(descriptor_->message_type());
+}
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+}  // namespace google
diff --git a/src/google/protobuf/compiler/java/java_map_field.h b/src/google/protobuf/compiler/java/java_map_field.h
new file mode 100644
index 00000000..80a94f45
--- /dev/null
+++ b/src/google/protobuf/compiler/java/java_map_field.h
@@ -0,0 +1,82 @@
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef GOOGLE_PROTOBUF_COMPILER_JAVA_MAP_FIELD_H__
+#define GOOGLE_PROTOBUF_COMPILER_JAVA_MAP_FIELD_H__
+
+#include <google/protobuf/compiler/java/java_field.h>
+
+namespace google {
+namespace protobuf {
+namespace compiler {
+namespace java {
+
+class ImmutableMapFieldGenerator : public ImmutableFieldGenerator {
+ public:
+  explicit ImmutableMapFieldGenerator(
+      const FieldDescriptor* descriptor, int messageBitIndex,
+      int builderBitIndex, Context* context);
+  ~ImmutableMapFieldGenerator();
+
+  // implements ImmutableFieldGenerator ---------------------------------------
+  int GetNumBitsForMessage() const;
+  int GetNumBitsForBuilder() const;
+  void GenerateInterfaceMembers(io::Printer* printer) const;
+  void GenerateMembers(io::Printer* printer) const;
+  void GenerateBuilderMembers(io::Printer* printer) const;
+  void GenerateInitializationCode(io::Printer* printer) const;
+  void GenerateBuilderClearCode(io::Printer* printer) const;
+  void GenerateMergingCode(io::Printer* printer) const;
+  void GenerateBuildingCode(io::Printer* printer) const;
+  void GenerateParsingCode(io::Printer* printer) const;
+  void GenerateParsingDoneCode(io::Printer* printer) const;
+  void GenerateSerializationCode(io::Printer* printer) const;
+  void GenerateSerializedSizeCode(io::Printer* printer) const;
+  void GenerateFieldBuilderInitializationCode(io::Printer* printer) const;
+  void GenerateEqualsCode(io::Printer* printer) const;
+  void GenerateHashCode(io::Printer* printer) const;
+
+  string GetBoxedType() const;
+
+ private:
+  const FieldDescriptor* descriptor_;
+  map<string, string> variables_;
+  const int messageBitIndex_;
+  const int builderBitIndex_;
+  Context* context_;
+  ClassNameResolver* name_resolver_;
+};
+
+}  // namespace java
+}  // namespace compiler
+}  // namespace protobuf
+
+}  // namespace google
+#endif  // GOOGLE_PROTOBUF_COMPILER_JAVA_MAP_FIELD_H__
diff --git a/src/google/protobuf/compiler/java/java_message.cc b/src/google/protobuf/compiler/java/java_message.cc
index 8aa89ac7..dd1ad6a6 100644
--- a/src/google/protobuf/compiler/java/java_message.cc
+++ b/src/google/protobuf/compiler/java/java_message.cc
@@ -38,6 +38,9 @@
 #include <google/protobuf/stubs/hash.h>
 #include <map>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <vector>
 
 #include <google/protobuf/compiler/java/java_context.h>
@@ -264,60 +267,36 @@ void ImmutableMessageGenerator::Generate(io::Printer* printer) {
     descriptor_->containing_type() == NULL &&
     MultipleJavaFiles(descriptor_->file(), /* immutable = */ true);
 
+  map<string, string> variables;
+  variables["static"] = is_own_file ? " " : " static ";
+  variables["classname"] = descriptor_->name();
+  variables["extra_interfaces"] = ExtraMessageInterfaces(descriptor_);
+  variables["lite"] = HasDescriptorMethods(descriptor_) ? "" : "Lite";
+
   WriteMessageDocComment(printer, descriptor_);
 
   // The builder_type stores the super type name of the nested Builder class.
   string builder_type;
   if (descriptor_->extension_range_count() > 0) {
-    if (HasDescriptorMethods(descriptor_)) {
-      printer->Print(
-        "public$static$final class $classname$ extends\n"
-        "    com.google.protobuf.GeneratedMessage.ExtendableMessage<\n"
-        "      $classname$> implements\n"
-        "    $extra_interfaces$\n"
-        "    $classname$OrBuilder {\n",
-        "static", is_own_file ? " " : " static ",
-        "classname", descriptor_->name(),
-        "extra_interfaces", ExtraMessageInterfaces(descriptor_));
-      builder_type = strings::Substitute(
-          "com.google.protobuf.GeneratedMessage.ExtendableBuilder<$0, ?>",
-          name_resolver_->GetImmutableClassName(descriptor_));
-    } else {
-      printer->Print(
-        "public$static$final class $classname$ extends\n"
-        "    com.google.protobuf.GeneratedMessageLite.ExtendableMessage<\n"
-        "      $classname$> implements\n"
-        "    $extra_interfaces$\n"
-        "    $classname$OrBuilder {\n",
-        "static", is_own_file ? " " : " static ",
-        "classname", descriptor_->name(),
-        "extra_interfaces", ExtraMessageInterfaces(descriptor_));
-      builder_type = strings::Substitute(
-          "com.google.protobuf.GeneratedMessageLite.ExtendableBuilder<$0, ?>",
-          name_resolver_->GetImmutableClassName(descriptor_));
-    }
+    printer->Print(variables,
+      "public $static$final class $classname$ extends\n"
+      "    com.google.protobuf.GeneratedMessage$lite$.ExtendableMessage<\n"
+      "      $classname$> implements\n"
+      "    $extra_interfaces$\n"
+      "    $classname$OrBuilder {\n");
+    builder_type = strings::Substitute(
+        "com.google.protobuf.GeneratedMessage$1.ExtendableBuilder<$0, ?>",
+        name_resolver_->GetImmutableClassName(descriptor_),
+        variables["lite"]);
   } else {
-    if (HasDescriptorMethods(descriptor_)) {
-      printer->Print(
-        "public$static$final class $classname$ extends\n"
-        "    com.google.protobuf.GeneratedMessage implements\n"
-        "    $extra_interfaces$\n"
-        "    $classname$OrBuilder {\n",
-        "static", is_own_file ? " " : " static ",
-        "classname", descriptor_->name(),
-        "extra_interfaces", ExtraMessageInterfaces(descriptor_));
-      builder_type = "com.google.protobuf.GeneratedMessage.Builder<?>";
-    } else {
-      printer->Print(
-        "public$static$final class $classname$ extends\n"
-        "    com.google.protobuf.GeneratedMessageLite implements\n"
-        "    $extra_interfaces$\n"
-        "    $classname$OrBuilder {\n",
-        "static", is_own_file ? " " : " static ",
-        "classname", descriptor_->name(),
-        "extra_interfaces", ExtraMessageInterfaces(descriptor_));
-      builder_type = "com.google.protobuf.GeneratedMessageLite.Builder";
-    }
+    printer->Print(variables,
+      "public $static$final class $classname$ extends\n"
+      "    com.google.protobuf.GeneratedMessage$lite$ implements\n"
+      "    $extra_interfaces$\n"
+      "    $classname$OrBuilder {\n");
+    builder_type = strings::Substitute(
+        "com.google.protobuf.GeneratedMessage$0.Builder",
+        variables["lite"]);
   }
   printer->Indent();
   // Using builder_type, instead of Builder, prevents the Builder class from
@@ -328,16 +307,22 @@ void ImmutableMessageGenerator::Generate(io::Printer* printer) {
     "// Use $classname$.newBuilder() to construct.\n"
     "private $classname$($buildertype$ builder) {\n"
     "  super(builder);\n"
-    "$set_unknown_fields$\n"
     "}\n",
     "classname", descriptor_->name(),
-    "buildertype", builder_type,
-    "set_unknown_fields",
-    "  this.unknownFields = builder.getUnknownFields();");
+    "buildertype", builder_type);
   printer->Print(
-    // Used when constructing the default instance, which cannot be initialized
-    // immediately because it may cyclically refer to other default instances.
-    "private $classname$(boolean noInit) {$set_default_unknown_fields$}\n"
+    "private $classname$() {\n",
+    "classname", descriptor_->name());
+  printer->Indent();
+  for (int i = 0; i < descriptor_->field_count(); i++) {
+    if (!descriptor_->field(i)->containing_oneof()) {
+      field_generators_.get(descriptor_->field(i))
+          .GenerateInitializationCode(printer);
+    }
+  }
+  printer->Outdent();
+  printer->Print(
+    "}\n"
     "\n"
     "private static final $classname$ defaultInstance;\n"
     "public static $classname$ getDefaultInstance() {\n"
@@ -349,23 +334,22 @@ void ImmutableMessageGenerator::Generate(io::Printer* printer) {
     "}\n"
     "\n",
     "classname", descriptor_->name(),
-    "set_default_unknown_fields", UseUnknownFieldSet(descriptor_)
-        ? " this.unknownFields ="
-          " com.google.protobuf.UnknownFieldSet.getDefaultInstance(); "
-        : " this.unknownFields = com.google.protobuf.ByteString.EMPTY;");
+    "lite", variables["lite"]);
 
-  if (UseUnknownFieldSet(descriptor_)) {
+  if (HasDescriptorMethods(descriptor_)) {
     printer->Print(
-        "private final com.google.protobuf.UnknownFieldSet unknownFields;\n"
-        ""
-        "@java.lang.Override\n"
-        "public final com.google.protobuf.UnknownFieldSet\n"
-        "    getUnknownFields() {\n"
-        "  return this.unknownFields;\n"
-        "}\n");
-  } else {
+      "@java.lang.Override\n"
+      "public final com.google.protobuf.UnknownFieldSet\n"
+      "getUnknownFields() {\n");
+    if (PreserveUnknownFields(descriptor_)) {
+      printer->Print(
+        "  return this.unknownFields;\n");
+    } else {
+      printer->Print(
+        "  return com.google.protobuf.UnknownFieldSet.getDefaultInstance();\n");
+    }
     printer->Print(
-        "private final com.google.protobuf.ByteString unknownFields;\n");
+      "}\n");
   }
 
   if (HasGeneratedMethods(descriptor_)) {
@@ -382,6 +366,8 @@ void ImmutableMessageGenerator::Generate(io::Printer* printer) {
   }
 
   for (int i = 0; i < descriptor_->nested_type_count(); i++) {
+    // Don't generate Java classes for map entry messages.
+    if (IsMapEntry(descriptor_->nested_type(i))) continue;
     ImmutableMessageGenerator messageGenerator(
         descriptor_->nested_type(i), context_);
     messageGenerator.GenerateInterface(printer);
@@ -480,20 +466,6 @@ void ImmutableMessageGenerator::Generate(io::Printer* printer) {
     printer->Print("\n");
   }
 
-  // Called by the constructor, except in the case of the default instance,
-  // in which case this is called by static init code later on.
-  printer->Print("private void initFields() {\n");
-  printer->Indent();
-  for (int i = 0; i < descriptor_->field_count(); i++) {
-    if (!descriptor_->field(i)->containing_oneof()) {
-      field_generators_.get(descriptor_->field(i))
-          .GenerateInitializationCode(printer);
-    }
-  }
-
-  printer->Outdent();
-  printer->Print("}\n");
-
   if (HasGeneratedMethods(descriptor_)) {
     GenerateIsInitialized(printer, MEMOIZE);
     GenerateMessageSerializationMethods(printer);
@@ -512,8 +484,7 @@ void ImmutableMessageGenerator::Generate(io::Printer* printer) {
   printer->Print(
     "\n"
     "static {\n"
-    "  defaultInstance = new $classname$(true);\n"
-    "  defaultInstance.initFields();\n"
+    "  defaultInstance = new $classname$();\n"
     "}\n"
     "\n"
     "// @@protoc_insertion_point(class_scope:$full_name$)\n",
@@ -593,17 +564,15 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
     }
   }
 
-  if (UseUnknownFieldSet(descriptor_)) {
-    if (descriptor_->options().message_set_wire_format()) {
+  if (PreserveUnknownFields(descriptor_)) {
+    if (descriptor_->options().message_set_wire_format()
+        && HasDescriptorMethods(descriptor_)) {
       printer->Print(
-        "getUnknownFields().writeAsMessageSetTo(output);\n");
+        "unknownFields.writeAsMessageSetTo(output);\n");
     } else {
       printer->Print(
-        "getUnknownFields().writeTo(output);\n");
+        "unknownFields.writeTo(output);\n");
     }
-  } else {
-    printer->Print(
-      "output.writeRawBytes(unknownFields);\n");
   }
 
   printer->Outdent();
@@ -632,17 +601,15 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
     }
   }
 
-  if (UseUnknownFieldSet(descriptor_)) {
-    if (descriptor_->options().message_set_wire_format()) {
+  if (PreserveUnknownFields(descriptor_)) {
+    if (descriptor_->options().message_set_wire_format()
+        && HasDescriptorMethods(descriptor_)) {
       printer->Print(
-        "size += getUnknownFields().getSerializedSizeAsMessageSet();\n");
+        "size += unknownFields.getSerializedSizeAsMessageSet();\n");
     } else {
       printer->Print(
-        "size += getUnknownFields().getSerializedSize();\n");
+        "size += unknownFields.getSerializedSize();\n");
     }
-  } else {
-    printer->Print(
-      "size += unknownFields.size();\n");
   }
 
   printer->Outdent();
@@ -653,13 +620,7 @@ GenerateMessageSerializationMethods(io::Printer* printer) {
     "\n");
 
   printer->Print(
-    "private static final long serialVersionUID = 0L;\n"
-    "@java.lang.Override\n"
-    "protected java.lang.Object writeReplace()\n"
-    "    throws java.io.ObjectStreamException {\n"
-    "  return super.writeReplace();\n"
-    "}\n"
-    "\n");
+    "private static final long serialVersionUID = 0L;\n");
 }
 
 void ImmutableMessageGenerator::
@@ -740,7 +701,7 @@ void ImmutableMessageGenerator::GenerateSerializeOneExtensionRange(
 
 void ImmutableMessageGenerator::GenerateBuilder(io::Printer* printer) {
   printer->Print(
-    "public static Builder newBuilder() { return Builder.create(); }\n"
+    "public static Builder newBuilder() { return new Builder(); }\n"
     "public Builder newBuilderForType() { return newBuilder(); }\n"
     "public static Builder newBuilder($classname$ prototype) {\n"
     "  return newBuilder().mergeFrom(prototype);\n"
@@ -809,7 +770,6 @@ void ImmutableMessageGenerator::GenerateBuilder(io::Printer* printer) {
 
   if (HasGeneratedMethods(descriptor_)) {
     GenerateIsInitialized(printer, DONT_MEMOIZE);
-    GenerateBuilderParsingMethods(printer);
   }
 
   // oneof
@@ -864,6 +824,20 @@ void ImmutableMessageGenerator::GenerateBuilder(io::Printer* printer) {
                      .GenerateBuilderMembers(printer);
   }
 
+  if (!PreserveUnknownFields(descriptor_)) {
+    printer->Print(
+      "public final Builder setUnknownFields(\n"
+      "    final com.google.protobuf.UnknownFieldSet unknownFields) {\n"
+      "  return this;\n"
+      "}\n"
+      "\n"
+      "public final Builder mergeUnknownFields(\n"
+      "    final com.google.protobuf.UnknownFieldSet unknownFields) {\n"
+      "  return this;\n"
+      "}\n"
+      "\n");
+  }
+
   printer->Print(
     "\n"
     "// @@protoc_insertion_point(builder_scope:$full_name$)\n",
@@ -886,6 +860,41 @@ GenerateDescriptorMethods(io::Printer* printer) {
         "fileclass", name_resolver_->GetImmutableClassName(descriptor_->file()),
         "identifier", UniqueFileScopeIdentifier(descriptor_));
     }
+    vector<const FieldDescriptor*> map_fields;
+    for (int i = 0; i < descriptor_->field_count(); i++) {
+      const FieldDescriptor* field = descriptor_->field(i);
+      if (GetJavaType(field) == JAVATYPE_MESSAGE &&
+          IsMapEntry(field->message_type())) {
+        map_fields.push_back(field);
+      }
+    }
+    if (!map_fields.empty()) {
+      printer->Print(
+        "@SuppressWarnings({\"rawtypes\"})\n"
+        "protected com.google.protobuf.MapField internalGetMapField(\n"
+        "    int number) {\n"
+        "  switch (number) {\n");
+      printer->Indent();
+      printer->Indent();
+      for (int i = 0; i < map_fields.size(); ++i) {
+        const FieldDescriptor* field = map_fields[i];
+        const FieldGeneratorInfo* info = context_->GetFieldGeneratorInfo(field);
+        printer->Print(
+          "case $number$:\n"
+          "  return $name$_;\n",
+          "number", SimpleItoa(field->number()),
+          "name", info->name);
+      }
+      printer->Print(
+          "default:\n"
+          "  throw new RuntimeException(\n"
+          "      \"Invalid map field number: \" + number);\n");
+      printer->Outdent();
+      printer->Outdent();
+      printer->Print(
+          "  }\n"
+          "}\n");
+    }
     printer->Print(
       "protected com.google.protobuf.GeneratedMessage.FieldAccessorTable\n"
       "    internalGetFieldAccessorTable() {\n"
@@ -949,13 +958,8 @@ GenerateCommonBuilderMethods(io::Printer* printer) {
   }
 
   printer->Print(
-    "private static Builder create() {\n"
-    "  return new Builder();\n"
-    "}\n"
-    "\n"
     "public Builder clear() {\n"
-    "  super.clear();\n",
-    "classname", name_resolver_->GetImmutableClassName(descriptor_));
+    "  super.clear();\n");
 
   printer->Indent();
 
@@ -979,12 +983,8 @@ GenerateCommonBuilderMethods(io::Printer* printer) {
   printer->Print(
     "  return this;\n"
     "}\n"
-    "\n"
-    "public Builder clone() {\n"
-    "  return create().mergeFrom(buildPartial());\n"
-    "}\n"
-    "\n",
-    "classname", name_resolver_->GetImmutableClassName(descriptor_));
+    "\n");
+
   if (HasDescriptorMethods(descriptor_)) {
     printer->Print(
       "public com.google.protobuf.Descriptors.Descriptor\n"
@@ -1153,13 +1153,13 @@ GenerateCommonBuilderMethods(io::Printer* printer) {
         "  this.mergeExtensionFields(other);\n");
     }
 
-    if (UseUnknownFieldSet(descriptor_)) {
+    if (PreserveUnknownFields(descriptor_)) {
       printer->Print(
-        "  this.mergeUnknownFields(other.getUnknownFields());\n");
-    } else {
-      printer->Print(
-        "  setUnknownFields(\n"
-        "      getUnknownFields().concat(other.unknownFields));\n");
+        "  this.mergeUnknownFields(other.unknownFields);\n");
+    }
+
+    if (HasDescriptorMethods(descriptor_)) {
+      printer->Print("  onChanged();\n");
     }
 
     printer->Print(
@@ -1171,31 +1171,6 @@ GenerateCommonBuilderMethods(io::Printer* printer) {
 
 // ===================================================================
 
-void ImmutableMessageGenerator::
-GenerateBuilderParsingMethods(io::Printer* printer) {
-  printer->Print(
-    "public Builder mergeFrom(\n"
-    "    com.google.protobuf.CodedInputStream input,\n"
-    "    com.google.protobuf.ExtensionRegistryLite extensionRegistry)\n"
-    "    throws java.io.IOException {\n"
-    "  $classname$ parsedMessage = null;\n"
-    "  try {\n"
-    "    parsedMessage = PARSER.parsePartialFrom(input, extensionRegistry);\n"
-    "  } catch (com.google.protobuf.InvalidProtocolBufferException e) {\n"
-    "    parsedMessage = ($classname$) e.getUnfinishedMessage();\n"
-    "    throw e;\n"
-    "  } finally {\n"
-    "    if (parsedMessage != null) {\n"
-    "      mergeFrom(parsedMessage);\n"
-    "    }\n"
-    "  }\n"
-    "  return this;\n"
-    "}\n",
-    "classname", name_resolver_->GetImmutableClassName(descriptor_));
-}
-
-// ===================================================================
-
 void ImmutableMessageGenerator::GenerateIsInitialized(
     io::Printer* printer, UseMemoization useMemoization) {
   bool memoization = useMemoization == MEMOIZE;
@@ -1256,15 +1231,26 @@ void ImmutableMessageGenerator::GenerateIsInitialized(
             "memoize", memoization ? "memoizedIsInitialized = 0;" : "");
           break;
         case FieldDescriptor::LABEL_OPTIONAL:
+          if (!SupportFieldPresence(descriptor_->file()) &&
+              field->containing_oneof() != NULL) {
+            const OneofDescriptor* oneof = field->containing_oneof();
+            const OneofGeneratorInfo* oneof_info =
+                context_->GetOneofGeneratorInfo(oneof);
+            printer->Print(
+              "if ($oneof_name$Case_ == $field_number$) {\n",
+              "oneof_name", oneof_info->name,
+              "field_number", SimpleItoa(field->number()));
+          } else {
+            printer->Print(
+              "if (has$name$()) {\n",
+              "name", info->capitalized_name);
+          }
           printer->Print(
-            "if (has$name$()) {\n"
             "  if (!get$name$().isInitialized()) {\n"
             "    $memoize$\n"
             "    return false;\n"
             "  }\n"
             "}\n",
-            "type", name_resolver_->GetImmutableClassName(
-                field->message_type()),
             "name", info->capitalized_name,
             "memoize", memoization ? "memoizedIsInitialized = 0;" : "");
           break;
@@ -1358,10 +1344,14 @@ GenerateEqualsAndHashCode(io::Printer* printer) {
         "}\n");
     }
   }
-  if (HasDescriptorMethods(descriptor_)) {
+  if (PreserveUnknownFields(descriptor_)) {
+    // Always consider unknown fields for equality. This will sometimes return
+    // false for non-canonical ordering when running in LITE_RUNTIME but it's
+    // the best we can do.
     printer->Print(
-      "result = result &&\n"
-      "    getUnknownFields().equals(other.getUnknownFields());\n");
+      "result = result && unknownFields.equals(other.unknownFields);\n");
+  }
+  if (HasDescriptorMethods(descriptor_)) {
     if (descriptor_->extension_range_count() > 0) {
       printer->Print(
         "result = result &&\n"
@@ -1421,13 +1411,8 @@ GenerateEqualsAndHashCode(io::Printer* printer) {
     }
   }
 
-  if (UseUnknownFieldSet(descriptor_)) {
-    printer->Print(
-      "hash = (29 * hash) + getUnknownFields().hashCode();\n");
-  } else {
-    printer->Print(
-      "hash = (29 * hash) + unknownFields.hashCode();\n");
-  }
+  printer->Print(
+    "hash = (29 * hash) + unknownFields.hashCode();\n");
   printer->Print(
     "memoizedHashCode = hash;\n"
     "return hash;\n");
@@ -1468,7 +1453,7 @@ GenerateParsingConstructor(io::Printer* printer) {
 
   // Initialize all fields to default.
   printer->Print(
-      "initFields();\n");
+      "this();\n");
 
   // Use builder bits to track mutable repeated fields.
   int totalBuilderBits = 0;
@@ -1483,17 +1468,16 @@ GenerateParsingConstructor(io::Printer* printer) {
       "bit_field_name", GetBitFieldName(i));
   }
 
-  if (UseUnknownFieldSet(descriptor_)) {
-    printer->Print(
-      "com.google.protobuf.UnknownFieldSet.Builder unknownFields =\n"
-      "    com.google.protobuf.UnknownFieldSet.newBuilder();\n");
-  } else {
-    printer->Print(
-      "com.google.protobuf.ByteString.Output unknownFieldsOutput =\n"
-      "    com.google.protobuf.ByteString.newOutput();\n"
-      "com.google.protobuf.CodedOutputStream unknownFieldsCodedOutput =\n"
-      "    com.google.protobuf.CodedOutputStream.newInstance(\n"
-      "        unknownFieldsOutput);\n");
+  if (PreserveUnknownFields(descriptor_)) {
+    if (HasDescriptorMethods(descriptor_)) {
+      printer->Print(
+        "com.google.protobuf.UnknownFieldSet.Builder unknownFields =\n"
+        "    com.google.protobuf.UnknownFieldSet.newBuilder();\n");
+    } else {
+      printer->Print(
+        "com.google.protobuf.UnknownFieldSetLite.Builder unknownFields =\n"
+        "    com.google.protobuf.UnknownFieldSetLite.newBuilder();\n");
+    }
   }
 
   printer->Print(
@@ -1513,16 +1497,41 @@ GenerateParsingConstructor(io::Printer* printer) {
   printer->Print(
     "case 0:\n"          // zero signals EOF / limit reached
     "  done = true;\n"
-    "  break;\n"
-    "default: {\n"
-    "  if (!parseUnknownField(input,$unknown_fields$\n"
-    "                         extensionRegistry, tag)) {\n"
-    "    done = true;\n"  // it's an endgroup tag
-    "  }\n"
-    "  break;\n"
-    "}\n",
-    "unknown_fields", UseUnknownFieldSet(descriptor_)
-        ? " unknownFields," : " unknownFieldsCodedOutput,");
+    "  break;\n");
+
+  if (PreserveUnknownFields(descriptor_)) {
+    if (!HasDescriptorMethods(descriptor_)
+        && descriptor_->extension_range_count() > 0) {
+      // Lite runtime directly invokes parseUnknownField to reduce method
+      // counts.
+      printer->Print(
+        "default: {\n"
+        "  if (!parseUnknownField(extensions, getDefaultInstanceForType(),\n"
+        "                         input, unknownFields,\n"
+        "                         extensionRegistry, tag)) {\n"
+        "    done = true;\n"  // it's an endgroup tag
+        "  }\n"
+        "  break;\n"
+        "}\n");
+    } else {
+      printer->Print(
+        "default: {\n"
+        "  if (!parseUnknownField(input, unknownFields,\n"
+        "                         extensionRegistry, tag)) {\n"
+        "    done = true;\n"  // it's an endgroup tag
+        "  }\n"
+        "  break;\n"
+        "}\n");
+    }
+  } else {
+    printer->Print(
+      "default: {\n"
+      "  if (!input.skipField(tag)) {\n"
+      "    done = true;\n"  // it's an endgroup tag
+      "  }\n"
+      "  break;\n"
+      "}\n");
+  }
 
   for (int i = 0; i < descriptor_->field_count(); i++) {
     const FieldDescriptor* field = sorted_fields[i];
@@ -1582,19 +1591,9 @@ GenerateParsingConstructor(io::Printer* printer) {
     field_generators_.get(field).GenerateParsingDoneCode(printer);
   }
 
-  // Make unknown fields immutable.
-  if (UseUnknownFieldSet(descriptor_)) {
-    printer->Print(
-        "this.unknownFields = unknownFields.build();\n");
-  } else {
-    printer->Print(
-        "try {\n"
-        "  unknownFieldsCodedOutput.flush();\n"
-        "} catch (java.io.IOException e) {\n"
-        "// Should not happen\n"
-        "} finally {\n"
-        "  unknownFields = unknownFieldsOutput.toByteString();\n"
-        "}\n");
+  if (PreserveUnknownFields(descriptor_)) {
+    // Make unknown fields immutable.
+    printer->Print("this.unknownFields = unknownFields.build();\n");
   }
 
   // Make extensions immutable.
@@ -1611,7 +1610,7 @@ GenerateParsingConstructor(io::Printer* printer) {
 // ===================================================================
 void ImmutableMessageGenerator::GenerateParser(io::Printer* printer) {
   printer->Print(
-      "public static com.google.protobuf.Parser<$classname$> PARSER =\n"
+      "public static final com.google.protobuf.Parser<$classname$> PARSER =\n"
       "    new com.google.protobuf.AbstractParser<$classname$>() {\n",
       "classname", descriptor_->name());
   printer->Indent();
diff --git a/src/google/protobuf/compiler/java/java_message.h b/src/google/protobuf/compiler/java/java_message.h
index fece1c21..2703016e 100644
--- a/src/google/protobuf/compiler/java/java_message.h
+++ b/src/google/protobuf/compiler/java/java_message.h
@@ -118,7 +118,6 @@ class ImmutableMessageGenerator : public MessageGenerator {
   void GenerateBuilder(io::Printer* printer);
   void GenerateCommonBuilderMethods(io::Printer* printer);
   void GenerateDescriptorMethods(io::Printer* printer);
-  void GenerateBuilderParsingMethods(io::Printer* printer);
   void GenerateIsInitialized(io::Printer* printer,
       UseMemoization useMemoization);
   void GenerateEqualsAndHashCode(io::Printer* printer);
diff --git a/src/google/protobuf/compiler/java/java_message_field.cc b/src/google/protobuf/compiler/java/java_message_field.cc
index e681314e..538f1248 100644
--- a/src/google/protobuf/compiler/java/java_message_field.cc
+++ b/src/google/protobuf/compiler/java/java_message_field.cc
@@ -179,7 +179,7 @@ GenerateMembers(io::Printer* printer) const {
     WriteFieldDocComment(printer, descriptor_);
     printer->Print(variables_,
       "$deprecation$public $type$ get$capitalized_name$() {\n"
-      "  return $name$_;\n"
+      "  return $name$_ == null ? $type$.getDefaultInstance() : $name$_;\n"
       "}\n");
 
     if (HasNestedBuilders(descriptor_->containing_type())) {
@@ -187,7 +187,7 @@ GenerateMembers(io::Printer* printer) const {
       printer->Print(variables_,
         "$deprecation$public $type$OrBuilder "
         "get$capitalized_name$OrBuilder() {\n"
-        "  return $name$_;\n"
+        "  return $name$_ == null ? $type$.getDefaultInstance() : $name$_;\n"
         "}\n");
     }
   } else {
@@ -257,14 +257,8 @@ GenerateBuilderMembers(io::Printer* printer) const {
 
   bool support_field_presence = SupportFieldPresence(descriptor_->file());
 
-  if (support_field_presence) {
-    printer->Print(variables_,
-      // Used when the builder is null.
-      "private $type$ $name$_ = $type$.getDefaultInstance();\n");
-  } else {
-    printer->Print(variables_,
-      "private $type$ $name$_ = null;\n");
-  }
+  printer->Print(variables_,
+    "private $type$ $name$_ = null;\n");
 
   if (HasNestedBuilders(descriptor_->containing_type())) {
     printer->Print(variables_,
@@ -296,13 +290,8 @@ GenerateBuilderMembers(io::Printer* printer) const {
   WriteFieldDocComment(printer, descriptor_);
   PrintNestedBuilderFunction(printer,
     "$deprecation$public $type$ get$capitalized_name$()",
-
-    support_field_presence
-        ?  "return $name$_;\n"
-        : "return $name$_ == null ? $type$.getDefaultInstance() : $name$_;\n",
-
+    "return $name$_ == null ? $type$.getDefaultInstance() : $name$_;\n",
     "return $name$Builder_.getMessage();\n",
-
     NULL);
 
   // Field.Builder setField(Field value)
@@ -342,6 +331,7 @@ GenerateBuilderMembers(io::Printer* printer) const {
 
     support_field_presence
         ? "if ($get_has_field_bit_builder$ &&\n"
+          "    $name$_ != null &&\n"
           "    $name$_ != $type$.getDefaultInstance()) {\n"
           "  $name$_ =\n"
           "    $type$.newBuilder($name$_).mergeFrom(value).buildPartial();\n"
@@ -367,11 +357,8 @@ GenerateBuilderMembers(io::Printer* printer) const {
   PrintNestedBuilderFunction(printer,
     "$deprecation$public Builder clear$capitalized_name$()",
 
-    support_field_presence
-        ? "$name$_ = $type$.getDefaultInstance();\n"
-          "$on_changed$\n"
-        : "$name$_ = null;\n"
-          "$on_changed$\n",
+    "$name$_ = null;\n"
+    "$on_changed$\n",
 
     support_field_presence
         ? "$name$Builder_.clear();\n"
@@ -394,16 +381,9 @@ GenerateBuilderMembers(io::Printer* printer) const {
       "$deprecation$public $type$OrBuilder get$capitalized_name$OrBuilder() {\n"
       "  if ($name$Builder_ != null) {\n"
       "    return $name$Builder_.getMessageOrBuilder();\n"
-      "  } else {\n");
-    if (support_field_presence) {
-      printer->Print(variables_,
-        "    return $name$_;\n");
-    } else {
-      printer->Print(variables_,
-        "    return $name$_ == null ?\n"
-        "        $type$.getDefaultInstance() : $name$_;\n");
-    }
-    printer->Print(variables_,
+      "  } else {\n"
+      "    return $name$_ == null ?\n"
+      "        $type$.getDefaultInstance() : $name$_;\n"
       "  }\n"
       "}\n");
     WriteFieldDocComment(printer, descriptor_);
@@ -434,17 +414,13 @@ GenerateFieldBuilderInitializationCode(io::Printer* printer)  const {
 
 
 void ImmutableMessageFieldGenerator::
-GenerateInitializationCode(io::Printer* printer) const {
-  if (SupportFieldPresence(descriptor_->file())) {
-    printer->Print(variables_, "$name$_ = $type$.getDefaultInstance();\n");
-  }
-}
+GenerateInitializationCode(io::Printer* printer) const {}
 
 void ImmutableMessageFieldGenerator::
 GenerateBuilderClearCode(io::Printer* printer) const {
   if (SupportFieldPresence(descriptor_->file())) {
     PrintNestedBuilderCondition(printer,
-      "$name$_ = $type$.getDefaultInstance();\n",
+      "$name$_ = null;\n",
 
       "$name$Builder_.clear();\n");
     printer->Print(variables_, "$clear_has_field_bit_builder$\n");
@@ -514,7 +490,7 @@ void ImmutableMessageFieldGenerator::
 GenerateSerializationCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if ($is_field_present_message$) {\n"
-    "  output.write$group_or_message$($number$, $name$_);\n"
+    "  output.write$group_or_message$($number$, get$capitalized_name$());\n"
     "}\n");
 }
 
@@ -523,7 +499,7 @@ GenerateSerializedSizeCode(io::Printer* printer) const {
   printer->Print(variables_,
     "if ($is_field_present_message$) {\n"
     "  size += com.google.protobuf.CodedOutputStream\n"
-    "    .compute$group_or_message$Size($number$, $name$_);\n"
+    "    .compute$group_or_message$Size($number$, get$capitalized_name$());\n"
     "}\n");
 }
 
diff --git a/src/google/protobuf/compiler/java/java_plugin_unittest.cc b/src/google/protobuf/compiler/java/java_plugin_unittest.cc
index c4d6995d..45aa8ffe 100644
--- a/src/google/protobuf/compiler/java/java_plugin_unittest.cc
+++ b/src/google/protobuf/compiler/java/java_plugin_unittest.cc
@@ -35,6 +35,9 @@
 //   worth.
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/compiler/java/java_generator.h>
 #include <google/protobuf/compiler/command_line_interface.h>
diff --git a/src/google/protobuf/compiler/java/java_primitive_field.cc b/src/google/protobuf/compiler/java/java_primitive_field.cc
index 6713d29a..e331d7a4 100644
--- a/src/google/protobuf/compiler/java/java_primitive_field.cc
+++ b/src/google/protobuf/compiler/java/java_primitive_field.cc
@@ -55,26 +55,6 @@ using internal::WireFormatLite;
 
 namespace {
 
-const char* PrimitiveTypeName(JavaType type) {
-  switch (type) {
-    case JAVATYPE_INT    : return "int";
-    case JAVATYPE_LONG   : return "long";
-    case JAVATYPE_FLOAT  : return "float";
-    case JAVATYPE_DOUBLE : return "double";
-    case JAVATYPE_BOOLEAN: return "boolean";
-    case JAVATYPE_STRING : return "java.lang.String";
-    case JAVATYPE_BYTES  : return "com.google.protobuf.ByteString";
-    case JAVATYPE_ENUM   : return NULL;
-    case JAVATYPE_MESSAGE: return NULL;
-
-    // No default because we want the compiler to complain if any new
-    // JavaTypes are added.
-  }
-
-  GOOGLE_LOG(FATAL) << "Can't get here.";
-  return NULL;
-}
-
 void SetPrimitiveVariables(const FieldDescriptor* descriptor,
                            int messageBitIndex,
                            int builderBitIndex,
diff --git a/src/google/protobuf/compiler/java/java_shared_code_generator.cc b/src/google/protobuf/compiler/java/java_shared_code_generator.cc
index ea77f792..f8723f2a 100644
--- a/src/google/protobuf/compiler/java/java_shared_code_generator.cc
+++ b/src/google/protobuf/compiler/java/java_shared_code_generator.cc
@@ -33,6 +33,9 @@
 #include <google/protobuf/compiler/java/java_shared_code_generator.h>
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/compiler/java/java_helpers.h>
 #include <google/protobuf/compiler/java/java_name_resolver.h>
@@ -176,7 +179,8 @@ void SharedCodeGenerator::GenerateDescriptors(io::Printer* printer) {
   // Invoke internalBuildGeneratedFileFrom() to build the file.
   printer->Print(
     "com.google.protobuf.Descriptors.FileDescriptor\n"
-    "  .internalBuildGeneratedFileFrom(descriptorData,\n"
+    "  .internalBuildGeneratedFileFrom(descriptorData,\n");
+  printer->Print(
     "    new com.google.protobuf.Descriptors.FileDescriptor[] {\n");
 
   for (int i = 0; i < dependencies.size(); i++) {
diff --git a/src/google/protobuf/compiler/java/java_shared_code_generator.h b/src/google/protobuf/compiler/java/java_shared_code_generator.h
index 1bb2f3dc..fdbe2ce8 100644
--- a/src/google/protobuf/compiler/java/java_shared_code_generator.h
+++ b/src/google/protobuf/compiler/java/java_shared_code_generator.h
@@ -36,6 +36,9 @@
 #define GOOGLE_PROTOBUF_COMPILER_JAVA_SHARED_CODE_GENERATOR_H__
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <string>
 #include <vector>
 
@@ -68,6 +71,7 @@ class SharedCodeGenerator {
 
   void Generate(GeneratorContext* generator_context,
                 vector<string>* file_list);
+
   void GenerateDescriptors(io::Printer* printer);
 
  private:
diff --git a/src/google/protobuf/compiler/java/java_string_field.cc b/src/google/protobuf/compiler/java/java_string_field.cc
index 8889a744..1c9302af 100644
--- a/src/google/protobuf/compiler/java/java_string_field.cc
+++ b/src/google/protobuf/compiler/java/java_string_field.cc
@@ -407,6 +407,15 @@ GenerateParsingCode(io::Printer* printer) const {
       "String s = input.readStringRequireUtf8();\n"
       "$set_has_field_bit_message$\n"
       "$name$_ = s;\n");
+  } else if (!HasDescriptorMethods(descriptor_->file())) {
+    // Lite runtime should attempt to reduce allocations by attempting to
+    // construct the string directly from the input stream buffer. This avoids
+    // spurious intermediary ByteString allocations, cutting overall allocations
+    // in half.
+    printer->Print(variables_,
+      "String s = input.readString();\n"
+      "$set_has_field_bit_message$\n"
+      "$name$_ = s;\n");
   } else {
     printer->Print(variables_,
       "com.google.protobuf.ByteString bs = input.readBytes();\n"
@@ -659,6 +668,15 @@ GenerateParsingCode(io::Printer* printer) const {
       "String s = input.readStringRequireUtf8();\n"
       "$set_oneof_case_message$;\n"
       "$oneof_name$_ = s;\n}\n");
+  } else if (!HasDescriptorMethods(descriptor_->file())) {
+    // Lite runtime should attempt to reduce allocations by attempting to
+    // construct the string directly from the input stream buffer. This avoids
+    // spurious intermediary ByteString allocations, cutting overall allocations
+    // in half.
+    printer->Print(variables_,
+      "String s = input.readString();\n"
+      "$set_oneof_case_message$;\n"
+      "$oneof_name$_ = s;\n");
   } else {
     printer->Print(variables_,
       "com.google.protobuf.ByteString bs = input.readBytes();\n"
@@ -923,6 +941,13 @@ GenerateParsingCode(io::Printer* printer) const {
   if (CheckUtf8(descriptor_)) {
     printer->Print(variables_,
     "String s = input.readStringRequireUtf8();\n");
+  } else if (!HasDescriptorMethods(descriptor_->file())) {
+    // Lite runtime should attempt to reduce allocations by attempting to
+    // construct the string directly from the input stream buffer. This avoids
+    // spurious intermediary ByteString allocations, cutting overall allocations
+    // in half.
+    printer->Print(variables_,
+    "String s = input.readString();\n");
   } else {
     printer->Print(variables_,
     "com.google.protobuf.ByteString bs = input.readBytes();\n");
@@ -932,7 +957,7 @@ GenerateParsingCode(io::Printer* printer) const {
     "  $name$_ = new com.google.protobuf.LazyStringArrayList();\n"
     "  $set_mutable_bit_parser$;\n"
     "}\n");
-  if (CheckUtf8(descriptor_)) {
+  if (CheckUtf8(descriptor_) || !HasDescriptorMethods(descriptor_->file())) {
     printer->Print(variables_,
       "$name$_.add(s);\n");
   } else {
diff --git a/src/google/protobuf/compiler/mock_code_generator.cc b/src/google/protobuf/compiler/mock_code_generator.cc
index 916b0ccd..70373c8e 100644
--- a/src/google/protobuf/compiler/mock_code_generator.cc
+++ b/src/google/protobuf/compiler/mock_code_generator.cc
@@ -33,6 +33,9 @@
 #include <google/protobuf/compiler/mock_code_generator.h>
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/testing/file.h>
 #include <google/protobuf/descriptor.pb.h>
diff --git a/src/google/protobuf/compiler/parser.cc b/src/google/protobuf/compiler/parser.cc
index 474a8f80..0ed80d54 100644
--- a/src/google/protobuf/compiler/parser.cc
+++ b/src/google/protobuf/compiler/parser.cc
@@ -84,6 +84,32 @@ TypeNameMap MakeTypeNameTable() {
 
 const TypeNameMap kTypeNames = MakeTypeNameTable();
 
+// Camel-case the field name and append "Entry" for generated map entry name.
+// e.g. map<KeyType, ValueType> foo_map => FooMapEntry
+string MapEntryName(const string& field_name) {
+  string result;
+  static const char kSuffix[] = "Entry";
+  result.reserve(field_name.size() + sizeof(kSuffix));
+  bool cap_next = true;
+  for (int i = 0; i < field_name.size(); ++i) {
+    if (field_name[i] == '_') {
+      cap_next = true;
+    } else if (cap_next) {
+      // Note: Do not use ctype.h due to locales.
+      if ('a' <= field_name[i] && field_name[i] <= 'z') {
+        result.push_back(field_name[i] - 'a' + 'A');
+      } else {
+        result.push_back(field_name[i]);
+      }
+      cap_next = false;
+    } else {
+      result.push_back(field_name[i]);
+    }
+  }
+  result.append(kSuffix);
+  return result;
+}
+
 }  // anonymous namespace
 
 // Makes code slightly more readable.  The meaning of "DO(foo)" is
@@ -439,6 +465,8 @@ bool Parser::Parse(io::Tokenizer* input, FileDescriptorProto* file) {
         // identifier.
         return false;
       }
+      // Store the syntax into the file.
+      if (file != NULL) file->set_syntax(syntax_identifier_);
     } else if (!stop_after_syntax_identifier_) {
       syntax_identifier_ = "proto2";
     }
@@ -467,7 +495,9 @@ bool Parser::Parse(io::Tokenizer* input, FileDescriptorProto* file) {
 }
 
 bool Parser::ParseSyntaxIdentifier() {
-  DO(Consume("syntax", "File must begin with 'syntax = \"proto2\";'."));
+  DO(Consume(
+      "syntax",
+      "File must begin with a syntax statement, e.g. 'syntax = \"proto2\";'."));
   DO(Consume("="));
   io::Tokenizer::Token syntax_token = input_->current();
   string syntax;
@@ -476,10 +506,11 @@ bool Parser::ParseSyntaxIdentifier() {
 
   syntax_identifier_ = syntax;
 
-  if (syntax != "proto2" && !stop_after_syntax_identifier_) {
+  if (syntax != "proto2" && syntax != "proto3" &&
+      !stop_after_syntax_identifier_) {
     AddError(syntax_token.line, syntax_token.column,
       "Unrecognized syntax identifier \"" + syntax + "\".  This parser "
-      "only recognizes \"proto2\".");
+      "only recognizes \"proto2\" and \"proto3\".");
     return false;
   }
 
@@ -673,8 +704,9 @@ bool Parser::ParseMessageField(FieldDescriptorProto* field,
     LocationRecorder location(field_location,
                               FieldDescriptorProto::kLabelFieldNumber);
     FieldDescriptorProto::Label label;
-    DO(ParseLabel(&label, containing_file));
-    field->set_label(label);
+    if (ParseLabel(&label, containing_file)) {
+      field->set_label(label);
+    }
   }
 
   return ParseMessageFieldNoLabel(field, messages, parent_location,
@@ -690,20 +722,75 @@ bool Parser::ParseMessageFieldNoLabel(
     int location_field_number_for_nested_type,
     const LocationRecorder& field_location,
     const FileDescriptorProto* containing_file) {
+  MapField map_field;
   // Parse type.
   {
     LocationRecorder location(field_location);  // add path later
     location.RecordLegacyLocation(field, DescriptorPool::ErrorCollector::TYPE);
 
+    bool type_parsed = false;
     FieldDescriptorProto::Type type = FieldDescriptorProto::TYPE_INT32;
     string type_name;
-    DO(ParseType(&type, &type_name));
-    if (type_name.empty()) {
-      location.AddPath(FieldDescriptorProto::kTypeFieldNumber);
-      field->set_type(type);
-    } else {
+
+    // Special case map field. We only treat the field as a map field if the
+    // field type name starts with the word "map" with a following "<".
+    if (TryConsume("map")) {
+      if (LookingAt("<")) {
+        map_field.is_map_field = true;
+      } else {
+        // False positive
+        type_parsed = true;
+        type_name = "map";
+      }
+    }
+    if (map_field.is_map_field) {
+      if (field->has_oneof_index()) {
+        AddError("Map fields are not allowed in oneofs.");
+        return false;
+      }
+      if (field->has_label()) {
+        AddError(
+            "Field labels (required/optional/repeated) are not allowed on "
+            "map fields.");
+        return false;
+      }
+      if (field->has_extendee()) {
+        AddError("Map fields are not allowed to be extensions.");
+        return false;
+      }
+      field->set_label(FieldDescriptorProto::LABEL_REPEATED);
+      DO(Consume("<"));
+      DO(ParseType(&map_field.key_type, &map_field.key_type_name));
+      DO(Consume(","));
+      DO(ParseType(&map_field.value_type, &map_field.value_type_name));
+      DO(Consume(">"));
+      // Defer setting of the type name of the map field until the
+      // field name is parsed. Add the source location though.
       location.AddPath(FieldDescriptorProto::kTypeNameFieldNumber);
-      field->set_type_name(type_name);
+    } else {
+      // Handle the case where no explicit label is given for a non-map field.
+      if (!field->has_label() && DefaultToOptionalFields()) {
+        field->set_label(FieldDescriptorProto::LABEL_OPTIONAL);
+      }
+      if (!field->has_label()) {
+        AddError("Expected \"required\", \"optional\", or \"repeated\".");
+        // We can actually reasonably recover here by just assuming the user
+        // forgot the label altogether.
+        field->set_label(FieldDescriptorProto::LABEL_OPTIONAL);
+      }
+
+      // Handle the case where the actual type is a message or enum named "map",
+      // which we already consumed in the code above.
+      if (!type_parsed) {
+        DO(ParseType(&type, &type_name));
+      }
+      if (type_name.empty()) {
+        location.AddPath(FieldDescriptorProto::kTypeFieldNumber);
+        field->set_type(type);
+      } else {
+        location.AddPath(FieldDescriptorProto::kTypeNameFieldNumber);
+        field->set_type_name(type_name);
+      }
     }
   }
 
@@ -781,9 +868,42 @@ bool Parser::ParseMessageFieldNoLabel(
     DO(ConsumeEndOfDeclaration(";", &field_location));
   }
 
+  // Create a map entry type if this is a map field.
+  if (map_field.is_map_field) {
+    GenerateMapEntry(map_field, field, messages);
+  }
+
   return true;
 }
 
+void Parser::GenerateMapEntry(const MapField& map_field,
+                              FieldDescriptorProto* field,
+                              RepeatedPtrField<DescriptorProto>* messages) {
+  DescriptorProto* entry = messages->Add();
+  string entry_name = MapEntryName(field->name());
+  field->set_type_name(entry_name);
+  entry->set_name(entry_name);
+  entry->mutable_options()->set_map_entry(true);
+  FieldDescriptorProto* key_field = entry->add_field();
+  key_field->set_name("key");
+  key_field->set_label(FieldDescriptorProto::LABEL_OPTIONAL);
+  key_field->set_number(1);
+  if (map_field.key_type_name.empty()) {
+    key_field->set_type(map_field.key_type);
+  } else {
+    key_field->set_type_name(map_field.key_type_name);
+  }
+  FieldDescriptorProto* value_field = entry->add_field();
+  value_field->set_name("value");
+  value_field->set_label(FieldDescriptorProto::LABEL_OPTIONAL);
+  value_field->set_number(2);
+  if (map_field.value_type_name.empty()) {
+    value_field->set_type(map_field.value_type);
+  } else {
+    value_field->set_type_name(map_field.value_type_name);
+  }
+}
+
 bool Parser::ParseFieldOptions(FieldDescriptorProto* field,
                                const LocationRecorder& field_location,
                                const FileDescriptorProto* containing_file) {
@@ -1588,13 +1708,8 @@ bool Parser::ParseLabel(FieldDescriptorProto::Label* label,
   } else if (TryConsume("required")) {
     *label = FieldDescriptorProto::LABEL_REQUIRED;
     return true;
-  } else {
-    AddError("Expected \"required\", \"optional\", or \"repeated\".");
-    // We can actually reasonably recover here by just assuming the user
-    // forgot the label altogether.
-    *label = FieldDescriptorProto::LABEL_OPTIONAL;
-    return true;
   }
+  return false;
 }
 
 bool Parser::ParseType(FieldDescriptorProto::Type* type,
diff --git a/src/google/protobuf/compiler/parser.h b/src/google/protobuf/compiler/parser.h
index d0a2359b..a15cc705 100644
--- a/src/google/protobuf/compiler/parser.h
+++ b/src/google/protobuf/compiler/parser.h
@@ -403,7 +403,7 @@ class LIBPROTOBUF_EXPORT Parser {
                     Message* mutable_options);
 
   // Parse "required", "optional", or "repeated" and fill in "label"
-  // with the value.
+  // with the value. Returns true if shuch a label is consumed.
   bool ParseLabel(FieldDescriptorProto::Label* label,
                   const FileDescriptorProto* containing_file);
 
@@ -460,6 +460,28 @@ class LIBPROTOBUF_EXPORT Parser {
   // the ending brace.
   bool ParseUninterpretedBlock(string* value);
 
+  struct MapField {
+    // Whether the field is a map field.
+    bool is_map_field;
+    // The types of the key and value if they are primitive types.
+    FieldDescriptorProto::Type key_type;
+    FieldDescriptorProto::Type value_type;
+    // Or the type names string if the types are customized types.
+    string key_type_name;
+    string value_type_name;
+
+    MapField() : is_map_field(false) {}
+  };
+  // Desugar the map syntax to generate a nested map entry message.
+  void GenerateMapEntry(const MapField& map_field, FieldDescriptorProto* field,
+                        RepeatedPtrField<DescriptorProto>* messages);
+
+  // Whether fields without label default to optional fields.
+  bool DefaultToOptionalFields() const {
+    return syntax_identifier_ == "proto3";
+  }
+
+
   // =================================================================
 
   io::Tokenizer* input_;
diff --git a/src/google/protobuf/compiler/parser_unittest.cc b/src/google/protobuf/compiler/parser_unittest.cc
index 9ec29a48..c2206ade 100644
--- a/src/google/protobuf/compiler/parser_unittest.cc
+++ b/src/google/protobuf/compiler/parser_unittest.cc
@@ -33,6 +33,9 @@
 //  Sanjay Ghemawat, Jeff Dean, and others.
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <vector>
 #include <algorithm>
 #include <map>
@@ -250,6 +253,7 @@ TEST_F(ParseMessageTest, ExplicitSyntaxIdentifier) {
     "  required int32 foo = 1;\n"
     "}\n",
 
+    "syntax: 'proto2' "
     "message_type {"
     "  name: \"TestMessage\""
     "  field { name:\"foo\" label:LABEL_REQUIRED type:TYPE_INT32 number:1 }"
@@ -265,6 +269,7 @@ TEST_F(ParseMessageTest, ExplicitRequiredSyntaxIdentifier) {
     "  required int32 foo = 1;\n"
     "}\n",
 
+    "syntax: 'proto2' "
     "message_type {"
     "  name: \"TestMessage\""
     "  field { name:\"foo\" label:LABEL_REQUIRED type:TYPE_INT32 number:1 }"
@@ -500,6 +505,54 @@ TEST_F(ParseMessageTest, MultipleOneofs) {
     "}");
 }
 
+TEST_F(ParseMessageTest, Maps) {
+  ExpectParsesTo(
+    "message TestMessage {\n"
+    "  map<int32, string> primitive_type_map = 1;\n"
+    "  map<KeyType, ValueType> composite_type_map = 2;\n"
+    "}\n",
+
+    "message_type {"
+    "  name: \"TestMessage\""
+    "  nested_type {"
+    "    name: \"PrimitiveTypeMapEntry\""
+    "    field { "
+    "       name: \"key\" number: 1 label:LABEL_OPTIONAL"
+    "       type:TYPE_INT32"
+    "    }"
+    "    field { "
+    "       name: \"value\" number: 2 label:LABEL_OPTIONAL"
+    "       type:TYPE_STRING"
+    "    }"
+    "    options { map_entry: true }"
+    "  }"
+    "  nested_type {"
+    "    name: \"CompositeTypeMapEntry\""
+    "    field { "
+    "       name: \"key\" number: 1 label:LABEL_OPTIONAL"
+    "       type_name: \"KeyType\""
+    "    }"
+    "    field { "
+    "       name: \"value\" number: 2 label:LABEL_OPTIONAL"
+    "       type_name: \"ValueType\""
+    "    }"
+    "    options { map_entry: true }"
+    "  }"
+    "  field {"
+    "    name: \"primitive_type_map\""
+    "    label: LABEL_REPEATED"
+    "    type_name: \"PrimitiveTypeMapEntry\""
+    "    number: 1"
+    "  }"
+    "  field {"
+    "    name: \"composite_type_map\""
+    "    label: LABEL_REPEATED"
+    "    type_name: \"CompositeTypeMapEntry\""
+    "    number: 2"
+    "  }"
+    "}");
+}
+
 TEST_F(ParseMessageTest, Group) {
   ExpectParsesTo(
     "message TestMessage {\n"
@@ -639,6 +692,20 @@ TEST_F(ParseMessageTest, MultipleExtensionsOneExtendee) {
     "            type_name:\"TestMessage\" extendee: \"Extendee1\" }");
 }
 
+TEST_F(ParseMessageTest, OptionalOptionalLabelProto3) {
+  ExpectParsesTo(
+    "syntax = \"proto3\";\n"
+    "message TestMessage {\n"
+    "  int32 foo = 1;\n"
+    "  optional int32 bar = 2;\n"
+    "}\n",
+
+    "syntax: \"proto3\" "
+    "message_type {"
+    "  name: \"TestMessage\""
+    "  field { name:\"foo\" label:LABEL_OPTIONAL type:TYPE_INT32 number:1 }"
+    "  field { name:\"bar\" label:LABEL_OPTIONAL type:TYPE_INT32 number:2 } }");
+}
 
 // ===================================================================
 
@@ -828,9 +895,9 @@ typedef ParserTest ParseErrorTest;
 
 TEST_F(ParseErrorTest, MissingSyntaxIdentifier) {
   require_syntax_identifier_ = true;
-  ExpectHasEarlyExitErrors(
-    "message TestMessage {}",
-    "0:0: File must begin with 'syntax = \"proto2\";'.\n");
+  ExpectHasEarlyExitErrors("message TestMessage {}",
+                           "0:0: File must begin with a syntax statement, e.g. "
+                           "'syntax = \"proto2\";'.\n");
   EXPECT_EQ("", parser_->GetSyntaxIdentifier());
 }
 
@@ -838,7 +905,7 @@ TEST_F(ParseErrorTest, UnknownSyntaxIdentifier) {
   ExpectHasEarlyExitErrors(
     "syntax = \"no_such_syntax\";",
     "0:9: Unrecognized syntax identifier \"no_such_syntax\".  This parser "
-      "only recognizes \"proto2\".\n");
+      "only recognizes \"proto2\" and \"proto3\".\n");
   EXPECT_EQ("no_such_syntax", parser_->GetSyntaxIdentifier());
 }
 
@@ -1041,6 +1108,55 @@ TEST_F(ParseErrorTest, LabelInOneof) {
       "/ repeated).\n");
 }
 
+TEST_F(ParseErrorTest, MapInOneof) {
+  ExpectHasErrors(
+    "message TestMessage {\n"
+    "  oneof foo {\n"
+    "    map<int32, int32> foo_map = 1;\n"
+    "    map message_field = 2;\n"  // a normal message field is OK
+    "  }\n"
+    "}\n",
+    "2:7: Map fields are not allowed in oneofs.\n");
+}
+
+TEST_F(ParseErrorTest, LabelForMap) {
+  ExpectHasErrors(
+    "message TestMessage {\n"
+    "  optional map<int32, int32> int_map = 1;\n"
+    "  required map<int32, int32> int_map2 = 2;\n"
+    "  repeated map<int32, int32> int_map3 = 3;\n"
+    "  optional map map_message = 4;\n"  // a normal message field is OK
+    "}\n",
+    "1:14: Field labels (required/optional/repeated) are not allowed on map "
+    "fields.\n"
+    "2:14: Field labels (required/optional/repeated) are not allowed on map "
+    "fields.\n"
+    "3:14: Field labels (required/optional/repeated) are not allowed on map "
+    "fields.\n");
+}
+
+TEST_F(ParseErrorTest, MalformedMaps) {
+  ExpectHasErrors(
+    "message TestMessage {\n"
+    "  map map_message = 1;\n"   // a normal message field lacking label
+    "  map<string> str_map = 2;\n"
+    "  map<string,> str_map2 = 3;\n"
+    "  map<,string> str_map3 = 4;\n"
+    "  map<> empty_map = 5;\n"
+    "  map<string,string str_map6 = 6;\n"
+    "}"
+    "extend SomeMessage {\n"
+    "  map<int32, int32> int_map = 1;\n"
+    "}",
+    "1:6: Expected \"required\", \"optional\", or \"repeated\".\n"
+    "2:12: Expected \",\".\n"
+    "3:13: Expected type name.\n"
+    "4:6: Expected type name.\n"
+    "5:6: Expected type name.\n"
+    "6:20: Expected \">\".\n"
+    "8:5: Map fields are not allowed to be extensions.\n");
+}
+
 TEST_F(ParseErrorTest, GroupNotCapitalized) {
   ExpectHasErrors(
     "message TestMessage {\n"
@@ -1413,7 +1529,7 @@ TEST_F(ParserValidationErrorTest, ResovledUndefinedOptionError) {
 // definitions again afoter parsing (note, however, that the order of messages
 // cannot be guaranteed to be the same)
 
-typedef ParserTest ParseDecriptorDebugTest;
+typedef ParserTest ParseDescriptorDebugTest;
 
 class CompareDescriptorNames {
  public:
@@ -1447,7 +1563,28 @@ void SortMessages(FileDescriptorProto *file_descriptor_proto) {
   sort(data, data + size, CompareDescriptorNames());
 }
 
-TEST_F(ParseDecriptorDebugTest, TestAllDescriptorTypes) {
+// Strips the message and enum field type names for comparison purpose only.
+void StripFieldTypeName(DescriptorProto* proto) {
+  for (int i = 0; i < proto->field_size(); ++i) {
+    string type_name = proto->field(i).type_name();
+    string::size_type pos = type_name.find_last_of(".");
+    if (pos != string::npos) {
+      proto->mutable_field(i)->mutable_type_name()->assign(
+          type_name.begin() + pos + 1, type_name.end());
+    }
+  }
+  for (int i = 0; i < proto->nested_type_size(); ++i) {
+    StripFieldTypeName(proto->mutable_nested_type(i));
+  }
+}
+
+void StripFieldTypeName(FileDescriptorProto* file_proto) {
+  for (int i = 0; i < file_proto->message_type_size(); ++i) {
+    StripFieldTypeName(file_proto->mutable_message_type(i));
+  }
+}
+
+TEST_F(ParseDescriptorDebugTest, TestAllDescriptorTypes) {
   const FileDescriptor* original_file =
      protobuf_unittest::TestAllTypes::descriptor()->file();
   FileDescriptorProto expected;
@@ -1499,7 +1636,7 @@ TEST_F(ParseDecriptorDebugTest, TestAllDescriptorTypes) {
   EXPECT_EQ(expected.DebugString(), parsed.DebugString());
 }
 
-TEST_F(ParseDecriptorDebugTest, TestCustomOptions) {
+TEST_F(ParseDescriptorDebugTest, TestCustomOptions) {
   const FileDescriptor* original_file =
      protobuf_unittest::AggregateMessage::descriptor()->file();
   FileDescriptorProto expected;
@@ -1538,6 +1675,106 @@ TEST_F(ParseDecriptorDebugTest, TestCustomOptions) {
   EXPECT_EQ(expected.DebugString(), parsed.DebugString());
 }
 
+// Ensure that DebugStringWithOptions(), with |include_comments| set to true,
+// includes comments from the original parser input in all of the appropriate
+// places.
+TEST_F(ParseDescriptorDebugTest, TestCommentsInDebugString) {
+  SetupParser(
+      "// Message comment.\n"
+      "message TestMessage1 {\n"
+      "  // Field comment.\n"
+      "  optional int32 foo = 1;\n"
+      "\n"
+      "  // Nested-message comment.\n"
+      "  message NestedMessage {\n"
+      "    optional int32 bar = 1;\n"
+      "  }\n"
+      "}\n"
+      "\n"
+      "// Enum comment.\n"
+      "enum MyEnumType {\n"
+      "  // Enum-value comment.\n"
+      "  ASDF = 1;\n"
+      "}\n"
+      "\n"
+      "// Service comment.\n"
+      "service MyService {\n"
+      "  // RPC comment.\n"
+      "  rpc MyRPCCall(TestMessage1) returns (TestMessage1) { }\n"
+      "}\n");
+
+  FileDescriptorProto parsed_desc;
+  parsed_desc.set_name("foo.proto");
+  SourceLocationTable source_locations;
+  parser_->RecordSourceLocationsTo(&source_locations);
+  parser_->Parse(input_.get(), &parsed_desc);
+  EXPECT_EQ(io::Tokenizer::TYPE_END, input_->current().type);
+  ASSERT_EQ("", error_collector_.text_);
+
+  // We need to import the FileDescriptorProto to get a FileDescriptor.
+  MockValidationErrorCollector collector(source_locations, &error_collector_);
+  const FileDescriptor* descriptor =
+      pool_.BuildFileCollectingErrors(parsed_desc, &collector);
+  ASSERT_TRUE(descriptor != NULL);
+
+  DebugStringOptions debug_string_options;
+  debug_string_options.include_comments = true;
+  const string debug_string =
+      descriptor->DebugStringWithOptions(debug_string_options);
+
+  // Ensure that each of the comments appears somewhere in the DebugString(),
+  // and that these comments appear in order. We don't test the exact comment
+  // placement or formatting, because we do not want to be too fragile here.
+  const char* expected_comments[] = {
+    "Message comment.",
+    "Field comment",
+    "Nested-message comment",
+    "Enum comment",
+    "Enum-value comment",
+    "Service comment",
+    "RPC comment",
+  };
+
+  for (int i = 0; i < GOOGLE_ARRAYSIZE(expected_comments); ++i) {
+    string::size_type found_pos = debug_string.find(expected_comments[i]);
+    ASSERT_TRUE(found_pos != string::npos);
+  }
+}
+
+TEST_F(ParseDescriptorDebugTest, TestMaps) {
+  SetupParser(
+      "syntax = \"proto3\"; "
+      "message Foo { "
+      "  message Bar { } "
+      "  map<int32, Bar> enum_message_map = 1; "
+      "  map<string, float> primitive_map = 2; "
+      "} ");
+  FileDescriptorProto original;
+  EXPECT_TRUE(parser_->Parse(input_.get(), &original));
+  original.set_name("foo.proto");
+  const FileDescriptor* file = pool_.BuildFile(original);
+  ASSERT_TRUE(file != NULL);
+
+  // Make sure the debug string uses map syntax and does not have the auto
+  // generated entry.
+  string debug_string = file->DebugString();
+  EXPECT_TRUE(debug_string.find("map<") != string::npos);
+  EXPECT_TRUE(debug_string.find("option map_entry") == string::npos);
+  EXPECT_TRUE(debug_string.find("MapEntry") == string::npos);
+
+  // Make sure the descriptor debug string is parsable.
+  FileDescriptorProto parsed;
+  SetupParser(debug_string.c_str());
+  parsed.set_name("foo.proto");
+  ASSERT_TRUE(parser_->Parse(input_.get(), &parsed));
+
+  original.clear_source_code_info();
+  parsed.clear_source_code_info();
+  StripFieldTypeName(&original);
+  StripFieldTypeName(&parsed);
+  EXPECT_EQ(original.DebugString(), parsed.DebugString());
+}
+
 // ===================================================================
 // SourceCodeInfo tests.
 
diff --git a/src/google/protobuf/compiler/plugin.pb.cc b/src/google/protobuf/compiler/plugin.pb.cc
index b5cd01b5..efa64f3d 100644
--- a/src/google/protobuf/compiler/plugin.pb.cc
+++ b/src/google/protobuf/compiler/plugin.pb.cc
@@ -53,11 +53,12 @@ void protobuf_AssignDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto() {
       CodeGeneratorRequest::default_instance_,
       CodeGeneratorRequest_offsets_,
       GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorRequest, _has_bits_[0]),
-      GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorRequest, _unknown_fields_),
+      -1,
       -1,
       ::google::protobuf::DescriptorPool::generated_pool(),
       ::google::protobuf::MessageFactory::generated_factory(),
-      sizeof(CodeGeneratorRequest));
+      sizeof(CodeGeneratorRequest),
+      GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorRequest, _internal_metadata_));
   CodeGeneratorResponse_descriptor_ = file->message_type(1);
   static const int CodeGeneratorResponse_offsets_[2] = {
     GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorResponse, error_),
@@ -69,11 +70,12 @@ void protobuf_AssignDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto() {
       CodeGeneratorResponse::default_instance_,
       CodeGeneratorResponse_offsets_,
       GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorResponse, _has_bits_[0]),
-      GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorResponse, _unknown_fields_),
+      -1,
       -1,
       ::google::protobuf::DescriptorPool::generated_pool(),
       ::google::protobuf::MessageFactory::generated_factory(),
-      sizeof(CodeGeneratorResponse));
+      sizeof(CodeGeneratorResponse),
+      GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorResponse, _internal_metadata_));
   CodeGeneratorResponse_File_descriptor_ = CodeGeneratorResponse_descriptor_->nested_type(0);
   static const int CodeGeneratorResponse_File_offsets_[3] = {
     GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorResponse_File, name_),
@@ -86,11 +88,12 @@ void protobuf_AssignDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto() {
       CodeGeneratorResponse_File::default_instance_,
       CodeGeneratorResponse_File_offsets_,
       GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorResponse_File, _has_bits_[0]),
-      GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorResponse_File, _unknown_fields_),
+      -1,
       -1,
       ::google::protobuf::DescriptorPool::generated_pool(),
       ::google::protobuf::MessageFactory::generated_factory(),
-      sizeof(CodeGeneratorResponse_File));
+      sizeof(CodeGeneratorResponse_File),
+      GOOGLE_PROTOBUF_GENERATED_MESSAGE_FIELD_OFFSET(CodeGeneratorResponse_File, _internal_metadata_));
 }
 
 namespace {
@@ -169,16 +172,27 @@ const int CodeGeneratorRequest::kProtoFileFieldNumber;
 #endif  // !_MSC_VER
 
 CodeGeneratorRequest::CodeGeneratorRequest()
-  : ::google::protobuf::Message() {
+  : ::google::protobuf::Message() , _internal_metadata_(NULL)  {
   SharedCtor();
   // @@protoc_insertion_point(constructor:google.protobuf.compiler.CodeGeneratorRequest)
 }
 
+CodeGeneratorRequest::CodeGeneratorRequest(::google::protobuf::Arena* arena)
+  : ::google::protobuf::Message(),
+  _internal_metadata_(arena),
+  file_to_generate_(arena),
+  proto_file_(arena) {
+  SharedCtor();
+  RegisterArenaDtor(arena);
+  // @@protoc_insertion_point(arena_constructor:google.protobuf.compiler.CodeGeneratorRequest)
+}
+
 void CodeGeneratorRequest::InitAsDefaultInstance() {
 }
 
 CodeGeneratorRequest::CodeGeneratorRequest(const CodeGeneratorRequest& from)
-  : ::google::protobuf::Message() {
+  : ::google::protobuf::Message(),
+    _internal_metadata_(NULL) {
   SharedCtor();
   MergeFrom(from);
   // @@protoc_insertion_point(copy_constructor:google.protobuf.compiler.CodeGeneratorRequest)
@@ -187,7 +201,7 @@ CodeGeneratorRequest::CodeGeneratorRequest(const CodeGeneratorRequest& from)
 void CodeGeneratorRequest::SharedCtor() {
   ::google::protobuf::internal::GetEmptyString();
   _cached_size_ = 0;
-  parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
+  parameter_.UnsafeSetDefault(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
 }
 
@@ -197,13 +211,21 @@ CodeGeneratorRequest::~CodeGeneratorRequest() {
 }
 
 void CodeGeneratorRequest::SharedDtor() {
-  if (parameter_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    delete parameter_;
+  if (GetArenaNoVirtual() != NULL) {
+    return;
   }
+
+  parameter_.Destroy(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
   if (this != default_instance_) {
   }
 }
 
+void CodeGeneratorRequest::ArenaDtor(void* object) {
+  CodeGeneratorRequest* _this = reinterpret_cast< CodeGeneratorRequest* >(object);
+  (void)_this;
+}
+void CodeGeneratorRequest::RegisterArenaDtor(::google::protobuf::Arena* arena) {
+}
 void CodeGeneratorRequest::SetCachedSize(int size) const {
   GOOGLE_SAFE_CONCURRENT_WRITES_BEGIN();
   _cached_size_ = size;
@@ -221,20 +243,20 @@ const CodeGeneratorRequest& CodeGeneratorRequest::default_instance() {
 
 CodeGeneratorRequest* CodeGeneratorRequest::default_instance_ = NULL;
 
-CodeGeneratorRequest* CodeGeneratorRequest::New() const {
-  return new CodeGeneratorRequest;
+CodeGeneratorRequest* CodeGeneratorRequest::New(::google::protobuf::Arena* arena) const {
+  return ::google::protobuf::Arena::CreateMessage<CodeGeneratorRequest>(arena);
 }
 
 void CodeGeneratorRequest::Clear() {
   if (has_parameter()) {
-    if (parameter_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-      parameter_->clear();
-    }
+    parameter_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
   }
   file_to_generate_.Clear();
   proto_file_.Clear();
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
-  mutable_unknown_fields()->Clear();
+  if (_internal_metadata_.have_unknown_fields()) {
+    mutable_unknown_fields()->Clear();
+  }
 }
 
 bool CodeGeneratorRequest::MergePartialFromCodedStream(
@@ -257,7 +279,7 @@ bool CodeGeneratorRequest::MergePartialFromCodedStream(
             this->file_to_generate(this->file_to_generate_size() - 1).data(),
             this->file_to_generate(this->file_to_generate_size() - 1).length(),
             ::google::protobuf::internal::WireFormat::PARSE,
-            "file_to_generate");
+            "google.protobuf.compiler.CodeGeneratorRequest.file_to_generate");
         } else {
           goto handle_unusual;
         }
@@ -275,7 +297,7 @@ bool CodeGeneratorRequest::MergePartialFromCodedStream(
           ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->parameter().data(), this->parameter().length(),
             ::google::protobuf::internal::WireFormat::PARSE,
-            "parameter");
+            "google.protobuf.compiler.CodeGeneratorRequest.parameter");
         } else {
           goto handle_unusual;
         }
@@ -327,7 +349,7 @@ void CodeGeneratorRequest::SerializeWithCachedSizes(
   ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
     this->file_to_generate(i).data(), this->file_to_generate(i).length(),
     ::google::protobuf::internal::WireFormat::SERIALIZE,
-    "file_to_generate");
+    "google.protobuf.compiler.CodeGeneratorRequest.file_to_generate");
     ::google::protobuf::internal::WireFormatLite::WriteString(
       1, this->file_to_generate(i), output);
   }
@@ -337,7 +359,7 @@ void CodeGeneratorRequest::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->parameter().data(), this->parameter().length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "parameter");
+      "google.protobuf.compiler.CodeGeneratorRequest.parameter");
     ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
       2, this->parameter(), output);
   }
@@ -348,7 +370,7 @@ void CodeGeneratorRequest::SerializeWithCachedSizes(
       15, this->proto_file(i), output);
   }
 
-  if (!unknown_fields().empty()) {
+  if (_internal_metadata_.have_unknown_fields()) {
     ::google::protobuf::internal::WireFormat::SerializeUnknownFields(
         unknown_fields(), output);
   }
@@ -363,7 +385,7 @@ void CodeGeneratorRequest::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->file_to_generate(i).data(), this->file_to_generate(i).length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "file_to_generate");
+      "google.protobuf.compiler.CodeGeneratorRequest.file_to_generate");
     target = ::google::protobuf::internal::WireFormatLite::
       WriteStringToArray(1, this->file_to_generate(i), target);
   }
@@ -373,7 +395,7 @@ void CodeGeneratorRequest::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->parameter().data(), this->parameter().length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "parameter");
+      "google.protobuf.compiler.CodeGeneratorRequest.parameter");
     target =
       ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
         2, this->parameter(), target);
@@ -386,7 +408,7 @@ void CodeGeneratorRequest::SerializeWithCachedSizes(
         15, this->proto_file(i), target);
   }
 
-  if (!unknown_fields().empty()) {
+  if (_internal_metadata_.have_unknown_fields()) {
     target = ::google::protobuf::internal::WireFormat::SerializeUnknownFieldsToArray(
         unknown_fields(), target);
   }
@@ -397,15 +419,13 @@ void CodeGeneratorRequest::SerializeWithCachedSizes(
 int CodeGeneratorRequest::ByteSize() const {
   int total_size = 0;
 
-  if (_has_bits_[1 / 32] & (0xffu << (1 % 32))) {
-    // optional string parameter = 2;
-    if (has_parameter()) {
-      total_size += 1 +
-        ::google::protobuf::internal::WireFormatLite::StringSize(
-          this->parameter());
-    }
-
+  // optional string parameter = 2;
+  if (has_parameter()) {
+    total_size += 1 +
+      ::google::protobuf::internal::WireFormatLite::StringSize(
+        this->parameter());
   }
+
   // repeated string file_to_generate = 1;
   total_size += 1 * this->file_to_generate_size();
   for (int i = 0; i < this->file_to_generate_size(); i++) {
@@ -421,7 +441,7 @@ int CodeGeneratorRequest::ByteSize() const {
         this->proto_file(i));
   }
 
-  if (!unknown_fields().empty()) {
+  if (_internal_metadata_.have_unknown_fields()) {
     total_size +=
       ::google::protobuf::internal::WireFormat::ComputeUnknownFieldsSize(
         unknown_fields());
@@ -453,7 +473,9 @@ void CodeGeneratorRequest::MergeFrom(const CodeGeneratorRequest& from) {
       set_parameter(from.parameter());
     }
   }
-  mutable_unknown_fields()->MergeFrom(from.unknown_fields());
+  if (from._internal_metadata_.have_unknown_fields()) {
+    mutable_unknown_fields()->MergeFrom(from.unknown_fields());
+  }
 }
 
 void CodeGeneratorRequest::CopyFrom(const ::google::protobuf::Message& from) {
@@ -475,15 +497,29 @@ bool CodeGeneratorRequest::IsInitialized() const {
 }
 
 void CodeGeneratorRequest::Swap(CodeGeneratorRequest* other) {
-  if (other != this) {
-    file_to_generate_.Swap(&other->file_to_generate_);
-    std::swap(parameter_, other->parameter_);
-    proto_file_.Swap(&other->proto_file_);
-    std::swap(_has_bits_[0], other->_has_bits_[0]);
-    _unknown_fields_.Swap(&other->_unknown_fields_);
-    std::swap(_cached_size_, other->_cached_size_);
+  if (other == this) return;
+  if (GetArenaNoVirtual() == other->GetArenaNoVirtual()) {
+    InternalSwap(other);
+  } else {
+    CodeGeneratorRequest temp;
+    temp.MergeFrom(*this);
+    CopyFrom(*other);
+    other->CopyFrom(temp);
   }
 }
+void CodeGeneratorRequest::UnsafeArenaSwap(CodeGeneratorRequest* other) {
+  if (other == this) return;
+  GOOGLE_DCHECK(GetArenaNoVirtual() == other->GetArenaNoVirtual());
+  InternalSwap(other);
+}
+void CodeGeneratorRequest::InternalSwap(CodeGeneratorRequest* other) {
+  file_to_generate_.UnsafeArenaSwap(&other->file_to_generate_);
+  parameter_.Swap(&other->parameter_);
+  proto_file_.UnsafeArenaSwap(&other->proto_file_);
+  std::swap(_has_bits_[0], other->_has_bits_[0]);
+  _internal_metadata_.Swap(&other->_internal_metadata_);
+  std::swap(_cached_size_, other->_cached_size_);
+}
 
 ::google::protobuf::Metadata CodeGeneratorRequest::GetMetadata() const {
   protobuf_AssignDescriptorsOnce();
@@ -503,16 +539,25 @@ const int CodeGeneratorResponse_File::kContentFieldNumber;
 #endif  // !_MSC_VER
 
 CodeGeneratorResponse_File::CodeGeneratorResponse_File()
-  : ::google::protobuf::Message() {
+  : ::google::protobuf::Message() , _internal_metadata_(NULL)  {
   SharedCtor();
   // @@protoc_insertion_point(constructor:google.protobuf.compiler.CodeGeneratorResponse.File)
 }
 
+CodeGeneratorResponse_File::CodeGeneratorResponse_File(::google::protobuf::Arena* arena)
+  : ::google::protobuf::Message(),
+  _internal_metadata_(arena) {
+  SharedCtor();
+  RegisterArenaDtor(arena);
+  // @@protoc_insertion_point(arena_constructor:google.protobuf.compiler.CodeGeneratorResponse.File)
+}
+
 void CodeGeneratorResponse_File::InitAsDefaultInstance() {
 }
 
 CodeGeneratorResponse_File::CodeGeneratorResponse_File(const CodeGeneratorResponse_File& from)
-  : ::google::protobuf::Message() {
+  : ::google::protobuf::Message(),
+    _internal_metadata_(NULL) {
   SharedCtor();
   MergeFrom(from);
   // @@protoc_insertion_point(copy_constructor:google.protobuf.compiler.CodeGeneratorResponse.File)
@@ -521,9 +566,9 @@ CodeGeneratorResponse_File::CodeGeneratorResponse_File(const CodeGeneratorRespon
 void CodeGeneratorResponse_File::SharedCtor() {
   ::google::protobuf::internal::GetEmptyString();
   _cached_size_ = 0;
-  name_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
-  insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
-  content_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
+  name_.UnsafeSetDefault(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
+  insertion_point_.UnsafeSetDefault(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
+  content_.UnsafeSetDefault(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
 }
 
@@ -533,19 +578,23 @@ CodeGeneratorResponse_File::~CodeGeneratorResponse_File() {
 }
 
 void CodeGeneratorResponse_File::SharedDtor() {
-  if (name_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    delete name_;
-  }
-  if (insertion_point_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    delete insertion_point_;
-  }
-  if (content_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    delete content_;
+  if (GetArenaNoVirtual() != NULL) {
+    return;
   }
+
+  name_.Destroy(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
+  insertion_point_.Destroy(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
+  content_.Destroy(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
   if (this != default_instance_) {
   }
 }
 
+void CodeGeneratorResponse_File::ArenaDtor(void* object) {
+  CodeGeneratorResponse_File* _this = reinterpret_cast< CodeGeneratorResponse_File* >(object);
+  (void)_this;
+}
+void CodeGeneratorResponse_File::RegisterArenaDtor(::google::protobuf::Arena* arena) {
+}
 void CodeGeneratorResponse_File::SetCachedSize(int size) const {
   GOOGLE_SAFE_CONCURRENT_WRITES_BEGIN();
   _cached_size_ = size;
@@ -563,30 +612,26 @@ const CodeGeneratorResponse_File& CodeGeneratorResponse_File::default_instance()
 
 CodeGeneratorResponse_File* CodeGeneratorResponse_File::default_instance_ = NULL;
 
-CodeGeneratorResponse_File* CodeGeneratorResponse_File::New() const {
-  return new CodeGeneratorResponse_File;
+CodeGeneratorResponse_File* CodeGeneratorResponse_File::New(::google::protobuf::Arena* arena) const {
+  return ::google::protobuf::Arena::CreateMessage<CodeGeneratorResponse_File>(arena);
 }
 
 void CodeGeneratorResponse_File::Clear() {
   if (_has_bits_[0 / 32] & 7) {
     if (has_name()) {
-      if (name_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-        name_->clear();
-      }
+      name_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
     }
     if (has_insertion_point()) {
-      if (insertion_point_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-        insertion_point_->clear();
-      }
+      insertion_point_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
     }
     if (has_content()) {
-      if (content_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-        content_->clear();
-      }
+      content_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
     }
   }
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
-  mutable_unknown_fields()->Clear();
+  if (_internal_metadata_.have_unknown_fields()) {
+    mutable_unknown_fields()->Clear();
+  }
 }
 
 bool CodeGeneratorResponse_File::MergePartialFromCodedStream(
@@ -607,7 +652,7 @@ bool CodeGeneratorResponse_File::MergePartialFromCodedStream(
           ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->name().data(), this->name().length(),
             ::google::protobuf::internal::WireFormat::PARSE,
-            "name");
+            "google.protobuf.compiler.CodeGeneratorResponse.File.name");
         } else {
           goto handle_unusual;
         }
@@ -624,7 +669,7 @@ bool CodeGeneratorResponse_File::MergePartialFromCodedStream(
           ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->insertion_point().data(), this->insertion_point().length(),
             ::google::protobuf::internal::WireFormat::PARSE,
-            "insertion_point");
+            "google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point");
         } else {
           goto handle_unusual;
         }
@@ -641,7 +686,7 @@ bool CodeGeneratorResponse_File::MergePartialFromCodedStream(
           ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->content().data(), this->content().length(),
             ::google::protobuf::internal::WireFormat::PARSE,
-            "content");
+            "google.protobuf.compiler.CodeGeneratorResponse.File.content");
         } else {
           goto handle_unusual;
         }
@@ -679,7 +724,7 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->name().data(), this->name().length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "name");
+      "google.protobuf.compiler.CodeGeneratorResponse.File.name");
     ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
       1, this->name(), output);
   }
@@ -689,7 +734,7 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->insertion_point().data(), this->insertion_point().length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "insertion_point");
+      "google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point");
     ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
       2, this->insertion_point(), output);
   }
@@ -699,12 +744,12 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->content().data(), this->content().length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "content");
+      "google.protobuf.compiler.CodeGeneratorResponse.File.content");
     ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
       15, this->content(), output);
   }
 
-  if (!unknown_fields().empty()) {
+  if (_internal_metadata_.have_unknown_fields()) {
     ::google::protobuf::internal::WireFormat::SerializeUnknownFields(
         unknown_fields(), output);
   }
@@ -719,7 +764,7 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->name().data(), this->name().length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "name");
+      "google.protobuf.compiler.CodeGeneratorResponse.File.name");
     target =
       ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
         1, this->name(), target);
@@ -730,7 +775,7 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->insertion_point().data(), this->insertion_point().length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "insertion_point");
+      "google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point");
     target =
       ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
         2, this->insertion_point(), target);
@@ -741,13 +786,13 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->content().data(), this->content().length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "content");
+      "google.protobuf.compiler.CodeGeneratorResponse.File.content");
     target =
       ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
         15, this->content(), target);
   }
 
-  if (!unknown_fields().empty()) {
+  if (_internal_metadata_.have_unknown_fields()) {
     target = ::google::protobuf::internal::WireFormat::SerializeUnknownFieldsToArray(
         unknown_fields(), target);
   }
@@ -758,7 +803,7 @@ void CodeGeneratorResponse_File::SerializeWithCachedSizes(
 int CodeGeneratorResponse_File::ByteSize() const {
   int total_size = 0;
 
-  if (_has_bits_[0 / 32] & (0xffu << (0 % 32))) {
+  if (_has_bits_[0 / 32] & 7) {
     // optional string name = 1;
     if (has_name()) {
       total_size += 1 +
@@ -781,7 +826,7 @@ int CodeGeneratorResponse_File::ByteSize() const {
     }
 
   }
-  if (!unknown_fields().empty()) {
+  if (_internal_metadata_.have_unknown_fields()) {
     total_size +=
       ::google::protobuf::internal::WireFormat::ComputeUnknownFieldsSize(
         unknown_fields());
@@ -817,7 +862,9 @@ void CodeGeneratorResponse_File::MergeFrom(const CodeGeneratorResponse_File& fro
       set_content(from.content());
     }
   }
-  mutable_unknown_fields()->MergeFrom(from.unknown_fields());
+  if (from._internal_metadata_.have_unknown_fields()) {
+    mutable_unknown_fields()->MergeFrom(from.unknown_fields());
+  }
 }
 
 void CodeGeneratorResponse_File::CopyFrom(const ::google::protobuf::Message& from) {
@@ -838,15 +885,29 @@ bool CodeGeneratorResponse_File::IsInitialized() const {
 }
 
 void CodeGeneratorResponse_File::Swap(CodeGeneratorResponse_File* other) {
-  if (other != this) {
-    std::swap(name_, other->name_);
-    std::swap(insertion_point_, other->insertion_point_);
-    std::swap(content_, other->content_);
-    std::swap(_has_bits_[0], other->_has_bits_[0]);
-    _unknown_fields_.Swap(&other->_unknown_fields_);
-    std::swap(_cached_size_, other->_cached_size_);
+  if (other == this) return;
+  if (GetArenaNoVirtual() == other->GetArenaNoVirtual()) {
+    InternalSwap(other);
+  } else {
+    CodeGeneratorResponse_File temp;
+    temp.MergeFrom(*this);
+    CopyFrom(*other);
+    other->CopyFrom(temp);
   }
 }
+void CodeGeneratorResponse_File::UnsafeArenaSwap(CodeGeneratorResponse_File* other) {
+  if (other == this) return;
+  GOOGLE_DCHECK(GetArenaNoVirtual() == other->GetArenaNoVirtual());
+  InternalSwap(other);
+}
+void CodeGeneratorResponse_File::InternalSwap(CodeGeneratorResponse_File* other) {
+  name_.Swap(&other->name_);
+  insertion_point_.Swap(&other->insertion_point_);
+  content_.Swap(&other->content_);
+  std::swap(_has_bits_[0], other->_has_bits_[0]);
+  _internal_metadata_.Swap(&other->_internal_metadata_);
+  std::swap(_cached_size_, other->_cached_size_);
+}
 
 ::google::protobuf::Metadata CodeGeneratorResponse_File::GetMetadata() const {
   protobuf_AssignDescriptorsOnce();
@@ -865,16 +926,26 @@ const int CodeGeneratorResponse::kFileFieldNumber;
 #endif  // !_MSC_VER
 
 CodeGeneratorResponse::CodeGeneratorResponse()
-  : ::google::protobuf::Message() {
+  : ::google::protobuf::Message() , _internal_metadata_(NULL)  {
   SharedCtor();
   // @@protoc_insertion_point(constructor:google.protobuf.compiler.CodeGeneratorResponse)
 }
 
+CodeGeneratorResponse::CodeGeneratorResponse(::google::protobuf::Arena* arena)
+  : ::google::protobuf::Message(),
+  _internal_metadata_(arena),
+  file_(arena) {
+  SharedCtor();
+  RegisterArenaDtor(arena);
+  // @@protoc_insertion_point(arena_constructor:google.protobuf.compiler.CodeGeneratorResponse)
+}
+
 void CodeGeneratorResponse::InitAsDefaultInstance() {
 }
 
 CodeGeneratorResponse::CodeGeneratorResponse(const CodeGeneratorResponse& from)
-  : ::google::protobuf::Message() {
+  : ::google::protobuf::Message(),
+    _internal_metadata_(NULL) {
   SharedCtor();
   MergeFrom(from);
   // @@protoc_insertion_point(copy_constructor:google.protobuf.compiler.CodeGeneratorResponse)
@@ -883,7 +954,7 @@ CodeGeneratorResponse::CodeGeneratorResponse(const CodeGeneratorResponse& from)
 void CodeGeneratorResponse::SharedCtor() {
   ::google::protobuf::internal::GetEmptyString();
   _cached_size_ = 0;
-  error_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
+  error_.UnsafeSetDefault(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
 }
 
@@ -893,13 +964,21 @@ CodeGeneratorResponse::~CodeGeneratorResponse() {
 }
 
 void CodeGeneratorResponse::SharedDtor() {
-  if (error_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    delete error_;
+  if (GetArenaNoVirtual() != NULL) {
+    return;
   }
+
+  error_.Destroy(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
   if (this != default_instance_) {
   }
 }
 
+void CodeGeneratorResponse::ArenaDtor(void* object) {
+  CodeGeneratorResponse* _this = reinterpret_cast< CodeGeneratorResponse* >(object);
+  (void)_this;
+}
+void CodeGeneratorResponse::RegisterArenaDtor(::google::protobuf::Arena* arena) {
+}
 void CodeGeneratorResponse::SetCachedSize(int size) const {
   GOOGLE_SAFE_CONCURRENT_WRITES_BEGIN();
   _cached_size_ = size;
@@ -917,19 +996,19 @@ const CodeGeneratorResponse& CodeGeneratorResponse::default_instance() {
 
 CodeGeneratorResponse* CodeGeneratorResponse::default_instance_ = NULL;
 
-CodeGeneratorResponse* CodeGeneratorResponse::New() const {
-  return new CodeGeneratorResponse;
+CodeGeneratorResponse* CodeGeneratorResponse::New(::google::protobuf::Arena* arena) const {
+  return ::google::protobuf::Arena::CreateMessage<CodeGeneratorResponse>(arena);
 }
 
 void CodeGeneratorResponse::Clear() {
   if (has_error()) {
-    if (error_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-      error_->clear();
-    }
+    error_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
   }
   file_.Clear();
   ::memset(_has_bits_, 0, sizeof(_has_bits_));
-  mutable_unknown_fields()->Clear();
+  if (_internal_metadata_.have_unknown_fields()) {
+    mutable_unknown_fields()->Clear();
+  }
 }
 
 bool CodeGeneratorResponse::MergePartialFromCodedStream(
@@ -950,7 +1029,7 @@ bool CodeGeneratorResponse::MergePartialFromCodedStream(
           ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
             this->error().data(), this->error().length(),
             ::google::protobuf::internal::WireFormat::PARSE,
-            "error");
+            "google.protobuf.compiler.CodeGeneratorResponse.error");
         } else {
           goto handle_unusual;
         }
@@ -1002,7 +1081,7 @@ void CodeGeneratorResponse::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->error().data(), this->error().length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "error");
+      "google.protobuf.compiler.CodeGeneratorResponse.error");
     ::google::protobuf::internal::WireFormatLite::WriteStringMaybeAliased(
       1, this->error(), output);
   }
@@ -1013,7 +1092,7 @@ void CodeGeneratorResponse::SerializeWithCachedSizes(
       15, this->file(i), output);
   }
 
-  if (!unknown_fields().empty()) {
+  if (_internal_metadata_.have_unknown_fields()) {
     ::google::protobuf::internal::WireFormat::SerializeUnknownFields(
         unknown_fields(), output);
   }
@@ -1028,7 +1107,7 @@ void CodeGeneratorResponse::SerializeWithCachedSizes(
     ::google::protobuf::internal::WireFormat::VerifyUTF8StringNamedField(
       this->error().data(), this->error().length(),
       ::google::protobuf::internal::WireFormat::SERIALIZE,
-      "error");
+      "google.protobuf.compiler.CodeGeneratorResponse.error");
     target =
       ::google::protobuf::internal::WireFormatLite::WriteStringToArray(
         1, this->error(), target);
@@ -1041,7 +1120,7 @@ void CodeGeneratorResponse::SerializeWithCachedSizes(
         15, this->file(i), target);
   }
 
-  if (!unknown_fields().empty()) {
+  if (_internal_metadata_.have_unknown_fields()) {
     target = ::google::protobuf::internal::WireFormat::SerializeUnknownFieldsToArray(
         unknown_fields(), target);
   }
@@ -1052,15 +1131,13 @@ void CodeGeneratorResponse::SerializeWithCachedSizes(
 int CodeGeneratorResponse::ByteSize() const {
   int total_size = 0;
 
-  if (_has_bits_[0 / 32] & (0xffu << (0 % 32))) {
-    // optional string error = 1;
-    if (has_error()) {
-      total_size += 1 +
-        ::google::protobuf::internal::WireFormatLite::StringSize(
-          this->error());
-    }
-
+  // optional string error = 1;
+  if (has_error()) {
+    total_size += 1 +
+      ::google::protobuf::internal::WireFormatLite::StringSize(
+        this->error());
   }
+
   // repeated .google.protobuf.compiler.CodeGeneratorResponse.File file = 15;
   total_size += 1 * this->file_size();
   for (int i = 0; i < this->file_size(); i++) {
@@ -1069,7 +1146,7 @@ int CodeGeneratorResponse::ByteSize() const {
         this->file(i));
   }
 
-  if (!unknown_fields().empty()) {
+  if (_internal_metadata_.have_unknown_fields()) {
     total_size +=
       ::google::protobuf::internal::WireFormat::ComputeUnknownFieldsSize(
         unknown_fields());
@@ -1100,7 +1177,9 @@ void CodeGeneratorResponse::MergeFrom(const CodeGeneratorResponse& from) {
       set_error(from.error());
     }
   }
-  mutable_unknown_fields()->MergeFrom(from.unknown_fields());
+  if (from._internal_metadata_.have_unknown_fields()) {
+    mutable_unknown_fields()->MergeFrom(from.unknown_fields());
+  }
 }
 
 void CodeGeneratorResponse::CopyFrom(const ::google::protobuf::Message& from) {
@@ -1121,14 +1200,28 @@ bool CodeGeneratorResponse::IsInitialized() const {
 }
 
 void CodeGeneratorResponse::Swap(CodeGeneratorResponse* other) {
-  if (other != this) {
-    std::swap(error_, other->error_);
-    file_.Swap(&other->file_);
-    std::swap(_has_bits_[0], other->_has_bits_[0]);
-    _unknown_fields_.Swap(&other->_unknown_fields_);
-    std::swap(_cached_size_, other->_cached_size_);
+  if (other == this) return;
+  if (GetArenaNoVirtual() == other->GetArenaNoVirtual()) {
+    InternalSwap(other);
+  } else {
+    CodeGeneratorResponse temp;
+    temp.MergeFrom(*this);
+    CopyFrom(*other);
+    other->CopyFrom(temp);
   }
 }
+void CodeGeneratorResponse::UnsafeArenaSwap(CodeGeneratorResponse* other) {
+  if (other == this) return;
+  GOOGLE_DCHECK(GetArenaNoVirtual() == other->GetArenaNoVirtual());
+  InternalSwap(other);
+}
+void CodeGeneratorResponse::InternalSwap(CodeGeneratorResponse* other) {
+  error_.Swap(&other->error_);
+  file_.UnsafeArenaSwap(&other->file_);
+  std::swap(_has_bits_[0], other->_has_bits_[0]);
+  _internal_metadata_.Swap(&other->_internal_metadata_);
+  std::swap(_cached_size_, other->_cached_size_);
+}
 
 ::google::protobuf::Metadata CodeGeneratorResponse::GetMetadata() const {
   protobuf_AssignDescriptorsOnce();
diff --git a/src/google/protobuf/compiler/plugin.pb.h b/src/google/protobuf/compiler/plugin.pb.h
index 567b30ef..636992a6 100644
--- a/src/google/protobuf/compiler/plugin.pb.h
+++ b/src/google/protobuf/compiler/plugin.pb.h
@@ -5,6 +5,7 @@
 #define PROTOBUF_google_2fprotobuf_2fcompiler_2fplugin_2eproto__INCLUDED
 
 #include <string>
+#include <stdint.h>
 
 #include <google/protobuf/stubs/common.h>
 
@@ -19,7 +20,10 @@
 #error regenerate this file with a newer version of protoc.
 #endif
 
+#include <google/protobuf/arena.h>
+#include <google/protobuf/arenastring.h>
 #include <google/protobuf/generated_message_util.h>
+#include <google/protobuf/metadata.h>
 #include <google/protobuf/message.h>
 #include <google/protobuf/repeated_field.h>
 #include <google/protobuf/extension_set.h>
@@ -55,21 +59,28 @@ class LIBPROTOC_EXPORT CodeGeneratorRequest : public ::google::protobuf::Message
   }
 
   inline const ::google::protobuf::UnknownFieldSet& unknown_fields() const {
-    return _unknown_fields_;
+    return _internal_metadata_.unknown_fields();
   }
 
   inline ::google::protobuf::UnknownFieldSet* mutable_unknown_fields() {
-    return &_unknown_fields_;
+    return _internal_metadata_.mutable_unknown_fields();
   }
 
+  inline ::google::protobuf::Arena* GetArena() const { return GetArenaNoVirtual(); }
+  inline void* GetMaybeArenaPointer() const {
+    return MaybeArenaPtr();
+  }
   static const ::google::protobuf::Descriptor* descriptor();
   static const CodeGeneratorRequest& default_instance();
 
+  void UnsafeArenaSwap(CodeGeneratorRequest* other);
   void Swap(CodeGeneratorRequest* other);
 
   // implements Message ----------------------------------------------
 
-  CodeGeneratorRequest* New() const;
+  inline CodeGeneratorRequest* New() const { return New(NULL); }
+
+  CodeGeneratorRequest* New(::google::protobuf::Arena* arena) const;
   void CopyFrom(const ::google::protobuf::Message& from);
   void MergeFrom(const ::google::protobuf::Message& from);
   void CopyFrom(const CodeGeneratorRequest& from);
@@ -88,7 +99,21 @@ class LIBPROTOC_EXPORT CodeGeneratorRequest : public ::google::protobuf::Message
   void SharedCtor();
   void SharedDtor();
   void SetCachedSize(int size) const;
+  void InternalSwap(CodeGeneratorRequest* other);
+  protected:
+  explicit CodeGeneratorRequest(::google::protobuf::Arena* arena);
+  private:
+  static void ArenaDtor(void* object);
+  inline void RegisterArenaDtor(::google::protobuf::Arena* arena);
+  private:
+  inline ::google::protobuf::Arena* GetArenaNoVirtual() const {
+    return _internal_metadata_.arena();
+  }
+  inline void* MaybeArenaPtr() const {
+    return _internal_metadata_.raw_arena_ptr();
+  }
   public:
+
   ::google::protobuf::Metadata GetMetadata() const;
 
   // nested types ----------------------------------------------------
@@ -122,6 +147,9 @@ class LIBPROTOC_EXPORT CodeGeneratorRequest : public ::google::protobuf::Message
   inline ::std::string* mutable_parameter();
   inline ::std::string* release_parameter();
   inline void set_allocated_parameter(::std::string* parameter);
+  inline ::std::string* unsafe_arena_release_parameter();
+  inline void unsafe_arena_set_allocated_parameter(
+      ::std::string* parameter);
 
   // repeated .google.protobuf.FileDescriptorProto proto_file = 15;
   inline int proto_file_size() const;
@@ -140,12 +168,14 @@ class LIBPROTOC_EXPORT CodeGeneratorRequest : public ::google::protobuf::Message
   inline void set_has_parameter();
   inline void clear_has_parameter();
 
-  ::google::protobuf::UnknownFieldSet _unknown_fields_;
-
+  ::google::protobuf::internal::InternalMetadataWithArena _internal_metadata_;
+  friend class ::google::protobuf::Arena;
+  typedef void InternalArenaConstructable_;
+  typedef void DestructorSkippable_;
   ::google::protobuf::uint32 _has_bits_[1];
   mutable int _cached_size_;
   ::google::protobuf::RepeatedPtrField< ::std::string> file_to_generate_;
-  ::std::string* parameter_;
+  ::google::protobuf::internal::ArenaStringPtr parameter_;
   ::google::protobuf::RepeatedPtrField< ::google::protobuf::FileDescriptorProto > proto_file_;
   friend void LIBPROTOC_EXPORT protobuf_AddDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
   friend void protobuf_AssignDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
@@ -169,21 +199,28 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse_File : public ::google::protobuf::M
   }
 
   inline const ::google::protobuf::UnknownFieldSet& unknown_fields() const {
-    return _unknown_fields_;
+    return _internal_metadata_.unknown_fields();
   }
 
   inline ::google::protobuf::UnknownFieldSet* mutable_unknown_fields() {
-    return &_unknown_fields_;
+    return _internal_metadata_.mutable_unknown_fields();
   }
 
+  inline ::google::protobuf::Arena* GetArena() const { return GetArenaNoVirtual(); }
+  inline void* GetMaybeArenaPointer() const {
+    return MaybeArenaPtr();
+  }
   static const ::google::protobuf::Descriptor* descriptor();
   static const CodeGeneratorResponse_File& default_instance();
 
+  void UnsafeArenaSwap(CodeGeneratorResponse_File* other);
   void Swap(CodeGeneratorResponse_File* other);
 
   // implements Message ----------------------------------------------
 
-  CodeGeneratorResponse_File* New() const;
+  inline CodeGeneratorResponse_File* New() const { return New(NULL); }
+
+  CodeGeneratorResponse_File* New(::google::protobuf::Arena* arena) const;
   void CopyFrom(const ::google::protobuf::Message& from);
   void MergeFrom(const ::google::protobuf::Message& from);
   void CopyFrom(const CodeGeneratorResponse_File& from);
@@ -202,7 +239,21 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse_File : public ::google::protobuf::M
   void SharedCtor();
   void SharedDtor();
   void SetCachedSize(int size) const;
+  void InternalSwap(CodeGeneratorResponse_File* other);
+  protected:
+  explicit CodeGeneratorResponse_File(::google::protobuf::Arena* arena);
+  private:
+  static void ArenaDtor(void* object);
+  inline void RegisterArenaDtor(::google::protobuf::Arena* arena);
+  private:
+  inline ::google::protobuf::Arena* GetArenaNoVirtual() const {
+    return _internal_metadata_.arena();
+  }
+  inline void* MaybeArenaPtr() const {
+    return _internal_metadata_.raw_arena_ptr();
+  }
   public:
+
   ::google::protobuf::Metadata GetMetadata() const;
 
   // nested types ----------------------------------------------------
@@ -220,6 +271,9 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse_File : public ::google::protobuf::M
   inline ::std::string* mutable_name();
   inline ::std::string* release_name();
   inline void set_allocated_name(::std::string* name);
+  inline ::std::string* unsafe_arena_release_name();
+  inline void unsafe_arena_set_allocated_name(
+      ::std::string* name);
 
   // optional string insertion_point = 2;
   inline bool has_insertion_point() const;
@@ -232,6 +286,9 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse_File : public ::google::protobuf::M
   inline ::std::string* mutable_insertion_point();
   inline ::std::string* release_insertion_point();
   inline void set_allocated_insertion_point(::std::string* insertion_point);
+  inline ::std::string* unsafe_arena_release_insertion_point();
+  inline void unsafe_arena_set_allocated_insertion_point(
+      ::std::string* insertion_point);
 
   // optional string content = 15;
   inline bool has_content() const;
@@ -244,6 +301,9 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse_File : public ::google::protobuf::M
   inline ::std::string* mutable_content();
   inline ::std::string* release_content();
   inline void set_allocated_content(::std::string* content);
+  inline ::std::string* unsafe_arena_release_content();
+  inline void unsafe_arena_set_allocated_content(
+      ::std::string* content);
 
   // @@protoc_insertion_point(class_scope:google.protobuf.compiler.CodeGeneratorResponse.File)
  private:
@@ -254,13 +314,15 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse_File : public ::google::protobuf::M
   inline void set_has_content();
   inline void clear_has_content();
 
-  ::google::protobuf::UnknownFieldSet _unknown_fields_;
-
+  ::google::protobuf::internal::InternalMetadataWithArena _internal_metadata_;
+  friend class ::google::protobuf::Arena;
+  typedef void InternalArenaConstructable_;
+  typedef void DestructorSkippable_;
   ::google::protobuf::uint32 _has_bits_[1];
   mutable int _cached_size_;
-  ::std::string* name_;
-  ::std::string* insertion_point_;
-  ::std::string* content_;
+  ::google::protobuf::internal::ArenaStringPtr name_;
+  ::google::protobuf::internal::ArenaStringPtr insertion_point_;
+  ::google::protobuf::internal::ArenaStringPtr content_;
   friend void LIBPROTOC_EXPORT protobuf_AddDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
   friend void protobuf_AssignDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
   friend void protobuf_ShutdownFile_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
@@ -283,21 +345,28 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse : public ::google::protobuf::Messag
   }
 
   inline const ::google::protobuf::UnknownFieldSet& unknown_fields() const {
-    return _unknown_fields_;
+    return _internal_metadata_.unknown_fields();
   }
 
   inline ::google::protobuf::UnknownFieldSet* mutable_unknown_fields() {
-    return &_unknown_fields_;
+    return _internal_metadata_.mutable_unknown_fields();
   }
 
+  inline ::google::protobuf::Arena* GetArena() const { return GetArenaNoVirtual(); }
+  inline void* GetMaybeArenaPointer() const {
+    return MaybeArenaPtr();
+  }
   static const ::google::protobuf::Descriptor* descriptor();
   static const CodeGeneratorResponse& default_instance();
 
+  void UnsafeArenaSwap(CodeGeneratorResponse* other);
   void Swap(CodeGeneratorResponse* other);
 
   // implements Message ----------------------------------------------
 
-  CodeGeneratorResponse* New() const;
+  inline CodeGeneratorResponse* New() const { return New(NULL); }
+
+  CodeGeneratorResponse* New(::google::protobuf::Arena* arena) const;
   void CopyFrom(const ::google::protobuf::Message& from);
   void MergeFrom(const ::google::protobuf::Message& from);
   void CopyFrom(const CodeGeneratorResponse& from);
@@ -316,7 +385,21 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse : public ::google::protobuf::Messag
   void SharedCtor();
   void SharedDtor();
   void SetCachedSize(int size) const;
+  void InternalSwap(CodeGeneratorResponse* other);
+  protected:
+  explicit CodeGeneratorResponse(::google::protobuf::Arena* arena);
+  private:
+  static void ArenaDtor(void* object);
+  inline void RegisterArenaDtor(::google::protobuf::Arena* arena);
+  private:
+  inline ::google::protobuf::Arena* GetArenaNoVirtual() const {
+    return _internal_metadata_.arena();
+  }
+  inline void* MaybeArenaPtr() const {
+    return _internal_metadata_.raw_arena_ptr();
+  }
   public:
+
   ::google::protobuf::Metadata GetMetadata() const;
 
   // nested types ----------------------------------------------------
@@ -336,6 +419,9 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse : public ::google::protobuf::Messag
   inline ::std::string* mutable_error();
   inline ::std::string* release_error();
   inline void set_allocated_error(::std::string* error);
+  inline ::std::string* unsafe_arena_release_error();
+  inline void unsafe_arena_set_allocated_error(
+      ::std::string* error);
 
   // repeated .google.protobuf.compiler.CodeGeneratorResponse.File file = 15;
   inline int file_size() const;
@@ -354,11 +440,13 @@ class LIBPROTOC_EXPORT CodeGeneratorResponse : public ::google::protobuf::Messag
   inline void set_has_error();
   inline void clear_has_error();
 
-  ::google::protobuf::UnknownFieldSet _unknown_fields_;
-
+  ::google::protobuf::internal::InternalMetadataWithArena _internal_metadata_;
+  friend class ::google::protobuf::Arena;
+  typedef void InternalArenaConstructable_;
+  typedef void DestructorSkippable_;
   ::google::protobuf::uint32 _has_bits_[1];
   mutable int _cached_size_;
-  ::std::string* error_;
+  ::google::protobuf::internal::ArenaStringPtr error_;
   ::google::protobuf::RepeatedPtrField< ::google::protobuf::compiler::CodeGeneratorResponse_File > file_;
   friend void LIBPROTOC_EXPORT protobuf_AddDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
   friend void protobuf_AssignDesc_google_2fprotobuf_2fcompiler_2fplugin_2eproto();
@@ -439,68 +527,67 @@ inline void CodeGeneratorRequest::clear_has_parameter() {
   _has_bits_[0] &= ~0x00000002u;
 }
 inline void CodeGeneratorRequest::clear_parameter() {
-  if (parameter_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    parameter_->clear();
-  }
+  parameter_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
   clear_has_parameter();
 }
 inline const ::std::string& CodeGeneratorRequest::parameter() const {
   // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorRequest.parameter)
-  return *parameter_;
+  return parameter_.Get(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
 }
 inline void CodeGeneratorRequest::set_parameter(const ::std::string& value) {
   set_has_parameter();
-  if (parameter_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    parameter_ = new ::std::string;
-  }
-  parameter_->assign(value);
+  parameter_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), value, GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorRequest.parameter)
 }
 inline void CodeGeneratorRequest::set_parameter(const char* value) {
   set_has_parameter();
-  if (parameter_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    parameter_ = new ::std::string;
-  }
-  parameter_->assign(value);
+  parameter_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
+              GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorRequest.parameter)
 }
-inline void CodeGeneratorRequest::set_parameter(const char* value, size_t size) {
+inline void CodeGeneratorRequest::set_parameter(const char* value,
+    size_t size) {
   set_has_parameter();
-  if (parameter_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    parameter_ = new ::std::string;
-  }
-  parameter_->assign(reinterpret_cast<const char*>(value), size);
+  parameter_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(
+      reinterpret_cast<const char*>(value), size), GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorRequest.parameter)
 }
 inline ::std::string* CodeGeneratorRequest::mutable_parameter() {
   set_has_parameter();
-  if (parameter_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    parameter_ = new ::std::string;
-  }
   // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorRequest.parameter)
-  return parameter_;
+  return parameter_.Mutable(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
 }
 inline ::std::string* CodeGeneratorRequest::release_parameter() {
   clear_has_parameter();
-  if (parameter_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    return NULL;
-  } else {
-    ::std::string* temp = parameter_;
-    parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
-    return temp;
-  }
+  return parameter_.Release(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
+}
+inline ::std::string* CodeGeneratorRequest::unsafe_arena_release_parameter() {
+  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);
+  clear_has_parameter();
+  return parameter_.UnsafeArenaRelease(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
+      GetArenaNoVirtual());
 }
 inline void CodeGeneratorRequest::set_allocated_parameter(::std::string* parameter) {
-  if (parameter_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    delete parameter_;
+  if (parameter != NULL) {
+    set_has_parameter();
+  } else {
+    clear_has_parameter();
   }
-  if (parameter) {
+  parameter_.SetAllocated(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), parameter,
+      GetArenaNoVirtual());
+  // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorRequest.parameter)
+}
+inline void CodeGeneratorRequest::unsafe_arena_set_allocated_parameter(
+    ::std::string* parameter) {
+  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);
+  if (parameter != NULL) {
     set_has_parameter();
-    parameter_ = parameter;
   } else {
     clear_has_parameter();
-    parameter_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   }
+  set_has_parameter();
+  parameter_.UnsafeArenaSetAllocated(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
+      parameter, GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorRequest.parameter)
 }
 
@@ -549,68 +636,67 @@ inline void CodeGeneratorResponse_File::clear_has_name() {
   _has_bits_[0] &= ~0x00000001u;
 }
 inline void CodeGeneratorResponse_File::clear_name() {
-  if (name_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    name_->clear();
-  }
+  name_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
   clear_has_name();
 }
 inline const ::std::string& CodeGeneratorResponse_File::name() const {
   // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorResponse.File.name)
-  return *name_;
+  return name_.Get(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
 }
 inline void CodeGeneratorResponse_File::set_name(const ::std::string& value) {
   set_has_name();
-  if (name_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    name_ = new ::std::string;
-  }
-  name_->assign(value);
+  name_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), value, GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorResponse.File.name)
 }
 inline void CodeGeneratorResponse_File::set_name(const char* value) {
   set_has_name();
-  if (name_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    name_ = new ::std::string;
-  }
-  name_->assign(value);
+  name_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
+              GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorResponse.File.name)
 }
-inline void CodeGeneratorResponse_File::set_name(const char* value, size_t size) {
+inline void CodeGeneratorResponse_File::set_name(const char* value,
+    size_t size) {
   set_has_name();
-  if (name_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    name_ = new ::std::string;
-  }
-  name_->assign(reinterpret_cast<const char*>(value), size);
+  name_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(
+      reinterpret_cast<const char*>(value), size), GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorResponse.File.name)
 }
 inline ::std::string* CodeGeneratorResponse_File::mutable_name() {
   set_has_name();
-  if (name_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    name_ = new ::std::string;
-  }
   // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorResponse.File.name)
-  return name_;
+  return name_.Mutable(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
 }
 inline ::std::string* CodeGeneratorResponse_File::release_name() {
   clear_has_name();
-  if (name_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    return NULL;
-  } else {
-    ::std::string* temp = name_;
-    name_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
-    return temp;
-  }
+  return name_.Release(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
+}
+inline ::std::string* CodeGeneratorResponse_File::unsafe_arena_release_name() {
+  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);
+  clear_has_name();
+  return name_.UnsafeArenaRelease(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
+      GetArenaNoVirtual());
 }
 inline void CodeGeneratorResponse_File::set_allocated_name(::std::string* name) {
-  if (name_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    delete name_;
+  if (name != NULL) {
+    set_has_name();
+  } else {
+    clear_has_name();
   }
-  if (name) {
+  name_.SetAllocated(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), name,
+      GetArenaNoVirtual());
+  // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.File.name)
+}
+inline void CodeGeneratorResponse_File::unsafe_arena_set_allocated_name(
+    ::std::string* name) {
+  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);
+  if (name != NULL) {
     set_has_name();
-    name_ = name;
   } else {
     clear_has_name();
-    name_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   }
+  set_has_name();
+  name_.UnsafeArenaSetAllocated(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
+      name, GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.File.name)
 }
 
@@ -625,68 +711,67 @@ inline void CodeGeneratorResponse_File::clear_has_insertion_point() {
   _has_bits_[0] &= ~0x00000002u;
 }
 inline void CodeGeneratorResponse_File::clear_insertion_point() {
-  if (insertion_point_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    insertion_point_->clear();
-  }
+  insertion_point_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
   clear_has_insertion_point();
 }
 inline const ::std::string& CodeGeneratorResponse_File::insertion_point() const {
   // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
-  return *insertion_point_;
+  return insertion_point_.Get(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
 }
 inline void CodeGeneratorResponse_File::set_insertion_point(const ::std::string& value) {
   set_has_insertion_point();
-  if (insertion_point_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    insertion_point_ = new ::std::string;
-  }
-  insertion_point_->assign(value);
+  insertion_point_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), value, GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
 }
 inline void CodeGeneratorResponse_File::set_insertion_point(const char* value) {
   set_has_insertion_point();
-  if (insertion_point_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    insertion_point_ = new ::std::string;
-  }
-  insertion_point_->assign(value);
+  insertion_point_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
+              GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
 }
-inline void CodeGeneratorResponse_File::set_insertion_point(const char* value, size_t size) {
+inline void CodeGeneratorResponse_File::set_insertion_point(const char* value,
+    size_t size) {
   set_has_insertion_point();
-  if (insertion_point_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    insertion_point_ = new ::std::string;
-  }
-  insertion_point_->assign(reinterpret_cast<const char*>(value), size);
+  insertion_point_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(
+      reinterpret_cast<const char*>(value), size), GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
 }
 inline ::std::string* CodeGeneratorResponse_File::mutable_insertion_point() {
   set_has_insertion_point();
-  if (insertion_point_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    insertion_point_ = new ::std::string;
-  }
   // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
-  return insertion_point_;
+  return insertion_point_.Mutable(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
 }
 inline ::std::string* CodeGeneratorResponse_File::release_insertion_point() {
   clear_has_insertion_point();
-  if (insertion_point_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    return NULL;
-  } else {
-    ::std::string* temp = insertion_point_;
-    insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
-    return temp;
-  }
+  return insertion_point_.Release(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
+}
+inline ::std::string* CodeGeneratorResponse_File::unsafe_arena_release_insertion_point() {
+  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);
+  clear_has_insertion_point();
+  return insertion_point_.UnsafeArenaRelease(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
+      GetArenaNoVirtual());
 }
 inline void CodeGeneratorResponse_File::set_allocated_insertion_point(::std::string* insertion_point) {
-  if (insertion_point_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    delete insertion_point_;
+  if (insertion_point != NULL) {
+    set_has_insertion_point();
+  } else {
+    clear_has_insertion_point();
   }
-  if (insertion_point) {
+  insertion_point_.SetAllocated(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), insertion_point,
+      GetArenaNoVirtual());
+  // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
+}
+inline void CodeGeneratorResponse_File::unsafe_arena_set_allocated_insertion_point(
+    ::std::string* insertion_point) {
+  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);
+  if (insertion_point != NULL) {
     set_has_insertion_point();
-    insertion_point_ = insertion_point;
   } else {
     clear_has_insertion_point();
-    insertion_point_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   }
+  set_has_insertion_point();
+  insertion_point_.UnsafeArenaSetAllocated(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
+      insertion_point, GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.File.insertion_point)
 }
 
@@ -701,68 +786,67 @@ inline void CodeGeneratorResponse_File::clear_has_content() {
   _has_bits_[0] &= ~0x00000004u;
 }
 inline void CodeGeneratorResponse_File::clear_content() {
-  if (content_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    content_->clear();
-  }
+  content_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
   clear_has_content();
 }
 inline const ::std::string& CodeGeneratorResponse_File::content() const {
   // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorResponse.File.content)
-  return *content_;
+  return content_.Get(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
 }
 inline void CodeGeneratorResponse_File::set_content(const ::std::string& value) {
   set_has_content();
-  if (content_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    content_ = new ::std::string;
-  }
-  content_->assign(value);
+  content_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), value, GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorResponse.File.content)
 }
 inline void CodeGeneratorResponse_File::set_content(const char* value) {
   set_has_content();
-  if (content_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    content_ = new ::std::string;
-  }
-  content_->assign(value);
+  content_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
+              GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorResponse.File.content)
 }
-inline void CodeGeneratorResponse_File::set_content(const char* value, size_t size) {
+inline void CodeGeneratorResponse_File::set_content(const char* value,
+    size_t size) {
   set_has_content();
-  if (content_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    content_ = new ::std::string;
-  }
-  content_->assign(reinterpret_cast<const char*>(value), size);
+  content_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(
+      reinterpret_cast<const char*>(value), size), GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorResponse.File.content)
 }
 inline ::std::string* CodeGeneratorResponse_File::mutable_content() {
   set_has_content();
-  if (content_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    content_ = new ::std::string;
-  }
   // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorResponse.File.content)
-  return content_;
+  return content_.Mutable(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
 }
 inline ::std::string* CodeGeneratorResponse_File::release_content() {
   clear_has_content();
-  if (content_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    return NULL;
-  } else {
-    ::std::string* temp = content_;
-    content_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
-    return temp;
-  }
+  return content_.Release(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
+}
+inline ::std::string* CodeGeneratorResponse_File::unsafe_arena_release_content() {
+  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);
+  clear_has_content();
+  return content_.UnsafeArenaRelease(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
+      GetArenaNoVirtual());
 }
 inline void CodeGeneratorResponse_File::set_allocated_content(::std::string* content) {
-  if (content_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    delete content_;
+  if (content != NULL) {
+    set_has_content();
+  } else {
+    clear_has_content();
   }
-  if (content) {
+  content_.SetAllocated(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), content,
+      GetArenaNoVirtual());
+  // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.File.content)
+}
+inline void CodeGeneratorResponse_File::unsafe_arena_set_allocated_content(
+    ::std::string* content) {
+  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);
+  if (content != NULL) {
     set_has_content();
-    content_ = content;
   } else {
     clear_has_content();
-    content_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   }
+  set_has_content();
+  content_.UnsafeArenaSetAllocated(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
+      content, GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.File.content)
 }
 
@@ -781,68 +865,67 @@ inline void CodeGeneratorResponse::clear_has_error() {
   _has_bits_[0] &= ~0x00000001u;
 }
 inline void CodeGeneratorResponse::clear_error() {
-  if (error_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    error_->clear();
-  }
+  error_.ClearToEmpty(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
   clear_has_error();
 }
 inline const ::std::string& CodeGeneratorResponse::error() const {
   // @@protoc_insertion_point(field_get:google.protobuf.compiler.CodeGeneratorResponse.error)
-  return *error_;
+  return error_.Get(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
 }
 inline void CodeGeneratorResponse::set_error(const ::std::string& value) {
   set_has_error();
-  if (error_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    error_ = new ::std::string;
-  }
-  error_->assign(value);
+  error_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), value, GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set:google.protobuf.compiler.CodeGeneratorResponse.error)
 }
 inline void CodeGeneratorResponse::set_error(const char* value) {
   set_has_error();
-  if (error_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    error_ = new ::std::string;
-  }
-  error_->assign(value);
+  error_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
+              GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_char:google.protobuf.compiler.CodeGeneratorResponse.error)
 }
-inline void CodeGeneratorResponse::set_error(const char* value, size_t size) {
+inline void CodeGeneratorResponse::set_error(const char* value,
+    size_t size) {
   set_has_error();
-  if (error_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    error_ = new ::std::string;
-  }
-  error_->assign(reinterpret_cast<const char*>(value), size);
+  error_.Set(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), ::std::string(
+      reinterpret_cast<const char*>(value), size), GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.compiler.CodeGeneratorResponse.error)
 }
 inline ::std::string* CodeGeneratorResponse::mutable_error() {
   set_has_error();
-  if (error_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    error_ = new ::std::string;
-  }
   // @@protoc_insertion_point(field_mutable:google.protobuf.compiler.CodeGeneratorResponse.error)
-  return error_;
+  return error_.Mutable(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
 }
 inline ::std::string* CodeGeneratorResponse::release_error() {
   clear_has_error();
-  if (error_ == &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    return NULL;
-  } else {
-    ::std::string* temp = error_;
-    error_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
-    return temp;
-  }
+  return error_.Release(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), GetArenaNoVirtual());
+}
+inline ::std::string* CodeGeneratorResponse::unsafe_arena_release_error() {
+  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);
+  clear_has_error();
+  return error_.UnsafeArenaRelease(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
+      GetArenaNoVirtual());
 }
 inline void CodeGeneratorResponse::set_allocated_error(::std::string* error) {
-  if (error_ != &::google::protobuf::internal::GetEmptyStringAlreadyInited()) {
-    delete error_;
+  if (error != NULL) {
+    set_has_error();
+  } else {
+    clear_has_error();
   }
-  if (error) {
+  error_.SetAllocated(&::google::protobuf::internal::GetEmptyStringAlreadyInited(), error,
+      GetArenaNoVirtual());
+  // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.error)
+}
+inline void CodeGeneratorResponse::unsafe_arena_set_allocated_error(
+    ::std::string* error) {
+  GOOGLE_DCHECK(GetArenaNoVirtual() != NULL);
+  if (error != NULL) {
     set_has_error();
-    error_ = error;
   } else {
     clear_has_error();
-    error_ = const_cast< ::std::string*>(&::google::protobuf::internal::GetEmptyStringAlreadyInited());
   }
+  set_has_error();
+  error_.UnsafeArenaSetAllocated(&::google::protobuf::internal::GetEmptyStringAlreadyInited(),
+      error, GetArenaNoVirtual());
   // @@protoc_insertion_point(field_set_allocated:google.protobuf.compiler.CodeGeneratorResponse.error)
 }
 
@@ -888,8 +971,8 @@ namespace google {
 namespace protobuf {
 
 
-}  // namespace google
 }  // namespace protobuf
+}  // namespace google
 #endif  // SWIG
 
 // @@protoc_insertion_point(global_scope)
diff --git a/src/google/protobuf/compiler/plugin.proto b/src/google/protobuf/compiler/plugin.proto
index b65379d7..e627289b 100644
--- a/src/google/protobuf/compiler/plugin.proto
+++ b/src/google/protobuf/compiler/plugin.proto
@@ -44,6 +44,7 @@
 // plugin should be named "protoc-gen-$NAME", and will then be used when the
 // flag "--${NAME}_out" is passed to protoc.
 
+syntax = "proto2";
 package google.protobuf.compiler;
 option java_package = "com.google.protobuf.compiler";
 option java_outer_classname = "PluginProtos";
diff --git a/src/google/protobuf/compiler/python/python_generator.cc b/src/google/protobuf/compiler/python/python_generator.cc
index 15e05da9..d72ca207 100644
--- a/src/google/protobuf/compiler/python/python_generator.cc
+++ b/src/google/protobuf/compiler/python/python_generator.cc
@@ -44,11 +44,15 @@
 // performance-minded Python code leverage the fast C++ implementation
 // directly.
 
+#include <google/protobuf/stubs/hash.h>
 #include <limits>
 #include <map>
-#include <utility>
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 #include <string>
+#include <utility>
 #include <vector>
 
 #include <google/protobuf/compiler/python/python_generator.h>
@@ -69,6 +73,41 @@ namespace python {
 
 namespace {
 
+const char* const kKeywordList[] = {
+  "and", "as", "break", "class", "continue", "def", "elif", "else", "except",
+  "False", "for", "from", "if", "import", "not", "or", "raise", "return",
+  "True", "try", "with", "while", "yield"
+};
+
+hash_set<string> MakeKeywordsMap() {
+  hash_set<string> result;
+  for (int i = 0; i < GOOGLE_ARRAYSIZE(kKeywordList); ++i) {
+    result.insert(kKeywordList[i]);
+  }
+  return result;
+}
+
+hash_set<string>* keywords_ = NULL;
+GOOGLE_PROTOBUF_DECLARE_ONCE(keywords_once_);
+
+void InitKeywords() {
+  keywords_ = new hash_set<string>();
+  *keywords_ = MakeKeywordsMap();
+}
+
+hash_set<string>& GetKeywords() {
+  ::google::protobuf::GoogleOnceInit(&keywords_once_, &InitKeywords);
+  return *keywords_;
+}
+
+string FieldName(const FieldDescriptor& field) {
+  string result = field.name();
+  if (GetKeywords().count(result) > 0) {
+    result.append("_");
+  }
+  return result;
+}
+
 // Returns a copy of |filename| with any trailing ".protodevel" or ".proto
 // suffix stripped.
 // TODO(robinson): Unify with copy in compiler/cpp/internal/helpers.cc.
@@ -88,6 +127,37 @@ string ModuleName(const string& filename) {
 }
 
 
+// Returns the alias we assign to the module of the given .proto filename
+// when importing. See testPackageInitializationImport in
+// google/protobuf/python/reflection_test.py
+// to see why we need the alias.
+string ModuleAlias(const string& filename) {
+  string module_name = ModuleName(filename);
+  // We can't have dots in the module name, so we replace each with _dot_.
+  // But that could lead to a collision between a.b and a_dot_b, so we also
+  // duplicate each underscore.
+  GlobalReplaceSubstring("_", "__", &module_name);
+  GlobalReplaceSubstring(".", "_dot_", &module_name);
+  return module_name;
+}
+
+
+// Returns an import statement of form "from X.Y.Z import T" for the given
+// .proto filename.
+string ModuleImportStatement(const string& filename) {
+  string module_name = ModuleName(filename);
+  int last_dot_pos = module_name.rfind('.');
+  if (last_dot_pos == string::npos) {
+    // NOTE(petya): this is not tested as it would require a protocol buffer
+    // outside of any package, and I don't think that is easily achievable.
+    return "import " + module_name;
+  } else {
+    return "from " + module_name.substr(0, last_dot_pos) + " import " +
+        module_name.substr(last_dot_pos + 1);
+  }
+}
+
+
 // Returns the name of all containing types for descriptor,
 // in order from outermost to innermost, followed by descriptor's
 // own name.  Each name is separated by |separator|.
@@ -309,9 +379,12 @@ bool Generator::Generate(const FileDescriptor* file,
 // Prints Python imports for all modules imported by |file|.
 void Generator::PrintImports() const {
   for (int i = 0; i < file_->dependency_count(); ++i) {
-    string module_name = ModuleName(file_->dependency(i)->name());
-    printer_->Print("import $module$\n", "module",
-                    module_name);
+    const string& filename = file_->dependency(i)->name();
+    string import_statement = ModuleImportStatement(filename);
+    string module_alias = ModuleAlias(filename);
+    printer_->Print("$statement$ as $alias$\n", "statement",
+                    import_statement, "alias", module_alias);
+    CopyPublicDependenciesAliases(module_alias, file_->dependency(i));
   }
   printer_->Print("\n");
 
@@ -342,8 +415,9 @@ void Generator::PrintFileDescriptor() const {
   if (file_->dependency_count() != 0) {
     printer_->Print(",\ndependencies=[");
     for (int i = 0; i < file_->dependency_count(); ++i) {
-      string module_name = ModuleName(file_->dependency(i)->name());
-      printer_->Print("$module_name$.DESCRIPTOR,", "module_name", module_name);
+      string module_alias = ModuleAlias(file_->dependency(i)->name());
+      printer_->Print("$module_alias$.DESCRIPTOR,", "module_alias",
+                      module_alias);
     }
     printer_->Print("]");
   }
@@ -457,7 +531,7 @@ void Generator::PrintTopLevelExtensions() const {
     printer_->Print("$constant_name$ = $number$\n",
       "constant_name", constant_name,
       "number", SimpleItoa(extension_field.number()));
-    printer_->Print("$name$ = ", "name", extension_field.name());
+    printer_->Print("$name$ = ", "name", FieldName(extension_field));
     PrintFieldDescriptor(extension_field, is_extension);
     printer_->Print("\n");
   }
@@ -804,7 +878,7 @@ void Generator::AddExtensionToFileDescriptor(
     const FieldDescriptor& descriptor) const {
   map<string, string> m;
   m["descriptor_name"] = kDescriptorKey;
-  m["field_name"] = descriptor.name();
+  m["field_name"] = FieldName(descriptor);
   const char file_descriptor_template[] =
       "$descriptor_name$.extensions_by_name['$field_name$'] = "
       "$field_name$\n";
@@ -857,12 +931,12 @@ string Generator::FieldReferencingExpression(
   GOOGLE_CHECK_EQ(field.file(), file_) << field.file()->name() << " vs. "
                                 << file_->name();
   if (!containing_type) {
-    return field.name();
+    return FieldName(field);
   }
   return strings::Substitute(
       "$0.$1['$2']",
       ModuleLevelDescriptorName(*containing_type),
-      python_dict_name, field.name());
+      python_dict_name, FieldName(field));
 }
 
 // Prints containing_type for nested descriptors or enum descriptors.
@@ -991,7 +1065,7 @@ void Generator::PrintFieldDescriptor(
   string options_string;
   field.options().SerializeToString(&options_string);
   map<string, string> m;
-  m["name"] = field.name();
+  m["name"] = FieldName(field);
   m["full_name"] = field.full_name();
   m["index"] = SimpleItoa(field.index());
   m["number"] = SimpleItoa(field.number());
@@ -1084,7 +1158,7 @@ string Generator::ModuleLevelDescriptorName(
   // We now have the name relative to its own module.  Also qualify with
   // the module name iff this descriptor is from a different .proto file.
   if (descriptor.file() != file_) {
-    name = ModuleName(descriptor.file()->name()) + "." + name;
+    name = ModuleAlias(descriptor.file()->name()) + "." + name;
   }
   return name;
 }
@@ -1096,7 +1170,7 @@ string Generator::ModuleLevelDescriptorName(
 string Generator::ModuleLevelMessageName(const Descriptor& descriptor) const {
   string name = NamePrefixedWithNestedTypes(descriptor, ".");
   if (descriptor.file() != file_) {
-    name = ModuleName(descriptor.file()->name()) + "." + name;
+    name = ModuleAlias(descriptor.file()->name()) + "." + name;
   }
   return name;
 }
@@ -1109,7 +1183,7 @@ string Generator::ModuleLevelServiceDescriptorName(
   UpperString(&name);
   name = "_" + name;
   if (descriptor.file() != file_) {
-    name = ModuleName(descriptor.file()->name()) + "." + name;
+    name = ModuleAlias(descriptor.file()->name()) + "." + name;
   }
   return name;
 }
@@ -1211,7 +1285,7 @@ void Generator::FixOptionsForField(
     if (field.is_extension()) {
       if (field.extension_scope() == NULL) {
         // Top level extensions.
-        field_name = field.name();
+        field_name = FieldName(field);
       } else {
         field_name = FieldReferencingExpression(
             field.extension_scope(), field, "extensions_by_name");
@@ -1256,6 +1330,18 @@ void Generator::FixOptionsForMessage(const Descriptor& descriptor) const {
   }
 }
 
+// If a dependency forwards other files through public dependencies, let's
+// copy over the corresponding module aliases.
+void Generator::CopyPublicDependenciesAliases(
+    const string& copy_from, const FileDescriptor* file) const {
+  for (int i = 0; i < file->public_dependency_count(); ++i) {
+    string module_alias = ModuleAlias(file->public_dependency(i)->name());
+    printer_->Print("$alias$ = $copy_from$.$alias$\n", "alias", module_alias,
+                    "copy_from", copy_from);
+    CopyPublicDependenciesAliases(copy_from, file->public_dependency(i));
+  }
+}
+
 }  // namespace python
 }  // namespace compiler
 }  // namespace protobuf
diff --git a/src/google/protobuf/compiler/python/python_generator.h b/src/google/protobuf/compiler/python/python_generator.h
index f86e9ea2..7e8f58e5 100644
--- a/src/google/protobuf/compiler/python/python_generator.h
+++ b/src/google/protobuf/compiler/python/python_generator.h
@@ -148,6 +148,9 @@ class LIBPROTOC_EXPORT Generator : public CodeGenerator {
   void FixOptionsForEnum(const EnumDescriptor& descriptor) const;
   void FixOptionsForMessage(const Descriptor& descriptor) const;
 
+  void CopyPublicDependenciesAliases(
+      const string& copy_from, const FileDescriptor* file) const;
+
   // Very coarse-grained lock to ensure that Generate() is reentrant.
   // Guards file_, printer_ and file_descriptor_serialized_.
   mutable Mutex mutex_;
diff --git a/src/google/protobuf/compiler/python/python_plugin_unittest.cc b/src/google/protobuf/compiler/python/python_plugin_unittest.cc
index 09dbc654..24c2f971 100644
--- a/src/google/protobuf/compiler/python/python_plugin_unittest.cc
+++ b/src/google/protobuf/compiler/python/python_plugin_unittest.cc
@@ -35,6 +35,9 @@
 //   worth.
 
 #include <memory>
+#ifndef _SHARED_PTR_H
+#include <google/protobuf/stubs/shared_ptr.h>
+#endif
 
 #include <google/protobuf/compiler/python/python_generator.h>
 #include <google/protobuf/compiler/command_line_interface.h>
author	Feng Xiao <xfxyjwf@gmail.com>	2014-11-10 17:34:54 -0800
committer	Feng Xiao <xfxyjwf@gmail.com>	2014-11-10 17:34:54 -0800
commit	6ef984af4b0c63c1c33127a12dcfc8e6359f0c9e (patch)
tree	d17c61ff9f3ae28224fbddac6d26bfc59e2cf755 /src/google/protobuf/compiler
parent	baca1a8a1aa180c42de6278d3b8286c4496c6a10 (diff)