Merge branch 'master' into php-wkt

BUILD

@@ -164,6 +164,7 @@ cc_library(
         # AUTOGEN(protobuf_lite_srcs)
         "src/google/protobuf/any_lite.cc",
         "src/google/protobuf/arena.cc",
+        "src/google/protobuf/arenastring.cc",
         "src/google/protobuf/extension_set.cc",
         "src/google/protobuf/generated_enum_util.cc",
         "src/google/protobuf/generated_message_table_driven_lite.cc",

CHANGES.txt

@@ -3,10 +3,13 @@ Unreleased Changes
   Protocol Compiler
   * The proto compiler no longer requires a .proto filename when it is not
     generating code.
+  * Added flag `--deterministic_output` to `protoc --encode=...`.
+  * Fixed deadlock when using google.protobuf.Any embedded in aggregate options.
 
   C++
   * Arenas are now unconditionally enabled. cc_enable_arenas no longer has
     any effect.
+  * Removed inlined string support, which is incompatible with arenas.
   * Fix a memory corruption bug in reflection when mixing optional and
     non-optional fields.
   * Make SpaceUsed() calculation more thorough for map fields.
@@ -20,9 +23,23 @@ Unreleased Changes
   * When running under ASAN, skip a test that makes huge allocations.
   * Fixed a crash that could happen when creating more than 256 extensions in
     a single message.
+  * Fix a crash in BuildFile when passing in invalid descriptor proto.
+  * Parser security fix when operating with CodedInputStream.
+  * Warn against the use of AllowUnknownExtension.
+  * Migrated to C++11 for-range loops instead of index-based loops where
+    possible. This fixes a lot of warnings when compiling with -Wsign-compare.
 
   Java
   * Bugfix in mergeFrom() when a oneof has multiple message fields.
+  * Fix RopeByteString.RopeInputStream.read() returning -1 when told to read
+    0 bytes when not at EOF.
+  * Redefine remove(Object) on primitive repeated field Lists to avoid
+    autoboxing.
+  * Support "\u" escapes in textformat string literals.
+  * Trailing empty spaces are no longer ignored for FieldMask.
+  * Fix FieldMaskUtil.subtract to recursively remove mask.
+  * Mark enums with `@java.lang.Deprecated` if the proto enum has option
+    `deprecated = true;`.
 
   Python
   * Print google.protobuf.NullValue as null instead of "NULL_VALUE" when it is

cmake/extract_includes.bat.in

@@ -53,7 +53,6 @@ copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\generated_message_tab
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\generated_message_util.h" include\google\protobuf\generated_message_util.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\has_bits.h" include\google\protobuf\has_bits.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\implicit_weak_message.h" include\google\protobuf\implicit_weak_message.h
-copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\inlined_string_field.h" include\google\protobuf\inlined_string_field.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\io\coded_stream.h" include\google\protobuf\io\coded_stream.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\io\gzip_stream.h" include\google\protobuf\io\gzip_stream.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\io\io_win32.h" include\google\protobuf\io\io_win32.h
@@ -88,7 +87,6 @@ copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\bytestream.h" i
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\callback.h" include\google\protobuf\stubs\callback.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\casts.h" include\google\protobuf\stubs\casts.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\common.h" include\google\protobuf\stubs\common.h
-copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\fastmem.h" include\google\protobuf\stubs\fastmem.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\hash.h" include\google\protobuf\stubs\hash.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\logging.h" include\google\protobuf\stubs\logging.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\stubs\macros.h" include\google\protobuf\stubs\macros.h

cmake/libprotobuf-lite.cmake

@@ -1,6 +1,7 @@
 set(libprotobuf_lite_files
   ${protobuf_source_dir}/src/google/protobuf/any_lite.cc
   ${protobuf_source_dir}/src/google/protobuf/arena.cc
+  ${protobuf_source_dir}/src/google/protobuf/arenastring.cc
   ${protobuf_source_dir}/src/google/protobuf/extension_set.cc
   ${protobuf_source_dir}/src/google/protobuf/generated_enum_util.cc
   ${protobuf_source_dir}/src/google/protobuf/generated_message_table_driven_lite.cc

cmake/protobuf-module.cmake.in

@@ -97,6 +97,10 @@ function(_protobuf_find_libraries name filename)
   else()
     get_target_property(${name}_LIBRARY_RELEASE protobuf::lib${filename}
       LOCATION_RELEASE)
+    get_target_property(${name}_LIBRARY_RELWITHDEBINFO protobuf::lib${filename}
+      LOCATION_RELWITHDEBINFO)
+    get_target_property(${name}_LIBRARY_MINSIZEREL protobuf::lib${filename}
+      LOCATION_MINSIZEREL)
     get_target_property(${name}_LIBRARY_DEBUG protobuf::lib${filename}
       LOCATION_DEBUG)
 
@@ -146,6 +150,14 @@ get_target_property(Protobuf_INCLUDE_DIRS protobuf::libprotobuf
 # Set the protoc Executable
 get_target_property(Protobuf_PROTOC_EXECUTABLE protobuf::protoc
   IMPORTED_LOCATION_RELEASE)
+if(NOT EXISTS "${Protobuf_PROTOC_EXECUTABLE}")
+  get_target_property(Protobuf_PROTOC_EXECUTABLE protobuf::protoc
+    IMPORTED_LOCATION_RELWITHDEBINFO)
+endif()
+if(NOT EXISTS "${Protobuf_PROTOC_EXECUTABLE}")
+  get_target_property(Protobuf_PROTOC_EXECUTABLE protobuf::protoc
+    IMPORTED_LOCATION_MINSIZEREL)
+endif()
 if(NOT EXISTS "${Protobuf_PROTOC_EXECUTABLE}")
   get_target_property(Protobuf_PROTOC_EXECUTABLE protobuf::protoc
     IMPORTED_LOCATION_DEBUG)

conformance/Makefile.am

@@ -333,7 +333,7 @@ conformance-php-c:
 
 # Targets for actually running tests.
 test_cpp: protoc_middleman conformance-test-runner conformance-cpp
-	./conformance-test-runner --enforce_recommended --failure_list failure_list_cpp.txt ./conformance-cpp
+	./conformance-test-runner --enforce_recommended --failure_list failure_list_cpp.txt --text_format_failure_list text_format_failure_list_cpp.txt ./conformance-cpp
 
 test_java: protoc_middleman conformance-test-runner conformance-java
 	./conformance-test-runner --enforce_recommended --failure_list failure_list_java.txt --text_format_failure_list text_format_failure_list_java.txt ./conformance-java
@@ -359,10 +359,24 @@ test_php_c_32: protoc_middleman conformance-test-runner conformance-php-c $(othe
 # These depend on library paths being properly set up.  The easiest way to
 # run them is to just use "tox" from the python dir.
 test_python: protoc_middleman conformance-test-runner
-	./conformance-test-runner --enforce_recommended --failure_list failure_list_python.txt --text_format_failure_list text_format_failure_list_python.txt ./conformance_python.py
+	VERSION="$(shell python --version 2>&1)"; \
+	if [[ "$$VERSION"  == "Python 2.7"* ]]; then \
+	  echo "Using Python 2.7 failure list."; \
+	  ./conformance-test-runner --enforce_recommended --failure_list failure_list_python.txt --text_format_failure_list text_format_failure_list_python_2.7.txt ./conformance_python.py; \
+	else \
+	  echo "Using Python >2.7 failure list."; \
+	  ./conformance-test-runner --enforce_recommended --failure_list failure_list_python.txt --text_format_failure_list text_format_failure_list_python.txt ./conformance_python.py; \
+	fi
 
 test_python_cpp: protoc_middleman conformance-test-runner
-	./conformance-test-runner --enforce_recommended --failure_list failure_list_python_cpp.txt ./conformance_python.py
+	VERSION="$(shell python --version 2>&1)"; \
+	if [[ "$$VERSION"  == "Python 2.7"* ]]; then \
+	  echo "Using Python 2.7 failure list."; \
+	  ./conformance-test-runner --enforce_recommended --failure_list failure_list_python_cpp.txt --text_format_failure_list text_format_failure_list_python_cpp_2.7.txt ./conformance_python.py; \
+	else \
+	  echo "Using Python >2.7 failure list."; \
+	  ./conformance-test-runner --enforce_recommended --failure_list failure_list_python_cpp.txt --text_format_failure_list text_format_failure_list_python_cpp.txt ./conformance_python.py; \
+	fi
 
 test_nodejs: protoc_middleman conformance-test-runner $(other_language_protoc_outputs)
 	NODE_PATH=../js:. ./conformance-test-runner --enforce_recommended --failure_list failure_list_js.txt ./conformance_nodejs.js

conformance/failure_list_js.txt

@@ -1 +0,0 @@
-

conformance/text_format_conformance_suite.cc

@@ -258,6 +258,84 @@ void TextFormatConformanceTestSuite::RunSuiteImpl() {
   RunValidTextFormatTest("FloatFieldLargerThanUint64", REQUIRED,
                          "optional_float: 18446744073709551616");
 
+  // String literals x {Strings, Bytes}
+  for (const auto& field_type : std::vector<std::string>{"String", "Bytes"}) {
+    const std::string field_name =
+        field_type == "String" ? "optional_string" : "optional_bytes";
+    RunValidTextFormatTest(
+        StrCat("StringLiteralConcat", field_type), REQUIRED,
+        StrCat(field_name, ": 'first' \"second\"\n'third'"));
+    RunValidTextFormatTest(
+        StrCat("StringLiteralBasicEscapes", field_type), REQUIRED,
+        StrCat(field_name, ": '\\a\\b\\f\\n\\r\\t\\v\\?\\\\\\'\\\"'"));
+    RunValidTextFormatTest(
+        StrCat("StringLiteralOctalEscapes", field_type), REQUIRED,
+        StrCat(field_name, ": '\\341\\210\\264'"));
+    RunValidTextFormatTest(StrCat("StringLiteralHexEscapes", field_type),
+                           REQUIRED,
+                           StrCat(field_name, ": '\\xe1\\x88\\xb4'"));
+    RunValidTextFormatTest(
+        StrCat("StringLiteralShortUnicodeEscape", field_type),
+        RECOMMENDED, StrCat(field_name, ": '\\u1234'"));
+    RunValidTextFormatTest(
+        StrCat("StringLiteralLongUnicodeEscapes", field_type),
+        RECOMMENDED, StrCat(field_name, ": '\\U00001234\\U00010437'"));
+    // String literals don't include line feeds.
+    ExpectParseFailure(StrCat("StringLiteralIncludesLF", field_type),
+                       REQUIRED,
+                       StrCat(field_name, ": 'first line\nsecond line'"));
+    // Unicode escapes don't include code points that lie beyond the planes
+    // (> 0x10ffff).
+    ExpectParseFailure(
+        StrCat("StringLiteralLongUnicodeEscapeTooLarge", field_type),
+        REQUIRED, StrCat(field_name, ": '\\U00110000'"));
+    // Unicode escapes don't include surrogates.
+    ExpectParseFailure(
+        StrCat("StringLiteralShortUnicodeEscapeSurrogatePair",
+                     field_type),
+        RECOMMENDED, StrCat(field_name, ": '\\ud801\\udc37'"));
+    ExpectParseFailure(
+        StrCat("StringLiteralShortUnicodeEscapeSurrogateFirstOnly",
+                     field_type),
+        RECOMMENDED, StrCat(field_name, ": '\\ud800'"));
+    ExpectParseFailure(
+        StrCat("StringLiteralShortUnicodeEscapeSurrogateSecondOnly",
+                     field_type),
+        RECOMMENDED, StrCat(field_name, ": '\\udc00'"));
+    ExpectParseFailure(
+        StrCat("StringLiteralLongUnicodeEscapeSurrogateFirstOnly",
+                     field_type),
+        RECOMMENDED, StrCat(field_name, ": '\\U0000d800'"));
+    ExpectParseFailure(
+        StrCat("StringLiteralLongUnicodeEscapeSurrogateSecondOnly",
+                     field_type),
+        RECOMMENDED, StrCat(field_name, ": '\\U0000dc00'"));
+    ExpectParseFailure(
+        StrCat("StringLiteralLongUnicodeEscapeSurrogatePair", field_type),
+        RECOMMENDED, StrCat(field_name, ": '\\U0000d801\\U00000dc37'"));
+    ExpectParseFailure(
+        StrCat("StringLiteralUnicodeEscapeSurrogatePairLongShort",
+                     field_type),
+        RECOMMENDED, StrCat(field_name, ": '\\U0000d801\\udc37'"));
+    ExpectParseFailure(
+        StrCat("StringLiteralUnicodeEscapeSurrogatePairShortLong",
+                     field_type),
+        RECOMMENDED, StrCat(field_name, ": '\\ud801\\U0000dc37'"));
+
+    // The following method depend on the type of field, as strings have extra
+    // validation.
+    const auto test_method =
+        field_type == "String"
+            ? &TextFormatConformanceTestSuite::ExpectParseFailure
+            : &TextFormatConformanceTestSuite::RunValidTextFormatTest;
+
+    // String fields reject invalid UTF-8 byte sequences; bytes fields don't.
+    (this->*test_method)(StrCat(field_type, "FieldBadUTF8Octal"),
+                         REQUIRED, StrCat(field_name, ": '\\300'"));
+    (this->*test_method)(StrCat(field_type, "FieldBadUTF8Hex"), REQUIRED,
+                         StrCat(field_name, ": '\\xc0'"));
+  }
+
   // Group fields
   RunValidTextFormatTestProto2("GroupFieldNoColon", REQUIRED,
                                "Data { group_int32: 1 }");

conformance/text_format_failure_list_cpp.txt

@@ -0,0 +1,20 @@
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateFirstOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateFirstOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogatePairBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogatePairString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateSecondOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateSecondOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateFirstOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateFirstOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogatePairBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogatePairString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateSecondOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateSecondOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairLongShortBytes
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairLongShortString
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairShortLongBytes
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairShortLongString
+Required.Proto3.TextFormatInput.StringFieldBadUTF8Hex
+Required.Proto3.TextFormatInput.StringFieldBadUTF8Octal
+Required.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeTooLargeBytes
+Required.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeTooLargeString

conformance/text_format_failure_list_java.txt

@@ -4,3 +4,10 @@ Recommended.Proto3.ProtobufInput.RepeatedUnknownFields_Drop.TextFormatOutput
 Recommended.Proto3.ProtobufInput.ScalarUnknownFields_Drop.TextFormatOutput
 Required.Proto3.TextFormatInput.AnyField.ProtobufOutput
 Required.Proto3.TextFormatInput.AnyField.TextFormatOutput
+
+Required.Proto3.TextFormatInput.StringFieldBadUTF8Hex
+Required.Proto3.TextFormatInput.StringFieldBadUTF8Octal
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesBytes.ProtobufOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesBytes.TextFormatOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesString.ProtobufOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesString.TextFormatOutput

conformance/text_format_failure_list_python.txt

@@ -3,3 +3,32 @@
 # TODO: These should be fixed.
 Required.Proto3.TextFormatInput.FloatFieldMaxValue.ProtobufOutput
 Required.Proto3.TextFormatInput.FloatFieldMaxValue.TextFormatOutput
+
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateFirstOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateFirstOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogatePairBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogatePairString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateSecondOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateSecondOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesBytes.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesBytes.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesString.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesString.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeBytes.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeBytes.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeString.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeString.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateFirstOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateFirstOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogatePairBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogatePairString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateSecondOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateSecondOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairLongShortBytes
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairLongShortString
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairShortLongBytes
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairShortLongString
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesBytes.ProtobufOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesBytes.TextFormatOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesString.ProtobufOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesString.TextFormatOutput

conformance/text_format_failure_list_python_2.7.txt

@@ -0,0 +1,36 @@
+# This is the list of text format conformance tests that are known to fail right
+# now.
+# TODO: These should be fixed.
+Required.Proto3.TextFormatInput.FloatFieldMaxValue.ProtobufOutput
+Required.Proto3.TextFormatInput.FloatFieldMaxValue.TextFormatOutput
+
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateFirstOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateFirstOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogatePairBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogatePairString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateSecondOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateSecondOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesBytes.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesBytes.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesString.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesString.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeBytes.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeBytes.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeString.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeString.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateFirstOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateFirstOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogatePairBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogatePairString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateSecondOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateSecondOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairLongShortBytes
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairLongShortString
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairShortLongBytes
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairShortLongString
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesBytes.ProtobufOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesBytes.TextFormatOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesString.ProtobufOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesString.TextFormatOutput
+Required.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeTooLargeBytes
+Required.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeTooLargeString

conformance/text_format_failure_list_python_cpp.txt

@@ -0,0 +1,28 @@
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateFirstOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateFirstOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogatePairBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogatePairString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateSecondOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateSecondOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesBytes.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesBytes.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesString.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesString.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeBytes.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeBytes.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeString.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeString.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateFirstOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateFirstOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogatePairBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogatePairString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateSecondOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateSecondOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairLongShortBytes
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairLongShortString
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairShortLongBytes
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairShortLongString
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesBytes.ProtobufOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesBytes.TextFormatOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesString.ProtobufOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesString.TextFormatOutput

conformance/text_format_failure_list_python_cpp_2.7.txt

@@ -0,0 +1,30 @@
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateFirstOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateFirstOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogatePairBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogatePairString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateSecondOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeSurrogateSecondOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesBytes.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesBytes.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesString.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapesString.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeBytes.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeBytes.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeString.ProtobufOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeString.TextFormatOutput
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateFirstOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateFirstOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogatePairBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogatePairString
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateSecondOnlyBytes
+Recommended.Proto3.TextFormatInput.StringLiteralShortUnicodeEscapeSurrogateSecondOnlyString
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairLongShortBytes
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairLongShortString
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairShortLongBytes
+Recommended.Proto3.TextFormatInput.StringLiteralUnicodeEscapeSurrogatePairShortLongString
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesBytes.ProtobufOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesBytes.TextFormatOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesString.ProtobufOutput
+Required.Proto3.TextFormatInput.StringLiteralBasicEscapesString.TextFormatOutput
+Required.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeTooLargeBytes
+Required.Proto3.TextFormatInput.StringLiteralLongUnicodeEscapeTooLargeString

csharp/src/Google.Protobuf.Test/ByteStringTest.cs

@@ -110,6 +110,18 @@ namespace Google.Protobuf
             Assert.AreEqual(10, bs[0]);
         }
 
+        [Test]
+        public void CopyFromReadOnlySpanCopiesContents()
+        {
+            byte[] data = new byte[1];
+            data[0] = 10;
+            ReadOnlySpan<byte> byteSpan = data;
+            var bs = ByteString.CopyFrom(byteSpan);
+            Assert.AreEqual(10, bs[0]);
+            data[0] = 5;
+            Assert.AreEqual(10, bs[0]);
+        }
+
         [Test]
         public void ToByteArrayCopiesContents()
         {

csharp/src/Google.Protobuf/ByteString.cs

@@ -245,6 +245,7 @@ namespace Google.Protobuf
         /// are copied, so further modifications to the span will not
         /// be reflected in the returned <see cref="ByteString" />.
         /// </summary>
+        [SecuritySafeCritical]
         public static ByteString CopyFrom(ReadOnlySpan<byte> bytes)
         {
             return new ByteString(bytes.ToArray());

editors/proto.vim

@@ -69,10 +69,10 @@ syn keyword pbBool      true false
 syn match   pbInt     /-\?\<\d\+\>/
 syn match   pbInt     /\<0[xX]\x+\>/
 syn match   pbFloat   /\<-\?\d*\(\.\d*\)\?/
-syn region  pbComment start="\/\*" end="\*\/" contains=@pbCommentGrp
-syn region  pbComment start="//" skip="\\$" end="$" keepend contains=@pbCommentGrp
-syn region  pbString  start=/"/ skip=/\\./ end=/"/
-syn region  pbString  start=/'/ skip=/\\./ end=/'/
+syn region  pbComment start="\/\*" end="\*\/" contains=@pbCommentGrp,@Spell
+syn region  pbComment start="//" skip="\\$" end="$" keepend contains=@pbCommentGrp,@Spell
+syn region  pbString  start=/"/ skip=/\\./ end=/"/ contains=@Spell
+syn region  pbString  start=/'/ skip=/\\./ end=/'/ contains=@Spell
 
 if version >= 508 || !exists("did_proto_syn_inits")
   if version < 508

java/core/src/main/java/com/google/protobuf/AbstractProtobufList.java

@@ -142,7 +142,12 @@ abstract class AbstractProtobufList<E> extends AbstractList<E> implements Protob
   @Override
   public boolean remove(Object o) {
     ensureIsMutable();
-    return super.remove(o);
+    int index = indexOf(o);
+    if (index == -1) {
+      return false;
+    }
+    remove(index);
+    return true;
   }
 
   @Override

java/core/src/main/java/com/google/protobuf/BooleanArrayList.java

@@ -267,20 +267,6 @@ final class BooleanArrayList extends AbstractProtobufList<Boolean>
     return true;
   }
 
-  @Override
-  public boolean remove(Object o) {
-    ensureIsMutable();
-    for (int i = 0; i < size; i++) {
-      if (o.equals(array[i])) {
-        System.arraycopy(array, i + 1, array, i, size - i - 1);
-        size--;
-        modCount++;
-        return true;
-      }
-    }
-    return false;
-  }
-
   @Override
   public Boolean remove(int index) {
     ensureIsMutable();

java/core/src/main/java/com/google/protobuf/CodedInputStream.java

@@ -41,6 +41,7 @@ import static com.google.protobuf.WireFormat.MAX_VARINT_SIZE;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.nio.Buffer;
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -2009,14 +2010,14 @@ public abstract class CodedInputStream {
       int prevPos = buffer.position();
       int prevLimit = buffer.limit();
       try {
-        buffer.position(bufferPos(begin));
-        buffer.limit(bufferPos(end));
+        ((Buffer) buffer).position(bufferPos(begin));
+        ((Buffer) buffer).limit(bufferPos(end));
         return buffer.slice();
       } catch (IllegalArgumentException e) {
         throw InvalidProtocolBufferException.truncatedMessage();
       } finally {
-        buffer.position(prevPos);
-        buffer.limit(prevLimit);
+        ((Buffer) buffer).position(prevPos);
+        ((Buffer) buffer).limit(prevLimit);
       }
     }
   }
@@ -3910,14 +3911,14 @@ public abstract class CodedInputStream {
       int prevPos = currentByteBuffer.position();
       int prevLimit = currentByteBuffer.limit();
       try {
-        currentByteBuffer.position(begin);
-        currentByteBuffer.limit(end);
+        ((Buffer) currentByteBuffer).position(begin);
+        ((Buffer) currentByteBuffer).limit(end);
         return currentByteBuffer.slice();
       } catch (IllegalArgumentException e) {
         throw InvalidProtocolBufferException.truncatedMessage();
       } finally {
-        currentByteBuffer.position(prevPos);
-        currentByteBuffer.limit(prevLimit);
+        ((Buffer) currentByteBuffer).position(prevPos);
+        ((Buffer) currentByteBuffer).limit(prevLimit);
       }
     }
   }

java/core/src/main/java/com/google/protobuf/Descriptors.java

@@ -764,7 +764,10 @@ public final class Descriptors {
     /**
      * Finds a field by name.
      *
-     * @param name The unqualified name of the field (e.g. "foo").
+     * @param name The unqualified name of the field (e.g. "foo"). For protocol buffer messages that
+     *     follow <a
+     *     href=https://developers.google.com/protocol-buffers/docs/style#message_and_field_names>Google's
+     *     guidance on naming</a> this will be a snake case string, such as <pre>song_name</pre>.
      * @return The field's descriptor, or {@code null} if not found.
      */
     public FieldDescriptor findFieldByName(final String name) {

java/core/src/main/java/com/google/protobuf/DoubleArrayList.java

@@ -267,20 +267,6 @@ final class DoubleArrayList extends AbstractProtobufList<Double>
     return true;
   }
 
-  @Override
-  public boolean remove(Object o) {
-    ensureIsMutable();
-    for (int i = 0; i < size; i++) {
-      if (o.equals(array[i])) {
-        System.arraycopy(array, i + 1, array, i, size - i - 1);
-        size--;
-        modCount++;
-        return true;
-      }
-    }
-    return false;
-  }
-
   @Override
   public Double remove(int index) {
     ensureIsMutable();

java/core/src/main/java/com/google/protobuf/ExtensionRegistryFactory.java

@@ -46,7 +46,6 @@ final class ExtensionRegistryFactory {
   @Nullable */
   static final Class<?> EXTENSION_REGISTRY_CLASS = reflectExtensionRegistry();
 
-  /* @Nullable */
   static Class<?> reflectExtensionRegistry() {
     try {
       return Class.forName(FULL_REGISTRY_CLASS_NAME);
@@ -77,7 +76,6 @@ final class ExtensionRegistryFactory {
         && EXTENSION_REGISTRY_CLASS.isAssignableFrom(registry.getClass());
   }
 
-  /* @Nullable */
   private static final ExtensionRegistryLite invokeSubclassFactory(String methodName) {
     if (EXTENSION_REGISTRY_CLASS == null) {
       return null;

java/core/src/main/java/com/google/protobuf/ExtensionRegistryLite.java

@@ -84,10 +84,8 @@ public class ExtensionRegistryLite {
   static final String EXTENSION_CLASS_NAME = "com.google.protobuf.Extension";
 
   private static class ExtensionClassHolder {
-    /* @Nullable */
     static final Class<?> INSTANCE = resolveExtensionClass();
 
-    /* @Nullable */
     static Class<?> resolveExtensionClass() {
       try {
         return Class.forName(EXTENSION_CLASS_NAME);

java/core/src/main/java/com/google/protobuf/FieldType.java

@@ -204,7 +204,6 @@ public enum FieldType {
    *
    * @return the {@link FieldType} or {@code null} if not found.
    */
-  /* @Nullable */
   public static FieldType forId(int id) {
     if (id < 0 || id >= VALUES.length) {
       return null;
@@ -228,7 +227,6 @@ public enum FieldType {
    *
    * @return the generic super class/interface, or {@code null} if not found.
    */
-  /* @Nullable */
   private static Type getGenericSuperList(Class<?> clazz) {
     // First look at interfaces.
     Type[] genericInterfaces = clazz.getGenericInterfaces();

java/core/src/main/java/com/google/protobuf/FloatArrayList.java

@@ -266,20 +266,6 @@ final class FloatArrayList extends AbstractProtobufList<Float>
     return true;
   }
 
-  @Override
-  public boolean remove(Object o) {
-    ensureIsMutable();
-    for (int i = 0; i < size; i++) {
-      if (o.equals(array[i])) {
-        System.arraycopy(array, i + 1, array, i, size - i - 1);
-        size--;
-        modCount++;
-        return true;
-      }
-    }
-    return false;
-  }
-
   @Override
   public Float remove(int index) {
     ensureIsMutable();

java/core/src/main/java/com/google/protobuf/IntArrayList.java

@@ -266,20 +266,6 @@ final class IntArrayList extends AbstractProtobufList<Integer>
     return true;
   }
 
-  @Override
-  public boolean remove(Object o) {
-    ensureIsMutable();
-    for (int i = 0; i < size; i++) {
-      if (o.equals(array[i])) {
-        System.arraycopy(array, i + 1, array, i, size - i - 1);
-        size--;
-        modCount++;
-        return true;
-      }
-    }
-    return false;
-  }
-
   @Override
   public Integer remove(int index) {
     ensureIsMutable();

java/core/src/main/java/com/google/protobuf/Internal.java

@@ -30,7 +30,6 @@
 
 package com.google.protobuf;
 
-import java.io.IOException;
 import java.lang.reflect.Method;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;

java/core/src/main/java/com/google/protobuf/LongArrayList.java

@@ -266,20 +266,6 @@ final class LongArrayList extends AbstractProtobufList<Long>
     return true;
   }
 
-  @Override
-  public boolean remove(Object o) {
-    ensureIsMutable();
-    for (int i = 0; i < size; i++) {
-      if (o.equals(array[i])) {
-        System.arraycopy(array, i + 1, array, i, size - i - 1);
-        size--;
-        modCount++;
-        return true;
-      }
-    }
-    return false;
-  }
-
   @Override
   public Long remove(int index) {
     ensureIsMutable();

java/core/src/main/java/com/google/protobuf/MessageSchema.java

@@ -2572,7 +2572,7 @@ final class MessageSchema<T> implements Schema<T> {
 
       int presenceMaskAndOffset = 0;
       int presenceMask = 0;
-      if (!proto3 && fieldType <= 17) {
+      if (fieldType <= 17) {
         presenceMaskAndOffset = buffer[pos + 2];
         final int presenceFieldOffset = presenceMaskAndOffset & OFFSET_MASK;
         if (presenceFieldOffset != currentPresenceFieldOffset) {

java/core/src/main/java/com/google/protobuf/NioByteString.java

@@ -37,6 +37,7 @@ import java.io.InputStream;
 import java.io.InvalidObjectException;
 import java.io.ObjectInputStream;
 import java.io.OutputStream;
+import java.nio.Buffer;
 import java.nio.ByteBuffer;
 import java.nio.ByteOrder;
 import java.nio.InvalidMarkException;
@@ -109,7 +110,7 @@ final class NioByteString extends ByteString.LeafByteString {
   protected void copyToInternal(
       byte[] target, int sourceOffset, int targetOffset, int numberToCopy) {
     ByteBuffer slice = buffer.slice();
-    slice.position(sourceOffset);
+    ((Buffer) slice).position(sourceOffset);
     slice.get(target, targetOffset, numberToCopy);
   }
 
@@ -285,8 +286,8 @@ final class NioByteString extends ByteString.LeafByteString {
     }
 
     ByteBuffer slice = buffer.slice();
-    slice.position(beginIndex - buffer.position());
-    slice.limit(endIndex - buffer.position());
+    ((Buffer) slice).position(beginIndex - buffer.position());
+    ((Buffer) slice).limit(endIndex - buffer.position());
     return slice;
   }
 }

java/core/src/main/java/com/google/protobuf/Protobuf.java

@@ -76,11 +76,8 @@ final class Protobuf {
     schemaFor(message).makeImmutable(message);
   }
 
-  /**
-   * Checks if all required fields are set. TODO(xiaofeng): Make this package private when the tests
-   * are moved to protobuf package.
-   */
-  public <T> boolean isInitialized(T message) {
+  /** Checks if all required fields are set. */
+  <T> boolean isInitialized(T message) {
     return schemaFor(message).isInitialized(message);
   }
 

java/core/src/main/java/com/google/protobuf/RopeByteString.java

@@ -845,7 +845,10 @@ final class RopeByteString extends ByteString {
         throw new IndexOutOfBoundsException();
       }
       int bytesRead = readSkipInternal(b, offset, length);
-      if (bytesRead == 0) {
+      if (bytesRead == 0 && (length > 0 || availableInternal() == 0)) {
+        // Modeling ByteArrayInputStream.read(byte[], int, int) behavior noted above:
+        // It's ok to read 0 bytes on purpose (length == 0) from a stream that isn't at EOF.
+        // It's not ok to try to read bytes (even 0 bytes) from a stream that is at EOF.
         return -1;
       } else {
         return bytesRead;
@@ -905,8 +908,7 @@ final class RopeByteString extends ByteString {
 
     @Override
     public int available() throws IOException {
-      int bytesRead = currentPieceOffsetInRope + currentPieceIndex;
-      return RopeByteString.this.size() - bytesRead;
+      return availableInternal();
     }
 
     @Override
@@ -955,5 +957,11 @@ final class RopeByteString extends ByteString {
         }
       }
     }
+
+    /** Computes the number of bytes still available to read. */
+    private int availableInternal() {
+      int bytesRead = currentPieceOffsetInRope + currentPieceIndex;
+      return RopeByteString.this.size() - bytesRead;
+    }
   }
 }

java/core/src/main/java/com/google/protobuf/TextFormat.java

@@ -30,6 +30,8 @@
 
 package com.google.protobuf;
 
+import static java.nio.charset.StandardCharsets.UTF_8;
+
 import com.google.protobuf.Descriptors.Descriptor;
 import com.google.protobuf.Descriptors.EnumDescriptor;
 import com.google.protobuf.Descriptors.EnumValueDescriptor;
@@ -2375,6 +2377,73 @@ public final class TextFormat {
                 result[pos++] = (byte) code;
                 break;
 
+              case 'u':
+                // Unicode escape
+                ++i;
+                if (i + 3 < input.size()
+                    && isHex(input.byteAt(i))
+                    && isHex(input.byteAt(i + 1))
+                    && isHex(input.byteAt(i + 2))
+                    && isHex(input.byteAt(i + 3))) {
+                  char ch =
+                      (char)
+                          (digitValue(input.byteAt(i)) << 12
+                              | digitValue(input.byteAt(i + 1)) << 8
+                              | digitValue(input.byteAt(i + 2)) << 4
+                              | digitValue(input.byteAt(i + 3)));
+                  if (Character.isSurrogate(ch)) {
+                    throw new InvalidEscapeSequenceException(
+                        "Invalid escape sequence: '\\u' refers to a surrogate");
+                  }
+                  byte[] chUtf8 = Character.toString(ch).getBytes(UTF_8);
+                  System.arraycopy(chUtf8, 0, result, pos, chUtf8.length);
+                  pos += chUtf8.length;
+                  i += 3;
+                } else {
+                  throw new InvalidEscapeSequenceException(
+                      "Invalid escape sequence: '\\u' with too few hex chars");
+                }
+                break;
+
+              case 'U':
+                // Unicode escape
+                ++i;
+                if (i + 7 >= input.size()) {
+                  throw new InvalidEscapeSequenceException(
+                      "Invalid escape sequence: '\\U' with too few hex chars");
+                }
+                int codepoint = 0;
+                for (int offset = i; offset < i + 8; offset++) {
+                  byte b = input.byteAt(offset);
+                  if (!isHex(b)) {
+                    throw new InvalidEscapeSequenceException(
+                        "Invalid escape sequence: '\\U' with too few hex chars");
+                  }
+                  codepoint = (codepoint << 4) | digitValue(b);
+                }
+                if (!Character.isValidCodePoint(codepoint)) {
+                  throw new InvalidEscapeSequenceException(
+                      "Invalid escape sequence: '\\U"
+                          + input.substring(i, i + 8).toStringUtf8()
+                          + "' is not a valid code point value");
+                }
+                Character.UnicodeBlock unicodeBlock = Character.UnicodeBlock.of(codepoint);
+                if (unicodeBlock.equals(Character.UnicodeBlock.LOW_SURROGATES)
+                    || unicodeBlock.equals(Character.UnicodeBlock.HIGH_SURROGATES)
+                    || unicodeBlock.equals(Character.UnicodeBlock.HIGH_PRIVATE_USE_SURROGATES)) {
+                  throw new InvalidEscapeSequenceException(
+                      "Invalid escape sequence: '\\U"
+                          + input.substring(i, i + 8).toStringUtf8()
+                          + "' refers to a surrogate code unit");
+                }
+                int[] codepoints = new int[1];
+                codepoints[0] = codepoint;
+                byte[] chUtf8 = new String(codepoints, 0, 1).getBytes(UTF_8);
+                System.arraycopy(chUtf8, 0, result, pos, chUtf8.length);
+                pos += chUtf8.length;
+                i += 7;
+                break;
+
               default:
                 throw new InvalidEscapeSequenceException(
                     "Invalid escape sequence: '\\" + (char) c + '\'');

java/core/src/main/java/com/google/protobuf/TypeRegistry.java

@@ -70,7 +70,6 @@ public class TypeRegistry {
   /**
    * Find a type by its typeUrl. Returns null if it cannot be found in this {@link TypeRegistry}.
    */
-  /* @Nullable */
   public final Descriptor getDescriptorForTypeUrl(String typeUrl)
       throws InvalidProtocolBufferException {
     return find(getTypeName(typeUrl));

java/core/src/main/java/com/google/protobuf/UnsafeUtil.java

@@ -41,7 +41,6 @@ import java.util.logging.Logger;
 
 /** Utility class for working with unsafe operations. */
 final class UnsafeUtil {
-  private static final Logger logger = Logger.getLogger(UnsafeUtil.class.getName());
   private static final sun.misc.Unsafe UNSAFE = getUnsafe();
   private static final Class<?> MEMORY_CLASS = Android.getMemoryClass();
   private static final boolean IS_ANDROID_64 = determineAndroidSupportByAddressSize(long.class);
@@ -363,9 +362,13 @@ final class UnsafeUtil {
 
       return true;
     } catch (Throwable e) {
-      logger.log(
-          Level.WARNING,
-          "platform method missing - proto runtime falling back to safer methods: " + e);
+      // Because log statements are fairly sparse in this class, this logger is initialized
+      // non-statically. Static initialization adds undue runtime costs to the first client to
+      // initialize this class.
+      Logger.getLogger(UnsafeUtil.class.getName())
+          .log(
+              Level.WARNING,
+              "platform method missing - proto runtime falling back to safer methods: " + e);
     }
     return false;
   }
@@ -397,9 +400,13 @@ final class UnsafeUtil {
       clazz.getMethod("copyMemory", Object.class, long.class, Object.class, long.class, long.class);
       return true;
     } catch (Throwable e) {
-      logger.log(
-          Level.WARNING,
-          "platform method missing - proto runtime falling back to safer methods: " + e);
+      // Because log statements are fairly sparse in this class, this logger is initialized
+      // non-statically. Static initialization adds undue runtime costs to the first client to
+      // initialize this class.
+      Logger.getLogger(UnsafeUtil.class.getName())
+          .log(
+              Level.WARNING,
+              "platform method missing - proto runtime falling back to safer methods: " + e);
     }
     return false;
   }

java/core/src/test/java/com/google/protobuf/LiteralByteStringTest.java

@@ -514,6 +514,20 @@ public class LiteralByteStringTest extends TestCase {
     assertEquals(classUnderTest + " InputStream must now be exhausted", -1, input.read());
   }
 
+  public void testNewInput_readZeroBytes() throws IOException {
+    InputStream input = stringUnderTest.newInput();
+    assertEquals(
+        classUnderTest + " InputStream.read() returns 0 when told to read 0 bytes and not at EOF",
+        0,
+        input.read(new byte[0]));
+
+    input.skip(input.available());
+    assertEquals(
+        classUnderTest + " InputStream.read() returns -1 when told to read 0 bytes at EOF",
+        -1,
+        input.read(new byte[0]));
+  }
+
   public void testNewInput_skip() throws IOException {
     InputStream input = stringUnderTest.newInput();
     int stringSize = stringUnderTest.size();

java/core/src/test/java/com/google/protobuf/MapForProto2LiteTest.java

@@ -77,44 +77,44 @@ public final class MapForProto2LiteTest extends TestCase {
 
   private void copyMapValues(TestMap source, TestMap.Builder destination) {
     destination
-        .putAllInt32ToInt32Field(source.getInt32ToInt32Field())
-        .putAllInt32ToStringField(source.getInt32ToStringField())
-        .putAllInt32ToBytesField(source.getInt32ToBytesField())
-        .putAllInt32ToEnumField(source.getInt32ToEnumField())
-        .putAllInt32ToMessageField(source.getInt32ToMessageField())
-        .putAllStringToInt32Field(source.getStringToInt32Field());
+        .putAllInt32ToInt32Field(source.getInt32ToInt32FieldMap())
+        .putAllInt32ToStringField(source.getInt32ToStringFieldMap())
+        .putAllInt32ToBytesField(source.getInt32ToBytesFieldMap())
+        .putAllInt32ToEnumField(source.getInt32ToEnumFieldMap())
+        .putAllInt32ToMessageField(source.getInt32ToMessageFieldMap())
+        .putAllStringToInt32Field(source.getStringToInt32FieldMap());
   }
 
   private void assertMapValuesSet(TestMap message) {
-    assertEquals(3, message.getInt32ToInt32Field().size());
-    assertEquals(11, message.getInt32ToInt32Field().get(1).intValue());
-    assertEquals(22, message.getInt32ToInt32Field().get(2).intValue());
-    assertEquals(33, message.getInt32ToInt32Field().get(3).intValue());
+    assertEquals(3, message.getInt32ToInt32FieldMap().size());
+    assertEquals(11, message.getInt32ToInt32FieldMap().get(1).intValue());
+    assertEquals(22, message.getInt32ToInt32FieldMap().get(2).intValue());
+    assertEquals(33, message.getInt32ToInt32FieldMap().get(3).intValue());
 
-    assertEquals(3, message.getInt32ToStringField().size());
-    assertEquals("11", message.getInt32ToStringField().get(1));
-    assertEquals("22", message.getInt32ToStringField().get(2));
-    assertEquals("33", message.getInt32ToStringField().get(3));
+    assertEquals(3, message.getInt32ToStringFieldMap().size());
+    assertEquals("11", message.getInt32ToStringFieldMap().get(1));
+    assertEquals("22", message.getInt32ToStringFieldMap().get(2));
+    assertEquals("33", message.getInt32ToStringFieldMap().get(3));
 
-    assertEquals(3, message.getInt32ToBytesField().size());
-    assertEquals(TestUtil.toBytes("11"), message.getInt32ToBytesField().get(1));
-    assertEquals(TestUtil.toBytes("22"), message.getInt32ToBytesField().get(2));
-    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesField().get(3));
+    assertEquals(3, message.getInt32ToBytesFieldMap().size());
+    assertEquals(TestUtil.toBytes("11"), message.getInt32ToBytesFieldMap().get(1));
+    assertEquals(TestUtil.toBytes("22"), message.getInt32ToBytesFieldMap().get(2));
+    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesFieldMap().get(3));
 
-    assertEquals(3, message.getInt32ToEnumField().size());
-    assertEquals(TestMap.EnumValue.FOO, message.getInt32ToEnumField().get(1));
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(2));
-    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumField().get(3));
+    assertEquals(3, message.getInt32ToEnumFieldMap().size());
+    assertEquals(TestMap.EnumValue.FOO, message.getInt32ToEnumFieldMap().get(1));
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(2));
+    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumFieldMap().get(3));
 
-    assertEquals(3, message.getInt32ToMessageField().size());
-    assertEquals(11, message.getInt32ToMessageField().get(1).getValue());
-    assertEquals(22, message.getInt32ToMessageField().get(2).getValue());
-    assertEquals(33, message.getInt32ToMessageField().get(3).getValue());
+    assertEquals(3, message.getInt32ToMessageFieldMap().size());
+    assertEquals(11, message.getInt32ToMessageFieldMap().get(1).getValue());
+    assertEquals(22, message.getInt32ToMessageFieldMap().get(2).getValue());
+    assertEquals(33, message.getInt32ToMessageFieldMap().get(3).getValue());
 
-    assertEquals(3, message.getStringToInt32Field().size());
-    assertEquals(11, message.getStringToInt32Field().get("1").intValue());
-    assertEquals(22, message.getStringToInt32Field().get("2").intValue());
-    assertEquals(33, message.getStringToInt32Field().get("3").intValue());
+    assertEquals(3, message.getStringToInt32FieldMap().size());
+    assertEquals(11, message.getStringToInt32FieldMap().get("1").intValue());
+    assertEquals(22, message.getStringToInt32FieldMap().get("2").intValue());
+    assertEquals(33, message.getStringToInt32FieldMap().get("3").intValue());
   }
 
   private void updateMapValues(TestMap.Builder builder) {
@@ -152,35 +152,35 @@ public final class MapForProto2LiteTest extends TestCase {
   }
 
   private void assertMapValuesUpdated(TestMap message) {
-    assertEquals(3, message.getInt32ToInt32Field().size());
-    assertEquals(111, message.getInt32ToInt32Field().get(1).intValue());
-    assertEquals(33, message.getInt32ToInt32Field().get(3).intValue());
-    assertEquals(44, message.getInt32ToInt32Field().get(4).intValue());
+    assertEquals(3, message.getInt32ToInt32FieldMap().size());
+    assertEquals(111, message.getInt32ToInt32FieldMap().get(1).intValue());
+    assertEquals(33, message.getInt32ToInt32FieldMap().get(3).intValue());
+    assertEquals(44, message.getInt32ToInt32FieldMap().get(4).intValue());
 
-    assertEquals(3, message.getInt32ToStringField().size());
-    assertEquals("111", message.getInt32ToStringField().get(1));
-    assertEquals("33", message.getInt32ToStringField().get(3));
-    assertEquals("44", message.getInt32ToStringField().get(4));
+    assertEquals(3, message.getInt32ToStringFieldMap().size());
+    assertEquals("111", message.getInt32ToStringFieldMap().get(1));
+    assertEquals("33", message.getInt32ToStringFieldMap().get(3));
+    assertEquals("44", message.getInt32ToStringFieldMap().get(4));
 
-    assertEquals(3, message.getInt32ToBytesField().size());
-    assertEquals(TestUtil.toBytes("111"), message.getInt32ToBytesField().get(1));
-    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesField().get(3));
-    assertEquals(TestUtil.toBytes("44"), message.getInt32ToBytesField().get(4));
+    assertEquals(3, message.getInt32ToBytesFieldMap().size());
+    assertEquals(TestUtil.toBytes("111"), message.getInt32ToBytesFieldMap().get(1));
+    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesFieldMap().get(3));
+    assertEquals(TestUtil.toBytes("44"), message.getInt32ToBytesFieldMap().get(4));
 
-    assertEquals(3, message.getInt32ToEnumField().size());
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(1));
-    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumField().get(3));
-    assertEquals(TestMap.EnumValue.QUX, message.getInt32ToEnumField().get(4));
+    assertEquals(3, message.getInt32ToEnumFieldMap().size());
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(1));
+    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumFieldMap().get(3));
+    assertEquals(TestMap.EnumValue.QUX, message.getInt32ToEnumFieldMap().get(4));
 
-    assertEquals(3, message.getInt32ToMessageField().size());
-    assertEquals(111, message.getInt32ToMessageField().get(1).getValue());
-    assertEquals(33, message.getInt32ToMessageField().get(3).getValue());
-    assertEquals(44, message.getInt32ToMessageField().get(4).getValue());
+    assertEquals(3, message.getInt32ToMessageFieldMap().size());
+    assertEquals(111, message.getInt32ToMessageFieldMap().get(1).getValue());
+    assertEquals(33, message.getInt32ToMessageFieldMap().get(3).getValue());
+    assertEquals(44, message.getInt32ToMessageFieldMap().get(4).getValue());
 
-    assertEquals(3, message.getStringToInt32Field().size());
-    assertEquals(111, message.getStringToInt32Field().get("1").intValue());
-    assertEquals(33, message.getStringToInt32Field().get("3").intValue());
-    assertEquals(44, message.getStringToInt32Field().get("4").intValue());
+    assertEquals(3, message.getStringToInt32FieldMap().size());
+    assertEquals(111, message.getStringToInt32FieldMap().get("1").intValue());
+    assertEquals(33, message.getStringToInt32FieldMap().get("3").intValue());
+    assertEquals(44, message.getStringToInt32FieldMap().get("4").intValue());
   }
 
   private void assertMapValuesCleared(TestMapOrBuilder testMapOrBuilder) {
@@ -206,13 +206,13 @@ public final class MapForProto2LiteTest extends TestCase {
     TestMap.Builder builder = TestMap.newBuilder();
     TestMap message = builder.build();
     builder.putInt32ToInt32Field(1, 2);
-    assertTrue(message.getInt32ToInt32Field().isEmpty());
+    assertTrue(message.getInt32ToInt32FieldMap().isEmpty());
     message = builder.build();
-    assertEquals(newMap(1, 2), message.getInt32ToInt32Field());
-    assertEquals(newMap(1, 2), builder.getInt32ToInt32Field());
+    assertEquals(newMap(1, 2), message.getInt32ToInt32FieldMap());
+    assertEquals(newMap(1, 2), builder.getInt32ToInt32FieldMap());
     builder.putInt32ToInt32Field(2, 3);
-    assertEquals(newMap(1, 2), message.getInt32ToInt32Field());
-    assertEquals(newMap(1, 2, 2, 3), builder.getInt32ToInt32Field());
+    assertEquals(newMap(1, 2), message.getInt32ToInt32FieldMap());
+    assertEquals(newMap(1, 2, 2, 3), builder.getInt32ToInt32FieldMap());
   }
 
   public void testGetMapIsImmutable() {
@@ -254,30 +254,31 @@ public final class MapForProto2LiteTest extends TestCase {
 
   public void testMutableMapLifecycle() {
     TestMap.Builder builder = TestMap.newBuilder().putInt32ToInt32Field(1, 2);
-    assertEquals(newMap(1, 2), builder.build().getInt32ToInt32Field());
-    assertEquals(newMap(1, 2), builder.getInt32ToInt32Field());
+    assertEquals(newMap(1, 2), builder.build().getInt32ToInt32FieldMap());
+    assertEquals(newMap(1, 2), builder.getInt32ToInt32FieldMap());
     builder.putInt32ToInt32Field(2, 3);
-    assertEquals(newMap(1, 2, 2, 3), builder.getInt32ToInt32Field());
+    assertEquals(newMap(1, 2, 2, 3), builder.getInt32ToInt32FieldMap());
 
     builder.putInt32ToEnumField(1, TestMap.EnumValue.BAR);
-    assertEquals(newMap(1, TestMap.EnumValue.BAR), builder.build().getInt32ToEnumField());
-    assertEquals(newMap(1, TestMap.EnumValue.BAR), builder.getInt32ToEnumField());
+    assertEquals(newMap(1, TestMap.EnumValue.BAR), builder.build().getInt32ToEnumFieldMap());
+    assertEquals(newMap(1, TestMap.EnumValue.BAR), builder.getInt32ToEnumFieldMap());
     builder.putInt32ToEnumField(2, TestMap.EnumValue.FOO);
     assertEquals(
-        newMap(1, TestMap.EnumValue.BAR, 2, TestMap.EnumValue.FOO), builder.getInt32ToEnumField());
+        newMap(1, TestMap.EnumValue.BAR, 2, TestMap.EnumValue.FOO),
+        builder.getInt32ToEnumFieldMap());
 
     builder.putInt32ToStringField(1, "1");
-    assertEquals(newMap(1, "1"), builder.build().getInt32ToStringField());
-    assertEquals(newMap(1, "1"), builder.getInt32ToStringField());
+    assertEquals(newMap(1, "1"), builder.build().getInt32ToStringFieldMap());
+    assertEquals(newMap(1, "1"), builder.getInt32ToStringFieldMap());
     builder.putInt32ToStringField(2, "2");
-    assertEquals(newMap(1, "1", 2, "2"), builder.getInt32ToStringField());
+    assertEquals(newMap(1, "1", 2, "2"), builder.getInt32ToStringFieldMap());
 
     builder.putInt32ToMessageField(1, TestMap.MessageValue.getDefaultInstance());
     assertEquals(
         newMap(1, TestMap.MessageValue.getDefaultInstance()),
-        builder.build().getInt32ToMessageField());
+        builder.build().getInt32ToMessageFieldMap());
     assertEquals(
-        newMap(1, TestMap.MessageValue.getDefaultInstance()), builder.getInt32ToMessageField());
+        newMap(1, TestMap.MessageValue.getDefaultInstance()), builder.getInt32ToMessageFieldMap());
     builder.putInt32ToMessageField(2, TestMap.MessageValue.getDefaultInstance());
     assertEquals(
         newMap(
@@ -285,7 +286,7 @@ public final class MapForProto2LiteTest extends TestCase {
             TestMap.MessageValue.getDefaultInstance(),
             2,
             TestMap.MessageValue.getDefaultInstance()),
-        builder.getInt32ToMessageField());
+        builder.getInt32ToMessageFieldMap());
   }
 
   public void testGettersAndSetters() throws Exception {
@@ -415,7 +416,7 @@ public final class MapForProto2LiteTest extends TestCase {
     } catch (InvalidProtocolBufferException expected) {
       assertTrue(expected.getUnfinishedMessage() instanceof TestMap);
       map = (TestMap) expected.getUnfinishedMessage();
-      assertTrue(map.getInt32ToMessageField().isEmpty());
+      assertTrue(map.getInt32ToMessageFieldMap().isEmpty());
     }
 
     map =
@@ -476,14 +477,14 @@ public final class MapForProto2LiteTest extends TestCase {
     TestMap message = TestMap.parseFrom(data);
     // Entries with unknown enum values will be stored into UnknownFieldSet so
     // there is only one entry in the map.
-    assertEquals(1, message.getInt32ToEnumField().size());
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(1));
+    assertEquals(1, message.getInt32ToEnumFieldMap().size());
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(1));
     // Serializing and parsing should preserve the unknown entry.
     data = message.toByteString();
     TestUnknownEnumValue messageWithUnknownEnums = TestUnknownEnumValue.parseFrom(data);
-    assertEquals(2, messageWithUnknownEnums.getInt32ToInt32Field().size());
-    assertEquals(1, messageWithUnknownEnums.getInt32ToInt32Field().get(1).intValue());
-    assertEquals(54321, messageWithUnknownEnums.getInt32ToInt32Field().get(2).intValue());
+    assertEquals(2, messageWithUnknownEnums.getInt32ToInt32FieldMap().size());
+    assertEquals(1, messageWithUnknownEnums.getInt32ToInt32FieldMap().get(1).intValue());
+    assertEquals(54321, messageWithUnknownEnums.getInt32ToInt32FieldMap().get(2).intValue());
   }
 
   public void testIterationOrder() throws Exception {
@@ -493,7 +494,7 @@ public final class MapForProto2LiteTest extends TestCase {
 
     assertEquals(
         Arrays.asList("1", "2", "3"),
-        new ArrayList<String>(message.getStringToInt32Field().keySet()));
+        new ArrayList<String>(message.getStringToInt32FieldMap().keySet()));
   }
 
   private static <K, V> Map<K, V> newMap(K key1, V value1) {
@@ -513,10 +514,10 @@ public final class MapForProto2LiteTest extends TestCase {
     TestMap.Builder builder = TestMap.newBuilder();
     setMapValues(builder);
     TestMap message = builder.build();
-    assertEquals(message.getStringToInt32Field(), message.getStringToInt32FieldMap());
-    assertEquals(message.getInt32ToBytesField(), message.getInt32ToBytesFieldMap());
-    assertEquals(message.getInt32ToEnumField(), message.getInt32ToEnumFieldMap());
-    assertEquals(message.getInt32ToMessageField(), message.getInt32ToMessageFieldMap());
+    assertEquals(message.getStringToInt32FieldMap(), message.getStringToInt32FieldMap());
+    assertEquals(message.getInt32ToBytesFieldMap(), message.getInt32ToBytesFieldMap());
+    assertEquals(message.getInt32ToEnumFieldMap(), message.getInt32ToEnumFieldMap());
+    assertEquals(message.getInt32ToMessageFieldMap(), message.getInt32ToMessageFieldMap());
   }
 
   public void testContains() {

java/core/src/test/java/com/google/protobuf/MapForProto2Test.java

@@ -119,12 +119,12 @@ public class MapForProto2Test extends TestCase {
 
   private void copyMapValues(TestMap source, TestMap.Builder destination) {
     destination
-        .putAllInt32ToInt32Field(source.getInt32ToInt32Field())
-        .putAllInt32ToStringField(source.getInt32ToStringField())
-        .putAllInt32ToBytesField(source.getInt32ToBytesField())
-        .putAllInt32ToEnumField(source.getInt32ToEnumField())
-        .putAllInt32ToMessageField(source.getInt32ToMessageField())
-        .putAllStringToInt32Field(source.getStringToInt32Field());
+        .putAllInt32ToInt32Field(source.getInt32ToInt32FieldMap())
+        .putAllInt32ToStringField(source.getInt32ToStringFieldMap())
+        .putAllInt32ToBytesField(source.getInt32ToBytesFieldMap())
+        .putAllInt32ToEnumField(source.getInt32ToEnumFieldMap())
+        .putAllInt32ToMessageField(source.getInt32ToMessageFieldMap())
+        .putAllStringToInt32Field(source.getStringToInt32FieldMap());
   }
 
   private void assertMapValuesSet(TestMapOrBuilder message) {
@@ -236,35 +236,35 @@ public class MapForProto2Test extends TestCase {
   }
 
   private void assertMapValuesUpdated(TestMap message) {
-    assertEquals(3, message.getInt32ToInt32Field().size());
-    assertEquals(111, message.getInt32ToInt32Field().get(1).intValue());
-    assertEquals(33, message.getInt32ToInt32Field().get(3).intValue());
-    assertEquals(44, message.getInt32ToInt32Field().get(4).intValue());
-
-    assertEquals(3, message.getInt32ToStringField().size());
-    assertEquals("111", message.getInt32ToStringField().get(1));
-    assertEquals("33", message.getInt32ToStringField().get(3));
-    assertEquals("44", message.getInt32ToStringField().get(4));
-
-    assertEquals(3, message.getInt32ToBytesField().size());
-    assertEquals(TestUtil.toBytes("111"), message.getInt32ToBytesField().get(1));
-    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesField().get(3));
-    assertEquals(TestUtil.toBytes("44"), message.getInt32ToBytesField().get(4));
-
-    assertEquals(3, message.getInt32ToEnumField().size());
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(1));
-    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumField().get(3));
-    assertEquals(TestMap.EnumValue.QUX, message.getInt32ToEnumField().get(4));
-
-    assertEquals(3, message.getInt32ToMessageField().size());
-    assertEquals(111, message.getInt32ToMessageField().get(1).getValue());
-    assertEquals(33, message.getInt32ToMessageField().get(3).getValue());
-    assertEquals(44, message.getInt32ToMessageField().get(4).getValue());
-
-    assertEquals(3, message.getStringToInt32Field().size());
-    assertEquals(111, message.getStringToInt32Field().get("1").intValue());
-    assertEquals(33, message.getStringToInt32Field().get("3").intValue());
-    assertEquals(44, message.getStringToInt32Field().get("4").intValue());
+    assertEquals(3, message.getInt32ToInt32FieldMap().size());
+    assertEquals(111, message.getInt32ToInt32FieldMap().get(1).intValue());
+    assertEquals(33, message.getInt32ToInt32FieldMap().get(3).intValue());
+    assertEquals(44, message.getInt32ToInt32FieldMap().get(4).intValue());
+
+    assertEquals(3, message.getInt32ToStringFieldMap().size());
+    assertEquals("111", message.getInt32ToStringFieldMap().get(1));
+    assertEquals("33", message.getInt32ToStringFieldMap().get(3));
+    assertEquals("44", message.getInt32ToStringFieldMap().get(4));
+
+    assertEquals(3, message.getInt32ToBytesFieldMap().size());
+    assertEquals(TestUtil.toBytes("111"), message.getInt32ToBytesFieldMap().get(1));
+    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesFieldMap().get(3));
+    assertEquals(TestUtil.toBytes("44"), message.getInt32ToBytesFieldMap().get(4));
+
+    assertEquals(3, message.getInt32ToEnumFieldMap().size());
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(1));
+    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumFieldMap().get(3));
+    assertEquals(TestMap.EnumValue.QUX, message.getInt32ToEnumFieldMap().get(4));
+
+    assertEquals(3, message.getInt32ToMessageFieldMap().size());
+    assertEquals(111, message.getInt32ToMessageFieldMap().get(1).getValue());
+    assertEquals(33, message.getInt32ToMessageFieldMap().get(3).getValue());
+    assertEquals(44, message.getInt32ToMessageFieldMap().get(4).getValue());
+
+    assertEquals(3, message.getStringToInt32FieldMap().size());
+    assertEquals(111, message.getStringToInt32FieldMap().get("1").intValue());
+    assertEquals(33, message.getStringToInt32FieldMap().get("3").intValue());
+    assertEquals(44, message.getStringToInt32FieldMap().get("4").intValue());
   }
 
   private void assertMapValuesCleared(TestMapOrBuilder testMapOrBuilder) {
@@ -563,7 +563,7 @@ public class MapForProto2Test extends TestCase {
     } catch (InvalidProtocolBufferException expected) {
       assertTrue(expected.getUnfinishedMessage() instanceof TestMap);
       map = (TestMap) expected.getUnfinishedMessage();
-      assertTrue(map.getInt32ToMessageField().isEmpty());
+      assertTrue(map.getInt32ToMessageFieldMap().isEmpty());
     }
 
     map =
@@ -698,8 +698,8 @@ public class MapForProto2Test extends TestCase {
     builder.clearField(f("int32_to_int32_field"));
     builder.clearField(f("int32_to_message_field"));
     message = builder.build();
-    assertEquals(0, message.getInt32ToInt32Field().size());
-    assertEquals(0, message.getInt32ToMessageField().size());
+    assertEquals(0, message.getInt32ToInt32FieldMap().size());
+    assertEquals(0, message.getInt32ToMessageFieldMap().size());
 
     // Test setField()
     setMapValues(builder, "int32_to_int32_field", mapForValues(11, 22, 33, 44));
@@ -710,10 +710,10 @@ public class MapForProto2Test extends TestCase {
             111, MessageValue.newBuilder().setValue(222).build(),
             333, MessageValue.newBuilder().setValue(444).build()));
     message = builder.build();
-    assertEquals(22, message.getInt32ToInt32Field().get(11).intValue());
-    assertEquals(44, message.getInt32ToInt32Field().get(33).intValue());
-    assertEquals(222, message.getInt32ToMessageField().get(111).getValue());
-    assertEquals(444, message.getInt32ToMessageField().get(333).getValue());
+    assertEquals(22, message.getInt32ToInt32FieldMap().get(11).intValue());
+    assertEquals(44, message.getInt32ToInt32FieldMap().get(33).intValue());
+    assertEquals(222, message.getInt32ToMessageFieldMap().get(111).getValue());
+    assertEquals(444, message.getInt32ToMessageFieldMap().get(333).getValue());
 
     // Test addRepeatedField
     builder.addRepeatedField(
@@ -726,8 +726,8 @@ public class MapForProto2Test extends TestCase {
             555,
             MessageValue.newBuilder().setValue(666).build()));
     message = builder.build();
-    assertEquals(66, message.getInt32ToInt32Field().get(55).intValue());
-    assertEquals(666, message.getInt32ToMessageField().get(555).getValue());
+    assertEquals(66, message.getInt32ToInt32FieldMap().get(55).intValue());
+    assertEquals(666, message.getInt32ToMessageFieldMap().get(555).getValue());
 
     // Test addRepeatedField (overriding existing values)
     builder.addRepeatedField(
@@ -740,8 +740,8 @@ public class MapForProto2Test extends TestCase {
             555,
             MessageValue.newBuilder().setValue(555).build()));
     message = builder.build();
-    assertEquals(55, message.getInt32ToInt32Field().get(55).intValue());
-    assertEquals(555, message.getInt32ToMessageField().get(555).getValue());
+    assertEquals(55, message.getInt32ToInt32FieldMap().get(55).intValue());
+    assertEquals(555, message.getInt32ToMessageFieldMap().get(555).getValue());
 
     // Test setRepeatedField
     for (int i = 0; i < builder.getRepeatedFieldCount(f("int32_to_int32_field")); i++) {
@@ -755,9 +755,9 @@ public class MapForProto2Test extends TestCase {
       builder.setRepeatedField(f("int32_to_int32_field"), i, mapEntryBuilder.build());
     }
     message = builder.build();
-    assertEquals(11, message.getInt32ToInt32Field().get(22).intValue());
-    assertEquals(33, message.getInt32ToInt32Field().get(44).intValue());
-    assertEquals(55, message.getInt32ToInt32Field().get(55).intValue());
+    assertEquals(11, message.getInt32ToInt32FieldMap().get(22).intValue());
+    assertEquals(33, message.getInt32ToInt32FieldMap().get(44).intValue());
+    assertEquals(55, message.getInt32ToInt32FieldMap().get(55).intValue());
   }
 
   // See additional coverage in TextFormatTest.java.
@@ -844,16 +844,16 @@ public class MapForProto2Test extends TestCase {
     TestMap message = TestMap.parseFrom(data);
     // Entries with unknown enum values will be stored into UnknownFieldSet so
     // there is only one entry in the map.
-    assertEquals(1, message.getInt32ToEnumField().size());
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(1));
+    assertEquals(1, message.getInt32ToEnumFieldMap().size());
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(1));
     // UnknownFieldSet should not be empty.
     assertFalse(message.getUnknownFields().asMap().isEmpty());
     // Serializing and parsing should preserve the unknown entry.
     data = message.toByteString();
     TestUnknownEnumValue messageWithUnknownEnums = TestUnknownEnumValue.parseFrom(data);
-    assertEquals(2, messageWithUnknownEnums.getInt32ToInt32Field().size());
-    assertEquals(1, messageWithUnknownEnums.getInt32ToInt32Field().get(1).intValue());
-    assertEquals(54321, messageWithUnknownEnums.getInt32ToInt32Field().get(2).intValue());
+    assertEquals(2, messageWithUnknownEnums.getInt32ToInt32FieldMap().size());
+    assertEquals(1, messageWithUnknownEnums.getInt32ToInt32FieldMap().get(1).intValue());
+    assertEquals(54321, messageWithUnknownEnums.getInt32ToInt32FieldMap().get(2).intValue());
   }
 
   public void testRequiredMessage() throws Exception {
@@ -885,7 +885,7 @@ public class MapForProto2Test extends TestCase {
 
     assertEquals(
         Arrays.asList("1", "2", "3"),
-        new ArrayList<String>(message.getStringToInt32Field().keySet()));
+        new ArrayList<String>(message.getStringToInt32FieldMap().keySet()));
   }
 
   public void testContains() {
@@ -1172,9 +1172,9 @@ public class MapForProto2Test extends TestCase {
     setMapValuesUsingAccessors(builder);
     assertMapValuesSet(builder);
     TestMap message = builder.build();
-    assertEquals(message.getStringToInt32Field(), message.getStringToInt32FieldMap());
-    assertEquals(message.getInt32ToBytesField(), message.getInt32ToBytesFieldMap());
-    assertEquals(message.getInt32ToEnumField(), message.getInt32ToEnumFieldMap());
-    assertEquals(message.getInt32ToMessageField(), message.getInt32ToMessageFieldMap());
+    assertEquals(message.getStringToInt32FieldMap(), message.getStringToInt32FieldMap());
+    assertEquals(message.getInt32ToBytesFieldMap(), message.getInt32ToBytesFieldMap());
+    assertEquals(message.getInt32ToEnumFieldMap(), message.getInt32ToEnumFieldMap());
+    assertEquals(message.getInt32ToMessageFieldMap(), message.getInt32ToMessageFieldMap());
   }
 }

java/core/src/test/java/com/google/protobuf/MapLiteTest.java

@@ -84,44 +84,44 @@ public final class MapLiteTest extends TestCase {
 
   private void copyMapValues(TestMap source, TestMap.Builder destination) {
     destination
-        .putAllInt32ToInt32Field(source.getInt32ToInt32Field())
-        .putAllInt32ToStringField(source.getInt32ToStringField())
-        .putAllInt32ToBytesField(source.getInt32ToBytesField())
-        .putAllInt32ToEnumField(source.getInt32ToEnumField())
-        .putAllInt32ToMessageField(source.getInt32ToMessageField())
-        .putAllStringToInt32Field(source.getStringToInt32Field());
+        .putAllInt32ToInt32Field(source.getInt32ToInt32FieldMap())
+        .putAllInt32ToStringField(source.getInt32ToStringFieldMap())
+        .putAllInt32ToBytesField(source.getInt32ToBytesFieldMap())
+        .putAllInt32ToEnumField(source.getInt32ToEnumFieldMap())
+        .putAllInt32ToMessageField(source.getInt32ToMessageFieldMap())
+        .putAllStringToInt32Field(source.getStringToInt32FieldMap());
   }
 
   private void assertMapValuesSet(TestMap message) {
-    assertEquals(3, message.getInt32ToInt32Field().size());
-    assertEquals(11, message.getInt32ToInt32Field().get(1).intValue());
-    assertEquals(22, message.getInt32ToInt32Field().get(2).intValue());
-    assertEquals(33, message.getInt32ToInt32Field().get(3).intValue());
+    assertEquals(3, message.getInt32ToInt32FieldMap().size());
+    assertEquals(11, message.getInt32ToInt32FieldMap().get(1).intValue());
+    assertEquals(22, message.getInt32ToInt32FieldMap().get(2).intValue());
+    assertEquals(33, message.getInt32ToInt32FieldMap().get(3).intValue());
 
-    assertEquals(3, message.getInt32ToStringField().size());
-    assertEquals("11", message.getInt32ToStringField().get(1));
-    assertEquals("22", message.getInt32ToStringField().get(2));
-    assertEquals("33", message.getInt32ToStringField().get(3));
+    assertEquals(3, message.getInt32ToStringFieldMap().size());
+    assertEquals("11", message.getInt32ToStringFieldMap().get(1));
+    assertEquals("22", message.getInt32ToStringFieldMap().get(2));
+    assertEquals("33", message.getInt32ToStringFieldMap().get(3));
 
-    assertEquals(3, message.getInt32ToBytesField().size());
-    assertEquals(TestUtil.toBytes("11"), message.getInt32ToBytesField().get(1));
-    assertEquals(TestUtil.toBytes("22"), message.getInt32ToBytesField().get(2));
-    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesField().get(3));
+    assertEquals(3, message.getInt32ToBytesFieldMap().size());
+    assertEquals(TestUtil.toBytes("11"), message.getInt32ToBytesFieldMap().get(1));
+    assertEquals(TestUtil.toBytes("22"), message.getInt32ToBytesFieldMap().get(2));
+    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesFieldMap().get(3));
 
-    assertEquals(3, message.getInt32ToEnumField().size());
-    assertEquals(TestMap.EnumValue.FOO, message.getInt32ToEnumField().get(1));
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(2));
-    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumField().get(3));
+    assertEquals(3, message.getInt32ToEnumFieldMap().size());
+    assertEquals(TestMap.EnumValue.FOO, message.getInt32ToEnumFieldMap().get(1));
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(2));
+    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumFieldMap().get(3));
 
-    assertEquals(3, message.getInt32ToMessageField().size());
-    assertEquals(11, message.getInt32ToMessageField().get(1).getValue());
-    assertEquals(22, message.getInt32ToMessageField().get(2).getValue());
-    assertEquals(33, message.getInt32ToMessageField().get(3).getValue());
+    assertEquals(3, message.getInt32ToMessageFieldMap().size());
+    assertEquals(11, message.getInt32ToMessageFieldMap().get(1).getValue());
+    assertEquals(22, message.getInt32ToMessageFieldMap().get(2).getValue());
+    assertEquals(33, message.getInt32ToMessageFieldMap().get(3).getValue());
 
-    assertEquals(3, message.getStringToInt32Field().size());
-    assertEquals(11, message.getStringToInt32Field().get("1").intValue());
-    assertEquals(22, message.getStringToInt32Field().get("2").intValue());
-    assertEquals(33, message.getStringToInt32Field().get("3").intValue());
+    assertEquals(3, message.getStringToInt32FieldMap().size());
+    assertEquals(11, message.getStringToInt32FieldMap().get("1").intValue());
+    assertEquals(22, message.getStringToInt32FieldMap().get("2").intValue());
+    assertEquals(33, message.getStringToInt32FieldMap().get("3").intValue());
   }
 
   private void updateMapValues(TestMap.Builder builder) {
@@ -159,35 +159,35 @@ public final class MapLiteTest extends TestCase {
   }
 
   private void assertMapValuesUpdated(TestMap message) {
-    assertEquals(3, message.getInt32ToInt32Field().size());
-    assertEquals(111, message.getInt32ToInt32Field().get(1).intValue());
-    assertEquals(33, message.getInt32ToInt32Field().get(3).intValue());
-    assertEquals(44, message.getInt32ToInt32Field().get(4).intValue());
+    assertEquals(3, message.getInt32ToInt32FieldMap().size());
+    assertEquals(111, message.getInt32ToInt32FieldMap().get(1).intValue());
+    assertEquals(33, message.getInt32ToInt32FieldMap().get(3).intValue());
+    assertEquals(44, message.getInt32ToInt32FieldMap().get(4).intValue());
 
-    assertEquals(3, message.getInt32ToStringField().size());
-    assertEquals("111", message.getInt32ToStringField().get(1));
-    assertEquals("33", message.getInt32ToStringField().get(3));
-    assertEquals("44", message.getInt32ToStringField().get(4));
+    assertEquals(3, message.getInt32ToStringFieldMap().size());
+    assertEquals("111", message.getInt32ToStringFieldMap().get(1));
+    assertEquals("33", message.getInt32ToStringFieldMap().get(3));
+    assertEquals("44", message.getInt32ToStringFieldMap().get(4));
 
-    assertEquals(3, message.getInt32ToBytesField().size());
-    assertEquals(TestUtil.toBytes("111"), message.getInt32ToBytesField().get(1));
-    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesField().get(3));
-    assertEquals(TestUtil.toBytes("44"), message.getInt32ToBytesField().get(4));
+    assertEquals(3, message.getInt32ToBytesFieldMap().size());
+    assertEquals(TestUtil.toBytes("111"), message.getInt32ToBytesFieldMap().get(1));
+    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesFieldMap().get(3));
+    assertEquals(TestUtil.toBytes("44"), message.getInt32ToBytesFieldMap().get(4));
 
-    assertEquals(3, message.getInt32ToEnumField().size());
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(1));
-    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumField().get(3));
-    assertEquals(TestMap.EnumValue.QUX, message.getInt32ToEnumField().get(4));
+    assertEquals(3, message.getInt32ToEnumFieldMap().size());
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(1));
+    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumFieldMap().get(3));
+    assertEquals(TestMap.EnumValue.QUX, message.getInt32ToEnumFieldMap().get(4));
 
-    assertEquals(3, message.getInt32ToMessageField().size());
-    assertEquals(111, message.getInt32ToMessageField().get(1).getValue());
-    assertEquals(33, message.getInt32ToMessageField().get(3).getValue());
-    assertEquals(44, message.getInt32ToMessageField().get(4).getValue());
+    assertEquals(3, message.getInt32ToMessageFieldMap().size());
+    assertEquals(111, message.getInt32ToMessageFieldMap().get(1).getValue());
+    assertEquals(33, message.getInt32ToMessageFieldMap().get(3).getValue());
+    assertEquals(44, message.getInt32ToMessageFieldMap().get(4).getValue());
 
-    assertEquals(3, message.getStringToInt32Field().size());
-    assertEquals(111, message.getStringToInt32Field().get("1").intValue());
-    assertEquals(33, message.getStringToInt32Field().get("3").intValue());
-    assertEquals(44, message.getStringToInt32Field().get("4").intValue());
+    assertEquals(3, message.getStringToInt32FieldMap().size());
+    assertEquals(111, message.getStringToInt32FieldMap().get("1").intValue());
+    assertEquals(33, message.getStringToInt32FieldMap().get("3").intValue());
+    assertEquals(44, message.getStringToInt32FieldMap().get("4").intValue());
   }
 
   private void assertMapValuesCleared(TestMapOrBuilder testMapOrBuilder) {
@@ -213,12 +213,12 @@ public final class MapLiteTest extends TestCase {
     TestMap.Builder builder = TestMap.newBuilder();
     TestMap message = builder.build();
     builder.putInt32ToInt32Field(1, 2);
-    assertTrue(message.getInt32ToInt32Field().isEmpty());
-    assertEquals(newMap(1, 2), builder.getInt32ToInt32Field());
+    assertTrue(message.getInt32ToInt32FieldMap().isEmpty());
+    assertEquals(newMap(1, 2), builder.getInt32ToInt32FieldMap());
     message = builder.build();
     builder.putInt32ToInt32Field(2, 3);
-    assertEquals(newMap(1, 2), message.getInt32ToInt32Field());
-    assertEquals(newMap(1, 2, 2, 3), builder.getInt32ToInt32Field());
+    assertEquals(newMap(1, 2), message.getInt32ToInt32FieldMap());
+    assertEquals(newMap(1, 2, 2, 3), builder.getInt32ToInt32FieldMap());
   }
 
   public void testGetMapIsImmutable() {
@@ -266,30 +266,31 @@ public final class MapLiteTest extends TestCase {
 
   public void testMutableMapLifecycle() {
     TestMap.Builder builder = TestMap.newBuilder().putInt32ToInt32Field(1, 2);
-    assertEquals(newMap(1, 2), builder.build().getInt32ToInt32Field());
-    assertEquals(newMap(1, 2), builder.getInt32ToInt32Field());
+    assertEquals(newMap(1, 2), builder.build().getInt32ToInt32FieldMap());
+    assertEquals(newMap(1, 2), builder.getInt32ToInt32FieldMap());
     builder.putInt32ToInt32Field(2, 3);
-    assertEquals(newMap(1, 2, 2, 3), builder.getInt32ToInt32Field());
+    assertEquals(newMap(1, 2, 2, 3), builder.getInt32ToInt32FieldMap());
 
     builder.putInt32ToEnumField(1, TestMap.EnumValue.BAR);
-    assertEquals(newMap(1, TestMap.EnumValue.BAR), builder.build().getInt32ToEnumField());
-    assertEquals(newMap(1, TestMap.EnumValue.BAR), builder.getInt32ToEnumField());
+    assertEquals(newMap(1, TestMap.EnumValue.BAR), builder.build().getInt32ToEnumFieldMap());
+    assertEquals(newMap(1, TestMap.EnumValue.BAR), builder.getInt32ToEnumFieldMap());
     builder.putInt32ToEnumField(2, TestMap.EnumValue.FOO);
     assertEquals(
-        newMap(1, TestMap.EnumValue.BAR, 2, TestMap.EnumValue.FOO), builder.getInt32ToEnumField());
+        newMap(1, TestMap.EnumValue.BAR, 2, TestMap.EnumValue.FOO),
+        builder.getInt32ToEnumFieldMap());
 
     builder.putInt32ToStringField(1, "1");
-    assertEquals(newMap(1, "1"), builder.build().getInt32ToStringField());
-    assertEquals(newMap(1, "1"), builder.getInt32ToStringField());
+    assertEquals(newMap(1, "1"), builder.build().getInt32ToStringFieldMap());
+    assertEquals(newMap(1, "1"), builder.getInt32ToStringFieldMap());
     builder.putInt32ToStringField(2, "2");
-    assertEquals(newMap(1, "1", 2, "2"), builder.getInt32ToStringField());
+    assertEquals(newMap(1, "1", 2, "2"), builder.getInt32ToStringFieldMap());
 
     builder.putInt32ToMessageField(1, TestMap.MessageValue.getDefaultInstance());
     assertEquals(
         newMap(1, TestMap.MessageValue.getDefaultInstance()),
-        builder.build().getInt32ToMessageField());
+        builder.build().getInt32ToMessageFieldMap());
     assertEquals(
-        newMap(1, TestMap.MessageValue.getDefaultInstance()), builder.getInt32ToMessageField());
+        newMap(1, TestMap.MessageValue.getDefaultInstance()), builder.getInt32ToMessageFieldMap());
     builder.putInt32ToMessageField(2, TestMap.MessageValue.getDefaultInstance());
     assertEquals(
         newMap(
@@ -297,7 +298,7 @@ public final class MapLiteTest extends TestCase {
             TestMap.MessageValue.getDefaultInstance(),
             2,
             TestMap.MessageValue.getDefaultInstance()),
-        builder.getInt32ToMessageField());
+        builder.getInt32ToMessageFieldMap());
   }
 
   public void testGettersAndSetters() throws Exception {
@@ -342,12 +343,12 @@ public final class MapLiteTest extends TestCase {
     TestMap source = sourceBuilder.build();
 
     TestMap.Builder destinationBuilder = TestMap.newBuilder();
-    destinationBuilder.putAllInt32ToEnumFieldValue(source.getInt32ToEnumFieldValue());
+    destinationBuilder.putAllInt32ToEnumFieldValue(source.getInt32ToEnumFieldValueMap());
     TestMap destination = destinationBuilder.build();
 
-    assertEquals(0, destination.getInt32ToEnumFieldValue().get(0).intValue());
-    assertEquals(1, destination.getInt32ToEnumFieldValue().get(1).intValue());
-    assertEquals(1000, destination.getInt32ToEnumFieldValue().get(2).intValue());
+    assertEquals(0, destination.getInt32ToEnumFieldValueMap().get(0).intValue());
+    assertEquals(1, destination.getInt32ToEnumFieldValueMap().get(1).intValue());
+    assertEquals(1000, destination.getInt32ToEnumFieldValueMap().get(2).intValue());
     assertEquals(3, destination.getInt32ToEnumFieldCount());
   }
 
@@ -459,7 +460,7 @@ public final class MapLiteTest extends TestCase {
     } catch (InvalidProtocolBufferException expected) {
       assertTrue(expected.getUnfinishedMessage() instanceof TestMap);
       map = (TestMap) expected.getUnfinishedMessage();
-      assertTrue(map.getInt32ToMessageField().isEmpty());
+      assertTrue(map.getInt32ToMessageFieldMap().isEmpty());
     }
 
     map =
@@ -524,24 +525,24 @@ public final class MapLiteTest extends TestCase {
             .putInt32ToEnumFieldValue(2, 1000); // unknown value.
     TestMap message = builder.build();
 
-    assertEquals(TestMap.EnumValue.FOO, message.getInt32ToEnumField().get(0));
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(1));
-    assertEquals(TestMap.EnumValue.UNRECOGNIZED, message.getInt32ToEnumField().get(2));
+    assertEquals(TestMap.EnumValue.FOO, message.getInt32ToEnumFieldMap().get(0));
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(1));
+    assertEquals(TestMap.EnumValue.UNRECOGNIZED, message.getInt32ToEnumFieldMap().get(2));
 
     builder.putAllInt32ToEnumFieldValue(newMap(2, 1000)); // unknown value.
     message = builder.build();
-    assertEquals(TestMap.EnumValue.UNRECOGNIZED, message.getInt32ToEnumField().get(2));
+    assertEquals(TestMap.EnumValue.UNRECOGNIZED, message.getInt32ToEnumFieldMap().get(2));
 
     // Unknown enum values should be preserved after:
     //   1. Serialization and parsing.
     //   2. toBuild().
     //   3. mergeFrom().
     message = TestMap.parseFrom(message.toByteString());
-    assertEquals(1000, message.getInt32ToEnumFieldValue().get(2).intValue());
+    assertEquals(1000, message.getInt32ToEnumFieldValueMap().get(2).intValue());
     builder = message.toBuilder();
-    assertEquals(1000, builder.getInt32ToEnumFieldValue().get(2).intValue());
+    assertEquals(1000, builder.getInt32ToEnumFieldValueMap().get(2).intValue());
     builder = TestMap.newBuilder().mergeFrom(message);
-    assertEquals(1000, builder.getInt32ToEnumFieldValue().get(2).intValue());
+    assertEquals(1000, builder.getInt32ToEnumFieldValueMap().get(2).intValue());
 
     // hashCode()/equals() should take unknown enum values into account.
     builder.putAllInt32ToEnumFieldValue(newMap(2, 1001));
@@ -550,7 +551,7 @@ public final class MapLiteTest extends TestCase {
     assertFalse(message.equals(message2));
     // Unknown values will be converted to UNRECOGNIZED so the resulted enum map
     // should be the same.
-    assertEquals(message2.getInt32ToEnumField(), message.getInt32ToEnumField());
+    assertEquals(message2.getInt32ToEnumFieldMap(), message.getInt32ToEnumFieldMap());
   }
 
   public void testIterationOrder() throws Exception {
@@ -559,18 +560,18 @@ public final class MapLiteTest extends TestCase {
     TestMap message = builder.build();
 
     assertEquals(
-        Arrays.asList("1", "2", "3"), new ArrayList<>(message.getStringToInt32Field().keySet()));
+        Arrays.asList("1", "2", "3"), new ArrayList<>(message.getStringToInt32FieldMap().keySet()));
   }
 
   public void testGetMap() {
     TestMap.Builder builder = TestMap.newBuilder();
     setMapValues(builder);
     TestMap message = builder.build();
-    assertEquals(message.getStringToInt32Field(), message.getStringToInt32FieldMap());
-    assertEquals(message.getInt32ToBytesField(), message.getInt32ToBytesFieldMap());
-    assertEquals(message.getInt32ToEnumField(), message.getInt32ToEnumFieldMap());
-    assertEquals(message.getInt32ToEnumFieldValue(), message.getInt32ToEnumFieldValueMap());
-    assertEquals(message.getInt32ToMessageField(), message.getInt32ToMessageFieldMap());
+    assertEquals(message.getStringToInt32FieldMap(), message.getStringToInt32FieldMap());
+    assertEquals(message.getInt32ToBytesFieldMap(), message.getInt32ToBytesFieldMap());
+    assertEquals(message.getInt32ToEnumFieldMap(), message.getInt32ToEnumFieldMap());
+    assertEquals(message.getInt32ToEnumFieldValueMap(), message.getInt32ToEnumFieldValueMap());
+    assertEquals(message.getInt32ToMessageFieldMap(), message.getInt32ToMessageFieldMap());
   }
 
   public void testContains() {

java/core/src/test/java/com/google/protobuf/MapTest.java

@@ -122,44 +122,44 @@ public class MapTest extends TestCase {
 
   private void copyMapValues(TestMap source, TestMap.Builder destination) {
     destination
-        .putAllInt32ToInt32Field(source.getInt32ToInt32Field())
-        .putAllInt32ToStringField(source.getInt32ToStringField())
-        .putAllInt32ToBytesField(source.getInt32ToBytesField())
-        .putAllInt32ToEnumField(source.getInt32ToEnumField())
-        .putAllInt32ToMessageField(source.getInt32ToMessageField())
-        .putAllStringToInt32Field(source.getStringToInt32Field());
+        .putAllInt32ToInt32Field(source.getInt32ToInt32FieldMap())
+        .putAllInt32ToStringField(source.getInt32ToStringFieldMap())
+        .putAllInt32ToBytesField(source.getInt32ToBytesFieldMap())
+        .putAllInt32ToEnumField(source.getInt32ToEnumFieldMap())
+        .putAllInt32ToMessageField(source.getInt32ToMessageFieldMap())
+        .putAllStringToInt32Field(source.getStringToInt32FieldMap());
   }
 
   private void assertMapValuesSet(TestMap message) {
-    assertEquals(3, message.getInt32ToInt32Field().size());
-    assertEquals(11, message.getInt32ToInt32Field().get(1).intValue());
-    assertEquals(22, message.getInt32ToInt32Field().get(2).intValue());
-    assertEquals(33, message.getInt32ToInt32Field().get(3).intValue());
+    assertEquals(3, message.getInt32ToInt32FieldMap().size());
+    assertEquals(11, message.getInt32ToInt32FieldMap().get(1).intValue());
+    assertEquals(22, message.getInt32ToInt32FieldMap().get(2).intValue());
+    assertEquals(33, message.getInt32ToInt32FieldMap().get(3).intValue());
 
-    assertEquals(3, message.getInt32ToStringField().size());
-    assertEquals("11", message.getInt32ToStringField().get(1));
-    assertEquals("22", message.getInt32ToStringField().get(2));
-    assertEquals("33", message.getInt32ToStringField().get(3));
+    assertEquals(3, message.getInt32ToStringFieldMap().size());
+    assertEquals("11", message.getInt32ToStringFieldMap().get(1));
+    assertEquals("22", message.getInt32ToStringFieldMap().get(2));
+    assertEquals("33", message.getInt32ToStringFieldMap().get(3));
 
-    assertEquals(3, message.getInt32ToBytesField().size());
-    assertEquals(TestUtil.toBytes("11"), message.getInt32ToBytesField().get(1));
-    assertEquals(TestUtil.toBytes("22"), message.getInt32ToBytesField().get(2));
-    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesField().get(3));
+    assertEquals(3, message.getInt32ToBytesFieldMap().size());
+    assertEquals(TestUtil.toBytes("11"), message.getInt32ToBytesFieldMap().get(1));
+    assertEquals(TestUtil.toBytes("22"), message.getInt32ToBytesFieldMap().get(2));
+    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesFieldMap().get(3));
 
-    assertEquals(3, message.getInt32ToEnumField().size());
-    assertEquals(TestMap.EnumValue.FOO, message.getInt32ToEnumField().get(1));
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(2));
-    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumField().get(3));
+    assertEquals(3, message.getInt32ToEnumFieldMap().size());
+    assertEquals(TestMap.EnumValue.FOO, message.getInt32ToEnumFieldMap().get(1));
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(2));
+    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumFieldMap().get(3));
 
-    assertEquals(3, message.getInt32ToMessageField().size());
-    assertEquals(11, message.getInt32ToMessageField().get(1).getValue());
-    assertEquals(22, message.getInt32ToMessageField().get(2).getValue());
-    assertEquals(33, message.getInt32ToMessageField().get(3).getValue());
+    assertEquals(3, message.getInt32ToMessageFieldMap().size());
+    assertEquals(11, message.getInt32ToMessageFieldMap().get(1).getValue());
+    assertEquals(22, message.getInt32ToMessageFieldMap().get(2).getValue());
+    assertEquals(33, message.getInt32ToMessageFieldMap().get(3).getValue());
 
-    assertEquals(3, message.getStringToInt32Field().size());
-    assertEquals(11, message.getStringToInt32Field().get("1").intValue());
-    assertEquals(22, message.getStringToInt32Field().get("2").intValue());
-    assertEquals(33, message.getStringToInt32Field().get("3").intValue());
+    assertEquals(3, message.getStringToInt32FieldMap().size());
+    assertEquals(11, message.getStringToInt32FieldMap().get("1").intValue());
+    assertEquals(22, message.getStringToInt32FieldMap().get("2").intValue());
+    assertEquals(33, message.getStringToInt32FieldMap().get("3").intValue());
   }
 
   private void updateMapValuesUsingMutableMap(TestMap.Builder builder) {
@@ -239,35 +239,35 @@ public class MapTest extends TestCase {
   }
 
   private void assertMapValuesUpdated(TestMap message) {
-    assertEquals(3, message.getInt32ToInt32Field().size());
-    assertEquals(111, message.getInt32ToInt32Field().get(1).intValue());
-    assertEquals(33, message.getInt32ToInt32Field().get(3).intValue());
-    assertEquals(44, message.getInt32ToInt32Field().get(4).intValue());
+    assertEquals(3, message.getInt32ToInt32FieldMap().size());
+    assertEquals(111, message.getInt32ToInt32FieldMap().get(1).intValue());
+    assertEquals(33, message.getInt32ToInt32FieldMap().get(3).intValue());
+    assertEquals(44, message.getInt32ToInt32FieldMap().get(4).intValue());
 
-    assertEquals(3, message.getInt32ToStringField().size());
-    assertEquals("111", message.getInt32ToStringField().get(1));
-    assertEquals("33", message.getInt32ToStringField().get(3));
-    assertEquals("44", message.getInt32ToStringField().get(4));
+    assertEquals(3, message.getInt32ToStringFieldMap().size());
+    assertEquals("111", message.getInt32ToStringFieldMap().get(1));
+    assertEquals("33", message.getInt32ToStringFieldMap().get(3));
+    assertEquals("44", message.getInt32ToStringFieldMap().get(4));
 
-    assertEquals(3, message.getInt32ToBytesField().size());
-    assertEquals(TestUtil.toBytes("111"), message.getInt32ToBytesField().get(1));
-    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesField().get(3));
-    assertEquals(TestUtil.toBytes("44"), message.getInt32ToBytesField().get(4));
+    assertEquals(3, message.getInt32ToBytesFieldMap().size());
+    assertEquals(TestUtil.toBytes("111"), message.getInt32ToBytesFieldMap().get(1));
+    assertEquals(TestUtil.toBytes("33"), message.getInt32ToBytesFieldMap().get(3));
+    assertEquals(TestUtil.toBytes("44"), message.getInt32ToBytesFieldMap().get(4));
 
-    assertEquals(3, message.getInt32ToEnumField().size());
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(1));
-    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumField().get(3));
-    assertEquals(TestMap.EnumValue.QUX, message.getInt32ToEnumField().get(4));
+    assertEquals(3, message.getInt32ToEnumFieldMap().size());
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(1));
+    assertEquals(TestMap.EnumValue.BAZ, message.getInt32ToEnumFieldMap().get(3));
+    assertEquals(TestMap.EnumValue.QUX, message.getInt32ToEnumFieldMap().get(4));
 
-    assertEquals(3, message.getInt32ToMessageField().size());
-    assertEquals(111, message.getInt32ToMessageField().get(1).getValue());
-    assertEquals(33, message.getInt32ToMessageField().get(3).getValue());
-    assertEquals(44, message.getInt32ToMessageField().get(4).getValue());
+    assertEquals(3, message.getInt32ToMessageFieldMap().size());
+    assertEquals(111, message.getInt32ToMessageFieldMap().get(1).getValue());
+    assertEquals(33, message.getInt32ToMessageFieldMap().get(3).getValue());
+    assertEquals(44, message.getInt32ToMessageFieldMap().get(4).getValue());
 
-    assertEquals(3, message.getStringToInt32Field().size());
-    assertEquals(111, message.getStringToInt32Field().get("1").intValue());
-    assertEquals(33, message.getStringToInt32Field().get("3").intValue());
-    assertEquals(44, message.getStringToInt32Field().get("4").intValue());
+    assertEquals(3, message.getStringToInt32FieldMap().size());
+    assertEquals(111, message.getStringToInt32FieldMap().get("1").intValue());
+    assertEquals(33, message.getStringToInt32FieldMap().get("3").intValue());
+    assertEquals(44, message.getStringToInt32FieldMap().get("4").intValue());
   }
 
   private void assertMapValuesCleared(TestMapOrBuilder testMapOrBuilder) {
@@ -468,11 +468,13 @@ public class MapTest extends TestCase {
             .build();
 
     TestMap destination =
-        TestMap.newBuilder().putAllInt32ToEnumFieldValue(source.getInt32ToEnumFieldValue()).build();
+        TestMap.newBuilder()
+            .putAllInt32ToEnumFieldValue(source.getInt32ToEnumFieldValueMap())
+            .build();
 
-    assertEquals(0, destination.getInt32ToEnumFieldValue().get(0).intValue());
-    assertEquals(1, destination.getInt32ToEnumFieldValue().get(1).intValue());
-    assertEquals(1000, destination.getInt32ToEnumFieldValue().get(2).intValue());
+    assertEquals(0, destination.getInt32ToEnumFieldValueMap().get(0).intValue());
+    assertEquals(1, destination.getInt32ToEnumFieldValueMap().get(1).intValue());
+    assertEquals(1000, destination.getInt32ToEnumFieldValueMap().get(2).intValue());
     assertEquals(3, destination.getInt32ToEnumFieldCount());
   }
 
@@ -583,7 +585,7 @@ public class MapTest extends TestCase {
     } catch (InvalidProtocolBufferException expected) {
       assertTrue(expected.getUnfinishedMessage() instanceof TestMap);
       map = (TestMap) expected.getUnfinishedMessage();
-      assertTrue(map.getInt32ToMessageField().isEmpty());
+      assertTrue(map.getInt32ToMessageFieldMap().isEmpty());
     }
 
     map =
@@ -644,14 +646,14 @@ public class MapTest extends TestCase {
     TestOnChangeEventPropagation.Builder parent = TestOnChangeEventPropagation.newBuilder();
     parent.getOptionalMessageBuilder().putInt32ToInt32Field(1, 2);
     TestOnChangeEventPropagation message = parent.build();
-    assertEquals(2, message.getOptionalMessage().getInt32ToInt32Field().get(1).intValue());
+    assertEquals(2, message.getOptionalMessage().getInt32ToInt32FieldMap().get(1).intValue());
 
     // Make a change using nested builder.
     parent.getOptionalMessageBuilder().putInt32ToInt32Field(1, 3);
 
     // Should be able to observe the change.
     message = parent.build();
-    assertEquals(3, message.getOptionalMessage().getInt32ToInt32Field().get(1).intValue());
+    assertEquals(3, message.getOptionalMessage().getInt32ToInt32FieldMap().get(1).intValue());
 
     // Make another change using mergeFrom()
     TestMap other = TestMap.newBuilder().putInt32ToInt32Field(1, 4).build();
@@ -659,14 +661,14 @@ public class MapTest extends TestCase {
 
     // Should be able to observe the change.
     message = parent.build();
-    assertEquals(4, message.getOptionalMessage().getInt32ToInt32Field().get(1).intValue());
+    assertEquals(4, message.getOptionalMessage().getInt32ToInt32FieldMap().get(1).intValue());
 
     // Make yet another change by clearing the nested builder.
     parent.getOptionalMessageBuilder().clear();
 
     // Should be able to observe the change.
     message = parent.build();
-    assertEquals(0, message.getOptionalMessage().getInt32ToInt32Field().size());
+    assertEquals(0, message.getOptionalMessage().getInt32ToInt32FieldMap().size());
   }
 
   public void testNestedBuilderOnChangeEventPropagationReflection() {
@@ -683,7 +685,7 @@ public class MapTest extends TestCase {
 
     // Should be able to observe the change.
     TestOnChangeEventPropagation message = parentBuilder.build();
-    assertEquals(1, message.getOptionalMessage().getInt32ToInt32Field().size());
+    assertEquals(1, message.getOptionalMessage().getInt32ToInt32FieldMap().size());
 
     // Change the entry value.
     entryBuilder.putInt32ToInt32Field(1, 4);
@@ -692,7 +694,7 @@ public class MapTest extends TestCase {
 
     // Should be able to observe the change.
     message = parentBuilder.build();
-    assertEquals(4, message.getOptionalMessage().getInt32ToInt32Field().get(1).intValue());
+    assertEquals(4, message.getOptionalMessage().getInt32ToInt32FieldMap().get(1).intValue());
 
     // Clear the nested builder.
     testMapBuilder = parentBuilder.getOptionalMessageBuilder();
@@ -700,7 +702,7 @@ public class MapTest extends TestCase {
 
     // Should be able to observe the change.
     message = parentBuilder.build();
-    assertEquals(0, message.getOptionalMessage().getInt32ToInt32Field().size());
+    assertEquals(0, message.getOptionalMessage().getInt32ToInt32FieldMap().size());
   }
 
   // The following methods are used to test reflection API.
@@ -789,8 +791,8 @@ public class MapTest extends TestCase {
     builder.clearField(f("int32_to_int32_field"));
     builder.clearField(f("int32_to_message_field"));
     message = builder.build();
-    assertEquals(0, message.getInt32ToInt32Field().size());
-    assertEquals(0, message.getInt32ToMessageField().size());
+    assertEquals(0, message.getInt32ToInt32FieldMap().size());
+    assertEquals(0, message.getInt32ToMessageFieldMap().size());
 
     // Test setField()
     setMapValues(builder, "int32_to_int32_field", mapForValues(11, 22, 33, 44));
@@ -801,10 +803,10 @@ public class MapTest extends TestCase {
             111, MessageValue.newBuilder().setValue(222).build(),
             333, MessageValue.newBuilder().setValue(444).build()));
     message = builder.build();
-    assertEquals(22, message.getInt32ToInt32Field().get(11).intValue());
-    assertEquals(44, message.getInt32ToInt32Field().get(33).intValue());
-    assertEquals(222, message.getInt32ToMessageField().get(111).getValue());
-    assertEquals(444, message.getInt32ToMessageField().get(333).getValue());
+    assertEquals(22, message.getInt32ToInt32FieldMap().get(11).intValue());
+    assertEquals(44, message.getInt32ToInt32FieldMap().get(33).intValue());
+    assertEquals(222, message.getInt32ToMessageFieldMap().get(111).getValue());
+    assertEquals(444, message.getInt32ToMessageFieldMap().get(333).getValue());
 
     // Test addRepeatedField
     builder.addRepeatedField(
@@ -817,8 +819,8 @@ public class MapTest extends TestCase {
             555,
             MessageValue.newBuilder().setValue(666).build()));
     message = builder.build();
-    assertEquals(66, message.getInt32ToInt32Field().get(55).intValue());
-    assertEquals(666, message.getInt32ToMessageField().get(555).getValue());
+    assertEquals(66, message.getInt32ToInt32FieldMap().get(55).intValue());
+    assertEquals(666, message.getInt32ToMessageFieldMap().get(555).getValue());
 
     // Test addRepeatedField (overriding existing values)
     builder.addRepeatedField(
@@ -831,8 +833,8 @@ public class MapTest extends TestCase {
             555,
             MessageValue.newBuilder().setValue(555).build()));
     message = builder.build();
-    assertEquals(55, message.getInt32ToInt32Field().get(55).intValue());
-    assertEquals(555, message.getInt32ToMessageField().get(555).getValue());
+    assertEquals(55, message.getInt32ToInt32FieldMap().get(55).intValue());
+    assertEquals(555, message.getInt32ToMessageFieldMap().get(555).getValue());
 
     // Test setRepeatedField
     for (int i = 0; i < builder.getRepeatedFieldCount(f("int32_to_int32_field")); i++) {
@@ -846,9 +848,9 @@ public class MapTest extends TestCase {
       builder.setRepeatedField(f("int32_to_int32_field"), i, mapEntryBuilder.build());
     }
     message = builder.build();
-    assertEquals(11, message.getInt32ToInt32Field().get(22).intValue());
-    assertEquals(33, message.getInt32ToInt32Field().get(44).intValue());
-    assertEquals(55, message.getInt32ToInt32Field().get(55).intValue());
+    assertEquals(11, message.getInt32ToInt32FieldMap().get(22).intValue());
+    assertEquals(33, message.getInt32ToInt32FieldMap().get(44).intValue());
+    assertEquals(55, message.getInt32ToInt32FieldMap().get(55).intValue());
   }
 
   // See additional coverage in TextFormatTest.java.
@@ -937,21 +939,21 @@ public class MapTest extends TestCase {
                     2, 1000)); // unknown value.
     TestMap message = builder.build();
 
-    assertEquals(TestMap.EnumValue.FOO, message.getInt32ToEnumField().get(0));
-    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumField().get(1));
-    assertEquals(TestMap.EnumValue.UNRECOGNIZED, message.getInt32ToEnumField().get(2));
-    assertEquals(1000, message.getInt32ToEnumFieldValue().get(2).intValue());
+    assertEquals(TestMap.EnumValue.FOO, message.getInt32ToEnumFieldMap().get(0));
+    assertEquals(TestMap.EnumValue.BAR, message.getInt32ToEnumFieldMap().get(1));
+    assertEquals(TestMap.EnumValue.UNRECOGNIZED, message.getInt32ToEnumFieldMap().get(2));
+    assertEquals(1000, message.getInt32ToEnumFieldValueMap().get(2).intValue());
 
     // Unknown enum values should be preserved after:
     //   1. Serialization and parsing.
     //   2. toBuild().
     //   3. mergeFrom().
     message = TestMap.parseFrom(message.toByteString());
-    assertEquals(1000, message.getInt32ToEnumFieldValue().get(2).intValue());
+    assertEquals(1000, message.getInt32ToEnumFieldValueMap().get(2).intValue());
     builder = message.toBuilder();
-    assertEquals(1000, builder.getInt32ToEnumFieldValue().get(2).intValue());
+    assertEquals(1000, builder.getInt32ToEnumFieldValueMap().get(2).intValue());
     builder = TestMap.newBuilder().mergeFrom(message);
-    assertEquals(1000, builder.getInt32ToEnumFieldValue().get(2).intValue());
+    assertEquals(1000, builder.getInt32ToEnumFieldValueMap().get(2).intValue());
 
     // hashCode()/equals() should take unknown enum values into account.
     builder.putAllInt32ToEnumFieldValue(newMap(2, 1001));
@@ -960,7 +962,7 @@ public class MapTest extends TestCase {
     assertFalse(message.equals(message2));
     // Unknown values will be converted to UNRECOGNIZED so the resulted enum map
     // should be the same.
-    assertEquals(message2.getInt32ToEnumField(), message.getInt32ToEnumField());
+    assertEquals(message2.getInt32ToEnumFieldMap(), message.getInt32ToEnumFieldMap());
   }
 
   public void testUnknownEnumValuesInReflectionApi() throws Exception {
@@ -991,7 +993,7 @@ public class MapTest extends TestCase {
 
     // Verify that enum values have been successfully updated.
     TestMap message = builder.build();
-    for (Map.Entry<Integer, Integer> entry : message.getInt32ToEnumFieldValue().entrySet()) {
+    for (Map.Entry<Integer, Integer> entry : message.getInt32ToEnumFieldValueMap().entrySet()) {
       assertEquals(data.get(entry.getKey()) + 1, entry.getValue().intValue());
     }
   }
@@ -1002,18 +1004,18 @@ public class MapTest extends TestCase {
     TestMap message = builder.build();
 
     assertEquals(
-        Arrays.asList("1", "2", "3"), new ArrayList<>(message.getStringToInt32Field().keySet()));
+        Arrays.asList("1", "2", "3"), new ArrayList<>(message.getStringToInt32FieldMap().keySet()));
   }
 
   public void testGetMap() {
     TestMap.Builder builder = TestMap.newBuilder();
     setMapValuesUsingAccessors(builder);
     TestMap message = builder.build();
-    assertEquals(message.getStringToInt32Field(), message.getStringToInt32FieldMap());
-    assertEquals(message.getInt32ToBytesField(), message.getInt32ToBytesFieldMap());
-    assertEquals(message.getInt32ToEnumField(), message.getInt32ToEnumFieldMap());
-    assertEquals(message.getInt32ToEnumFieldValue(), message.getInt32ToEnumFieldValueMap());
-    assertEquals(message.getInt32ToMessageField(), message.getInt32ToMessageFieldMap());
+    assertEquals(message.getStringToInt32FieldMap(), message.getStringToInt32FieldMap());
+    assertEquals(message.getInt32ToBytesFieldMap(), message.getInt32ToBytesFieldMap());
+    assertEquals(message.getInt32ToEnumFieldMap(), message.getInt32ToEnumFieldMap());
+    assertEquals(message.getInt32ToEnumFieldValueMap(), message.getInt32ToEnumFieldValueMap());
+    assertEquals(message.getInt32ToMessageFieldMap(), message.getInt32ToMessageFieldMap());
   }
 
   public void testContains() {

java/core/src/test/java/com/google/protobuf/TextFormatTest.java

@@ -30,6 +30,7 @@
 
 package com.google.protobuf;
 
+import static com.google.common.truth.Truth.assertThat;
 import static com.google.protobuf.TestUtil.TEST_REQUIRED_INITIALIZED;
 import static com.google.protobuf.TestUtil.TEST_REQUIRED_UNINITIALIZED;
 
@@ -866,6 +867,12 @@ public class TextFormatTest extends TestCase {
     assertEquals(bytes(0xe1, 0x88, 0xb4), TextFormat.unescapeBytes("\\341\\210\\264"));
     assertEquals("\u1234", TextFormat.unescapeText("\\xe1\\x88\\xb4"));
     assertEquals(bytes(0xe1, 0x88, 0xb4), TextFormat.unescapeBytes("\\xe1\\x88\\xb4"));
+    assertEquals("\u1234", TextFormat.unescapeText("\\u1234"));
+    assertEquals(bytes(0xe1, 0x88, 0xb4), TextFormat.unescapeBytes("\\u1234"));
+    assertEquals(bytes(0xe1, 0x88, 0xb4), TextFormat.unescapeBytes("\\U00001234"));
+    assertEquals(
+        new String(new int[] {0x10437}, 0, 1), TextFormat.unescapeText("\\xf0\\x90\\x90\\xb7"));
+    assertEquals(bytes(0xf0, 0x90, 0x90, 0xb7), TextFormat.unescapeBytes("\\U00010437"));
 
     // Handling of strings with unescaped Unicode characters > 255.
     final String zh = "\u9999\u6e2f\u4e0a\u6d77\ud84f\udf80\u8c50\u9280\u884c";
@@ -893,6 +900,87 @@ public class TextFormatTest extends TestCase {
     } catch (TextFormat.InvalidEscapeSequenceException e) {
       // success
     }
+
+    try {
+      TextFormat.unescapeText("\\u");
+      fail("Should have thrown an exception.");
+    } catch (TextFormat.InvalidEscapeSequenceException e) {
+      assertThat(e)
+          .hasMessageThat()
+          .isEqualTo("Invalid escape sequence: '\\u' with too few hex chars");
+    }
+
+    try {
+      TextFormat.unescapeText("\\ud800");
+      fail("Should have thrown an exception.");
+    } catch (TextFormat.InvalidEscapeSequenceException e) {
+      assertThat(e)
+          .hasMessageThat()
+          .isEqualTo("Invalid escape sequence: '\\u' refers to a surrogate");
+    }
+
+    try {
+      TextFormat.unescapeText("\\ud800\\u1234");
+      fail("Should have thrown an exception.");
+    } catch (TextFormat.InvalidEscapeSequenceException e) {
+      assertThat(e)
+          .hasMessageThat()
+          .isEqualTo("Invalid escape sequence: '\\u' refers to a surrogate");
+    }
+
+    try {
+      TextFormat.unescapeText("\\udc00");
+      fail("Should have thrown an exception.");
+    } catch (TextFormat.InvalidEscapeSequenceException e) {
+      assertThat(e)
+          .hasMessageThat()
+          .isEqualTo("Invalid escape sequence: '\\u' refers to a surrogate");
+    }
+
+    try {
+      TextFormat.unescapeText("\\ud801\\udc37");
+      fail("Should have thrown an exception.");
+    } catch (TextFormat.InvalidEscapeSequenceException e) {
+      assertThat(e)
+          .hasMessageThat()
+          .isEqualTo("Invalid escape sequence: '\\u' refers to a surrogate");
+    }
+
+    try {
+      TextFormat.unescapeText("\\U1234");
+      fail("Should have thrown an exception.");
+    } catch (TextFormat.InvalidEscapeSequenceException e) {
+      assertThat(e)
+          .hasMessageThat()
+          .isEqualTo("Invalid escape sequence: '\\U' with too few hex chars");
+    }
+
+    try {
+      TextFormat.unescapeText("\\U1234no more hex");
+      fail("Should have thrown an exception.");
+    } catch (TextFormat.InvalidEscapeSequenceException e) {
+      assertThat(e)
+          .hasMessageThat()
+          .isEqualTo("Invalid escape sequence: '\\U' with too few hex chars");
+    }
+
+    try {
+      TextFormat.unescapeText("\\U00110000");
+      fail("Should have thrown an exception.");
+    } catch (TextFormat.InvalidEscapeSequenceException e) {
+      assertThat(e)
+          .hasMessageThat()
+          .isEqualTo("Invalid escape sequence: '\\U00110000' is not a valid code point value");
+    }
+
+    try {
+      TextFormat.unescapeText("\\U0000d801\\U00000dc37");
+      fail("Should have thrown an exception.");
+    } catch (TextFormat.InvalidEscapeSequenceException e) {
+      assertThat(e)
+          .hasMessageThat()
+          .isEqualTo("Invalid escape sequence: '\\U0000d801' refers to a surrogate code unit");
+    }
   }
 
   public void testParseInteger() throws Exception {

java/lite/src/test/java/com/google/protobuf/Proto2MessageLiteInfoFactory.java

@@ -174,8 +174,9 @@ public final class Proto2MessageLiteInfoFactory implements MessageInfoFactory {
           "fieldRequiredSint6487_",
           "fieldRequiredGroup88_",
         };
-    // To update this after a proto change, run protoc on proto2_message_lite.proto and copy over
-    // the content of the generated buildMessageInfo() method here.
+    // To update this after a proto change, run blaze build on proto2_message_lite.proto and copy
+    // over the String info from the proto2_message_lite_proto-lite-src.jar file in the
+    // blaze-genfiles directory.
     java.lang.String info =
         "\u0001U\u0001\u0002\u0001XU\u0000 \u0015\u0001\u1000\u0000\u0002\u1001\u0001\u0003"
             + "\u1002\u0002\u0004\u1003\u0003\u0005\u1004\u0004\u0006\u1005\u0005\u0007\u1006\u0006\b\u1007\u0007"

java/util/src/main/java/com/google/protobuf/util/FieldMaskTree.java

@@ -137,11 +137,19 @@ final class FieldMaskTree {
   }
 
   /**
-   * Remove {@code path} from the tree.
+   * Removes {@code path} from the tree.
    *
-   * <p>When removing a field path from the tree, all sub-paths will be removed. That is, after
-   * removing "foo.bar" from the tree, "foo.bar.baz" will be removed. Likewise, if the field path to
-   * remove is a non-exist sub-path, nothing will be changed.
+   * <ul>
+   *   When removing a field path from the tree:
+   *   <li>All sub-paths will be removed. That is, after removing "foo.bar" from the tree,
+   *       "foo.bar.baz" will be removed.
+   *   <li>If all children of a node has been removed, the node itself will be removed as well.
+   *       That is, if "foo" only has one child "bar" and "foo.bar" only has one child "baz",
+   *       removing "foo.bar.barz" would remove both "foo" and "foo.bar".
+   *       If "foo" has both "bar" and "qux" as children, removing "foo.bar" would leave the path
+   *       "foo.qux" intact.
+   *   <li>If the field path to remove is a non-exist sub-path, nothing will be changed.
+   * </ul>
    */
   @CanIgnoreReturnValue
   FieldMaskTree removeFieldPath(String path) {
@@ -149,23 +157,35 @@ final class FieldMaskTree {
     if (parts.isEmpty()) {
       return this;
     }
-    Node node = root;
-    for (int i = 0; i < parts.size(); i++) {
-      String key = parts.get(i);
-      if (!node.children.containsKey(key)) {
-        // Path does not exist.
-        return this;
-      }
-      if (i == parts.size() - 1) {
-        // Remove path.
-        node.children.remove(key);
-        return this;
-      }
-      node = node.children.get(key);
-    }
+    removeFieldPath(root, parts, 0);
     return this;
   }
 
+  /**
+   * Removes {@code parts} from {@code node} recursively.
+   *
+   * @return a boolean value indicating whether current {@code node} should be removed.
+   */
+  @CanIgnoreReturnValue
+  private static boolean removeFieldPath(Node node, List<String> parts, int index) {
+    String key = parts.get(index);
+
+    // Base case 1: path not match.
+    if (!node.children.containsKey(key)) {
+      return false;
+    }
+    // Base case 2: last element in parts.
+    if (index == parts.size() - 1) {
+      node.children.remove(key);
+      return node.children.isEmpty();
+    }
+    // Recursive remove sub-path.
+    if (removeFieldPath(node.children.get(key), parts, index + 1)) {
+      node.children.remove(key);
+    }
+    return node.children.isEmpty();
+  }
+
   /** Removes all field paths in {@code mask} from this tree. */
   @CanIgnoreReturnValue
   FieldMaskTree removeFromFieldMask(FieldMask mask) {
@@ -187,10 +207,8 @@ final class FieldMaskTree {
     return FieldMask.newBuilder().addAllPaths(paths).build();
   }
 
-  /**
-   * Gathers all field paths in a sub-tree.
-   */
-  private void getFieldPaths(Node node, String path, List<String> paths) {
+  /** Gathers all field paths in a sub-tree. */
+  private static void getFieldPaths(Node node, String path, List<String> paths) {
     if (node.children.isEmpty()) {
       paths.add(path);
       return;
@@ -247,10 +265,8 @@ final class FieldMaskTree {
     merge(root, "", source, destination, options);
   }
 
-  /**
-   * Merges all fields specified by a sub-tree from {@code source} to {@code destination}.
-   */
-  private void merge(
+  /** Merges all fields specified by a sub-tree from {@code source} to {@code destination}. */
+  private static void merge(
       Node node,
       String path,
       Message source,

java/util/src/main/java/com/google/protobuf/util/FieldMaskUtil.java

@@ -276,7 +276,13 @@ public final class FieldMaskUtil {
     return maskTree.toFieldMask();
   }
 
-  /** Subtracts {@code secondMask} and {@code otherMasks} from {@code firstMask}. */
+  /**
+   * Subtracts {@code secondMask} and {@code otherMasks} from {@code firstMask}.
+   *
+   * <p>This method disregards proto structure. That is, if {@code firstMask} is "foo" and {@code
+   * secondMask} is "foo.bar", the response will always be "foo" without considering the internal
+   * proto structure of message "foo".
+   */
   public static FieldMask subtract(
       FieldMask firstMask, FieldMask secondMask, FieldMask... otherMasks) {
     FieldMaskTree maskTree = new FieldMaskTree(firstMask).removeFromFieldMask(secondMask);

java/util/src/main/java/com/google/protobuf/util/JsonFormat.java

@@ -525,7 +525,6 @@ public class JsonFormat {
       return types.get(name);
     }
 
-    /* @Nullable */
     Descriptor getDescriptorForTypeUrl(String typeUrl) throws InvalidProtocolBufferException {
       return find(getTypeName(typeUrl));
     }

java/util/src/test/java/com/google/protobuf/util/FieldMaskTreeTest.java

@@ -77,25 +77,37 @@ public class FieldMaskTreeTest extends TestCase {
 
   public void testRemoveFieldPath() throws Exception {
     String initialTreeString = "bar.baz,bar.quz.bar,foo";
-    FieldMaskTree tree = new FieldMaskTree(FieldMaskUtil.fromString(initialTreeString));
+    FieldMaskTree tree;
+
     // Empty path.
+    tree = new FieldMaskTree(FieldMaskUtil.fromString(initialTreeString));
     tree.removeFieldPath("");
     assertEquals(initialTreeString, tree.toString());
+
     // Non-exist sub-path of an existing leaf.
+    tree = new FieldMaskTree(FieldMaskUtil.fromString(initialTreeString));
     tree.removeFieldPath("foo.bar");
     assertEquals(initialTreeString, tree.toString());
+
     // Non-exist path.
+    tree = new FieldMaskTree(FieldMaskUtil.fromString(initialTreeString));
     tree.removeFieldPath("bar.foo");
     assertEquals(initialTreeString, tree.toString());
-    // Match an existing leaf node.
+
+    // Match an existing leaf node -> remove leaf node.
+    tree = new FieldMaskTree(FieldMaskUtil.fromString(initialTreeString));
     tree.removeFieldPath("foo");
     assertEquals("bar.baz,bar.quz.bar", tree.toString());
-    // Match sub-path of an existing leaf node.
+
+    // Match sub-path of an existing leaf node -> recursive removal.
+    tree = new FieldMaskTree(FieldMaskUtil.fromString(initialTreeString));
     tree.removeFieldPath("bar.quz.bar");
-    assertEquals("bar.baz,bar.quz", tree.toString());
-    // Match a non-leaf node.
+    assertEquals("bar.baz,foo", tree.toString());
+
+    // Match a non-leaf node -> remove all children.
+    tree = new FieldMaskTree(FieldMaskUtil.fromString(initialTreeString));
     tree.removeFieldPath("bar");
-    assertThat(tree.toString()).isEmpty();
+    assertEquals("foo", tree.toString());
   }
 
   public void testRemoveFromFieldMask() throws Exception {

java/util/src/test/java/com/google/protobuf/util/FieldMaskUtilTest.java

@@ -239,7 +239,7 @@ public class FieldMaskUtilTest extends TestCase {
     FieldMask mask3 = FieldMaskUtil.fromString("bar.quz");
     FieldMask mask4 = FieldMaskUtil.fromString("foo,bar.baz");
     FieldMask result = FieldMaskUtil.subtract(mask1, mask2, mask3, mask4);
-    assertEquals("bar", FieldMaskUtil.toString(result));
+    assertThat(FieldMaskUtil.toString(result)).isEmpty();
   }
 
   public void testIntersection() throws Exception {

java/util/src/test/java/com/google/protobuf/util/JsonFormatTest.java

@@ -722,8 +722,8 @@ public class JsonFormatTest extends TestCase {
     mergeFromJson(
         "{\n" + "  int32ToInt32Map: {1: 2},\n" + "  stringToInt32Map: {hello: 3}\n" + "}", builder);
     TestMap message = builder.build();
-    assertEquals(2, message.getInt32ToInt32Map().get(1).intValue());
-    assertEquals(3, message.getStringToInt32Map().get("hello").intValue());
+    assertEquals(2, message.getInt32ToInt32MapMap().get(1).intValue());
+    assertEquals(3, message.getStringToInt32MapMap().get("hello").intValue());
   }
 
   public void testWrappers() throws Exception {

js/binary/constants.js

@@ -31,6 +31,7 @@
 /**
  * @fileoverview This file contains constants and typedefs used by
  * jspb.BinaryReader and BinaryWriter.
+ * @suppress {missingRequire} TODO(b/152540451): this shouldn't be needed
  *
  * @author aappleby@google.com (Austin Appleby)
  */

js/binary/decoder.js

@@ -40,6 +40,7 @@
  * intact, you _must_ read them using one of the Hash64 methods, which return
  * an 8-character string.
  *
+ * @suppress {missingRequire} TODO(b/152540451): this shouldn't be needed
  * @author aappleby@google.com (Austin Appleby)
  */
 

js/binary/reader.js

@@ -41,6 +41,7 @@
  * using the typed jspb code generator, but if you bypass that you'll need
  * to keep things in sync by hand.
  *
+ * @suppress {missingRequire} TODO(b/152540451): this shouldn't be needed
  * @author aappleby@google.com (Austin Appleby)
  */
 

js/binary/utils.js

@@ -32,6 +32,7 @@
  * @fileoverview This file contains helper code used by jspb.BinaryReader
  * and BinaryWriter.
  *
+ * @suppress {missingRequire} TODO(b/152540451): this shouldn't be needed
  * @author aappleby@google.com (Austin Appleby)
  */
 

js/binary/writer.js

@@ -52,6 +52,7 @@
  * Major caveat 3 - This class uses typed arrays and must not be used on older
  * browsers that do not support them.
  *
+ * @suppress {missingRequire} TODO(b/152540451): this shouldn't be needed
  * @author aappleby@google.com (Austin Appleby)
  */
 

js/map.js

@@ -1,3 +1,4 @@
+
 // Protocol Buffers - Google's data interchange format
 // Copyright 2008 Google Inc.  All rights reserved.
 // https://developers.google.com/protocol-buffers/
@@ -28,6 +29,10 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+/**
+ * @fileoverview
+ * @suppress {missingRequire} TODO(b/152540451): this shouldn't be needed
+ */
 goog.provide('jspb.Map');
 
 goog.require('goog.asserts');

js/message.js

@@ -31,6 +31,7 @@
 /**
  * @fileoverview Definition of jspb.Message.
  *
+ * @suppress {missingRequire} TODO(b/152540451): this shouldn't be needed
  * @author mwr@google.com (Mark Rawling)
  */
 

objectivec/GPBMessage.m

@@ -71,6 +71,8 @@ static NSString *const kGPBDataCoderKey = @"GPBData";
  @package
   GPBUnknownFieldSet *unknownFields_;
   NSMutableDictionary *extensionMap_;
+  // Readonly access to autocreatedExtensionMap_ is protected via
+  // readOnlySemaphore_.
   NSMutableDictionary *autocreatedExtensionMap_;
 
   // If the object was autocreated, we remember the creator so that if we get
@@ -79,10 +81,10 @@ static NSString *const kGPBDataCoderKey = @"GPBData";
   GPBFieldDescriptor *autocreatorField_;
   GPBExtensionDescriptor *autocreatorExtension_;
 
-  // A lock to provide mutual exclusion from internal data that can be modified
-  // by *read* operations such as getters (autocreation of message fields and
-  // message extensions, not setting of values). Used to guarantee thread safety
-  // for concurrent reads on the message.
+  // Message can only be mutated from one thread. But some *readonly* operations
+  // modifify internal state because they autocreate things. The
+  // autocreatedExtensionMap_ is one such structure. Access during readonly
+  // operations is protected via this semaphore.
   // NOTE: OSSpinLock may seem like a good fit here but Apple engineers have
   // pointed out that they are vulnerable to live locking on iOS in cases of
   // priority inversion:
@@ -583,19 +585,30 @@ static id GetOrCreateArrayIvarWithField(GPBMessage *self,
 // This is like GPBGetObjectIvarWithField(), but for arrays, it should
 // only be used to wire the method into the class.
 static id GetArrayIvarWithField(GPBMessage *self, GPBFieldDescriptor *field) {
-  id array = GPBGetObjectIvarWithFieldNoAutocreate(self, field);
-  if (!array) {
-    // Check again after getting the lock.
-    GPBPrepareReadOnlySemaphore(self);
-    dispatch_semaphore_wait(self->readOnlySemaphore_, DISPATCH_TIME_FOREVER);
-    array = GPBGetObjectIvarWithFieldNoAutocreate(self, field);
-    if (!array) {
-      array = CreateArrayForField(field, self);
-      GPBSetAutocreatedRetainedObjectIvarWithField(self, field, array);
-    }
-    dispatch_semaphore_signal(self->readOnlySemaphore_);
+  uint8_t *storage = (uint8_t *)self->messageStorage_;
+  _Atomic(id) *typePtr = (_Atomic(id) *)&storage[field->description_->offset];
+  id array = atomic_load(typePtr);
+  if (array) {
+    return array;
   }
-  return array;
+
+  id expected = nil;
+  id autocreated = CreateArrayForField(field, self);
+  if (atomic_compare_exchange_strong(typePtr, &expected, autocreated)) {
+    // Value was set, return it.
+    return autocreated;
+  }
+
+  // Some other thread set it, release the one created and return what got set.
+  if (GPBFieldDataTypeIsObject(field)) {
+    GPBAutocreatedArray *autoArray = autocreated;
+    autoArray->_autocreator = nil;
+  } else {
+    GPBInt32Array *gpbArray = autocreated;
+    gpbArray->_autocreator = nil;
+  }
+  [autocreated release];
+  return expected;
 }
 
 static id GetOrCreateMapIvarWithField(GPBMessage *self,
@@ -613,19 +626,31 @@ static id GetOrCreateMapIvarWithField(GPBMessage *self,
 // This is like GPBGetObjectIvarWithField(), but for maps, it should
 // only be used to wire the method into the class.
 static id GetMapIvarWithField(GPBMessage *self, GPBFieldDescriptor *field) {
-  id dict = GPBGetObjectIvarWithFieldNoAutocreate(self, field);
-  if (!dict) {
-    // Check again after getting the lock.
-    GPBPrepareReadOnlySemaphore(self);
-    dispatch_semaphore_wait(self->readOnlySemaphore_, DISPATCH_TIME_FOREVER);
-    dict = GPBGetObjectIvarWithFieldNoAutocreate(self, field);
-    if (!dict) {
-      dict = CreateMapForField(field, self);
-      GPBSetAutocreatedRetainedObjectIvarWithField(self, field, dict);
-    }
-    dispatch_semaphore_signal(self->readOnlySemaphore_);
+  uint8_t *storage = (uint8_t *)self->messageStorage_;
+  _Atomic(id) *typePtr = (_Atomic(id) *)&storage[field->description_->offset];
+  id dict = atomic_load(typePtr);
+  if (dict) {
+    return dict;
   }
-  return dict;
+
+  id expected = nil;
+  id autocreated = CreateMapForField(field, self);
+  if (atomic_compare_exchange_strong(typePtr, &expected, autocreated)) {
+    // Value was set, return it.
+    return autocreated;
+  }
+
+  // Some other thread set it, release the one created and return what got set.
+  if ((field.mapKeyDataType == GPBDataTypeString) &&
+      GPBFieldDataTypeIsObject(field)) {
+    GPBAutocreatedDictionary *autoDict = autocreated;
+    autoDict->_autocreator = nil;
+  } else {
+    GPBInt32Int32Dictionary *gpbDict = autocreated;
+    gpbDict->_autocreator = nil;
+  }
+  [autocreated release];
+  return expected;
 }
 
 #endif  // !defined(__clang_analyzer__)
@@ -3337,30 +3362,34 @@ id GPBGetMessageMapField(GPBMessage *self, GPBFieldDescriptor *field) {
 
 id GPBGetObjectIvarWithField(GPBMessage *self, GPBFieldDescriptor *field) {
   NSCAssert(!GPBFieldIsMapOrArray(field), @"Shouldn't get here");
-  if (GPBGetHasIvarField(self, field)) {
-    uint8_t *storage = (uint8_t *)self->messageStorage_;
-    id *typePtr = (id *)&storage[field->description_->offset];
-    return *typePtr;
-  }
-  // Not set...
-
-  // Non messages (string/data), get their default.
   if (!GPBFieldDataTypeIsMessage(field)) {
+    if (GPBGetHasIvarField(self, field)) {
+      uint8_t *storage = (uint8_t *)self->messageStorage_;
+      id *typePtr = (id *)&storage[field->description_->offset];
+      return *typePtr;
+    }
+    // Not set...non messages (string/data), get their default.
     return field.defaultValue.valueMessage;
   }
 
-  GPBPrepareReadOnlySemaphore(self);
-  dispatch_semaphore_wait(self->readOnlySemaphore_, DISPATCH_TIME_FOREVER);
-  GPBMessage *result = GPBGetObjectIvarWithFieldNoAutocreate(self, field);
-  if (!result) {
-    // For non repeated messages, create the object, set it and return it.
-    // This object will not initially be visible via GPBGetHasIvar, so
-    // we save its creator so it can become visible if it's mutated later.
-    result = GPBCreateMessageWithAutocreator(field.msgClass, self, field);
-    GPBSetAutocreatedRetainedObjectIvarWithField(self, field, result);
-  }
-  dispatch_semaphore_signal(self->readOnlySemaphore_);
-  return result;
+  uint8_t *storage = (uint8_t *)self->messageStorage_;
+  _Atomic(id) *typePtr = (_Atomic(id) *)&storage[field->description_->offset];
+  id msg = atomic_load(typePtr);
+  if (msg) {
+    return msg;
+  }
+
+  id expected = nil;
+  id autocreated = GPBCreateMessageWithAutocreator(field.msgClass, self, field);
+  if (atomic_compare_exchange_strong(typePtr, &expected, autocreated)) {
+    // Value was set, return it.
+    return autocreated;
+  }
+
+  // Some other thread set it, release the one created and return what got set.
+  GPBClearMessageAutocreator(autocreated);
+  [autocreated release];
+  return expected;
 }
 
 #pragma clang diagnostic pop

objectivec/GPBUtilities.m

@@ -504,15 +504,6 @@ static void GPBMaybeClearOneofPrivate(GPBMessage *self,
 // Object types are handled slightly differently, they need to be released
 // and retained.
 
-void GPBSetAutocreatedRetainedObjectIvarWithField(
-    GPBMessage *self, GPBFieldDescriptor *field,
-    id __attribute__((ns_consumed)) value) {
-  uint8_t *storage = (uint8_t *)self->messageStorage_;
-  id *typePtr = (id *)&storage[field->description_->offset];
-  NSCAssert(*typePtr == NULL, @"Can't set autocreated object more than once.");
-  *typePtr = value;
-}
-
 void GPBClearAutocreatedMessageIvarWithField(GPBMessage *self,
                                              GPBFieldDescriptor *field) {
   if (GPBGetHasIvarField(self, field)) {

objectivec/GPBUtilities_PackagePrivate.h

@@ -289,10 +289,6 @@ void GPBSetRetainedObjectIvarWithFieldPrivate(GPBMessage *self,
 id GPBGetObjectIvarWithFieldNoAutocreate(GPBMessage *self,
                                          GPBFieldDescriptor *field);
 
-void GPBSetAutocreatedRetainedObjectIvarWithField(
-    GPBMessage *self, GPBFieldDescriptor *field,
-    id __attribute__((ns_consumed)) value);
-
 // Clears and releases the autocreated message ivar, if it's autocreated. If
 // it's not set as autocreated, this method does nothing.
 void GPBClearAutocreatedMessageIvarWithField(GPBMessage *self,

python/google/protobuf/internal/api_implementation.py

@@ -60,11 +60,16 @@ if _api_version < 0:  # Still unspecified?
       raise ImportError('_use_fast_cpp_protos import succeeded but was None')
     del _use_fast_cpp_protos
     _api_version = 2
+    # Can not import both use_fast_cpp_protos and use_pure_python.
+    from google.protobuf import use_pure_python
+    raise RuntimeError(
+        'Conflict depend on both use_fast_cpp_protos and use_pure_python')
   except ImportError:
     try:
       # pylint: disable=g-import-not-at-top
-      from google.protobuf.internal import use_pure_python
+      from google.protobuf import use_pure_python
       del use_pure_python  # Avoids a pylint error and namespace pollution.
+      _api_version = 0
     except ImportError:
       # TODO(b/74017912): It's unsafe to enable :use_fast_cpp_protos by default;
       # it can cause data loss if you have any Python-only extensions to any

python/google/protobuf/internal/containers.py

@@ -629,7 +629,8 @@ class MessageMap(MutableMapping):
     return repr(self._values)
 
   def MergeFrom(self, other):
-    for key in other:
+    # pylint: disable=protected-access
+    for key in other._values:
       # According to documentation: "When parsing from the wire or when merging,
       # if there are duplicate map keys the last key seen is used".
       if key in self:

python/google/protobuf/internal/message_test.py

@@ -2107,6 +2107,11 @@ class Proto3Test(unittest.TestCase):
     self.assertEqual(msg.map_int32_foreign_message[222].d, 20)
     self.assertNotEqual(msg.map_int32_foreign_message[222].c, 123)
 
+    # Merge a dict to map field is not accepted
+    with self.assertRaises(AttributeError):
+      m1.map_int32_all_types.MergeFrom(
+          {1: unittest_proto3_arena_pb2.TestAllTypes()})
+
   def testMergeFromBadType(self):
     msg = map_unittest_pb2.TestMap()
     with self.assertRaisesRegexp(

python/google/protobuf/pyext/map_container.cc

@@ -339,6 +339,11 @@ PyObject* GetEntryClass(PyObject* _self) {
 
 PyObject* MapReflectionFriend::MergeFrom(PyObject* _self, PyObject* arg) {
   MapContainer* self = GetMap(_self);
+  if (!PyObject_TypeCheck(arg, ScalarMapContainer_Type) &&
+      !PyObject_TypeCheck(arg, MessageMapContainer_Type)) {
+    PyErr_SetString(PyExc_AttributeError, "Not a map field");
+    return nullptr;
+  }
   MapContainer* other_map = GetMap(arg);
   Message* message = self->GetMutableMessage();
   const Message* other_message = other_map->parent->message;

python/google/protobuf/pyext/message.cc

@@ -809,7 +809,7 @@ bool CheckAndSetString(
     return false;
   }
 
-  string value_string(value, value_len);
+  std::string value_string(value, value_len);
   if (append) {
     reflection->AddString(message, descriptor, std::move(value_string));
   } else if (index < 0) {

python/google/protobuf/text_format.py

@@ -882,8 +882,11 @@ class _Parser(object):
           raise tokenizer.ParseErrorPreviousToken('Expected "%s".' %
                                                   (expanded_any_end_token,))
         self._MergeField(tokenizer, expanded_any_sub_message)
+      deterministic = False
+
       message.Pack(expanded_any_sub_message,
-                   type_url_prefix=type_url_prefix)
+                   type_url_prefix=type_url_prefix,
+                   deterministic=deterministic)
       return
 
     if tokenizer.TryConsume('['):

src/Makefile.am

@@ -68,7 +68,6 @@ nobase_include_HEADERS =                                         \
   google/protobuf/stubs/bytestream.h                             \
   google/protobuf/stubs/casts.h                                  \
   google/protobuf/stubs/common.h                                 \
-  google/protobuf/stubs/fastmem.h                                \
   google/protobuf/stubs/hash.h                                   \
   google/protobuf/stubs/logging.h                                \
   google/protobuf/stubs/macros.h                                 \
@@ -104,7 +103,6 @@ nobase_include_HEADERS =                                         \
   google/protobuf/generated_message_util.h                       \
   google/protobuf/has_bits.h                                     \
   google/protobuf/implicit_weak_message.h                        \
-  google/protobuf/inlined_string_field.h                         \
   google/protobuf/io/io_win32.h                                \
   google/protobuf/map_entry.h                                    \
   google/protobuf/map_entry_lite.h                               \
@@ -202,6 +200,7 @@ libprotobuf_lite_la_SOURCES =                                  \
   google/protobuf/stubs/time.h                                 \
   google/protobuf/any_lite.cc                                  \
   google/protobuf/arena.cc                                     \
+  google/protobuf/arenastring.cc                               \
   google/protobuf/extension_set.cc                             \
   google/protobuf/generated_enum_util.cc                       \
   google/protobuf/generated_message_util.cc                    \

src/google/protobuf/any.cc

@@ -51,9 +51,8 @@ void AnyMetadata::PackFrom(const Message& message,
       &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyString(),
       GetTypeUrl(message.GetDescriptor()->full_name(), type_url_prefix),
       nullptr);
-  message.SerializeToString(value_->Mutable(
-      &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(),
-      nullptr));
+  message.SerializeToString(
+      value_->Mutable(ArenaStringPtr::EmptyDefault{}, nullptr));
 }
 
 bool AnyMetadata::UnpackTo(Message* message) const {

src/google/protobuf/any.h

@@ -60,7 +60,8 @@ class PROTOBUF_EXPORT AnyMetadata {
   typedef ArenaStringPtr ValueType;
  public:
   // AnyMetadata does not take ownership of "type_url" and "value".
-  AnyMetadata(UrlType* type_url, ValueType* value);
+  constexpr AnyMetadata(UrlType* type_url, ValueType* value)
+      : type_url_(type_url), value_(value) {}
 
   // Packs a message using the default type URL prefix: "type.googleapis.com".
   // The resulted type URL will be "type.googleapis.com/<message_full_name>".

src/google/protobuf/any.pb.cc

@@ -112,12 +112,12 @@ Any::Any(const Any& from)
   _internal_metadata_.MergeFrom<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(from._internal_metadata_);
   type_url_.UnsafeSetDefault(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited());
   if (!from._internal_type_url().empty()) {
-    type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), from._internal_type_url(),
+    type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, from._internal_type_url(), 
       GetArena());
   }
   value_.UnsafeSetDefault(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited());
   if (!from._internal_value().empty()) {
-    value_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), from._internal_value(),
+    value_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, from._internal_value(), 
       GetArena());
   }
   // @@protoc_insertion_point(copy_constructor:google.protobuf.Any)
@@ -162,8 +162,8 @@ void Any::Clear() {
   // Prevent compiler warnings about cached_has_bits being unused
   (void) cached_has_bits;
 
-  type_url_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
-  value_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  type_url_.ClearToEmpty();
+  value_.ClearToEmpty();
   _internal_metadata_.Clear<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>();
 }
 

src/google/protobuf/any.pb.h

@@ -25,7 +25,6 @@
 #include <google/protobuf/arenastring.h>
 #include <google/protobuf/generated_message_table_driven.h>
 #include <google/protobuf/generated_message_util.h>
-#include <google/protobuf/inlined_string_field.h>
 #include <google/protobuf/metadata_lite.h>
 #include <google/protobuf/generated_message_reflection.h>
 #include <google/protobuf/message.h>
@@ -272,7 +271,7 @@ class PROTOBUF_EXPORT Any PROTOBUF_FINAL :
 
 // string type_url = 1;
 inline void Any::clear_type_url() {
-  type_url_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  type_url_.ClearToEmpty();
 }
 inline const std::string& Any::type_url() const {
   // @@protoc_insertion_point(field_get:google.protobuf.Any.type_url)
@@ -291,31 +290,30 @@ inline const std::string& Any::_internal_type_url() const {
 }
 inline void Any::_internal_set_type_url(const std::string& value) {
   
-  type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), value, GetArena());
+  type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, value, GetArena());
 }
 inline void Any::set_type_url(std::string&& value) {
   
   type_url_.Set(
-    &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::move(value), GetArena());
+    ::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::move(value), GetArena());
   // @@protoc_insertion_point(field_set_rvalue:google.protobuf.Any.type_url)
 }
 inline void Any::set_type_url(const char* value) {
   GOOGLE_DCHECK(value != nullptr);
   
-  type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
-              GetArena());
+  type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(value), GetArena());
   // @@protoc_insertion_point(field_set_char:google.protobuf.Any.type_url)
 }
 inline void Any::set_type_url(const char* value,
     size_t size) {
   
-  type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(
+  type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(
       reinterpret_cast<const char*>(value), size), GetArena());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.Any.type_url)
 }
 inline std::string* Any::_internal_mutable_type_url() {
   
-  return type_url_.Mutable(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  return type_url_.Mutable(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, GetArena());
 }
 inline std::string* Any::release_type_url() {
   // @@protoc_insertion_point(field_release:google.protobuf.Any.type_url)
@@ -334,7 +332,7 @@ inline void Any::set_allocated_type_url(std::string* type_url) {
 
 // bytes value = 2;
 inline void Any::clear_value() {
-  value_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  value_.ClearToEmpty();
 }
 inline const std::string& Any::value() const {
   // @@protoc_insertion_point(field_get:google.protobuf.Any.value)
@@ -353,31 +351,30 @@ inline const std::string& Any::_internal_value() const {
 }
 inline void Any::_internal_set_value(const std::string& value) {
   
-  value_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), value, GetArena());
+  value_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, value, GetArena());
 }
 inline void Any::set_value(std::string&& value) {
   
   value_.Set(
-    &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::move(value), GetArena());
+    ::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::move(value), GetArena());
   // @@protoc_insertion_point(field_set_rvalue:google.protobuf.Any.value)
 }
 inline void Any::set_value(const char* value) {
   GOOGLE_DCHECK(value != nullptr);
   
-  value_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
-              GetArena());
+  value_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(value), GetArena());
   // @@protoc_insertion_point(field_set_char:google.protobuf.Any.value)
 }
 inline void Any::set_value(const void* value,
     size_t size) {
   
-  value_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(
+  value_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(
       reinterpret_cast<const char*>(value), size), GetArena());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.Any.value)
 }
 inline std::string* Any::_internal_mutable_value() {
   
-  return value_.Mutable(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  return value_.Mutable(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, GetArena());
 }
 inline std::string* Any::release_value() {
   // @@protoc_insertion_point(field_release:google.protobuf.Any.value)

src/google/protobuf/any_lite.cc

@@ -53,16 +53,13 @@ const char kAnyFullTypeName[] = "google.protobuf.Any";
 const char kTypeGoogleApisComPrefix[] = "type.googleapis.com/";
 const char kTypeGoogleProdComPrefix[] = "type.googleprod.com/";
 
-AnyMetadata::AnyMetadata(UrlType* type_url, ValueType* value)
-    : type_url_(type_url), value_(value) {}
-
 void AnyMetadata::InternalPackFrom(const MessageLite& message,
                                    StringPiece type_url_prefix,
                                    StringPiece type_name) {
   type_url_->Set(&::google::protobuf::internal::GetEmptyString(),
                  GetTypeUrl(type_name, type_url_prefix), nullptr);
-  message.SerializeToString(value_->Mutable(
-      &::google::protobuf::internal::GetEmptyStringAlreadyInited(), nullptr));
+  message.SerializeToString(
+      value_->Mutable(ArenaStringPtr::EmptyDefault{}, nullptr));
 }
 
 bool AnyMetadata::InternalUnpackTo(StringPiece type_name,

src/google/protobuf/any_test.cc

@@ -33,10 +33,18 @@
 #include <gtest/gtest.h>
 
 
+// Must be included last.
+#include <google/protobuf/port_def.inc>
+
 namespace google {
 namespace protobuf {
 namespace {
 
+TEST(AnyMetadataTest, ConstInit) {
+  PROTOBUF_CONSTINIT static internal::AnyMetadata metadata(nullptr, nullptr);
+  (void)metadata;
+}
+
 TEST(AnyTest, TestPackAndUnpack) {
   protobuf_unittest::TestAny submessage;
   submessage.set_int32_value(12345);

src/google/protobuf/api.pb.cc

@@ -204,12 +204,12 @@ Api::Api(const Api& from)
   _internal_metadata_.MergeFrom<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(from._internal_metadata_);
   name_.UnsafeSetDefault(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited());
   if (!from._internal_name().empty()) {
-    name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), from._internal_name(),
+    name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, from._internal_name(), 
       GetArena());
   }
   version_.UnsafeSetDefault(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited());
   if (!from._internal_version().empty()) {
-    version_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), from._internal_version(),
+    version_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, from._internal_version(), 
       GetArena());
   }
   if (from._internal_has_source_context()) {
@@ -268,8 +268,8 @@ void Api::Clear() {
   methods_.Clear();
   options_.Clear();
   mixins_.Clear();
-  name_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
-  version_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  name_.ClearToEmpty();
+  version_.ClearToEmpty();
   if (GetArena() == nullptr && source_context_ != nullptr) {
     delete source_context_;
   }
@@ -614,17 +614,17 @@ Method::Method(const Method& from)
   _internal_metadata_.MergeFrom<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(from._internal_metadata_);
   name_.UnsafeSetDefault(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited());
   if (!from._internal_name().empty()) {
-    name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), from._internal_name(),
+    name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, from._internal_name(), 
       GetArena());
   }
   request_type_url_.UnsafeSetDefault(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited());
   if (!from._internal_request_type_url().empty()) {
-    request_type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), from._internal_request_type_url(),
+    request_type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, from._internal_request_type_url(), 
       GetArena());
   }
   response_type_url_.UnsafeSetDefault(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited());
   if (!from._internal_response_type_url().empty()) {
-    response_type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), from._internal_response_type_url(),
+    response_type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, from._internal_response_type_url(), 
       GetArena());
   }
   ::memcpy(&request_streaming_, &from.request_streaming_,
@@ -679,9 +679,9 @@ void Method::Clear() {
   (void) cached_has_bits;
 
   options_.Clear();
-  name_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
-  request_type_url_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
-  response_type_url_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  name_.ClearToEmpty();
+  request_type_url_.ClearToEmpty();
+  response_type_url_.ClearToEmpty();
   ::memset(&request_streaming_, 0, static_cast<size_t>(
       reinterpret_cast<char*>(&syntax_) -
       reinterpret_cast<char*>(&request_streaming_)) + sizeof(syntax_));
@@ -1008,12 +1008,12 @@ Mixin::Mixin(const Mixin& from)
   _internal_metadata_.MergeFrom<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>(from._internal_metadata_);
   name_.UnsafeSetDefault(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited());
   if (!from._internal_name().empty()) {
-    name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), from._internal_name(),
+    name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, from._internal_name(), 
       GetArena());
   }
   root_.UnsafeSetDefault(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited());
   if (!from._internal_root().empty()) {
-    root_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), from._internal_root(),
+    root_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, from._internal_root(), 
       GetArena());
   }
   // @@protoc_insertion_point(copy_constructor:google.protobuf.Mixin)
@@ -1058,8 +1058,8 @@ void Mixin::Clear() {
   // Prevent compiler warnings about cached_has_bits being unused
   (void) cached_has_bits;
 
-  name_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
-  root_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  name_.ClearToEmpty();
+  root_.ClearToEmpty();
   _internal_metadata_.Clear<::PROTOBUF_NAMESPACE_ID::UnknownFieldSet>();
 }
 

src/google/protobuf/api.pb.h

@@ -25,7 +25,6 @@
 #include <google/protobuf/arenastring.h>
 #include <google/protobuf/generated_message_table_driven.h>
 #include <google/protobuf/generated_message_util.h>
-#include <google/protobuf/inlined_string_field.h>
 #include <google/protobuf/metadata_lite.h>
 #include <google/protobuf/generated_message_reflection.h>
 #include <google/protobuf/message.h>
@@ -732,7 +731,7 @@ class PROTOBUF_EXPORT Mixin PROTOBUF_FINAL :
 
 // string name = 1;
 inline void Api::clear_name() {
-  name_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  name_.ClearToEmpty();
 }
 inline const std::string& Api::name() const {
   // @@protoc_insertion_point(field_get:google.protobuf.Api.name)
@@ -751,31 +750,30 @@ inline const std::string& Api::_internal_name() const {
 }
 inline void Api::_internal_set_name(const std::string& value) {
   
-  name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), value, GetArena());
+  name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, value, GetArena());
 }
 inline void Api::set_name(std::string&& value) {
   
   name_.Set(
-    &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::move(value), GetArena());
+    ::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::move(value), GetArena());
   // @@protoc_insertion_point(field_set_rvalue:google.protobuf.Api.name)
 }
 inline void Api::set_name(const char* value) {
   GOOGLE_DCHECK(value != nullptr);
   
-  name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
-              GetArena());
+  name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(value), GetArena());
   // @@protoc_insertion_point(field_set_char:google.protobuf.Api.name)
 }
 inline void Api::set_name(const char* value,
     size_t size) {
   
-  name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(
+  name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(
       reinterpret_cast<const char*>(value), size), GetArena());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.Api.name)
 }
 inline std::string* Api::_internal_mutable_name() {
   
-  return name_.Mutable(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  return name_.Mutable(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, GetArena());
 }
 inline std::string* Api::release_name() {
   // @@protoc_insertion_point(field_release:google.protobuf.Api.name)
@@ -869,7 +867,7 @@ Api::options() const {
 
 // string version = 4;
 inline void Api::clear_version() {
-  version_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  version_.ClearToEmpty();
 }
 inline const std::string& Api::version() const {
   // @@protoc_insertion_point(field_get:google.protobuf.Api.version)
@@ -888,31 +886,30 @@ inline const std::string& Api::_internal_version() const {
 }
 inline void Api::_internal_set_version(const std::string& value) {
   
-  version_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), value, GetArena());
+  version_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, value, GetArena());
 }
 inline void Api::set_version(std::string&& value) {
   
   version_.Set(
-    &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::move(value), GetArena());
+    ::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::move(value), GetArena());
   // @@protoc_insertion_point(field_set_rvalue:google.protobuf.Api.version)
 }
 inline void Api::set_version(const char* value) {
   GOOGLE_DCHECK(value != nullptr);
   
-  version_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
-              GetArena());
+  version_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(value), GetArena());
   // @@protoc_insertion_point(field_set_char:google.protobuf.Api.version)
 }
 inline void Api::set_version(const char* value,
     size_t size) {
   
-  version_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(
+  version_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(
       reinterpret_cast<const char*>(value), size), GetArena());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.Api.version)
 }
 inline std::string* Api::_internal_mutable_version() {
   
-  return version_.Mutable(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  return version_.Mutable(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, GetArena());
 }
 inline std::string* Api::release_version() {
   // @@protoc_insertion_point(field_release:google.protobuf.Api.version)
@@ -1071,7 +1068,7 @@ inline void Api::set_syntax(PROTOBUF_NAMESPACE_ID::Syntax value) {
 
 // string name = 1;
 inline void Method::clear_name() {
-  name_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  name_.ClearToEmpty();
 }
 inline const std::string& Method::name() const {
   // @@protoc_insertion_point(field_get:google.protobuf.Method.name)
@@ -1090,31 +1087,30 @@ inline const std::string& Method::_internal_name() const {
 }
 inline void Method::_internal_set_name(const std::string& value) {
   
-  name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), value, GetArena());
+  name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, value, GetArena());
 }
 inline void Method::set_name(std::string&& value) {
   
   name_.Set(
-    &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::move(value), GetArena());
+    ::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::move(value), GetArena());
   // @@protoc_insertion_point(field_set_rvalue:google.protobuf.Method.name)
 }
 inline void Method::set_name(const char* value) {
   GOOGLE_DCHECK(value != nullptr);
   
-  name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
-              GetArena());
+  name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(value), GetArena());
   // @@protoc_insertion_point(field_set_char:google.protobuf.Method.name)
 }
 inline void Method::set_name(const char* value,
     size_t size) {
   
-  name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(
+  name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(
       reinterpret_cast<const char*>(value), size), GetArena());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.Method.name)
 }
 inline std::string* Method::_internal_mutable_name() {
   
-  return name_.Mutable(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  return name_.Mutable(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, GetArena());
 }
 inline std::string* Method::release_name() {
   // @@protoc_insertion_point(field_release:google.protobuf.Method.name)
@@ -1133,7 +1129,7 @@ inline void Method::set_allocated_name(std::string* name) {
 
 // string request_type_url = 2;
 inline void Method::clear_request_type_url() {
-  request_type_url_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  request_type_url_.ClearToEmpty();
 }
 inline const std::string& Method::request_type_url() const {
   // @@protoc_insertion_point(field_get:google.protobuf.Method.request_type_url)
@@ -1152,31 +1148,30 @@ inline const std::string& Method::_internal_request_type_url() const {
 }
 inline void Method::_internal_set_request_type_url(const std::string& value) {
   
-  request_type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), value, GetArena());
+  request_type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, value, GetArena());
 }
 inline void Method::set_request_type_url(std::string&& value) {
   
   request_type_url_.Set(
-    &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::move(value), GetArena());
+    ::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::move(value), GetArena());
   // @@protoc_insertion_point(field_set_rvalue:google.protobuf.Method.request_type_url)
 }
 inline void Method::set_request_type_url(const char* value) {
   GOOGLE_DCHECK(value != nullptr);
   
-  request_type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
-              GetArena());
+  request_type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(value), GetArena());
   // @@protoc_insertion_point(field_set_char:google.protobuf.Method.request_type_url)
 }
 inline void Method::set_request_type_url(const char* value,
     size_t size) {
   
-  request_type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(
+  request_type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(
       reinterpret_cast<const char*>(value), size), GetArena());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.Method.request_type_url)
 }
 inline std::string* Method::_internal_mutable_request_type_url() {
   
-  return request_type_url_.Mutable(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  return request_type_url_.Mutable(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, GetArena());
 }
 inline std::string* Method::release_request_type_url() {
   // @@protoc_insertion_point(field_release:google.protobuf.Method.request_type_url)
@@ -1215,7 +1210,7 @@ inline void Method::set_request_streaming(bool value) {
 
 // string response_type_url = 4;
 inline void Method::clear_response_type_url() {
-  response_type_url_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  response_type_url_.ClearToEmpty();
 }
 inline const std::string& Method::response_type_url() const {
   // @@protoc_insertion_point(field_get:google.protobuf.Method.response_type_url)
@@ -1234,31 +1229,30 @@ inline const std::string& Method::_internal_response_type_url() const {
 }
 inline void Method::_internal_set_response_type_url(const std::string& value) {
   
-  response_type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), value, GetArena());
+  response_type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, value, GetArena());
 }
 inline void Method::set_response_type_url(std::string&& value) {
   
   response_type_url_.Set(
-    &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::move(value), GetArena());
+    ::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::move(value), GetArena());
   // @@protoc_insertion_point(field_set_rvalue:google.protobuf.Method.response_type_url)
 }
 inline void Method::set_response_type_url(const char* value) {
   GOOGLE_DCHECK(value != nullptr);
   
-  response_type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
-              GetArena());
+  response_type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(value), GetArena());
   // @@protoc_insertion_point(field_set_char:google.protobuf.Method.response_type_url)
 }
 inline void Method::set_response_type_url(const char* value,
     size_t size) {
   
-  response_type_url_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(
+  response_type_url_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(
       reinterpret_cast<const char*>(value), size), GetArena());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.Method.response_type_url)
 }
 inline std::string* Method::_internal_mutable_response_type_url() {
   
-  return response_type_url_.Mutable(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  return response_type_url_.Mutable(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, GetArena());
 }
 inline std::string* Method::release_response_type_url() {
   // @@protoc_insertion_point(field_release:google.protobuf.Method.response_type_url)
@@ -1357,7 +1351,7 @@ inline void Method::set_syntax(PROTOBUF_NAMESPACE_ID::Syntax value) {
 
 // string name = 1;
 inline void Mixin::clear_name() {
-  name_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  name_.ClearToEmpty();
 }
 inline const std::string& Mixin::name() const {
   // @@protoc_insertion_point(field_get:google.protobuf.Mixin.name)
@@ -1376,31 +1370,30 @@ inline const std::string& Mixin::_internal_name() const {
 }
 inline void Mixin::_internal_set_name(const std::string& value) {
   
-  name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), value, GetArena());
+  name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, value, GetArena());
 }
 inline void Mixin::set_name(std::string&& value) {
   
   name_.Set(
-    &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::move(value), GetArena());
+    ::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::move(value), GetArena());
   // @@protoc_insertion_point(field_set_rvalue:google.protobuf.Mixin.name)
 }
 inline void Mixin::set_name(const char* value) {
   GOOGLE_DCHECK(value != nullptr);
   
-  name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
-              GetArena());
+  name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(value), GetArena());
   // @@protoc_insertion_point(field_set_char:google.protobuf.Mixin.name)
 }
 inline void Mixin::set_name(const char* value,
     size_t size) {
   
-  name_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(
+  name_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(
       reinterpret_cast<const char*>(value), size), GetArena());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.Mixin.name)
 }
 inline std::string* Mixin::_internal_mutable_name() {
   
-  return name_.Mutable(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  return name_.Mutable(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, GetArena());
 }
 inline std::string* Mixin::release_name() {
   // @@protoc_insertion_point(field_release:google.protobuf.Mixin.name)
@@ -1419,7 +1412,7 @@ inline void Mixin::set_allocated_name(std::string* name) {
 
 // string root = 2;
 inline void Mixin::clear_root() {
-  root_.ClearToEmpty(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  root_.ClearToEmpty();
 }
 inline const std::string& Mixin::root() const {
   // @@protoc_insertion_point(field_get:google.protobuf.Mixin.root)
@@ -1438,31 +1431,30 @@ inline const std::string& Mixin::_internal_root() const {
 }
 inline void Mixin::_internal_set_root(const std::string& value) {
   
-  root_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), value, GetArena());
+  root_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, value, GetArena());
 }
 inline void Mixin::set_root(std::string&& value) {
   
   root_.Set(
-    &::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::move(value), GetArena());
+    ::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::move(value), GetArena());
   // @@protoc_insertion_point(field_set_rvalue:google.protobuf.Mixin.root)
 }
 inline void Mixin::set_root(const char* value) {
   GOOGLE_DCHECK(value != nullptr);
   
-  root_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(value),
-              GetArena());
+  root_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(value), GetArena());
   // @@protoc_insertion_point(field_set_char:google.protobuf.Mixin.root)
 }
 inline void Mixin::set_root(const char* value,
     size_t size) {
   
-  root_.Set(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), ::std::string(
+  root_.Set(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, ::std::string(
       reinterpret_cast<const char*>(value), size), GetArena());
   // @@protoc_insertion_point(field_set_pointer:google.protobuf.Mixin.root)
 }
 inline std::string* Mixin::_internal_mutable_root() {
   
-  return root_.Mutable(&::PROTOBUF_NAMESPACE_ID::internal::GetEmptyStringAlreadyInited(), GetArena());
+  return root_.Mutable(::PROTOBUF_NAMESPACE_ID::internal::ArenaStringPtr::EmptyDefault{}, GetArena());
 }
 inline std::string* Mixin::release_root() {
   // @@protoc_insertion_point(field_release:google.protobuf.Mixin.root)

src/google/protobuf/arena.cc

@@ -47,10 +47,14 @@ static const size_t kMaxCleanupListElements = 64;  // 1kB on 64-bit.
 
 namespace google {
 namespace protobuf {
+
+PROTOBUF_EXPORT /*static*/ void* (*const ArenaOptions::kDefaultBlockAlloc)(
+    size_t) = &::operator new;
+
 namespace internal {
 
 
-std::atomic<LifecycleId> ArenaImpl::lifecycle_id_generator_;
+ArenaImpl::CacheAlignedLifecycleIdGenerator ArenaImpl::lifecycle_id_generator_;
 #if defined(GOOGLE_PROTOBUF_NO_THREADLOCAL)
 ArenaImpl::ThreadCache& ArenaImpl::thread_cache() {
   static internal::ThreadLocalStorage<ThreadCache>* thread_cache_ =
@@ -59,78 +63,205 @@ ArenaImpl::ThreadCache& ArenaImpl::thread_cache() {
 }
 #elif defined(PROTOBUF_USE_DLLS)
 ArenaImpl::ThreadCache& ArenaImpl::thread_cache() {
-  static PROTOBUF_THREAD_LOCAL ThreadCache thread_cache_ = {-1, NULL};
+  static PROTOBUF_THREAD_LOCAL ThreadCache thread_cache_ = {
+      0, static_cast<LifecycleIdAtomic>(-1), nullptr};
   return thread_cache_;
 }
 #else
-PROTOBUF_THREAD_LOCAL ArenaImpl::ThreadCache ArenaImpl::thread_cache_ = {-1,
-                                                                         NULL};
+PROTOBUF_THREAD_LOCAL ArenaImpl::ThreadCache ArenaImpl::thread_cache_ = {
+    0, static_cast<LifecycleIdAtomic>(-1), nullptr};
+#endif
+
+void ArenaFree(void* object, size_t size) {
+#if defined(__GXX_DELETE_WITH_SIZE__) || defined(__cpp_sized_deallocation)
+  ::operator delete(object, size);
+#else
+  (void)size;
+  ::operator delete(object);
 #endif
+}
+
+ArenaImpl::ArenaImpl(const ArenaOptions& options) {
+  ArenaMetricsCollector* collector = nullptr;
+  bool record_allocs = false;
+  if (options.make_metrics_collector != nullptr) {
+    collector = (*options.make_metrics_collector)();
+    record_allocs = (collector && collector->RecordAllocs());
+  }
+
+  // Get memory where we can store non-default options if needed.
+  // Use supplied initial_block if it is large enough.
+  size_t min_block_size = kOptionsSize + kBlockHeaderSize + kSerialArenaSize;
+  char* mem = options.initial_block;
+  size_t mem_size = options.initial_block_size;
+  GOOGLE_DCHECK_EQ(reinterpret_cast<uintptr_t>(mem) & 7, 0);
+  if (mem == nullptr || mem_size < min_block_size) {
+    // Supplied initial block is not big enough.
+    mem_size = std::max(min_block_size, options.start_block_size);
+    mem = reinterpret_cast<char*>((*options.block_alloc)(mem_size));
+  }
 
-void ArenaImpl::Init() {
-  lifecycle_id_ =
-      lifecycle_id_generator_.fetch_add(1, std::memory_order_relaxed);
+  // Create the special block.
+  const bool special = true;
+  const bool user_owned = (mem == options.initial_block);
+  auto block =
+      new (mem) SerialArena::Block(mem_size, nullptr, special, user_owned);
+
+  // Options occupy the beginning of the initial block.
+  options_ = new (block->Pointer(block->pos())) Options;
+#ifdef ADDRESS_SANITIZER
+  ASAN_UNPOISON_MEMORY_REGION(options_, kOptionsSize);
+#endif  // ADDRESS_SANITIZER
+  options_->start_block_size = options.start_block_size;
+  options_->max_block_size = options.max_block_size;
+  options_->block_alloc = options.block_alloc;
+  options_->block_dealloc = options.block_dealloc;
+  options_->metrics_collector = collector;
+  block->set_pos(block->pos() + kOptionsSize);
+
+  Init(record_allocs);
+  SetInitialBlock(block);
+}
+
+void ArenaImpl::Init(bool record_allocs) {
+  ThreadCache& tc = thread_cache();
+  auto id = tc.next_lifecycle_id;
+  constexpr uint64 kInc = ThreadCache::kPerThreadIds * 2;
+  if (PROTOBUF_PREDICT_FALSE((id & (kInc - 1)) == 0)) {
+    if (sizeof(lifecycle_id_generator_.id) == 4) {
+      // 2^32 is dangerous low to guarantee uniqueness. If we start dolling out
+      // unique id's in ranges of kInc it's unacceptably low. In this case
+      // we increment by 1. The additional range of kPerThreadIds that are used
+      // per thread effectively pushes the overflow time from weeks to years
+      // of continuous running.
+      id = lifecycle_id_generator_.id.fetch_add(1, std::memory_order_relaxed) *
+           kInc;
+    } else {
+      id =
+          lifecycle_id_generator_.id.fetch_add(kInc, std::memory_order_relaxed);
+    }
+  }
+  tc.next_lifecycle_id = id + 2;
+  // We store "record_allocs" in the low bit of lifecycle_id_.
+  lifecycle_id_ = id | (record_allocs ? 1 : 0);
   hint_.store(nullptr, std::memory_order_relaxed);
   threads_.store(nullptr, std::memory_order_relaxed);
+  space_allocated_.store(0, std::memory_order_relaxed);
+}
 
-  if (initial_block_) {
-    // Thread which calls Init() owns the first block. This allows the
-    // single-threaded case to allocate on the first block without having to
-    // perform atomic operations.
-    new (initial_block_) Block(options_.initial_block_size, NULL);
-    SerialArena* serial =
-        SerialArena::New(initial_block_, &thread_cache(), this);
-    serial->set_next(NULL);
-    threads_.store(serial, std::memory_order_relaxed);
-    space_allocated_.store(options_.initial_block_size,
-                           std::memory_order_relaxed);
-    CacheSerialArena(serial);
-  } else {
-    space_allocated_.store(0, std::memory_order_relaxed);
-  }
+void ArenaImpl::SetInitialBlock(SerialArena::Block* block) {
+  // Calling thread owns the first block. This allows the single-threaded case
+  // to allocate on the first block without having to perform atomic operations.
+  SerialArena* serial = SerialArena::New(block, &thread_cache(), this);
+  serial->set_next(NULL);
+  threads_.store(serial, std::memory_order_relaxed);
+  space_allocated_.store(block->size(), std::memory_order_relaxed);
+  CacheSerialArena(serial);
 }
 
 ArenaImpl::~ArenaImpl() {
   // Have to do this in a first pass, because some of the destructors might
   // refer to memory in other blocks.
   CleanupList();
-  FreeBlocks();
+
+  ArenaMetricsCollector* collector = nullptr;
+  auto deallocator = &ArenaFree;
+  if (options_) {
+    collector = options_->metrics_collector;
+    deallocator = options_->block_dealloc;
+  }
+
+  PerBlock([deallocator](SerialArena::Block* b) {
+#ifdef ADDRESS_SANITIZER
+    // This memory was provided by the underlying allocator as unpoisoned, so
+    // return it in an unpoisoned state.
+    ASAN_UNPOISON_MEMORY_REGION(b->Pointer(0), b->size());
+#endif  // ADDRESS_SANITIZER
+    if (!b->user_owned()) {
+      (*deallocator)(b, b->size());
+    }
+  });
+
+  if (collector) {
+    collector->OnDestroy(SpaceAllocated());
+  }
 }
 
 uint64 ArenaImpl::Reset() {
+  if (options_ && options_->metrics_collector) {
+    options_->metrics_collector->OnReset(SpaceAllocated());
+  }
+
   // Have to do this in a first pass, because some of the destructors might
   // refer to memory in other blocks.
   CleanupList();
-  uint64 space_allocated = FreeBlocks();
-  Init();
 
+  // Discard all blocks except the special block (if present).
+  uint64 space_allocated = 0;
+  SerialArena::Block* special_block = nullptr;
+  auto deallocator = (options_ ? options_->block_dealloc : &ArenaFree);
+  PerBlock(
+      [&space_allocated, &special_block, deallocator](SerialArena::Block* b) {
+        space_allocated += b->size();
+#ifdef ADDRESS_SANITIZER
+        // This memory was provided by the underlying allocator as unpoisoned,
+        // so return it in an unpoisoned state.
+        ASAN_UNPOISON_MEMORY_REGION(b->Pointer(0), b->size());
+#endif  // ADDRESS_SANITIZER
+        if (!b->special()) {
+          (*deallocator)(b, b->size());
+        } else {
+          // Prepare special block for reuse.
+          // Note: if options_ is present, it occupies the beginning of the
+          // block and therefore pos is advanced past it.
+          GOOGLE_DCHECK(special_block == nullptr);
+          special_block = b;
+        }
+      });
+
+  Init(record_allocs());
+  if (special_block != nullptr) {
+    // next() should still be nullptr since we are using a stack discipline, but
+    // clear it anyway to reduce fragility.
+    GOOGLE_DCHECK_EQ(special_block->next(), nullptr);
+    special_block->clear_next();
+    special_block->set_pos(kBlockHeaderSize + (options_ ? kOptionsSize : 0));
+    SetInitialBlock(special_block);
+  }
   return space_allocated;
 }
 
-ArenaImpl::Block* ArenaImpl::NewBlock(Block* last_block, size_t min_bytes) {
+std::pair<void*, size_t> ArenaImpl::NewBuffer(size_t last_size,
+                                              size_t min_bytes) {
   size_t size;
-  if (last_block) {
+  if (last_size != -1) {
     // Double the current block size, up to a limit.
-    size = std::min(2 * last_block->size(), options_.max_block_size);
+    auto max_size = options_ ? options_->max_block_size : kDefaultMaxBlockSize;
+    size = std::min(2 * last_size, max_size);
   } else {
-    size = options_.start_block_size;
+    size = options_ ? options_->start_block_size : kDefaultStartBlockSize;
   }
   // Verify that min_bytes + kBlockHeaderSize won't overflow.
   GOOGLE_CHECK_LE(min_bytes, std::numeric_limits<size_t>::max() - kBlockHeaderSize);
   size = std::max(size, kBlockHeaderSize + min_bytes);
 
-  void* mem = options_.block_alloc(size);
-  Block* b = new (mem) Block(size, last_block);
+  void* mem = options_ ? (*options_->block_alloc)(size) : ::operator new(size);
   space_allocated_.fetch_add(size, std::memory_order_relaxed);
-  return b;
+  return {mem, size};
 }
 
-ArenaImpl::Block::Block(size_t size, Block* next)
-    : next_(next), pos_(kBlockHeaderSize), size_(size) {}
+SerialArena::Block* SerialArena::NewBlock(SerialArena::Block* last_block,
+                                          size_t min_bytes, ArenaImpl* arena) {
+  void* mem;
+  size_t size;
+  std::tie(mem, size) =
+      arena->NewBuffer(last_block ? last_block->size() : -1, min_bytes);
+  Block* b = new (mem) Block(size, last_block, false, false);
+  return b;
+}
 
 PROTOBUF_NOINLINE
-void ArenaImpl::SerialArena::AddCleanupFallback(void* elem,
-                                                void (*cleanup)(void*)) {
+void SerialArena::AddCleanupFallback(void* elem, void (*cleanup)(void*)) {
   size_t size = cleanup_ ? cleanup_->size * 2 : kMinCleanupListElements;
   size = std::min(size, kMaxCleanupListElements);
   size_t bytes = internal::AlignUpTo8(CleanupChunk::SizeOf(size));
@@ -182,11 +313,11 @@ void ArenaImpl::AddCleanupFallback(void* elem, void (*cleanup)(void*)) {
 }
 
 PROTOBUF_NOINLINE
-void* ArenaImpl::SerialArena::AllocateAlignedFallback(size_t n) {
+void* SerialArena::AllocateAlignedFallback(size_t n) {
   // Sync back to current's pos.
   head_->set_pos(head_->size() - (limit_ - ptr_));
 
-  head_ = arena_->NewBlock(head_, n);
+  head_ = NewBlock(head_, n, arena_);
   ptr_ = head_->Pointer(head_->pos());
   limit_ = head_->Pointer(head_->size());
 
@@ -207,10 +338,14 @@ uint64 ArenaImpl::SpaceUsed() const {
   for (; serial; serial = serial->next()) {
     space_used += serial->SpaceUsed();
   }
+  // Remove the overhead of Options structure, if any.
+  if (options_) {
+    space_used -= kOptionsSize;
+  }
   return space_used;
 }
 
-uint64 ArenaImpl::SerialArena::SpaceUsed() const {
+uint64 SerialArena::SpaceUsed() const {
   // Get current block's size from ptr_ (since we can't trust head_->pos().
   uint64 space_used = ptr_ - head_->Pointer(kBlockHeaderSize);
   // Get subsequent block size from b->pos().
@@ -218,57 +353,10 @@ uint64 ArenaImpl::SerialArena::SpaceUsed() const {
     space_used += (b->pos() - kBlockHeaderSize);
   }
   // Remove the overhead of the SerialArena itself.
-  space_used -= kSerialArenaSize;
+  space_used -= ArenaImpl::kSerialArenaSize;
   return space_used;
 }
 
-uint64 ArenaImpl::FreeBlocks() {
-  uint64 space_allocated = 0;
-  // By omitting an Acquire barrier we ensure that any user code that doesn't
-  // properly synchronize Reset() or the destructor will throw a TSAN warning.
-  SerialArena* serial = threads_.load(std::memory_order_relaxed);
-
-  while (serial) {
-    // This is inside a block we are freeing, so we need to read it now.
-    SerialArena* next = serial->next();
-    space_allocated += ArenaImpl::SerialArena::Free(serial, initial_block_,
-                                                    options_.block_dealloc);
-    // serial is dead now.
-    serial = next;
-  }
-
-  return space_allocated;
-}
-
-uint64 ArenaImpl::SerialArena::Free(ArenaImpl::SerialArena* serial,
-                                    Block* initial_block,
-                                    void (*block_dealloc)(void*, size_t)) {
-  uint64 space_allocated = 0;
-
-  // We have to be careful in this function, since we will be freeing the Block
-  // that contains this SerialArena.  Be careful about accessing |serial|.
-
-  for (Block* b = serial->head_; b;) {
-    // This is inside the block we are freeing, so we need to read it now.
-    Block* next_block = b->next();
-    space_allocated += (b->size());
-
-#ifdef ADDRESS_SANITIZER
-    // This memory was provided by the underlying allocator as unpoisoned, so
-    // return it in an unpoisoned state.
-    ASAN_UNPOISON_MEMORY_REGION(b->Pointer(0), b->size());
-#endif  // ADDRESS_SANITIZER
-
-    if (b != initial_block) {
-      block_dealloc(b, b->size());
-    }
-
-    b = next_block;
-  }
-
-  return space_allocated;
-}
-
 void ArenaImpl::CleanupList() {
   // By omitting an Acquire barrier we ensure that any user code that doesn't
   // properly synchronize Reset() or the destructor will throw a TSAN warning.
@@ -279,13 +367,13 @@ void ArenaImpl::CleanupList() {
   }
 }
 
-void ArenaImpl::SerialArena::CleanupList() {
+void SerialArena::CleanupList() {
   if (cleanup_ != NULL) {
     CleanupListFallback();
   }
 }
 
-void ArenaImpl::SerialArena::CleanupListFallback() {
+void SerialArena::CleanupListFallback() {
   // The first chunk might be only partially full, so calculate its size
   // from cleanup_ptr_. Subsequent chunks are always full, so use list->size.
   size_t n = cleanup_ptr_ - &cleanup_->nodes[0];
@@ -305,13 +393,11 @@ void ArenaImpl::SerialArena::CleanupListFallback() {
   }
 }
 
-ArenaImpl::SerialArena* ArenaImpl::SerialArena::New(Block* b, void* owner,
-                                                    ArenaImpl* arena) {
-  GOOGLE_DCHECK_EQ(b->pos(), kBlockHeaderSize);  // Should be a fresh block
-  GOOGLE_DCHECK_LE(kBlockHeaderSize + kSerialArenaSize, b->size());
-  SerialArena* serial =
-      reinterpret_cast<SerialArena*>(b->Pointer(kBlockHeaderSize));
-  b->set_pos(kBlockHeaderSize + kSerialArenaSize);
+SerialArena* SerialArena::New(Block* b, void* owner, ArenaImpl* arena) {
+  auto pos = b->pos();
+  GOOGLE_DCHECK_LE(pos + ArenaImpl::kSerialArenaSize, b->size());
+  SerialArena* serial = reinterpret_cast<SerialArena*>(b->Pointer(pos));
+  b->set_pos(pos + ArenaImpl::kSerialArenaSize);
   serial->arena_ = arena;
   serial->owner_ = owner;
   serial->head_ = b;
@@ -324,7 +410,7 @@ ArenaImpl::SerialArena* ArenaImpl::SerialArena::New(Block* b, void* owner,
 }
 
 PROTOBUF_NOINLINE
-ArenaImpl::SerialArena* ArenaImpl::GetSerialArenaFallback(void* me) {
+SerialArena* ArenaImpl::GetSerialArenaFallback(void* me) {
   // Look for this SerialArena in our linked list.
   SerialArena* serial = threads_.load(std::memory_order_acquire);
   for (; serial; serial = serial->next()) {
@@ -336,7 +422,7 @@ ArenaImpl::SerialArena* ArenaImpl::GetSerialArenaFallback(void* me) {
   if (!serial) {
     // This thread doesn't have any SerialArena, which also means it doesn't
     // have any blocks yet.  So we'll allocate its first block now.
-    Block* b = NewBlock(NULL, kSerialArenaSize);
+    SerialArena::Block* b = SerialArena::NewBlock(NULL, kSerialArenaSize, this);
     serial = SerialArena::New(b, me, this);
 
     SerialArena* head = threads_.load(std::memory_order_relaxed);
@@ -350,6 +436,8 @@ ArenaImpl::SerialArena* ArenaImpl::GetSerialArenaFallback(void* me) {
   return serial;
 }
 
+ArenaMetricsCollector::~ArenaMetricsCollector() {}
+
 }  // namespace internal
 
 PROTOBUF_FUNC_ALIGN(32)
@@ -357,25 +445,5 @@ void* Arena::AllocateAlignedNoHook(size_t n) {
   return impl_.AllocateAligned(n);
 }
 
-void Arena::CallDestructorHooks() {
-  uint64 space_allocated = impl_.SpaceAllocated();
-  // Call the reset hook
-  if (on_arena_reset_ != NULL) {
-    on_arena_reset_(this, hooks_cookie_, space_allocated);
-  }
-
-  // Call the destruction hook
-  if (on_arena_destruction_ != NULL) {
-    on_arena_destruction_(this, hooks_cookie_, space_allocated);
-  }
-}
-
-void Arena::OnArenaAllocation(const std::type_info* allocated_type,
-                              size_t n) const {
-  if (on_arena_allocation_ != NULL) {
-    on_arena_allocation_(allocated_type, n, hooks_cookie_);
-  }
-}
-
 }  // namespace protobuf
 }  // namespace google

src/google/protobuf/arena.h

@@ -102,15 +102,6 @@ template <typename T>
 void arena_delete_object(void* object) {
   delete reinterpret_cast<T*>(object);
 }
-inline void arena_free(void* object, size_t size) {
-#if defined(__GXX_DELETE_WITH_SIZE__) || defined(__cpp_sized_deallocation)
-  ::operator delete(object, size);
-#else
-  (void)size;
-  ::operator delete(object);
-#endif
-}
-
 }  // namespace internal
 
 // ArenaOptions provides optional additional parameters to arena construction
@@ -151,44 +142,30 @@ struct ArenaOptions {
         max_block_size(kDefaultMaxBlockSize),
         initial_block(NULL),
         initial_block_size(0),
-        block_alloc(&::operator new),
-        block_dealloc(&internal::arena_free),
-        on_arena_init(NULL),
-        on_arena_reset(NULL),
-        on_arena_destruction(NULL),
-        on_arena_allocation(NULL) {}
+        block_alloc(kDefaultBlockAlloc),
+        block_dealloc(&internal::ArenaFree),
+        make_metrics_collector(nullptr) {}
+
+  PROTOBUF_EXPORT static void* (*const kDefaultBlockAlloc)(size_t);
 
  private:
-  // Hooks for adding external functionality such as user-specific metrics
-  // collection, specific debugging abilities, etc.
-  // Init hook (if set) will always be called at Arena init time. Init hook may
-  // return a pointer to a cookie to be stored in the arena. Reset and
-  // destruction hooks will then be called with the same cookie pointer. This
-  // allows us to save an external object per arena instance and use it on the
-  // other hooks (Note: If init hook returns NULL, the other hooks will NOT be
-  // called on this arena instance).
-  // on_arena_reset and on_arena_destruction also receive the space used in the
-  // arena just before the reset.
-  void* (*on_arena_init)(Arena* arena);
-  void (*on_arena_reset)(Arena* arena, void* cookie, uint64 space_used);
-  void (*on_arena_destruction)(Arena* arena, void* cookie, uint64 space_used);
-
-  // type_info is promised to be static - its lifetime extends to
-  // match program's lifetime (It is given by typeid operator).
-  // Note: typeid(void) will be passed as allocated_type every time we
-  // intentionally want to avoid monitoring an allocation. (i.e. internal
-  // allocations for managing the arena)
-  void (*on_arena_allocation)(const std::type_info* allocated_type,
-                              uint64 alloc_size, void* cookie);
+  // If make_metrics_collector is not nullptr, it will be called at Arena init
+  // time. It may return a pointer to a collector instance that will be notified
+  // of interesting events related to the arena.
+  internal::ArenaMetricsCollector* (*make_metrics_collector)();
 
   // Constants define default starting block size and max block size for
   // arena allocator behavior -- see descriptions above.
-  static const size_t kDefaultStartBlockSize = 256;
-  static const size_t kDefaultMaxBlockSize = 8192;
+  static const size_t kDefaultStartBlockSize =
+      internal::ArenaImpl::kDefaultStartBlockSize;
+  static const size_t kDefaultMaxBlockSize =
+      internal::ArenaImpl::kDefaultMaxBlockSize;
 
   friend void arena_metrics::EnableArenaMetrics(ArenaOptions*);
+
   friend class Arena;
   friend class ArenaOptionsTestFriend;
+  friend class internal::ArenaImpl;
 };
 
 // Support for non-RTTI environments. (The metrics hooks API uses type
@@ -246,11 +223,20 @@ struct ArenaOptions {
 // should not rely on this protocol.
 class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
  public:
-  // Arena constructor taking custom options. See ArenaOptions below for
+  // Default constructor with sensible default options, tuned for average
+  // use-cases.
+  inline Arena() : impl_() {}
+
+  // Construct an arena with default options, except for the supplied
+  // initial block. It is more efficient to use this constructor
+  // instead of passing ArenaOptions if the only configuration needed
+  // by the caller is supplying an initial block.
+  inline Arena(char* initial_block, size_t initial_block_size)
+      : impl_(initial_block, initial_block_size) {}
+
+  // Arena constructor taking custom options. See ArenaOptions above for
   // descriptions of the options available.
-  explicit Arena(const ArenaOptions& options) : impl_(options) {
-    Init(options);
-  }
+  explicit Arena(const ArenaOptions& options) : impl_(options) {}
 
   // Block overhead.  Use this as a guide for how much to over-allocate the
   // initial block if you want an allocation of size N to fit inside it.
@@ -261,27 +247,10 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
   static const size_t kBlockOverhead = internal::ArenaImpl::kBlockHeaderSize +
                                        internal::ArenaImpl::kSerialArenaSize;
 
-  // Default constructor with sensible default options, tuned for average
-  // use-cases.
-  Arena() : impl_(ArenaOptions()) { Init(ArenaOptions()); }
-
-  ~Arena() {
-    if (hooks_cookie_) {
-      CallDestructorHooks();
-    }
-  }
+  inline ~Arena() {}
 
-  void Init(const ArenaOptions& options) {
-    on_arena_allocation_ = options.on_arena_allocation;
-    on_arena_reset_ = options.on_arena_reset;
-    on_arena_destruction_ = options.on_arena_destruction;
-    // Call the initialization hook
-    if (options.on_arena_init != NULL) {
-      hooks_cookie_ = options.on_arena_init(this);
-    } else {
-      hooks_cookie_ = NULL;
-    }
-  }
+  // TODO(protobuf-team): Fix callers to use constructor and delete this method.
+  void Init(const ArenaOptions&) {}
 
   // API to create proto2 message objects on the arena. If the arena passed in
   // is NULL, then a heap allocated object is returned. Type T must be a message
@@ -362,13 +331,7 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
   // Any objects allocated on this arena are unusable after this call. It also
   // returns the total space used by the arena which is the sums of the sizes
   // of the allocated blocks. This method is not thread-safe.
-  PROTOBUF_NOINLINE uint64 Reset() {
-    // Call the reset hook
-    if (on_arena_reset_ != NULL) {
-      on_arena_reset_(this, hooks_cookie_, impl_.SpaceAllocated());
-    }
-    return impl_.Reset();
-  }
+  uint64 Reset() { return impl_.Reset(); }
 
   // Adds |object| to a list of heap-allocated objects to be freed with |delete|
   // when the arena is destroyed or reset.
@@ -515,28 +478,31 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
     }
   }
 
-  void CallDestructorHooks();
-  void OnArenaAllocation(const std::type_info* allocated_type, size_t n) const;
   inline void AllocHook(const std::type_info* allocated_type, size_t n) const {
-    if (PROTOBUF_PREDICT_FALSE(hooks_cookie_ != NULL)) {
-      OnArenaAllocation(allocated_type, n);
-    }
+    impl_.RecordAlloc(allocated_type, n);
   }
 
-  // Allocate and also optionally call on_arena_allocation callback with the
-  // allocated type info when the hooks are in place in ArenaOptions and
-  // the cookie is not null.
+  // Allocate and also optionally call collector with the allocated type info
+  // when allocation recording is enabled.
   template <typename T>
   PROTOBUF_ALWAYS_INLINE void* AllocateInternal(bool skip_explicit_ownership) {
-    static_assert(alignof(T) <= 8, "T is overaligned, see b/151247138");
     const size_t n = internal::AlignUpTo8(sizeof(T));
-    AllocHook(RTTI_TYPE_ID(T), n);
     // Monitor allocation if needed.
+    impl_.RecordAlloc(RTTI_TYPE_ID(T), n);
     if (skip_explicit_ownership) {
-      return AllocateAlignedNoHook(n);
+      return AllocateAlignedTo<alignof(T)>(sizeof(T));
     } else {
-      return impl_.AllocateAlignedAndAddCleanup(
-          n, &internal::arena_destruct_object<T>);
+      if (alignof(T) <= 8) {
+        return impl_.AllocateAlignedAndAddCleanup(
+            n, &internal::arena_destruct_object<T>);
+      } else {
+        auto ptr =
+            reinterpret_cast<uintptr_t>(impl_.AllocateAlignedAndAddCleanup(
+                sizeof(T) + alignof(T) - 8,
+                &internal::arena_destruct_object<T>));
+        return reinterpret_cast<void*>((ptr + alignof(T) - 8) &
+                                       (~alignof(T) + 1));
+      }
     }
   }
 
@@ -591,10 +557,12 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
   PROTOBUF_ALWAYS_INLINE T* CreateInternalRawArray(size_t num_elements) {
     GOOGLE_CHECK_LE(num_elements, std::numeric_limits<size_t>::max() / sizeof(T))
         << "Requested size is too large to fit into size_t.";
+    // We count on compiler to realize that if sizeof(T) is a multiple of
+    // 8 AlignUpTo can be elided.
     const size_t n = internal::AlignUpTo8(sizeof(T) * num_elements);
     // Monitor allocation if needed.
-    AllocHook(RTTI_TYPE_ID(T), n);
-    return static_cast<T*>(AllocateAlignedNoHook(n));
+    impl_.RecordAlloc(RTTI_TYPE_ID(T), n);
+    return static_cast<T*>(AllocateAlignedTo<alignof(T)>(n));
   }
 
   template <typename T, typename... Args>
@@ -687,7 +655,6 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
 
   // For friends of arena.
   void* AllocateAligned(size_t n) {
-    AllocHook(NULL, n);
     return AllocateAlignedNoHook(internal::AlignUpTo8(n));
   }
   template<size_t Align>
@@ -698,7 +665,7 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
     // TODO(b/151247138): if the pointer would have been aligned already,
     // this is wasting space. We should pass the alignment down.
     uintptr_t ptr = reinterpret_cast<uintptr_t>(AllocateAligned(n + Align - 8));
-    ptr = (ptr + Align - 1) & -Align;
+    ptr = (ptr + Align - 1) & (~Align + 1);
     return reinterpret_cast<void*>(ptr);
   }
 
@@ -706,15 +673,6 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
 
   internal::ArenaImpl impl_;
 
-  void (*on_arena_allocation_)(const std::type_info* allocated_type,
-                               uint64 alloc_size, void* cookie);
-  void (*on_arena_reset_)(Arena* arena, void* cookie, uint64 space_used);
-  void (*on_arena_destruction_)(Arena* arena, void* cookie, uint64 space_used);
-
-  // The arena may save a cookie it receives from the external on_init hook
-  // and then use it when calling the on_reset and on_destruction hooks.
-  void* hooks_cookie_;
-
   template <typename Type>
   friend class internal::GenericTypeHandler;
   friend struct internal::ArenaStringPtr;  // For AllocateAligned.

src/google/protobuf/arena_impl.h

@@ -48,6 +48,9 @@
 
 namespace google {
 namespace protobuf {
+
+struct ArenaOptions;
+
 namespace internal {
 
 inline size_t AlignUpTo8(size_t n) {
@@ -55,7 +58,195 @@ inline size_t AlignUpTo8(size_t n) {
   return (n + 7) & static_cast<size_t>(-8);
 }
 
-using LifecycleId = int64_t;
+using LifecycleIdAtomic = uint64_t;
+
+void PROTOBUF_EXPORT ArenaFree(void* object, size_t size);
+
+// MetricsCollector collects stats for a particular arena.
+class PROTOBUF_EXPORT ArenaMetricsCollector {
+ public:
+  virtual ~ArenaMetricsCollector();
+
+  // Invoked when the arena is about to be destroyed. This method will
+  // typically finalize any metric collection and delete the collector.
+  // space_allocated is the space used by the arena.
+  virtual void OnDestroy(uint64 space_allocated) = 0;
+
+  // OnReset() is called when the associated arena is reset.
+  // space_allocated is the space used by the arena just before the reset.
+  virtual void OnReset(uint64 space_allocated) = 0;
+
+  // Does OnAlloc() need to be called?  If false, metric collection overhead
+  // will be reduced since we will not do extra work per allocation.
+  virtual bool RecordAllocs() = 0;
+
+  // OnAlloc is called when an allocation happens.
+  // type_info is promised to be static - its lifetime extends to
+  // match program's lifetime (It is given by typeid operator).
+  // Note: typeid(void) will be passed as allocated_type every time we
+  // intentionally want to avoid monitoring an allocation. (i.e. internal
+  // allocations for managing the arena)
+  virtual void OnAlloc(const std::type_info* allocated_type,
+                       uint64 alloc_size) = 0;
+};
+
+class ArenaImpl;
+
+// A thread-unsafe Arena that can only be used within its owning thread.
+class PROTOBUF_EXPORT SerialArena {
+ public:
+  // Blocks are variable length malloc-ed objects.  The following structure
+  // describes the common header for all blocks.
+  class PROTOBUF_EXPORT Block {
+   public:
+    Block(size_t size, Block* next, bool special, bool user_owned)
+        : next_and_bits_(reinterpret_cast<uintptr_t>(next) | (special ? 1 : 0) |
+                         (user_owned ? 2 : 0)),
+          pos_(kBlockHeaderSize),
+          size_(size) {
+      GOOGLE_DCHECK_EQ(reinterpret_cast<uintptr_t>(next) & 3, 0u);
+    }
+
+    char* Pointer(size_t n) {
+      GOOGLE_DCHECK(n <= size_);
+      return reinterpret_cast<char*>(this) + n;
+    }
+
+    // One of the blocks may be special. This is either a user-supplied
+    // initial block, or a block we created at startup to hold Options info.
+    // A special block is not deleted by Reset.
+    bool special() const { return (next_and_bits_ & 1) != 0; }
+
+    // Whether or not this current block is owned by the user.
+    // Only special blocks can be user_owned.
+    bool user_owned() const { return (next_and_bits_ & 2) != 0; }
+
+    Block* next() const {
+      const uintptr_t bottom_bits = 3;
+      return reinterpret_cast<Block*>(next_and_bits_ & ~bottom_bits);
+    }
+
+    void clear_next() {
+      next_and_bits_ &= 3;  // Set next to nullptr, preserve bottom bits.
+    }
+
+    size_t pos() const { return pos_; }
+    size_t size() const { return size_; }
+    void set_pos(size_t pos) { pos_ = pos; }
+
+   private:
+    // Holds pointer to next block for this thread + special/user_owned bits.
+    uintptr_t next_and_bits_;
+
+    size_t pos_;
+    size_t size_;
+    // data follows
+  };
+
+  // The allocate/free methods here are a little strange, since SerialArena is
+  // allocated inside a Block which it also manages.  This is to avoid doing
+  // an extra allocation for the SerialArena itself.
+
+  // Creates a new SerialArena inside Block* and returns it.
+  static SerialArena* New(Block* b, void* owner, ArenaImpl* arena);
+
+  void CleanupList();
+  uint64 SpaceUsed() const;
+
+  bool HasSpace(size_t n) { return n <= static_cast<size_t>(limit_ - ptr_); }
+
+  void* AllocateAligned(size_t n) {
+    GOOGLE_DCHECK_EQ(internal::AlignUpTo8(n), n);  // Must be already aligned.
+    GOOGLE_DCHECK_GE(limit_, ptr_);
+    if (PROTOBUF_PREDICT_FALSE(!HasSpace(n))) {
+      return AllocateAlignedFallback(n);
+    }
+    void* ret = ptr_;
+    ptr_ += n;
+#ifdef ADDRESS_SANITIZER
+    ASAN_UNPOISON_MEMORY_REGION(ret, n);
+#endif  // ADDRESS_SANITIZER
+    return ret;
+  }
+
+  // Allocate space if the current region provides enough space.
+  bool MaybeAllocateAligned(size_t n, void** out) {
+    GOOGLE_DCHECK_EQ(internal::AlignUpTo8(n), n);  // Must be already aligned.
+    GOOGLE_DCHECK_GE(limit_, ptr_);
+    if (PROTOBUF_PREDICT_FALSE(!HasSpace(n))) return false;
+    void* ret = ptr_;
+    ptr_ += n;
+#ifdef ADDRESS_SANITIZER
+    ASAN_UNPOISON_MEMORY_REGION(ret, n);
+#endif  // ADDRESS_SANITIZER
+    *out = ret;
+    return true;
+  }
+
+  void AddCleanup(void* elem, void (*cleanup)(void*)) {
+    if (PROTOBUF_PREDICT_FALSE(cleanup_ptr_ == cleanup_limit_)) {
+      AddCleanupFallback(elem, cleanup);
+      return;
+    }
+    cleanup_ptr_->elem = elem;
+    cleanup_ptr_->cleanup = cleanup;
+    cleanup_ptr_++;
+  }
+
+  void* AllocateAlignedAndAddCleanup(size_t n, void (*cleanup)(void*)) {
+    void* ret = AllocateAligned(n);
+    AddCleanup(ret, cleanup);
+    return ret;
+  }
+
+  Block* head() const { return head_; }
+  void* owner() const { return owner_; }
+  SerialArena* next() const { return next_; }
+  void set_next(SerialArena* next) { next_ = next; }
+  static Block* NewBlock(Block* last_block, size_t min_bytes, ArenaImpl* arena);
+
+ private:
+  // Node contains the ptr of the object to be cleaned up and the associated
+  // cleanup function ptr.
+  struct CleanupNode {
+    void* elem;              // Pointer to the object to be cleaned up.
+    void (*cleanup)(void*);  // Function pointer to the destructor or deleter.
+  };
+
+  // Cleanup uses a chunked linked list, to reduce pointer chasing.
+  struct CleanupChunk {
+    static size_t SizeOf(size_t i) {
+      return sizeof(CleanupChunk) + (sizeof(CleanupNode) * (i - 1));
+    }
+    size_t size;           // Total elements in the list.
+    CleanupChunk* next;    // Next node in the list.
+    CleanupNode nodes[1];  // True length is |size|.
+  };
+
+  ArenaImpl* arena_;       // Containing arena.
+  void* owner_;            // &ThreadCache of this thread;
+  Block* head_;            // Head of linked list of blocks.
+  CleanupChunk* cleanup_;  // Head of cleanup list.
+  SerialArena* next_;      // Next SerialArena in this linked list.
+
+  // Next pointer to allocate from.  Always 8-byte aligned.  Points inside
+  // head_ (and head_->pos will always be non-canonical).  We keep these
+  // here to reduce indirection.
+  char* ptr_;
+  char* limit_;
+
+  // Next CleanupList members to append to.  These point inside cleanup_.
+  CleanupNode* cleanup_ptr_;
+  CleanupNode* cleanup_limit_;
+
+  void* AllocateAlignedFallback(size_t n);
+  void AddCleanupFallback(void* elem, void (*cleanup)(void*));
+  void CleanupListFallback();
+
+ public:
+  static constexpr size_t kBlockHeaderSize =
+      (sizeof(Block) + 7) & static_cast<size_t>(-8);
+};
 
 // This class provides the core Arena memory allocation library. Different
 // implementations only need to implement the public interface below.
@@ -65,37 +256,23 @@ using LifecycleId = int64_t;
 // use #ifdef the select the best implementation based on hardware / OS.
 class PROTOBUF_EXPORT ArenaImpl {
  public:
-  struct Options {
-    size_t start_block_size;
-    size_t max_block_size;
-    char* initial_block;
-    size_t initial_block_size;
-    void* (*block_alloc)(size_t);
-    void (*block_dealloc)(void*, size_t);
+  static const size_t kDefaultStartBlockSize = 256;
+  static const size_t kDefaultMaxBlockSize = 8192;
 
-    template <typename O>
-    explicit Options(const O& options)
-        : start_block_size(options.start_block_size),
-          max_block_size(options.max_block_size),
-          initial_block(options.initial_block),
-          initial_block_size(options.initial_block_size),
-          block_alloc(options.block_alloc),
-          block_dealloc(options.block_dealloc) {}
-  };
+  ArenaImpl() { Init(false); }
 
-  template <typename O>
-  explicit ArenaImpl(const O& options) : options_(options) {
-    if (options_.initial_block != NULL && options_.initial_block_size > 0) {
-      GOOGLE_CHECK_GE(options_.initial_block_size, sizeof(Block))
-          << ": Initial block size too small for header.";
-      initial_block_ = reinterpret_cast<Block*>(options_.initial_block);
-    } else {
-      initial_block_ = NULL;
-    }
+  ArenaImpl(char* mem, size_t size) {
+    GOOGLE_DCHECK_EQ(reinterpret_cast<uintptr_t>(mem) & 7, 0u);
+    Init(false);
 
-    Init();
+    // Ignore initial block if it is too small.
+    if (mem != nullptr && size >= kBlockHeaderSize + kSerialArenaSize) {
+      SetInitialBlock(new (mem) SerialArena::Block(size, nullptr, true, true));
+    }
   }
 
+  explicit ArenaImpl(const ArenaOptions& options);
+
   // Destructor deletes all owned heap allocated objects, and destructs objects
   // that have non-trivial destructors, except for proto2 message objects whose
   // destructors can be skipped. Also, frees all blocks except the initial block
@@ -134,178 +311,64 @@ class PROTOBUF_EXPORT ArenaImpl {
   // Add object pointer and cleanup function pointer to the list.
   void AddCleanup(void* elem, void (*cleanup)(void*));
 
- private:
-  friend class ArenaBenchmark;
-
-  void* AllocateAlignedFallback(size_t n);
-  void* AllocateAlignedAndAddCleanupFallback(size_t n, void (*cleanup)(void*));
-  void AddCleanupFallback(void* elem, void (*cleanup)(void*));
-
-  // Node contains the ptr of the object to be cleaned up and the associated
-  // cleanup function ptr.
-  struct CleanupNode {
-    void* elem;              // Pointer to the object to be cleaned up.
-    void (*cleanup)(void*);  // Function pointer to the destructor or deleter.
-  };
-
-  // Cleanup uses a chunked linked list, to reduce pointer chasing.
-  struct CleanupChunk {
-    static size_t SizeOf(size_t i) {
-      return sizeof(CleanupChunk) + (sizeof(CleanupNode) * (i - 1));
+  inline void RecordAlloc(const std::type_info* allocated_type,
+                          size_t n) const {
+    if (PROTOBUF_PREDICT_FALSE(record_allocs())) {
+      options_->metrics_collector->OnAlloc(allocated_type, n);
     }
-    size_t size;           // Total elements in the list.
-    CleanupChunk* next;    // Next node in the list.
-    CleanupNode nodes[1];  // True length is |size|.
-  };
-
-  class Block;
-
-  // A thread-unsafe Arena that can only be used within its owning thread.
-  class PROTOBUF_EXPORT SerialArena {
-   public:
-    // The allocate/free methods here are a little strange, since SerialArena is
-    // allocated inside a Block which it also manages.  This is to avoid doing
-    // an extra allocation for the SerialArena itself.
+  }
 
-    // Creates a new SerialArena inside Block* and returns it.
-    static SerialArena* New(Block* b, void* owner, ArenaImpl* arena);
+  std::pair<void*, size_t> NewBuffer(size_t last_size, size_t min_bytes);
 
-    // Destroys this SerialArena, freeing all blocks with the given dealloc
-    // function, except any block equal to |initial_block|.
-    static uint64 Free(SerialArena* serial, Block* initial_block,
-                       void (*block_dealloc)(void*, size_t));
+ private:
+  // Pointer to a linked list of SerialArena.
+  std::atomic<SerialArena*> threads_;
+  std::atomic<SerialArena*> hint_;       // Fast thread-local block access
+  std::atomic<size_t> space_allocated_;  // Total size of all allocated blocks.
 
-    void CleanupList();
-    uint64 SpaceUsed() const;
+  // Unique for each arena. Changes on Reset().
+  // Least-significant-bit is 1 iff allocations should be recorded.
+  uint64 lifecycle_id_;
 
-    bool HasSpace(size_t n) { return n <= static_cast<size_t>(limit_ - ptr_); }
+  struct Options {
+    size_t start_block_size;
+    size_t max_block_size;
+    void* (*block_alloc)(size_t);
+    void (*block_dealloc)(void*, size_t);
+    ArenaMetricsCollector* metrics_collector;
+  };
 
-    void* AllocateAligned(size_t n) {
-      GOOGLE_DCHECK_EQ(internal::AlignUpTo8(n), n);  // Must be already aligned.
-      GOOGLE_DCHECK_GE(limit_, ptr_);
-      if (PROTOBUF_PREDICT_FALSE(!HasSpace(n))) {
-        return AllocateAlignedFallback(n);
-      }
-      void* ret = ptr_;
-      ptr_ += n;
-#ifdef ADDRESS_SANITIZER
-      ASAN_UNPOISON_MEMORY_REGION(ret, n);
-#endif  // ADDRESS_SANITIZER
-      return ret;
-    }
+  Options* options_ = nullptr;
 
-    // Allocate space if the current region provides enough space.
-    bool MaybeAllocateAligned(size_t n, void** out) {
-      GOOGLE_DCHECK_EQ(internal::AlignUpTo8(n), n);  // Must be already aligned.
-      GOOGLE_DCHECK_GE(limit_, ptr_);
-      if (PROTOBUF_PREDICT_FALSE(!HasSpace(n))) return false;
-      void* ret = ptr_;
-      ptr_ += n;
-#ifdef ADDRESS_SANITIZER
-      ASAN_UNPOISON_MEMORY_REGION(ret, n);
-#endif  // ADDRESS_SANITIZER
-      *out = ret;
-      return true;
-    }
+  void* AllocateAlignedFallback(size_t n);
+  void* AllocateAlignedAndAddCleanupFallback(size_t n, void (*cleanup)(void*));
+  void AddCleanupFallback(void* elem, void (*cleanup)(void*));
 
-    void AddCleanup(void* elem, void (*cleanup)(void*)) {
-      if (PROTOBUF_PREDICT_FALSE(cleanup_ptr_ == cleanup_limit_)) {
-        AddCleanupFallback(elem, cleanup);
-        return;
+  void Init(bool record_allocs);
+  void SetInitialBlock(
+      SerialArena::Block* block);  // Can be called right after Init()
+
+  // Return true iff allocations should be recorded in a metrics collector.
+  inline bool record_allocs() const { return lifecycle_id_ & 1; }
+
+  // Invoke fn(b) for every Block* b.
+  template <typename Functor>
+  void PerBlock(Functor fn) {
+    // By omitting an Acquire barrier we ensure that any user code that doesn't
+    // properly synchronize Reset() or the destructor will throw a TSAN warning.
+    SerialArena* serial = threads_.load(std::memory_order_relaxed);
+    while (serial) {
+      // fn() may delete blocks and arenas, so fetch next pointers before fn();
+      SerialArena* cur = serial;
+      serial = serial->next();
+      for (auto* block = cur->head(); block != nullptr;) {
+        auto* b = block;
+        block = b->next();
+        fn(b);
       }
-      cleanup_ptr_->elem = elem;
-      cleanup_ptr_->cleanup = cleanup;
-      cleanup_ptr_++;
     }
+  }
 
-    void* AllocateAlignedAndAddCleanup(size_t n, void (*cleanup)(void*)) {
-      void* ret = AllocateAligned(n);
-      AddCleanup(ret, cleanup);
-      return ret;
-    }
-
-    void* owner() const { return owner_; }
-    SerialArena* next() const { return next_; }
-    void set_next(SerialArena* next) { next_ = next; }
-
-   private:
-    void* AllocateAlignedFallback(size_t n);
-    void AddCleanupFallback(void* elem, void (*cleanup)(void*));
-    void CleanupListFallback();
-
-    ArenaImpl* arena_;       // Containing arena.
-    void* owner_;            // &ThreadCache of this thread;
-    Block* head_;            // Head of linked list of blocks.
-    CleanupChunk* cleanup_;  // Head of cleanup list.
-    SerialArena* next_;      // Next SerialArena in this linked list.
-
-    // Next pointer to allocate from.  Always 8-byte aligned.  Points inside
-    // head_ (and head_->pos will always be non-canonical).  We keep these
-    // here to reduce indirection.
-    char* ptr_;
-    char* limit_;
-
-    // Next CleanupList members to append to.  These point inside cleanup_.
-    CleanupNode* cleanup_ptr_;
-    CleanupNode* cleanup_limit_;
-  };
-
-  // Blocks are variable length malloc-ed objects.  The following structure
-  // describes the common header for all blocks.
-  class PROTOBUF_EXPORT Block {
-   public:
-    Block(size_t size, Block* next);
-
-    char* Pointer(size_t n) {
-      GOOGLE_DCHECK(n <= size_);
-      return reinterpret_cast<char*>(this) + n;
-    }
-
-    Block* next() const { return next_; }
-    size_t pos() const { return pos_; }
-    size_t size() const { return size_; }
-    void set_pos(size_t pos) { pos_ = pos; }
-
-   private:
-    Block* next_;  // Next block for this thread.
-    size_t pos_;
-    size_t size_;
-    // data follows
-  };
-
-  struct ThreadCache {
-#if defined(GOOGLE_PROTOBUF_NO_THREADLOCAL)
-    // If we are using the ThreadLocalStorage class to store the ThreadCache,
-    // then the ThreadCache's default constructor has to be responsible for
-    // initializing it.
-    ThreadCache() : last_lifecycle_id_seen(-1), last_serial_arena(NULL) {}
-#endif
-
-    // The ThreadCache is considered valid as long as this matches the
-    // lifecycle_id of the arena being used.
-    LifecycleId last_lifecycle_id_seen;
-    SerialArena* last_serial_arena;
-  };
-  static std::atomic<LifecycleId> lifecycle_id_generator_;
-#if defined(GOOGLE_PROTOBUF_NO_THREADLOCAL)
-  // Android ndk does not support __thread keyword so we use a custom thread
-  // local storage class we implemented.
-  // iOS also does not support the __thread keyword.
-  static ThreadCache& thread_cache();
-#elif defined(PROTOBUF_USE_DLLS)
-  // Thread local variables cannot be exposed through DLL interface but we can
-  // wrap them in static functions.
-  static ThreadCache& thread_cache();
-#else
-  static PROTOBUF_THREAD_LOCAL ThreadCache thread_cache_;
-  static ThreadCache& thread_cache() { return thread_cache_; }
-#endif
-
-  void Init();
-
-  // Free all blocks and return the total space used which is the sums of sizes
-  // of the all the allocated blocks.
-  uint64 FreeBlocks();
   // Delete or Destruct all objects owned by the arena.
   void CleanupList();
 
@@ -319,16 +382,6 @@ class PROTOBUF_EXPORT ArenaImpl {
     hint_.store(serial, std::memory_order_release);
   }
 
-  std::atomic<SerialArena*>
-      threads_;                     // Pointer to a linked list of SerialArena.
-  std::atomic<SerialArena*> hint_;  // Fast thread-local block access
-  std::atomic<size_t> space_allocated_;  // Total size of all allocated blocks.
-
-  Block* initial_block_;  // If non-NULL, points to the block that came from
-                          // user data.
-
-  Block* NewBlock(Block* last_block, size_t min_bytes);
-
   PROTOBUF_ALWAYS_INLINE bool GetSerialArenaFast(SerialArena** arena) {
     if (GetSerialArenaFromThreadCache(arena)) return true;
 
@@ -356,9 +409,58 @@ class PROTOBUF_EXPORT ArenaImpl {
     return false;
   }
   SerialArena* GetSerialArenaFallback(void* me);
-  LifecycleId lifecycle_id_;  // Unique for each arena. Changes on Reset().
 
-  Options options_;
+#ifdef _MSC_VER
+#pragma warning(disable : 4324)
+#endif
+  struct alignas(64) ThreadCache {
+#if defined(GOOGLE_PROTOBUF_NO_THREADLOCAL)
+    // If we are using the ThreadLocalStorage class to store the ThreadCache,
+    // then the ThreadCache's default constructor has to be responsible for
+    // initializing it.
+    ThreadCache()
+        : next_lifecycle_id(0),
+          last_lifecycle_id_seen(-1),
+          last_serial_arena(NULL) {}
+#endif
+
+    // Number of per-thread lifecycle IDs to reserve. Must be power of two.
+    // To reduce contention on a global atomic, each thread reserves a batch of
+    // IDs.  The following number is calculated based on a stress test with
+    // ~6500 threads all frequently allocating a new arena.
+    static constexpr size_t kPerThreadIds = 256;
+    // Next lifecycle ID available to this thread. We need to reserve a new
+    // batch, if `next_lifecycle_id & (kPerThreadIds - 1) == 0`.
+    uint64 next_lifecycle_id;
+    // The ThreadCache is considered valid as long as this matches the
+    // lifecycle_id of the arena being used.
+    uint64 last_lifecycle_id_seen;
+    SerialArena* last_serial_arena;
+  };
+
+  // Lifecycle_id can be highly contended variable in a situation of lots of
+  // arena creation. Make sure that other global variables are not sharing the
+  // cacheline.
+#ifdef _MSC_VER
+#pragma warning(disable : 4324)
+#endif
+  struct alignas(64) CacheAlignedLifecycleIdGenerator {
+    std::atomic<LifecycleIdAtomic> id;
+  };
+  static CacheAlignedLifecycleIdGenerator lifecycle_id_generator_;
+#if defined(GOOGLE_PROTOBUF_NO_THREADLOCAL)
+  // Android ndk does not support __thread keyword so we use a custom thread
+  // local storage class we implemented.
+  // iOS also does not support the __thread keyword.
+  static ThreadCache& thread_cache();
+#elif defined(PROTOBUF_USE_DLLS)
+  // Thread local variables cannot be exposed through DLL interface but we can
+  // wrap them in static functions.
+  static ThreadCache& thread_cache();
+#else
+  static PROTOBUF_THREAD_LOCAL ThreadCache thread_cache_;
+  static ThreadCache& thread_cache() { return thread_cache_; }
+#endif
 
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(ArenaImpl);
   // All protos have pointers back to the arena hence Arena must have
@@ -369,10 +471,11 @@ class PROTOBUF_EXPORT ArenaImpl {
  public:
   // kBlockHeaderSize is sizeof(Block), aligned up to the nearest multiple of 8
   // to protect the invariant that pos is always at a multiple of 8.
-  static const size_t kBlockHeaderSize =
-      (sizeof(Block) + 7) & static_cast<size_t>(-8);
-  static const size_t kSerialArenaSize =
+  static constexpr size_t kBlockHeaderSize = SerialArena::kBlockHeaderSize;
+  static constexpr size_t kSerialArenaSize =
       (sizeof(SerialArena) + 7) & static_cast<size_t>(-8);
+  static constexpr size_t kOptionsSize =
+      (sizeof(Options) + 7) & static_cast<size_t>(-8);
   static_assert(kBlockHeaderSize % 8 == 0,
                 "kBlockHeaderSize must be a multiple of 8.");
   static_assert(kSerialArenaSize % 8 == 0,

src/google/protobuf/arena_unittest.cc

@@ -31,6 +31,7 @@
 #include <google/protobuf/arena.h>
 
 #include <algorithm>
+#include <cstddef>
 #include <cstring>
 #include <memory>
 #include <string>
@@ -272,28 +273,36 @@ TEST(ArenaTest, CreateWithMoveArguments) {
 }
 
 TEST(ArenaTest, InitialBlockTooSmall) {
-  // Construct a small (64 byte) initial block of memory to be used by the
-  // arena allocator; then, allocate an object which will not fit in the
-  // initial block.
-  std::vector<char> arena_block(96);
-  ArenaOptions options;
-  options.initial_block = &arena_block[0];
-  options.initial_block_size = arena_block.size();
-  Arena arena(options);
+  // Construct a small blocks of memory to be used by the arena allocator; then,
+  // allocate an object which will not fit in the initial block.
+  for (int size = 0; size <= Arena::kBlockOverhead + 32; size++) {
+    std::vector<char> arena_block(size);
+    ArenaOptions options;
+    options.initial_block = arena_block.data();
+    options.initial_block_size = arena_block.size();
+
+    // Try sometimes with non-default block sizes so that we exercise paths
+    // with and without ArenaImpl::Options.
+    if ((size % 2) != 0) {
+      options.start_block_size += 8;
+    }
 
-  char* p = Arena::CreateArray<char>(&arena, 96);
-  uintptr_t allocation = reinterpret_cast<uintptr_t>(p);
+    Arena arena(options);
+
+    char* p = Arena::CreateArray<char>(&arena, 96);
+    uintptr_t allocation = reinterpret_cast<uintptr_t>(p);
 
-  // Ensure that the arena allocator did not return memory pointing into the
-  // initial block of memory.
-  uintptr_t arena_start = reinterpret_cast<uintptr_t>(&arena_block[0]);
-  uintptr_t arena_end = arena_start + arena_block.size();
-  EXPECT_FALSE(allocation >= arena_start && allocation < arena_end);
+    // Ensure that the arena allocator did not return memory pointing into the
+    // initial block of memory.
+    uintptr_t arena_start = reinterpret_cast<uintptr_t>(arena_block.data());
+    uintptr_t arena_end = arena_start + arena_block.size();
+    EXPECT_FALSE(allocation >= arena_start && allocation < arena_end);
 
-  // Write to the memory we allocated; this should (but is not guaranteed to)
-  // trigger a check for heap corruption if the object was allocated from the
-  // initially-provided block.
-  memset(p, '\0', 96);
+    // Write to the memory we allocated; this should (but is not guaranteed to)
+    // trigger a check for heap corruption if the object was allocated from the
+    // initially-provided block.
+    memset(p, '\0', 96);
+  }
 }
 
 TEST(ArenaTest, Parsing) {
@@ -988,10 +997,7 @@ TEST(ArenaTest, ExtensionsOnArena) {
 TEST(ArenaTest, RepeatedFieldOnArena) {
   // Preallocate an initial arena block to avoid mallocs during hooked region.
   std::vector<char> arena_block(1024 * 1024);
-  ArenaOptions options;
-  options.initial_block = &arena_block[0];
-  options.initial_block_size = arena_block.size();
-  Arena arena(options);
+  Arena arena(arena_block.data(), arena_block.size());
 
   {
     internal::NoHeapChecker no_heap;
@@ -1189,10 +1195,7 @@ TEST(ArenaTest, RepeatedFieldWithNonPODType) {
 uint64 Align8(uint64 n) { return (n + 7) & -8; }
 
 TEST(ArenaTest, SpaceAllocated_and_Used) {
-  ArenaOptions options;
-  options.start_block_size = 256;
-  options.max_block_size = 8192;
-  Arena arena_1(options);
+  Arena arena_1;
   EXPECT_EQ(0, arena_1.SpaceAllocated());
   EXPECT_EQ(0, arena_1.SpaceUsed());
   EXPECT_EQ(0, arena_1.Reset());
@@ -1204,6 +1207,9 @@ TEST(ArenaTest, SpaceAllocated_and_Used) {
 
   // Test with initial block.
   std::vector<char> arena_block(1024);
+  ArenaOptions options;
+  options.start_block_size = 256;
+  options.max_block_size = 8192;
   options.initial_block = &arena_block[0];
   options.initial_block_size = arena_block.size();
   Arena arena_2(options);
@@ -1214,19 +1220,25 @@ TEST(ArenaTest, SpaceAllocated_and_Used) {
   EXPECT_EQ(1024, arena_2.SpaceAllocated());
   EXPECT_EQ(Align8(55), arena_2.SpaceUsed());
   EXPECT_EQ(1024, arena_2.Reset());
+}
 
-  // Reset options to test doubling policy explicitly.
-  options.initial_block = NULL;
-  options.initial_block_size = 0;
-  Arena arena_3(options);
-  EXPECT_EQ(0, arena_3.SpaceUsed());
-  Arena::CreateArray<char>(&arena_3, 160);
-  EXPECT_EQ(256, arena_3.SpaceAllocated());
-  EXPECT_EQ(Align8(160), arena_3.SpaceUsed());
-  Arena::CreateArray<char>(&arena_3, 70);
-  EXPECT_EQ(256 + 512, arena_3.SpaceAllocated());
-  EXPECT_EQ(Align8(160) + Align8(70), arena_3.SpaceUsed());
-  EXPECT_EQ(256 + 512, arena_3.Reset());
+TEST(ArenaTest, BlockSizeDoubling) {
+  Arena arena;
+  EXPECT_EQ(0, arena.SpaceUsed());
+  EXPECT_EQ(0, arena.SpaceAllocated());
+
+  // Allocate something to get initial block size.
+  Arena::CreateArray<char>(&arena, 1);
+  auto first_block_size = arena.SpaceAllocated();
+
+  // Keep allocating until space used increases.
+  while (arena.SpaceAllocated() == first_block_size) {
+    Arena::CreateArray<char>(&arena, 1);
+  }
+  ASSERT_GT(arena.SpaceAllocated(), first_block_size);
+  auto second_block_size = (arena.SpaceAllocated() - first_block_size);
+
+  EXPECT_EQ(second_block_size, 2*first_block_size);
 }
 
 TEST(ArenaTest, Alignment) {
@@ -1304,81 +1316,93 @@ TEST(ArenaTest, AddCleanup) {
   }
 }
 
-// A helper utility class to only contain static hook functions, some
-// counters to be used to verify the counters have been called and a cookie
-// value to be verified.
-class ArenaHooksTestUtil {
+namespace {
+uint32 hooks_num_init = 0;
+uint32 hooks_num_allocations = 0;
+uint32 hooks_num_reset = 0;
+uint32 hooks_num_destruct = 0;
+
+void ClearHookCounts() {
+  hooks_num_init = 0;
+  hooks_num_allocations = 0;
+  hooks_num_reset = 0;
+  hooks_num_destruct = 0;
+}
+}  // namespace
+
+// A helper utility class that handles arena callbacks.
+class ArenaOptionsTestFriend : public internal::ArenaMetricsCollector {
  public:
-  static void* on_init(Arena* arena) {
-    ++num_init;
-    int* cookie = new int(kCookieValue);
-    return static_cast<void*>(cookie);
+  static internal::ArenaMetricsCollector* NewWithAllocs() {
+    return new ArenaOptionsTestFriend(true);
   }
 
-  static void on_allocation(const std::type_info* /*unused*/, uint64 alloc_size,
-                            void* cookie) {
-    ++num_allocations;
-    int cookie_value = *static_cast<int*>(cookie);
-    EXPECT_EQ(kCookieValue, cookie_value);
+  static internal::ArenaMetricsCollector* NewWithoutAllocs() {
+    return new ArenaOptionsTestFriend(false);
   }
 
-  static void on_reset(Arena* arena, void* cookie, uint64 space_used) {
-    ++num_reset;
-    int cookie_value = *static_cast<int*>(cookie);
-    EXPECT_EQ(kCookieValue, cookie_value);
+  static void Enable(ArenaOptions* options) {
+    ClearHookCounts();
+    options->make_metrics_collector = &ArenaOptionsTestFriend::NewWithAllocs;
   }
 
-  static void on_destruction(Arena* arena, void* cookie, uint64 space_used) {
-    ++num_destruct;
-    int cookie_value = *static_cast<int*>(cookie);
-    EXPECT_EQ(kCookieValue, cookie_value);
-    delete static_cast<int*>(cookie);
+  static void EnableWithoutAllocs(ArenaOptions* options) {
+    ClearHookCounts();
+    options->make_metrics_collector = &ArenaOptionsTestFriend::NewWithoutAllocs;
   }
 
-  static const int kCookieValue = 999;
-  static uint32 num_init;
-  static uint32 num_allocations;
-  static uint32 num_reset;
-  static uint32 num_destruct;
-};
-uint32 ArenaHooksTestUtil::num_init = 0;
-uint32 ArenaHooksTestUtil::num_allocations = 0;
-uint32 ArenaHooksTestUtil::num_reset = 0;
-uint32 ArenaHooksTestUtil::num_destruct = 0;
-const int ArenaHooksTestUtil::kCookieValue;
-
-class ArenaOptionsTestFriend {
- public:
-  static void Set(ArenaOptions* options) {
-    options->on_arena_init = ArenaHooksTestUtil::on_init;
-    options->on_arena_allocation = ArenaHooksTestUtil::on_allocation;
-    options->on_arena_reset = ArenaHooksTestUtil::on_reset;
-    options->on_arena_destruction = ArenaHooksTestUtil::on_destruction;
+  explicit ArenaOptionsTestFriend(bool record_allocs)
+      : record_allocs_(record_allocs) {
+    ++hooks_num_init;
   }
+  void OnDestroy(uint64 space_allocated) override {
+    ++hooks_num_destruct;
+    delete this;
+  }
+  void OnReset(uint64 space_allocated) override { ++hooks_num_reset; }
+  bool RecordAllocs() override { return record_allocs_; }
+  void OnAlloc(const std::type_info* allocated_type,
+               uint64 alloc_size) override {
+    ++hooks_num_allocations;
+  }
+
+ private:
+  bool record_allocs_;
 };
 
-// Test the hooks are correctly called and that the cookie is passed.
+// Test the hooks are correctly called.
 TEST(ArenaTest, ArenaHooksSanity) {
   ArenaOptions options;
-  ArenaOptionsTestFriend::Set(&options);
+  ArenaOptionsTestFriend::Enable(&options);
 
   // Scope for defining the arena
   {
     Arena arena(options);
-    EXPECT_EQ(1, ArenaHooksTestUtil::num_init);
-    EXPECT_EQ(0, ArenaHooksTestUtil::num_allocations);
+    EXPECT_EQ(1, hooks_num_init);
+    EXPECT_EQ(0, hooks_num_allocations);
     Arena::Create<uint64>(&arena);
     if (std::is_trivially_destructible<uint64>::value) {
-      EXPECT_EQ(1, ArenaHooksTestUtil::num_allocations);
+      EXPECT_EQ(1, hooks_num_allocations);
     } else {
-      EXPECT_EQ(2, ArenaHooksTestUtil::num_allocations);
+      EXPECT_EQ(2, hooks_num_allocations);
     }
     arena.Reset();
     arena.Reset();
-    EXPECT_EQ(2, ArenaHooksTestUtil::num_reset);
+    EXPECT_EQ(2, hooks_num_reset);
   }
-  EXPECT_EQ(3, ArenaHooksTestUtil::num_reset);
-  EXPECT_EQ(1, ArenaHooksTestUtil::num_destruct);
+  EXPECT_EQ(2, hooks_num_reset);
+  EXPECT_EQ(1, hooks_num_destruct);
+}
+
+// Test that allocation hooks are not called when we don't need them.
+TEST(ArenaTest, ArenaHooksWhenAllocationsNotNeeded) {
+  ArenaOptions options;
+  ArenaOptionsTestFriend::EnableWithoutAllocs(&options);
+
+  Arena arena(options);
+  EXPECT_EQ(0, hooks_num_allocations);
+  Arena::Create<uint64>(&arena);
+  EXPECT_EQ(0, hooks_num_allocations);
 }
 
 

src/google/protobuf/arenastring.cc

@@ -0,0 +1,254 @@
+// 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/arenastring.h>
+
+#include <google/protobuf/stubs/logging.h>
+#include <google/protobuf/stubs/common.h>
+#include <google/protobuf/parse_context.h>
+#include <google/protobuf/io/coded_stream.h>
+#include <google/protobuf/message_lite.h>
+#include <google/protobuf/stubs/mutex.h>
+#include <google/protobuf/stubs/strutil.h>
+#include <google/protobuf/stubs/stl_util.h>
+
+// clang-format off
+#include <google/protobuf/port_def.inc>
+// clang-format on
+
+namespace google {
+namespace protobuf {
+namespace internal {
+
+const std::string& LazyString::Init() const {
+  static WrappedMutex mu{GOOGLE_PROTOBUF_LINKER_INITIALIZED};
+  mu.Lock();
+  const std::string* res = inited_.load(std::memory_order_acquire);
+  if (res == nullptr) {
+    auto init_value = init_value_;
+    res = ::new (static_cast<void*>(string_buf_))
+        std::string(init_value.ptr, init_value.size);
+    inited_.store(res, std::memory_order_release);
+  }
+  mu.Unlock();
+  return *res;
+}
+
+
+void ArenaStringPtr::Set(const std::string* default_value,
+                         ConstStringParam value, ::google::protobuf::Arena* arena) {
+  if (IsDefault(default_value)) {
+    tagged_ptr_.Set(Arena::Create<std::string>(arena, value));
+  } else {
+    UnsafeMutablePointer()->assign(value.data(), value.length());
+  }
+}
+
+void ArenaStringPtr::Set(const std::string* default_value, std::string&& value,
+                         ::google::protobuf::Arena* arena) {
+  if (IsDefault(default_value)) {
+    if (arena == nullptr) {
+      tagged_ptr_.Set(new std::string(std::move(value)));
+    } else {
+      tagged_ptr_.Set(Arena::Create<std::string>(arena, std::move(value)));
+    }
+  } else if (IsDonatedString()) {
+    std::string* current = tagged_ptr_.Get();
+    auto* s = new (current) std::string(std::move(value));
+    arena->OwnDestructor(s);
+    tagged_ptr_.Set(s);
+  } else /* !IsDonatedString() */ {
+    *UnsafeMutablePointer() = std::move(value);
+  }
+}
+
+void ArenaStringPtr::Set(EmptyDefault, ConstStringParam value,
+                         ::google::protobuf::Arena* arena) {
+  Set(&GetEmptyStringAlreadyInited(), value, arena);
+}
+
+void ArenaStringPtr::Set(EmptyDefault, std::string&& value,
+                         ::google::protobuf::Arena* arena) {
+  Set(&GetEmptyStringAlreadyInited(), std::move(value), arena);
+}
+
+void ArenaStringPtr::Set(NonEmptyDefault, ConstStringParam value,
+                         ::google::protobuf::Arena* arena) {
+  Set(nullptr, value, arena);
+}
+
+void ArenaStringPtr::Set(NonEmptyDefault, std::string&& value,
+                         ::google::protobuf::Arena* arena) {
+  Set(nullptr, std::move(value), arena);
+}
+
+std::string* ArenaStringPtr::Mutable(EmptyDefault, ::google::protobuf::Arena* arena) {
+  if (!IsDonatedString() && !IsDefault(&GetEmptyStringAlreadyInited())) {
+    return UnsafeMutablePointer();
+  } else {
+    return MutableSlow(arena);
+  }
+}
+
+std::string* ArenaStringPtr::Mutable(const LazyString& default_value,
+                                     ::google::protobuf::Arena* arena) {
+  if (!IsDonatedString() && !IsDefault(nullptr)) {
+    return UnsafeMutablePointer();
+  } else {
+    return MutableSlow(arena, default_value);
+  }
+}
+
+std::string* ArenaStringPtr::MutableNoCopy(const std::string* default_value,
+                                           ::google::protobuf::Arena* arena) {
+  if (!IsDonatedString() && !IsDefault(default_value)) {
+    return UnsafeMutablePointer();
+  } else {
+    GOOGLE_DCHECK(IsDefault(default_value));
+    // Allocate empty. The contents are not relevant.
+    std::string* new_string = Arena::Create<std::string>(arena);
+    tagged_ptr_.Set(new_string);
+    return new_string;
+  }
+}
+
+template <typename... Lazy>
+std::string* ArenaStringPtr::MutableSlow(::google::protobuf::Arena* arena,
+                                         const Lazy&... lazy_default) {
+  const std::string* const default_value =
+      sizeof...(Lazy) == 0 ? &GetEmptyStringAlreadyInited() : nullptr;
+  GOOGLE_DCHECK(IsDefault(default_value));
+  std::string* new_string =
+      Arena::Create<std::string>(arena, lazy_default.get()...);
+  tagged_ptr_.Set(new_string);
+  return new_string;
+}
+
+std::string* ArenaStringPtr::Release(const std::string* default_value,
+                                     ::google::protobuf::Arena* arena) {
+  if (IsDefault(default_value)) {
+    return nullptr;
+  } else {
+    return ReleaseNonDefault(default_value, arena);
+  }
+}
+
+std::string* ArenaStringPtr::ReleaseNonDefault(const std::string* default_value,
+                                               ::google::protobuf::Arena* arena) {
+  GOOGLE_DCHECK(!IsDefault(default_value));
+
+  if (!IsDonatedString()) {
+    std::string* released;
+    if (arena != nullptr) {
+      released = new std::string;
+      released->swap(*UnsafeMutablePointer());
+    } else {
+      released = UnsafeMutablePointer();
+    }
+    tagged_ptr_.Set(const_cast<std::string*>(default_value));
+    return released;
+  } else /* IsDonatedString() */ {
+    GOOGLE_DCHECK(arena != nullptr);
+    std::string* released = new std::string(Get());
+    tagged_ptr_.Set(const_cast<std::string*>(default_value));
+    return released;
+  }
+}
+
+void ArenaStringPtr::SetAllocated(const std::string* default_value,
+                                  std::string* value, ::google::protobuf::Arena* arena) {
+  // Release what we have first.
+  if (arena == nullptr && !IsDefault(default_value)) {
+    delete UnsafeMutablePointer();
+  }
+  if (value == nullptr) {
+    tagged_ptr_.Set(const_cast<std::string*>(default_value));
+  } else {
+#ifdef NDEBUG
+    tagged_ptr_.Set(value);
+    if (arena != nullptr) {
+      arena->Own(value);
+    }
+#else
+    // On debug builds, copy the string so the address differs.  delete will
+    // fail if value was a stack-allocated temporary/etc., which would have
+    // failed when arena ran its cleanup list.
+    std::string* new_value = Arena::Create<std::string>(arena, *value);
+    delete value;
+    tagged_ptr_.Set(new_value);
+#endif
+  }
+}
+
+void ArenaStringPtr::Destroy(const std::string* default_value,
+                             ::google::protobuf::Arena* arena) {
+  if (arena == nullptr) {
+    GOOGLE_DCHECK(!IsDonatedString());
+    if (!IsDefault(default_value)) {
+      delete UnsafeMutablePointer();
+    }
+  }
+}
+
+void ArenaStringPtr::Destroy(EmptyDefault, ::google::protobuf::Arena* arena) {
+  Destroy(&GetEmptyStringAlreadyInited(), arena);
+}
+
+void ArenaStringPtr::Destroy(NonEmptyDefault, ::google::protobuf::Arena* arena) {
+  Destroy(nullptr, arena);
+}
+
+void ArenaStringPtr::ClearToEmpty() {
+  if (IsDefault(&GetEmptyStringAlreadyInited())) {
+    // Already set to default -- do nothing.
+  } else {
+    // Unconditionally mask away the tag.
+    //
+    // UpdateDonatedString uses assign when capacity is larger than the new
+    // value, which is trivially true in the donated string case.
+    // const_cast<std::string*>(PtrValue<std::string>())->clear();
+    tagged_ptr_.Get()->clear();
+  }
+}
+
+void ArenaStringPtr::ClearToDefault(const LazyString& default_value,
+                                    ::google::protobuf::Arena* arena) {
+  (void)arena;
+  if (IsDefault(nullptr)) {
+    // Already set to default -- do nothing.
+  } else if (!IsDonatedString()) {
+    UnsafeMutablePointer()->assign(default_value.get());
+  }
+}
+
+
+}  // namespace internal
+}  // namespace protobuf
+}  // namespace google

src/google/protobuf/arenastring.h

@@ -37,7 +37,6 @@
 
 #include <google/protobuf/stubs/logging.h>
 #include <google/protobuf/stubs/common.h>
-#include <google/protobuf/stubs/fastmem.h>
 #include <google/protobuf/arena.h>
 #include <google/protobuf/port.h>
 
@@ -48,261 +47,329 @@
 #endif
 
 
-// This is the implementation of arena string fields written for the open-source
-// release. The ArenaStringPtr struct below is an internal implementation class
-// and *should not be used* by user code. It is used to collect string
-// operations together into one place and abstract away the underlying
-// string-field pointer representation, so that (for example) an alternate
-// implementation that knew more about ::std::string's internals could integrate
-// more closely with the arena allocator.
-
 namespace google {
 namespace protobuf {
 namespace internal {
 
+// Lazy string instance to support string fields with non-empty default.
+// These are initialized on the first call to .get().
+class PROTOBUF_EXPORT LazyString {
+ public:
+  // We explicitly make LazyString an aggregate so that MSVC can do constant
+  // initialization on it without marking it `constexpr`.
+  // We do not want to use `constexpr` because it makes it harder to have extern
+  // storage for it and causes library bloat.
+  struct InitValue {
+    const char* ptr;
+    size_t size;
+  };
+  // We keep a union of the initialization value and the std::string to save on
+  // space. We don't need the string array after Init() is done.
+  union {
+    mutable InitValue init_value_;
+    alignas(std::string) mutable char string_buf_[sizeof(std::string)];
+  };
+  mutable std::atomic<const std::string*> inited_;
+
+  const std::string& get() const {
+    // This check generates less code than a call-once invocation.
+    auto* res = inited_.load(std::memory_order_acquire);
+    if (PROTOBUF_PREDICT_FALSE(res == nullptr)) return Init();
+    return *res;
+  }
+
+ private:
+  // Initialize the string in `string_buf_`, update `inited_` and return it.
+  // We return it here to avoid having to read it again in the inlined code.
+  const std::string& Init() const;
+};
+
 template <typename T>
 class TaggedPtr {
  public:
-  void Set(T* p) { ptr_ = reinterpret_cast<uintptr_t>(p); }
-  T* Get() const { return reinterpret_cast<T*>(ptr_); }
+  TaggedPtr() = default;
+  explicit constexpr TaggedPtr(const std::string* ptr)
+      : ptr_(const_cast<std::string*>(ptr)) {}
+
+  void SetTagged(T* p) {
+    Set(p);
+    ptr_ = reinterpret_cast<void*>(as_int() | 1);
+  }
+  void Set(T* p) { ptr_ = p; }
+  T* Get() const { return reinterpret_cast<T*>(as_int() & -2); }
+  bool IsTagged() const { return as_int() & 1; }
 
-  bool IsNull() { return ptr_ == 0; }
+  // Returned value is only safe to dereference if IsTagged() == false.
+  // It is safe to compare.
+  T* UnsafeGet() const { return static_cast<T*>(ptr_); }
+
+  bool IsNull() { return ptr_ == nullptr; }
 
  private:
-  uintptr_t ptr_;
+  uintptr_t as_int() const { return reinterpret_cast<uintptr_t>(ptr_); }
+  void* ptr_;
 };
 
-struct PROTOBUF_EXPORT ArenaStringPtr {
-  inline void Set(const ::std::string* default_value,
-                  const ::std::string& value, Arena* arena) {
-    if (ptr_ == default_value) {
-      CreateInstance(arena, &value);
-    } else {
-      *ptr_ = value;
-    }
-  }
+static_assert(std::is_trivial<TaggedPtr<std::string>>::value,
+              "TaggedPtr must be trivial");
 
-  inline void SetLite(const ::std::string* default_value,
-                      const ::std::string& value, Arena* arena) {
-    Set(default_value, value, arena);
-  }
+// This class encapsulates a pointer to a std::string with or without a donated
+// buffer, tagged by bottom bit. It is a high-level wrapper that almost directly
+// corresponds to the interface required by string fields in generated
+// code. It replaces the old std::string* pointer in such cases.
+//
+// The object has different but similar code paths for when the default value is
+// the empty string and when it is a non-empty string.
+// The empty string is handled different throughout the library and there is a
+// single global instance of it we can share.
+//
+// For fields with an empty string default value, there are three distinct
+// states:
+//
+// - Pointer set to 'String' tag (LSB is 0), equal to
+//   &GetEmptyStringAlreadyInited(): field is set to its default value. Points
+//   to a true std::string*, but we do not own that std::string* (it's a
+//   globally shared instance).
+//
+// - Pointer set to 'String' tag (LSB is 0), but not equal to the global empty
+//   string: field points to a true std::string* instance that we own. This
+//   instance is either on the heap or on the arena (i.e. registered on
+//   free()/destructor-call list) as appropriate.
+//
+// - Pointer set to 'DonatedString' tag (LSB is 1): points to a std::string
+//   instance with a buffer on the arena (arena != NULL, always, in this case).
+//
+// For fields with a non-empty string default value, there are three distinct
+// states:
+//
+// - Pointer set to 'String' tag (LSB is 0), equal to `nullptr`:
+//   Field is in "default" mode and does not point to any actual instance.
+//   Methods that might need to create an instance of the object will pass a
+//   `const LazyString&` for it.
+//
+// - Pointer set to 'String' tag (LSB is 0), but not equal to `nullptr`:
+//   field points to a true std::string* instance that we own. This instance is
+//   either on the heap or on the arena (i.e. registered on
+//   free()/destructor-call list) as appropriate.
+//
+// - Pointer set to 'DonatedString' tag (LSB is 1): points to a std::string
+//   instance with a buffer on the arena (arena != NULL, always, in this case).
+//
+// Generated code and reflection code both ensure that ptr_ is never null for
+// fields with an empty default.
+// Because ArenaStringPtr is used in oneof unions, its constructor is a NOP and
+// so the field is always manually initialized via method calls.
+//
+// Side-note: why pass information about the default on every API call? Because
+// we don't want to hold it in a member variable, or else this would go into
+// every proto message instance. This would be a huge waste of space, since the
+// default instance pointer is typically a global (static class field). We want
+// the generated code to be as efficient as possible, and if we take
+// the default value information as a parameter that's in practice taken from a
+// static class field, and compare ptr_ to the default value, we end up with a
+// single "cmp %reg, GLOBAL" in the resulting machine code. (Note that this also
+// requires the String tag to be 0 so we can avoid the mask before comparing.)
+struct PROTOBUF_EXPORT ArenaStringPtr {
+  ArenaStringPtr() = default;
+  explicit constexpr ArenaStringPtr(const std::string* default_value)
+      : tagged_ptr_(default_value) {}
+
+  // Some methods below are overloaded on a `default_value` and on tags.
+  // The tagged overloads help reduce code size in the callers in generated
+  // code, while the `default_value` overloads are useful from reflection.
+  // By-value empty struct arguments are elided in the ABI.
+  struct EmptyDefault {};
+  struct NonEmptyDefault {};
+
+  void Set(const std::string* default_value, ConstStringParam value,
+           ::google::protobuf::Arena* arena);
+  void Set(const std::string* default_value, std::string&& value,
+           ::google::protobuf::Arena* arena);
+  void Set(EmptyDefault, ConstStringParam value, ::google::protobuf::Arena* arena);
+  void Set(EmptyDefault, std::string&& value, ::google::protobuf::Arena* arena);
+  void Set(NonEmptyDefault, ConstStringParam value, ::google::protobuf::Arena* arena);
+  void Set(NonEmptyDefault, std::string&& value, ::google::protobuf::Arena* arena);
 
   // Basic accessors.
-  inline const ::std::string& Get() const { return *ptr_; }
-
-  inline ::std::string* Mutable(const ::std::string* default_value,
-                                Arena* arena) {
-    if (ptr_ == default_value) {
-      CreateInstance(arena, default_value);
-    }
-    return ptr_;
+  const std::string& Get() const PROTOBUF_ALWAYS_INLINE {
+    // Unconditionally mask away the tag.
+    return *tagged_ptr_.Get();
   }
-
-  // Release returns a ::std::string* instance that is heap-allocated and is not
-  // Own()'d by any arena. If the field was not set, it returns NULL. The caller
-  // retains ownership. Clears this field back to NULL state. Used to implement
-  // release_<field>() methods on generated classes.
-  inline ::std::string* Release(const ::std::string* default_value,
-                                Arena* arena) {
-    if (ptr_ == default_value) {
-      return NULL;
-    }
-    return ReleaseNonDefault(default_value, arena);
+  const std::string* GetPointer() const PROTOBUF_ALWAYS_INLINE {
+    // Unconditionally mask away the tag.
+    return tagged_ptr_.Get();
   }
 
-  // Similar to Release, but ptr_ cannot be the default_value.
-  inline ::std::string* ReleaseNonDefault(const ::std::string* default_value,
-                                          Arena* arena) {
-    GOOGLE_DCHECK(!IsDefault(default_value));
-    ::std::string* released = NULL;
-    if (arena != NULL) {
-      // ptr_ is owned by the arena.
-      released = new ::std::string;
-      released->swap(*ptr_);
-    } else {
-      released = ptr_;
-    }
-    ptr_ = const_cast< ::std::string*>(default_value);
-    return released;
-  }
-
-  // UnsafeArenaRelease returns a ::std::string*, but it may be arena-owned
-  // (i.e.  have its destructor already registered) if arena != NULL. If the
-  // field was not set, this returns NULL. This method clears this field back to
-  // NULL state. Used to implement unsafe_arena_release_<field>() methods on
-  // generated classes.
-  inline ::std::string* UnsafeArenaRelease(const ::std::string* default_value,
-                                           Arena* /* arena */) {
-    if (ptr_ == default_value) {
-      return NULL;
-    }
-    ::std::string* released = ptr_;
-    ptr_ = const_cast< ::std::string*>(default_value);
-    return released;
-  }
-
-  // Takes a string that is heap-allocated, and takes ownership. The string's
-  // destructor is registered with the arena. Used to implement
+  // For fields with an empty default value.
+  std::string* Mutable(EmptyDefault, ::google::protobuf::Arena* arena);
+  // For fields with a non-empty default value.
+  std::string* Mutable(const LazyString& default_value, ::google::protobuf::Arena* arena);
+
+  // Release returns a std::string* instance that is heap-allocated and is not
+  // Own()'d by any arena. If the field is not set, this returns NULL. The
+  // caller retains ownership. Clears this field back to NULL state. Used to
+  // implement release_<field>() methods on generated classes.
+  std::string* Release(const std::string* default_value,
+                       ::google::protobuf::Arena* arena);
+  std::string* ReleaseNonDefault(const std::string* default_value,
+                                 ::google::protobuf::Arena* arena);
+
+  // Takes a std::string that is heap-allocated, and takes ownership. The
+  // std::string's destructor is registered with the arena. Used to implement
   // set_allocated_<field> in generated classes.
-  inline void SetAllocated(const ::std::string* default_value,
-                           ::std::string* value, Arena* arena) {
-    if (arena == NULL && ptr_ != default_value) {
-      Destroy(default_value, arena);
-    }
-    if (value != NULL) {
-      ptr_ = value;
-      if (arena != NULL) {
-        arena->Own(value);
-      }
-    } else {
-      ptr_ = const_cast< ::std::string*>(default_value);
-    }
-  }
-
-  // Takes a string that has lifetime equal to the arena's lifetime. The arena
-  // must be non-null. It is safe only to pass this method a value returned by
-  // UnsafeArenaRelease() on another field of a message in the same arena. Used
-  // to implement unsafe_arena_set_allocated_<field> in generated classes.
-  inline void UnsafeArenaSetAllocated(const ::std::string* default_value,
-                                      ::std::string* value,
-                                      Arena* /* arena */) {
-    if (value != NULL) {
-      ptr_ = value;
-    } else {
-      ptr_ = const_cast< ::std::string*>(default_value);
-    }
-  }
+  void SetAllocated(const std::string* default_value, std::string* value,
+                    ::google::protobuf::Arena* arena);
 
   // Swaps internal pointers. Arena-safety semantics: this is guarded by the
   // logic in Swap()/UnsafeArenaSwap() at the message level, so this method is
   // 'unsafe' if called directly.
-  PROTOBUF_ALWAYS_INLINE void Swap(ArenaStringPtr* other) {
-    std::swap(ptr_, other->ptr_);
-  }
-  PROTOBUF_ALWAYS_INLINE void Swap(ArenaStringPtr* other,
-                                   const ::std::string* default_value,
-                                   Arena* arena) {
-#ifndef NDEBUG
-    // For debug builds, we swap the contents of the string, rather than the
-    // string instances themselves.  This invalidates previously taken const
-    // references that are (per our documentation) invalidated by calling Swap()
-    // on the message.
-    //
-    // If both strings are the default_value, swapping is uninteresting.
-    // Otherwise, we use ArenaStringPtr::Mutable() to access the string, to
-    // ensure that we do not try to mutate default_value itself.
-    if (IsDefault(default_value) && other->IsDefault(default_value)) {
-      return;
-    }
-
-    ::std::string* this_ptr = Mutable(default_value, arena);
-    ::std::string* other_ptr = other->Mutable(default_value, arena);
-
-    this_ptr->swap(*other_ptr);
-#else
-    std::swap(ptr_, other->ptr_);
-    (void)default_value;
-    (void)arena;
-#endif
-  }
+  inline void Swap(ArenaStringPtr* other, const std::string* default_value,
+                   Arena* arena) PROTOBUF_ALWAYS_INLINE;
 
   // Frees storage (if not on an arena).
-  inline void Destroy(const ::std::string* default_value, Arena* arena) {
-    if (arena == NULL && ptr_ != default_value) {
-      delete ptr_;
-    }
-  }
+  void Destroy(const std::string* default_value, ::google::protobuf::Arena* arena);
+  void Destroy(EmptyDefault, ::google::protobuf::Arena* arena);
+  void Destroy(NonEmptyDefault, ::google::protobuf::Arena* arena);
 
-  // Clears content, but keeps allocated string if arena != NULL, to avoid the
-  // overhead of heap operations. After this returns, the content (as seen by
-  // the user) will always be the empty string. Assumes that |default_value|
-  // is an empty string.
-  inline void ClearToEmpty(const ::std::string* default_value,
-                           Arena* /* arena */) {
-    if (ptr_ == default_value) {
-      // Already set to default (which is empty) -- do nothing.
-    } else {
-      ptr_->clear();
-    }
-  }
+  // Clears content, but keeps allocated std::string, to avoid the overhead of
+  // heap operations. After this returns, the content (as seen by the user) will
+  // always be the empty std::string. Assumes that |default_value| is an empty
+  // std::string.
+  void ClearToEmpty();
 
-  // Clears content, assuming that the current value is not the empty string
-  // default.
-  inline void ClearNonDefaultToEmpty() { ptr_->clear(); }
-
-  // Clears content, but keeps allocated string if arena != NULL, to avoid the
-  // overhead of heap operations. After this returns, the content (as seen by
-  // the user) will always be equal to |default_value|.
-  inline void ClearToDefault(const ::std::string* default_value,
-                             Arena* /* arena */) {
-    if (ptr_ == default_value) {
-      // Already set to default -- do nothing.
-    } else {
-      // Have another allocated string -- rather than throwing this away and
-      // resetting ptr_ to the canonical default string instance, we just reuse
-      // this instance.
-      *ptr_ = *default_value;
-    }
-  }
+  // Clears content, assuming that the current value is not the empty
+  // string default.
+  void ClearNonDefaultToEmpty();
+
+  // Clears content, but keeps allocated std::string if arena != NULL, to avoid
+  // the overhead of heap operations. After this returns, the content (as seen
+  // by the user) will always be equal to |default_value|.
+  void ClearToDefault(const LazyString& default_value, ::google::protobuf::Arena* arena);
 
   // Called from generated code / reflection runtime only. Resets value to point
-  // to a default string pointer, with the semantics that this ArenaStringPtr
-  // does not own the pointed-to memory. Disregards initial value of ptr_ (so
-  // this is the *ONLY* safe method to call after construction or when
-  // reinitializing after becoming the active field in a oneof union).
-  inline void UnsafeSetDefault(const ::std::string* default_value) {
-    // Casting away 'const' is safe here: accessors ensure that ptr_ is only
-    // returned as a const if it is equal to default_value.
-    ptr_ = const_cast< ::std::string*>(default_value);
-  }
+  // to a default string pointer, with the semantics that this
+  // ArenaStringPtr does not own the pointed-to memory. Disregards initial value
+  // of ptr_ (so this is the *ONLY* safe method to call after construction or
+  // when reinitializing after becoming the active field in a oneof union).
+  inline void UnsafeSetDefault(const std::string* default_value);
+
+  // Returns a mutable pointer, but doesn't initialize the string to the
+  // default value.
+  std::string* MutableNoArenaNoDefault(const std::string* default_value);
+
+  // Get a mutable pointer with unspecified contents.
+  // Similar to `MutableNoArenaNoDefault`, but also handles the arena case.
+  // If the value was donated, the contents are discarded.
+  std::string* MutableNoCopy(const std::string* default_value,
+                             ::google::protobuf::Arena* arena);
 
   // Destroy the string. Assumes `arena == nullptr`.
-  inline void DestroyNoArena(const ::std::string* default_value) {
-    if (ptr_ != default_value) {
-      delete ptr_;
-    }
-  }
-
-  // Internal accessor used only at parse time to provide direct access to the
-  // raw pointer from the shared parse routine (in the non-arenas case). The
-  // parse routine does the string allocation in order to save code size in the
-  // generated parsing code.
-  inline ::std::string** UnsafeRawStringPointer() { return &ptr_; }
-
-  inline bool IsDefault(const ::std::string* default_value) const {
-    return ptr_ == default_value;
-  }
+  void DestroyNoArena(const std::string* default_value);
 
-  // Internal accessors!!!!
-  void UnsafeSetTaggedPointer(TaggedPtr< ::std::string> value) {
-    ptr_ = value.Get();
+  // Internal setter used only at parse time to directly set a donated string
+  // value.
+  void UnsafeSetTaggedPointer(TaggedPtr<std::string> value) {
+    tagged_ptr_ = value;
   }
   // Generated code only! An optimization, in certain cases the generated
-  // code is certain we can obtain a string with no default checks and
+  // code is certain we can obtain a std::string with no default checks and
   // tag tests.
-  ::std::string* UnsafeMutablePointer() { return ptr_; }
+  std::string* UnsafeMutablePointer() PROTOBUF_RETURNS_NONNULL;
+
+  inline bool IsDefault(const std::string* default_value) const {
+    // Relies on the fact that kPtrTagString == 0, so if IsString(), ptr_ is the
+    // actual std::string pointer (and if !IsString(), ptr_ will never be equal
+    // to any aligned |default_value| pointer). The key is that we want to avoid
+    // masking in the fastpath const-pointer Get() case for non-arena code.
+    return tagged_ptr_.UnsafeGet() == default_value;
+  }
 
  private:
-  ::std::string* ptr_;
+  TaggedPtr<std::string> tagged_ptr_;
+
+  bool IsDonatedString() const { return false; }
+
+  // Slow paths.
 
-  PROTOBUF_NOINLINE
-  void CreateInstance(Arena* arena, const ::std::string* initial_value) {
-    GOOGLE_DCHECK(initial_value != NULL);
-    // uses "new ::std::string" when arena is nullptr
-    ptr_ = Arena::Create< ::std::string>(arena, *initial_value);
+  // MutableSlow requires that !IsString() || IsDefault
+  // Variadic to support 0 args for EmptyDefault and 1 arg for LazyString.
+  template <typename... Lazy>
+  std::string* MutableSlow(::google::protobuf::Arena* arena, const Lazy&... lazy_default);
+
+};
+
+inline void ArenaStringPtr::UnsafeSetDefault(const std::string* value) {
+  tagged_ptr_.Set(const_cast<std::string*>(value));
+}
+
+inline void ArenaStringPtr::Swap(ArenaStringPtr* other,
+                                 const std::string* default_value,
+                                 Arena* arena) {
+#ifndef NDEBUG
+  // For debug builds, we swap the contents of the string, rather than the
+  // std::string instances themselves.  This invalidates previously taken const
+  // references that are (per our documentation) invalidated by calling Swap()
+  // on the message.
+  //
+  // If both strings are the default_value, swapping is uninteresting.
+  // Otherwise, we use ArenaStringPtr::Mutable() to access the std::string, to
+  // ensure that we do not try to mutate default_value itself.
+  if (IsDefault(default_value) && other->IsDefault(default_value)) {
+    return;
   }
-  PROTOBUF_NOINLINE
-  void CreateInstanceNoArena(const ::std::string* initial_value) {
-    GOOGLE_DCHECK(initial_value != NULL);
-    ptr_ = new ::std::string(*initial_value);
+
+  if (default_value == nullptr) {
+    // If we have non-empty default, then `default_value` is null and we can't
+    // call Mutable the same way. Just do the regular swap.
+    std::swap(tagged_ptr_, other->tagged_ptr_);
+  } else {
+    std::string* this_ptr = Mutable(EmptyDefault{}, arena);
+    std::string* other_ptr = other->Mutable(EmptyDefault{}, arena);
+
+    this_ptr->swap(*other_ptr);
   }
-};
+#else
+  std::swap(tagged_ptr_, other->tagged_ptr_);
+#endif
+}
+
+inline void ArenaStringPtr::ClearNonDefaultToEmpty() {
+  // Unconditionally mask away the tag.
+  tagged_ptr_.Get()->clear();
+}
+
+inline std::string* ArenaStringPtr::MutableNoArenaNoDefault(
+    const std::string* default_value) {
+  // VERY IMPORTANT for performance and code size: this will reduce to a member
+  // variable load, a pointer check (against |default_value|, in practice a
+  // static global) and a branch to the slowpath (which calls operator new and
+  // the ctor). DO NOT add any tagged-pointer operations here.
+  if (IsDefault(default_value)) {
+    std::string* new_string = new std::string();
+    tagged_ptr_.Set(new_string);
+    return new_string;
+  } else {
+    return UnsafeMutablePointer();
+  }
+}
+
+inline void ArenaStringPtr::DestroyNoArena(const std::string* default_value) {
+  if (!IsDefault(default_value)) {
+    delete UnsafeMutablePointer();
+  }
+}
+
+inline std::string* ArenaStringPtr::UnsafeMutablePointer() {
+  GOOGLE_DCHECK(!tagged_ptr_.IsTagged());
+  GOOGLE_DCHECK(tagged_ptr_.UnsafeGet() != nullptr);
+  return tagged_ptr_.UnsafeGet();
+}
+
 
 }  // namespace internal
 }  // namespace protobuf
 }  // namespace google
 
-
 #include <google/protobuf/port_undef.inc>
 
 #endif  // GOOGLE_PROTOBUF_ARENASTRING_H__

src/google/protobuf/arenastring_unittest.cc

@@ -28,8 +28,6 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-// Based on mvels@'s frankenstring.
-
 #include <google/protobuf/arenastring.h>
 
 #include <algorithm>
@@ -42,10 +40,14 @@
 #include <google/protobuf/stubs/common.h>
 #include <google/protobuf/io/coded_stream.h>
 #include <google/protobuf/io/zero_copy_stream_impl.h>
+#include <google/protobuf/generated_message_util.h>
 #include <gtest/gtest.h>
 #include <google/protobuf/stubs/strutil.h>
 
 
+// Must be included last.
+#include <google/protobuf/port_def.inc>
+
 namespace google {
 namespace protobuf {
 
@@ -53,82 +55,119 @@ using internal::ArenaStringPtr;
 
 static std::string WrapString(const char* value) { return value; }
 
+using EmptyDefault = ArenaStringPtr::EmptyDefault;
+
+const internal::LazyString nonempty_default{{{"default", 7}}, {nullptr}};
+
 // Test ArenaStringPtr with arena == NULL.
 TEST(ArenaStringPtrTest, ArenaStringPtrOnHeap) {
   ArenaStringPtr field;
-  std::string default_value = "default";
-  field.UnsafeSetDefault(&default_value);
-  EXPECT_EQ(std::string("default"), field.Get());
-  field.Set(&default_value, WrapString("Test short"), NULL);
+  const std::string* empty_default = &internal::GetEmptyString();
+  field.UnsafeSetDefault(empty_default);
+  EXPECT_EQ(std::string(""), field.Get());
+  field.Set(empty_default, WrapString("Test short"), NULL);
   EXPECT_EQ(std::string("Test short"), field.Get());
-  field.Set(&default_value, WrapString("Test long long long long value"), NULL);
+  field.Set(empty_default, WrapString("Test long long long long value"), NULL);
   EXPECT_EQ(std::string("Test long long long long value"), field.Get());
-  field.Set(&default_value, std::string(""), NULL);
-  field.Destroy(&default_value, NULL);
+  field.Set(empty_default, std::string(""), NULL);
+  field.Destroy(empty_default, NULL);
 
   ArenaStringPtr field2;
-  field2.UnsafeSetDefault(&default_value);
-  std::string* mut = field2.Mutable(&default_value, NULL);
-  EXPECT_EQ(mut, field2.Mutable(&default_value, NULL));
+  field2.UnsafeSetDefault(empty_default);
+  std::string* mut = field2.Mutable(EmptyDefault{}, NULL);
+  EXPECT_EQ(mut, field2.Mutable(EmptyDefault{}, NULL));
   EXPECT_EQ(mut, &field2.Get());
-  EXPECT_NE(&default_value, mut);
-  EXPECT_EQ(std::string("default"), *mut);
+  EXPECT_NE(empty_default, mut);
+  EXPECT_EQ(std::string(""), *mut);
   *mut = "Test long long long long value";  // ensure string allocates storage
   EXPECT_EQ(std::string("Test long long long long value"), field2.Get());
-  field2.Destroy(&default_value, NULL);
+  field2.Destroy(empty_default, NULL);
+
+  ArenaStringPtr field3;
+  field3.UnsafeSetDefault(nullptr);
+  mut = field3.Mutable(nonempty_default, NULL);
+  EXPECT_EQ(mut, field3.Mutable(nonempty_default, NULL));
+  EXPECT_EQ(mut, &field3.Get());
+  EXPECT_NE(nullptr, mut);
+  EXPECT_EQ(std::string("default"), *mut);
+  *mut = "Test long long long long value";  // ensure string allocates storage
+  EXPECT_EQ(std::string("Test long long long long value"), field3.Get());
+  field3.Destroy(nullptr, NULL);
 }
 
 TEST(ArenaStringPtrTest, ArenaStringPtrOnArena) {
   Arena arena;
   ArenaStringPtr field;
-  std::string default_value = "default";
-  field.UnsafeSetDefault(&default_value);
-  EXPECT_EQ(std::string("default"), field.Get());
-  field.Set(&default_value, WrapString("Test short"), &arena);
+  const std::string* empty_default = &internal::GetEmptyString();
+  field.UnsafeSetDefault(empty_default);
+  EXPECT_EQ(std::string(""), field.Get());
+  field.Set(empty_default, WrapString("Test short"), &arena);
   EXPECT_EQ(std::string("Test short"), field.Get());
-  field.Set(&default_value, WrapString("Test long long long long value"),
+  field.Set(empty_default, WrapString("Test long long long long value"),
             &arena);
   EXPECT_EQ(std::string("Test long long long long value"), field.Get());
-  field.Set(&default_value, std::string(""), &arena);
-  field.Destroy(&default_value, &arena);
+  field.Set(empty_default, std::string(""), &arena);
+  field.Destroy(empty_default, &arena);
 
   ArenaStringPtr field2;
-  field2.UnsafeSetDefault(&default_value);
-  std::string* mut = field2.Mutable(&default_value, &arena);
-  EXPECT_EQ(mut, field2.Mutable(&default_value, &arena));
+  field2.UnsafeSetDefault(empty_default);
+  std::string* mut = field2.Mutable(EmptyDefault{}, &arena);
+  EXPECT_EQ(mut, field2.Mutable(EmptyDefault{}, &arena));
   EXPECT_EQ(mut, &field2.Get());
-  EXPECT_NE(&default_value, mut);
-  EXPECT_EQ(std::string("default"), *mut);
+  EXPECT_NE(empty_default, mut);
+  EXPECT_EQ(std::string(""), *mut);
   *mut = "Test long long long long value";  // ensure string allocates storage
   EXPECT_EQ(std::string("Test long long long long value"), field2.Get());
-  field2.Destroy(&default_value, &arena);
+  field2.Destroy(empty_default, &arena);
+
+  ArenaStringPtr field3;
+  field3.UnsafeSetDefault(nullptr);
+  mut = field3.Mutable(nonempty_default, &arena);
+  EXPECT_EQ(mut, field3.Mutable(nonempty_default, &arena));
+  EXPECT_EQ(mut, &field3.Get());
+  EXPECT_NE(nullptr, mut);
+  EXPECT_EQ(std::string("default"), *mut);
+  *mut = "Test long long long long value";  // ensure string allocates storage
+  EXPECT_EQ(std::string("Test long long long long value"), field3.Get());
+  field3.Destroy(nullptr, &arena);
 }
 
 TEST(ArenaStringPtrTest, ArenaStringPtrOnArenaNoSSO) {
   Arena arena;
   ArenaStringPtr field;
-  std::string default_value = "default";
-  field.UnsafeSetDefault(&default_value);
-  EXPECT_EQ(std::string("default"), field.Get());
+  const std::string* empty_default = &internal::GetEmptyString();
+  field.UnsafeSetDefault(empty_default);
+  EXPECT_EQ(std::string(""), field.Get());
 
   // Avoid triggering the SSO optimization by setting the string to something
   // larger than the internal buffer.
-  field.Set(&default_value, WrapString("Test long long long long value"),
+  field.Set(empty_default, WrapString("Test long long long long value"),
             &arena);
   EXPECT_EQ(std::string("Test long long long long value"), field.Get());
-  field.Set(&default_value, std::string(""), &arena);
-  field.Destroy(&default_value, &arena);
+  field.Set(empty_default, std::string(""), &arena);
+  field.Destroy(empty_default, &arena);
 
   ArenaStringPtr field2;
-  field2.UnsafeSetDefault(&default_value);
-  std::string* mut = field2.Mutable(&default_value, &arena);
-  EXPECT_EQ(mut, field2.Mutable(&default_value, &arena));
+  field2.UnsafeSetDefault(empty_default);
+  std::string* mut = field2.Mutable(EmptyDefault{}, &arena);
+  EXPECT_EQ(mut, field2.Mutable(EmptyDefault{}, &arena));
   EXPECT_EQ(mut, &field2.Get());
-  EXPECT_NE(&default_value, mut);
-  EXPECT_EQ(std::string("default"), *mut);
+  EXPECT_NE(empty_default, mut);
+  EXPECT_EQ(std::string(""), *mut);
   *mut = "Test long long long long value";  // ensure string allocates storage
   EXPECT_EQ(std::string("Test long long long long value"), field2.Get());
-  field2.Destroy(&default_value, &arena);
+  field2.Destroy(empty_default, &arena);
+
+  ArenaStringPtr field3;
+  field3.UnsafeSetDefault(nullptr);
+  mut = field3.Mutable(nonempty_default, &arena);
+  EXPECT_EQ(mut, field3.Mutable(nonempty_default, &arena));
+  EXPECT_EQ(mut, &field3.Get());
+  EXPECT_NE(nullptr, mut);
+  EXPECT_EQ(std::string("default"), *mut);
+  *mut = "Test long long long long value";  // ensure string allocates storage
+  EXPECT_EQ(std::string("Test long long long long value"), field3.Get());
+  field3.Destroy(nullptr, &arena);
 }
 
 

src/google/protobuf/compiler/command_line_interface.cc

@@ -1233,6 +1233,7 @@ bool CommandLineInterface::AllowProto3Optional(
   return false;
 }
 
+
 bool CommandLineInterface::VerifyInputFilesInDescriptors(
     DescriptorDatabase* database) {
   for (const auto& input_file : input_files_) {
@@ -1251,6 +1252,7 @@ bool CommandLineInterface::VerifyInputFilesInDescriptors(
                 << std::endl;
       return false;
     }
+
   }
   return true;
 }
@@ -1301,6 +1303,7 @@ bool CommandLineInterface::ParseInputFiles(
       break;
     }
 
+
     // Enforce --direct_dependencies
     if (direct_dependencies_explicitly_set_) {
       bool indirect_imports = false;
@@ -1347,6 +1350,7 @@ void CommandLineInterface::Clear() {
   disallow_services_ = false;
   direct_dependencies_explicitly_set_ = false;
   allow_proto3_optional_ = false;
+  deterministic_output_ = false;
 }
 
 bool CommandLineInterface::MakeProtoProtoPathRelative(
@@ -1582,6 +1586,11 @@ CommandLineInterface::ParseArgumentStatus CommandLineInterface::ParseArguments(
               << std::endl;
     return PARSE_ARGUMENT_FAIL;
   }
+  if (mode_ != MODE_ENCODE && deterministic_output_) {
+    std::cerr << "Can only use --deterministic_output with --encode."
+              << std::endl;
+    return PARSE_ARGUMENT_FAIL;
+  }
   if (!dependency_out_name_.empty() && input_files_.size() > 1) {
     std::cerr
         << "Can only process one input file when using --dependency_out=FILE."
@@ -1650,7 +1659,8 @@ bool CommandLineInterface::ParseArgument(const char* arg, std::string* name,
       *name == "--include_imports" || *name == "--include_source_info" ||
       *name == "--version" || *name == "--decode_raw" ||
       *name == "--print_free_field_numbers" ||
-      *name == "--experimental_allow_proto3_optional") {
+      *name == "--experimental_allow_proto3_optional" ||
+      *name == "--deterministic_output") {
     // HACK:  These are the only flags that don't take a value.
     //   They probably should not be hard-coded like this but for now it's
     //   not worth doing better.
@@ -1857,6 +1867,7 @@ CommandLineInterface::InterpretArgument(const std::string& name,
   } else if (name == "--disallow_services") {
     disallow_services_ = true;
 
+
   } else if (name == "--experimental_allow_proto3_optional") {
     allow_proto3_optional_ = true;
 
@@ -1890,6 +1901,9 @@ CommandLineInterface::InterpretArgument(const std::string& name,
 
     codec_type_ = value;
 
+  } else if (name == "--deterministic_output") {
+    deterministic_output_ = true;
+
   } else if (name == "--error_format") {
     if (value == "gcc") {
       error_format_ = ERROR_FORMAT_GCC;
@@ -2032,6 +2046,12 @@ void CommandLineInterface::PrintHelpText() {
          "must\n"
          "                              be defined in PROTO_FILES or their "
          "imports.\n"
+         "  --deterministic_output      When using --encode, ensure map fields "
+         "are\n"
+         "                              deterministically ordered. Note that"
+         "this order is not\n"
+         "                              canonical, and changes across builds"
+         "or releases of protoc.\n"
          "  --decode=MESSAGE_TYPE       Read a binary message of the given "
          "type from\n"
          "                              standard input and write it in text "
@@ -2444,7 +2464,9 @@ bool CommandLineInterface::EncodeOrDecode(const DescriptorPool* pool) {
 
   if (mode_ == MODE_ENCODE) {
     // Output is binary.
-    if (!message->SerializePartialToZeroCopyStream(&out)) {
+    io::CodedOutputStream coded_out(&out);
+    coded_out.SetSerializationDeterministic(deterministic_output_);
+    if (!message->SerializePartialToCodedStream(&coded_out)) {
       std::cerr << "output: I/O error." << std::endl;
       return false;
     }

src/google/protobuf/compiler/command_line_interface.h

@@ -451,6 +451,9 @@ class PROTOC_EXPORT CommandLineInterface {
   // Was the --experimental_allow_proto3_optional flag used?
   bool allow_proto3_optional_ = false;
 
+  // When using --encode, this will be passed to SetSerializationDeterministic.
+  bool deterministic_output_ = false;
+
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(CommandLineInterface);
 };
 

src/google/protobuf/compiler/command_line_interface_unittest.cc

@@ -40,12 +40,14 @@
 #include <unistd.h>
 #endif
 #include <memory>
+#include <string>
 #include <vector>
 
 #include <google/protobuf/stubs/stringprintf.h>
 #include <google/protobuf/testing/file.h>
 #include <google/protobuf/testing/file.h>
 #include <google/protobuf/testing/file.h>
+#include <google/protobuf/any.pb.h>
 #include <google/protobuf/compiler/mock_code_generator.h>
 #include <google/protobuf/compiler/subprocess.h>
 #include <google/protobuf/compiler/code_generator.h>
@@ -59,10 +61,10 @@
 #include <google/protobuf/descriptor.h>
 #include <google/protobuf/testing/googletest.h>
 #include <gtest/gtest.h>
+#include <google/protobuf/stubs/strutil.h>
 #include <google/protobuf/stubs/substitute.h>
 #include <google/protobuf/io/io_win32.h>
 
-#include <google/protobuf/stubs/strutil.h>
 
 namespace google {
 namespace protobuf {
@@ -122,7 +124,7 @@ class CommandLineInterfaceTest : public testing::Test {
   void SwitchToTempDirectory() {
     File::ChangeWorkingDirectory(temp_directory_);
   }
-#else   // !PROTOBUF_OPENSOURCE
+#else  // !PROTOBUF_OPENSOURCE
   // TODO(teboring): Figure out how to change and get working directory in
   // google3.
 #endif  // !PROTOBUF_OPENSOURCE
@@ -680,6 +682,9 @@ TEST_F(CommandLineInterfaceTest, MultipleInputs_UnusedImport_DescriptorSetIn) {
       FileDescriptorProto::descriptor()->file();
   descriptor_file->CopyTo(file_descriptor_set.add_file());
 
+  FileDescriptorProto& any_proto = *file_descriptor_set.add_file();
+  google::protobuf::Any::descriptor()->file()->CopyTo(&any_proto);
+
   const FileDescriptor* custom_file =
       protobuf_unittest::AggregateMessage::descriptor()->file();
   FileDescriptorProto* file_descriptor_proto = file_descriptor_set.add_file();
@@ -1387,6 +1392,7 @@ TEST_F(CommandLineInterfaceTest, AllowServicesHasService) {
   ExpectGenerated("test_generator", "", "foo.proto", "Foo");
 }
 
+
 TEST_F(CommandLineInterfaceTest, DirectDependencies_Missing_EmptyList) {
   CreateTempFile("foo.proto",
                  "syntax = \"proto2\";\n"
@@ -2567,7 +2573,10 @@ class EncodeDecodeTest : public testing::TestWithParam<EncodeDecodeTestMode> {
   bool Run(const std::string& command, bool specify_proto_files = true) {
     std::vector<std::string> args;
     args.push_back("protoc");
-    SplitStringUsing(command, " ", &args);
+    for (StringPiece split_piece :
+         Split(command, " ", true)) {
+      args.push_back(std::string(split_piece));
+    }
     if (specify_proto_files) {
       switch (GetParam()) {
         case PROTO_PATH:
@@ -2726,6 +2735,32 @@ TEST_P(EncodeDecodeTest, ProtoParseError) {
       "net/proto2/internal/no_such_file.proto: No such file or directory\n");
 }
 
+TEST_P(EncodeDecodeTest, EncodeDeterministicOutput) {
+  RedirectStdinFromFile(TestUtil::GetTestDataPath(
+      "net/proto2/internal/"
+      "testdata/text_format_unittest_data_oneof_implemented.txt"));
+  std::string args;
+  if (GetParam() != DESCRIPTOR_SET_IN) {
+    args.append(
+        TestUtil::MaybeTranslatePath("net/proto2/internal/unittest.proto"));
+  }
+  EXPECT_TRUE(Run(
+      args + " --encode=protobuf_unittest.TestAllTypes --deterministic_output"));
+  ExpectStdoutMatchesBinaryFile(TestUtil::GetTestDataPath(
+      "net/proto2/internal/testdata/golden_message_oneof_implemented"));
+  ExpectStderrMatchesText("");
+}
+
+TEST_P(EncodeDecodeTest, DecodeDeterministicOutput) {
+  RedirectStdinFromFile(TestUtil::GetTestDataPath(
+      "net/proto2/internal/testdata/golden_message_oneof_implemented"));
+  EXPECT_FALSE(
+      Run(TestUtil::MaybeTranslatePath("net/proto2/internal/unittest.proto") +
+          " --decode=protobuf_unittest.TestAllTypes --deterministic_output"));
+  ExpectStderrMatchesText(
+      "Can only use --deterministic_output with --encode.\n");
+}
+
 INSTANTIATE_TEST_SUITE_P(FileDescriptorSetSource, EncodeDecodeTest,
                          testing::Values(PROTO_PATH, DESCRIPTOR_SET_IN));
 }  // anonymous namespace

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

@@ -164,10 +164,6 @@ class FieldGenerator {
     return false;
   }
 
-  // Generate code that allocates the fields's default instance.
-  virtual void GenerateDefaultInstanceAllocator(
-      io::Printer* /*printer*/) const {}
-
   // Generate lines to serialize this field directly to the array "target",
   // which are placed within the message's SerializeWithCachedSizesToArray()
   // method. This must also advance "target" past the written bytes.
@@ -178,11 +174,6 @@ class FieldGenerator {
   // are placed in the message's ByteSize() method.
   virtual void GenerateByteSize(io::Printer* printer) const = 0;
 
-  // Any tags about field layout decisions (such as inlining) to embed in the
-  // offset.
-  virtual uint32 CalculateFieldTag() const { return 0; }
-  virtual bool IsInlined() const { return false; }
-
   void SetHasBitIndex(int32 has_bit_index);
 
  protected:

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

@@ -941,7 +941,6 @@ void FileGenerator::GenerateInitForSCC(const SCC* scc,
     if (scc_analyzer_.GetSCC(message_generators_[i]->descriptor_) != scc) {
       continue;
     }
-    message_generators_[i]->GenerateFieldDefaultInstances(printer);
     format(
         "{\n"
         "  void* ptr = &$1$;\n"
@@ -1198,7 +1197,6 @@ void FileGenerator::GenerateForwardDeclarations(io::Printer* printer) {
       decls[Namespace(d, options_)].AddEnum(d);
   }
 
-
   {
     NamespaceOpener ns(format);
     for (const auto& pair : decls) {
@@ -1281,7 +1279,6 @@ void FileGenerator::GenerateLibraryIncludes(io::Printer* printer) {
   IncludeFile("net/proto2/public/arenastring.h", printer);
   IncludeFile("net/proto2/public/generated_message_table_driven.h", printer);
   IncludeFile("net/proto2/public/generated_message_util.h", printer);
-  IncludeFile("net/proto2/public/inlined_string_field.h", printer);
   IncludeFile("net/proto2/public/metadata_lite.h", printer);
 
   if (HasDescriptorMethods(file_, options_)) {

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

@@ -787,25 +787,6 @@ std::string SafeFunctionName(const Descriptor* descriptor,
   return function_name;
 }
 
-bool IsStringInlined(const FieldDescriptor* descriptor,
-                     const Options& options) {
-  if (options.opensource_runtime) return false;
-
-  // TODO(ckennelly): Handle inlining for any.proto.
-  if (IsAnyMessage(descriptor->containing_type(), options)) return false;
-  if (descriptor->containing_type()->options().map_entry()) return false;
-
-  // We rely on has bits to distinguish field presence for release_$name$.  When
-  // there is no hasbit, we cannot use the address of the string instance when
-  // the field has been inlined.
-  if (!HasHasbit(descriptor)) return false;
-
-  if (options.access_info_map) {
-    if (descriptor->is_required()) return true;
-  }
-  return false;
-}
-
 static bool HasLazyFields(const Descriptor* descriptor,
                           const Options& options) {
   for (int field_idx = 0; field_idx < descriptor->field_count(); field_idx++) {
@@ -1470,8 +1451,7 @@ class ParseLoopGenerator {
         GetOptimizeFor(field->file(), options_) != FileOptions::LITE_RUNTIME &&
         // For now only use arena string for strings with empty defaults.
         field->default_value_string().empty() &&
-        !IsStringInlined(field, options_) && !field->real_containing_oneof() &&
-        ctype == FieldOptions::STRING) {
+        !field->real_containing_oneof() && ctype == FieldOptions::STRING) {
       GenerateArenaString(field);
     } else {
       std::string name;

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

@@ -318,8 +318,6 @@ inline bool IsWeak(const FieldDescriptor* field, const Options& options) {
   return false;
 }
 
-bool IsStringInlined(const FieldDescriptor* descriptor, const Options& options);
-
 // For a string field, returns the effective ctype.  If the actual ctype is
 // not supported, returns the default of STRING.
 FieldOptions::CType EffectiveStringCType(const FieldDescriptor* field,
@@ -410,14 +408,6 @@ inline bool IsProto2MessageSet(const Descriptor* descriptor,
          descriptor->full_name() == "google.protobuf.bridge.MessageSet";
 }
 
-inline bool IsProto2MessageSetFile(const FileDescriptor* file,
-                                   const Options& options) {
-  return !options.opensource_runtime &&
-         options.enforce_mode != EnforceOptimizeMode::kLiteRuntime &&
-         !options.lite_implicit_weak_fields &&
-         file->name() == "net/proto2/bridge/proto/message_set.proto";
-}
-
 inline bool IsMapEntryMessage(const Descriptor* descriptor) {
   return descriptor->options().map_entry();
 }

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

@@ -1699,9 +1699,6 @@ uint32 CalcFieldNum(const FieldGenerator& generator,
   int type = field->type();
   if (type == FieldDescriptor::TYPE_STRING ||
       type == FieldDescriptor::TYPE_BYTES) {
-    if (generator.IsInlined()) {
-      type = internal::FieldMetadata::kInlinedType;
-    }
     // string field
     if (IsCord(field, options)) {
       type = internal::FieldMetadata::kCordType;
@@ -1902,13 +1899,6 @@ int MessageGenerator::GenerateFieldMetadata(io::Printer* printer) {
   return num_field_metadata;
 }
 
-void MessageGenerator::GenerateFieldDefaultInstances(io::Printer* printer) {
-  // Construct the default instances for all fields that need one.
-  for (auto field : FieldRange(descriptor_)) {
-    field_generators_.get(field).GenerateDefaultInstanceAllocator(printer);
-  }
-}
-
 void MessageGenerator::GenerateClassMethods(io::Printer* printer) {
   Formatter format(printer, variables_);
   if (IsMapEntryMessage(descriptor_)) {
@@ -2111,14 +2101,9 @@ size_t MessageGenerator::GenerateParseOffsets(io::Printer* printer) {
     }
 
     processing_type = static_cast<unsigned>(field->type());
-    const FieldGenerator& generator = field_generators_.get(field);
     if (field->type() == FieldDescriptor::TYPE_STRING) {
       switch (EffectiveStringCType(field, options_)) {
         case FieldOptions::STRING:
-          if (generator.IsInlined()) {
-            processing_type = internal::TYPE_STRING_INLINED;
-            break;
-          }
           break;
         case FieldOptions::CORD:
           processing_type = internal::TYPE_STRING_CORD;
@@ -2130,10 +2115,6 @@ size_t MessageGenerator::GenerateParseOffsets(io::Printer* printer) {
     } else if (field->type() == FieldDescriptor::TYPE_BYTES) {
       switch (EffectiveStringCType(field, options_)) {
         case FieldOptions::STRING:
-          if (generator.IsInlined()) {
-            processing_type = internal::TYPE_BYTES_INLINED;
-            break;
-          }
           break;
         case FieldOptions::CORD:
           processing_type = internal::TYPE_BYTES_CORD;
@@ -2317,11 +2298,6 @@ std::pair<size_t, size_t> MessageGenerator::GenerateOffsets(
       format("PROTOBUF_FIELD_OFFSET($classtype$, $1$_)", FieldName(field));
     }
 
-    uint32 tag = field_generators_.get(field).CalculateFieldTag();
-    if (tag != 0) {
-      format(" | $1$", tag);
-    }
-
     if (!IsFieldUsed(field, options_)) {
       format(" | 0x80000000u, // unused\n");
     } else {

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

@@ -82,9 +82,6 @@ class MessageGenerator {
 
   // Source file stuff.
 
-  // Generates code that creates default instances for fields.
-  void GenerateFieldDefaultInstances(io::Printer* printer);
-
   // Generate all non-inline methods for this class.
   void GenerateClassMethods(io::Printer* printer);
 

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

@@ -55,12 +55,31 @@ void SetStringVariables(const FieldDescriptor* descriptor,
       StrCat(descriptor->default_value_string().length());
   std::string default_variable_string = MakeDefaultName(descriptor);
   (*variables)["default_variable_name"] = default_variable_string;
-  (*variables)["default_variable"] =
+
+  if (!descriptor->default_value_string().empty()) {
+    (*variables)["lazy_variable"] =
+        QualifiedClassName(descriptor->containing_type(), options) +
+        "::" + default_variable_string;
+  }
+
+  (*variables)["default_string"] =
+      descriptor->default_value_string().empty()
+          ? "::" + (*variables)["proto_ns"] +
+                "::internal::GetEmptyStringAlreadyInited()"
+          : (*variables)["lazy_variable"] + ".get()";
+  (*variables)["init_value"] =
       descriptor->default_value_string().empty()
           ? "&::" + (*variables)["proto_ns"] +
                 "::internal::GetEmptyStringAlreadyInited()"
-          : "&" + QualifiedClassName(descriptor->containing_type(), options) +
-                "::" + default_variable_string + ".get()";
+          : "nullptr";
+  (*variables)["default_value_tag"] =
+      "::" + (*variables)["proto_ns"] + "::internal::ArenaStringPtr::" +
+      (descriptor->default_value_string().empty() ? "Empty" : "NonEmpty") +
+      "Default{}";
+  (*variables)["default_variable_or_tag"] =
+      (*variables)[descriptor->default_value_string().empty()
+                       ? "default_value_tag"
+                       : "lazy_variable"];
   (*variables)["pointer_type"] =
       descriptor->type() == FieldDescriptor::TYPE_BYTES ? "void" : "char";
   (*variables)["null_check"] = (*variables)["DCHK"] + "(value != nullptr);\n";
@@ -75,9 +94,6 @@ void SetStringVariables(const FieldDescriptor* descriptor,
   } else {
     (*variables)["string_piece"] = "::StringPiece";
   }
-
-  (*variables)["lite"] =
-      HasDescriptorMethods(descriptor->file(), options) ? "" : "Lite";
 }
 
 }  // namespace
@@ -86,9 +102,7 @@ void SetStringVariables(const FieldDescriptor* descriptor,
 
 StringFieldGenerator::StringFieldGenerator(const FieldDescriptor* descriptor,
                                            const Options& options)
-    : FieldGenerator(descriptor, options),
-      lite_(!HasDescriptorMethods(descriptor->file(), options)),
-      inlined_(IsStringInlined(descriptor, options)) {
+    : FieldGenerator(descriptor, options) {
   SetStringVariables(descriptor, &variables_, options);
 }
 
@@ -96,23 +110,15 @@ StringFieldGenerator::~StringFieldGenerator() {}
 
 void StringFieldGenerator::GeneratePrivateMembers(io::Printer* printer) const {
   Formatter format(printer, variables_);
-  if (inlined_) {
-    format("::$proto_ns$::internal::InlinedStringField $name$_;\n");
-  } else {
-    format("::$proto_ns$::internal::ArenaStringPtr $name$_;\n");
-  }
+  format("::$proto_ns$::internal::ArenaStringPtr $name$_;\n");
 }
 
 void StringFieldGenerator::GenerateStaticMembers(io::Printer* printer) const {
   Formatter format(printer, variables_);
   if (!descriptor_->default_value_string().empty()) {
-    // We make the default instance public, so it can be initialized by
-    // non-friend code.
     format(
-        "public:\n"
-        "static ::$proto_ns$::internal::ExplicitlyConstructed<std::string>"
-        " $default_variable_name$;\n"
-        "private:\n");
+        "static const ::$proto_ns$::internal::LazyString"
+        " $default_variable_name$;\n");
   }
 }
 
@@ -187,7 +193,13 @@ void StringFieldGenerator::GenerateInlineAccessorDefinitions(
   format(
       "inline const std::string& $classname$::$name$() const {\n"
       "$annotate_accessor$"
-      "  // @@protoc_insertion_point(field_get:$full_name$)\n"
+      "  // @@protoc_insertion_point(field_get:$full_name$)\n");
+  if (!descriptor_->default_value_string().empty()) {
+    format(
+        "  if ($name$_.IsDefault(nullptr)) return "
+        "$default_variable_name$.get();\n");
+  }
+  format(
       "  return _internal_$name$();\n"
       "}\n"
       "inline void $classname$::set_$name$(const std::string& value) {\n"
@@ -206,21 +218,20 @@ void StringFieldGenerator::GenerateInlineAccessorDefinitions(
       "inline void $classname$::_internal_set_$name$(const std::string& "
       "value) {\n"
       "  $set_hasbit$\n"
-      "  $name$_.Set$lite$($default_variable$, value, GetArena());\n"
+      "  $name$_.Set($default_value_tag$, value, GetArena());\n"
       "}\n"
       "inline void $classname$::set_$name$(std::string&& value) {\n"
       "$annotate_accessor$"
       "  $set_hasbit$\n"
-      "  $name$_.Set$lite$(\n"
-      "    $default_variable$, ::std::move(value), GetArena());\n"
+      "  $name$_.Set(\n"
+      "    $default_value_tag$, ::std::move(value), GetArena());\n"
       "  // @@protoc_insertion_point(field_set_rvalue:$full_name$)\n"
       "}\n"
       "inline void $classname$::set_$name$(const char* value) {\n"
       "$annotate_accessor$"
       "  $null_check$"
       "  $set_hasbit$\n"
-      "  $name$_.Set$lite$($default_variable$, $string_piece$(value),\n"
-      "              GetArena());\n"
+      "  $name$_.Set($default_value_tag$, $string_piece$(value), GetArena());\n"
       "  // @@protoc_insertion_point(field_set_char:$full_name$)\n"
       "}\n");
   if (!options_.opensource_runtime) {
@@ -228,7 +239,7 @@ void StringFieldGenerator::GenerateInlineAccessorDefinitions(
         "inline void $classname$::set_$name$(::StringPiece value) {\n"
         "$annotate_accessor$"
         "  $set_hasbit$\n"
-        "  $name$_.Set$lite$($default_variable$, value,GetArena());\n"
+        "  $name$_.Set($default_value_tag$, value,GetArena());\n"
         "  // @@protoc_insertion_point(field_set_string_piece:$full_name$)\n"
         "}\n");
   }
@@ -238,13 +249,13 @@ void StringFieldGenerator::GenerateInlineAccessorDefinitions(
       "    size_t size) {\n"
       "$annotate_accessor$"
       "  $set_hasbit$\n"
-      "  $name$_.Set$lite$($default_variable$, $string_piece$(\n"
+      "  $name$_.Set($default_value_tag$, $string_piece$(\n"
       "      reinterpret_cast<const char*>(value), size), GetArena());\n"
       "  // @@protoc_insertion_point(field_set_pointer:$full_name$)\n"
       "}\n"
       "inline std::string* $classname$::_internal_mutable_$name$() {\n"
       "  $set_hasbit$\n"
-      "  return $name$_.Mutable($default_variable$, GetArena());\n"
+      "  return $name$_.Mutable($default_variable_or_tag$, GetArena());\n"
       "}\n"
       "inline std::string* $classname$::$release_name$() {\n"
       "$annotate_accessor$"
@@ -256,10 +267,9 @@ void StringFieldGenerator::GenerateInlineAccessorDefinitions(
         "    return nullptr;\n"
         "  }\n"
         "  $clear_hasbit$\n"
-        "  return $name$_.ReleaseNonDefault("
-        "$default_variable$, GetArena());\n");
+        "  return $name$_.ReleaseNonDefault($init_value$, GetArena());\n");
   } else {
-    format("  return $name$_.Release($default_variable$, GetArena());\n");
+    format("  return $name$_.Release($init_value$, GetArena());\n");
   }
 
   format(
@@ -271,7 +281,7 @@ void StringFieldGenerator::GenerateInlineAccessorDefinitions(
       "  } else {\n"
       "    $clear_hasbit$\n"
       "  }\n"
-      "  $name$_.SetAllocated($default_variable$, $name$,\n"
+      "  $name$_.SetAllocated($init_value$, $name$,\n"
       "      GetArena());\n"
       "  // @@protoc_insertion_point(field_set_allocated:$full_name$)\n"
       "}\n");
@@ -281,23 +291,19 @@ void StringFieldGenerator::GenerateNonInlineAccessorDefinitions(
     io::Printer* printer) const {
   Formatter format(printer, variables_);
   if (!descriptor_->default_value_string().empty()) {
-    // Initialized in GenerateDefaultInstanceAllocator.
     format(
-        "::$proto_ns$::internal::ExplicitlyConstructed<std::string> "
-        "$classname$::$default_variable_name$;\n");
+        "const ::$proto_ns$::internal::LazyString "
+        "$classname$::$default_variable_name$"
+        "{{{$default$, $default_length$}}, {nullptr}};\n");
   }
 }
 
 void StringFieldGenerator::GenerateClearingCode(io::Printer* printer) const {
   Formatter format(printer, variables_);
-  // 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 (descriptor_->default_value_string().empty()) {
-    format("$name$_.ClearToEmpty($default_variable$, GetArena());\n");
+    format("$name$_.ClearToEmpty();\n");
   } else {
-    format("$name$_.ClearToDefault($default_variable$, GetArena());\n");
+    format("$name$_.ClearToDefault($lazy_variable$, GetArena());\n");
   }
 }
 
@@ -311,31 +317,19 @@ void StringFieldGenerator::GenerateMessageClearingCode(
 
   // If we have a hasbit, then the Clear() method of the protocol buffer
   // will have checked that this field is set.  If so, we can avoid redundant
-  // checks against default_variable.
+  // checks against the default variable.
   const bool must_be_present = HasHasbit(descriptor_);
 
-  if (inlined_ && must_be_present) {
-    // Calling mutable_$name$() gives us a string reference and sets the has bit
-    // for $name$ (in proto2).  We may get here when the string field is inlined
-    // but the string's contents have not been changed by the user, so we cannot
-    // make an assertion about the contents of the string and could never make
-    // an assertion about the string instance.
-    //
-    // For non-inlined strings, we distinguish from non-default by comparing
-    // instances, rather than contents.
-    format("$DCHK$(!$name$_.IsDefault($default_variable$));\n");
-  }
-
   if (descriptor_->default_value_string().empty()) {
     if (must_be_present) {
       format("$name$_.ClearNonDefaultToEmpty();\n");
     } else {
-      format("$name$_.ClearToEmpty($default_variable$, GetArena());\n");
+      format("$name$_.ClearToEmpty();\n");
     }
   } else {
     // Clear to a non-empty default is more involved, as we try to use the
     // Arena if one is present and may need to reallocate the string.
-    format("$name$_.ClearToDefault($default_variable$, GetArena());\n");
+    format("$name$_.ClearToDefault($lazy_variable$, GetArena());\n ");
   }
 }
 
@@ -347,23 +341,12 @@ void StringFieldGenerator::GenerateMergingCode(io::Printer* printer) const {
 
 void StringFieldGenerator::GenerateSwappingCode(io::Printer* printer) const {
   Formatter format(printer, variables_);
-  if (inlined_) {
-    format("$name$_.Swap(&other->$name$_);\n");
-  } else {
-    format("$name$_.Swap(&other->$name$_, $default_variable$, GetArena());\n");
-  }
+  format("$name$_.Swap(&other->$name$_, $init_value$, GetArena());\n");
 }
 
 void StringFieldGenerator::GenerateConstructorCode(io::Printer* printer) const {
   Formatter format(printer, variables_);
-  // TODO(ckennelly): Construct non-empty strings as part of the initializer
-  // list.
-  if (inlined_ && descriptor_->default_value_string().empty()) {
-    // Automatic initialization will construct the string.
-    return;
-  }
-
-  format("$name$_.UnsafeSetDefault($default_variable$);\n");
+  format("$name$_.UnsafeSetDefault($init_value$);\n");
 }
 
 void StringFieldGenerator::GenerateCopyConstructorCode(
@@ -381,7 +364,7 @@ void StringFieldGenerator::GenerateCopyConstructorCode(
 
   // TODO(gpike): improve this
   format(
-      "$name$_.Set$lite$($default_variable$, from._internal_$name$(),\n"
+      "$name$_.Set($default_value_tag$, from._internal_$name$(), \n"
       "  GetArena());\n");
 
   format.Outdent();
@@ -390,40 +373,7 @@ void StringFieldGenerator::GenerateCopyConstructorCode(
 
 void StringFieldGenerator::GenerateDestructorCode(io::Printer* printer) const {
   Formatter format(printer, variables_);
-  if (inlined_) {
-    // The destructor is automatically invoked.
-    return;
-  }
-
-  format("$name$_.DestroyNoArena($default_variable$);\n");
-}
-
-bool StringFieldGenerator::GenerateArenaDestructorCode(
-    io::Printer* printer) const {
-  Formatter format(printer, variables_);
-  if (!inlined_) {
-    return false;
-  }
-
-  format("_this->$name$_.DestroyNoArena($default_variable$);\n");
-  return true;
-}
-
-void StringFieldGenerator::GenerateDefaultInstanceAllocator(
-    io::Printer* printer) const {
-  Formatter format(printer, variables_);
-  if (!descriptor_->default_value_string().empty()) {
-    format(
-        "$ns$::$classname$::$default_variable_name$.DefaultConstruct();\n"
-        "*$ns$::$classname$::$default_variable_name$.get_mutable() = "
-        "std::string($default$, $default_length$);\n"
-        "::$proto_ns$::internal::OnShutdownDestroyString(\n"
-        "    $ns$::$classname$::$default_variable_name$.get_mutable());\n");
-  }
-}
-
-bool StringFieldGenerator::MergeFromCodedStreamNeedsArena() const {
-  return !lite_ && !inlined_ && !options_.opensource_runtime;
+  format("$name$_.DestroyNoArena($init_value$);\n");
 }
 
 void StringFieldGenerator::GenerateSerializeWithCachedSizesToArray(
@@ -449,17 +399,11 @@ void StringFieldGenerator::GenerateByteSize(io::Printer* printer) const {
       "    this->_internal_$name$());\n");
 }
 
-uint32 StringFieldGenerator::CalculateFieldTag() const {
-  return inlined_ ? 1 : 0;
-}
-
 // ===================================================================
 
 StringOneofFieldGenerator::StringOneofFieldGenerator(
     const FieldDescriptor* descriptor, const Options& options)
     : StringFieldGenerator(descriptor, options) {
-  inlined_ = false;
-
   SetCommonOneofFieldVariables(descriptor, &variables_);
   variables_["field_name"] = UnderscoresToCamelCase(descriptor->name(), true);
   variables_["oneof_index"] =
@@ -491,16 +435,16 @@ void StringOneofFieldGenerator::GenerateInlineAccessorDefinitions(
       "  if (_internal_has_$name$()) {\n"
       "    return $field_member$.Get();\n"
       "  }\n"
-      "  return *$default_variable$;\n"
+      "  return $default_string$;\n"
       "}\n"
       "inline void $classname$::_internal_set_$name$(const std::string& "
       "value) {\n"
       "  if (!_internal_has_$name$()) {\n"
       "    clear_$oneof_name$();\n"
       "    set_has_$name$();\n"
-      "    $field_member$.UnsafeSetDefault($default_variable$);\n"
+      "    $field_member$.UnsafeSetDefault($init_value$);\n"
       "  }\n"
-      "  $field_member$.Set$lite$($default_variable$, value, GetArena());\n"
+      "  $field_member$.Set($default_value_tag$, value, GetArena());\n"
       "}\n"
       "inline void $classname$::set_$name$(std::string&& value) {\n"
       "$annotate_accessor$"
@@ -508,10 +452,10 @@ void StringOneofFieldGenerator::GenerateInlineAccessorDefinitions(
       "  if (!_internal_has_$name$()) {\n"
       "    clear_$oneof_name$();\n"
       "    set_has_$name$();\n"
-      "    $field_member$.UnsafeSetDefault($default_variable$);\n"
+      "    $field_member$.UnsafeSetDefault($init_value$);\n"
       "  }\n"
-      "  $field_member$.Set$lite$(\n"
-      "    $default_variable$, ::std::move(value), GetArena());\n"
+      "  $field_member$.Set(\n"
+      "    $default_value_tag$, ::std::move(value), GetArena());\n"
       "  // @@protoc_insertion_point(field_set_rvalue:$full_name$)\n"
       "}\n"
       "inline void $classname$::set_$name$(const char* value) {\n"
@@ -520,9 +464,9 @@ void StringOneofFieldGenerator::GenerateInlineAccessorDefinitions(
       "  if (!_internal_has_$name$()) {\n"
       "    clear_$oneof_name$();\n"
       "    set_has_$name$();\n"
-      "    $field_member$.UnsafeSetDefault($default_variable$);\n"
+      "    $field_member$.UnsafeSetDefault($init_value$);\n"
       "  }\n"
-      "  $field_member$.Set$lite$($default_variable$,\n"
+      "  $field_member$.Set($default_value_tag$,\n"
       "      $string_piece$(value), GetArena());\n"
       "  // @@protoc_insertion_point(field_set_char:$full_name$)\n"
       "}\n");
@@ -533,10 +477,9 @@ void StringOneofFieldGenerator::GenerateInlineAccessorDefinitions(
         "  if (!_internal_has_$name$()) {\n"
         "    clear_$oneof_name$();\n"
         "    set_has_$name$();\n"
-        "    $field_member$.UnsafeSetDefault($default_variable$);\n"
+        "    $field_member$.UnsafeSetDefault($init_value$);\n"
         "  }\n"
-        "  $field_member$.Set$lite$($default_variable$, value,\n"
-        "      GetArena());\n"
+        "  $field_member$.Set($default_value_tag$, value, GetArena());\n"
         "  // @@protoc_insertion_point(field_set_string_piece:$full_name$)\n"
         "}\n");
   }
@@ -548,10 +491,10 @@ void StringOneofFieldGenerator::GenerateInlineAccessorDefinitions(
       "  if (!_internal_has_$name$()) {\n"
       "    clear_$oneof_name$();\n"
       "    set_has_$name$();\n"
-      "    $field_member$.UnsafeSetDefault($default_variable$);\n"
+      "    $field_member$.UnsafeSetDefault($init_value$);\n"
       "  }\n"
-      "  $field_member$.Set$lite$(\n"
-      "      $default_variable$, $string_piece$(\n"
+      "  $field_member$.Set(\n"
+      "      $default_value_tag$, $string_piece$(\n"
       "      reinterpret_cast<const char*>(value), size),\n"
       "      GetArena());\n"
       "  // @@protoc_insertion_point(field_set_pointer:$full_name$)\n"
@@ -560,16 +503,17 @@ void StringOneofFieldGenerator::GenerateInlineAccessorDefinitions(
       "  if (!_internal_has_$name$()) {\n"
       "    clear_$oneof_name$();\n"
       "    set_has_$name$();\n"
-      "    $field_member$.UnsafeSetDefault($default_variable$);\n"
+      "    $field_member$.UnsafeSetDefault($init_value$);\n"
       "  }\n"
-      "  return $field_member$.Mutable($default_variable$, GetArena());\n"
+      "  return $field_member$.Mutable(\n"
+      "      $default_variable_or_tag$, GetArena());\n"
       "}\n"
       "inline std::string* $classname$::$release_name$() {\n"
       "$annotate_accessor$"
       "  // @@protoc_insertion_point(field_release:$full_name$)\n"
       "  if (_internal_has_$name$()) {\n"
       "    clear_has_$oneof_name$();\n"
-      "    return $field_member$.Release($default_variable$, GetArena());\n"
+      "    return $field_member$.ReleaseNonDefault($init_value$, GetArena());\n"
       "  } else {\n"
       "    return nullptr;\n"
       "  }\n"
@@ -594,7 +538,7 @@ void StringOneofFieldGenerator::GenerateInlineAccessorDefinitions(
 void StringOneofFieldGenerator::GenerateClearingCode(
     io::Printer* printer) const {
   Formatter format(printer, variables_);
-  format("$field_member$.Destroy($default_variable$, GetArena());\n");
+  format("$field_member$.Destroy($default_value_tag$, GetArena());\n");
 }
 
 void StringOneofFieldGenerator::GenerateMessageClearingCode(
@@ -609,10 +553,7 @@ void StringOneofFieldGenerator::GenerateSwappingCode(
 
 void StringOneofFieldGenerator::GenerateConstructorCode(
     io::Printer* printer) const {
-  Formatter format(printer, variables_);
-  format(
-      "$ns$::_$classname$_default_instance_.$name$_.UnsafeSetDefault(\n"
-      "    $default_variable$);\n");
+  // Nothing required here.
 }
 
 // ===================================================================

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

@@ -63,18 +63,8 @@ class StringFieldGenerator : public FieldGenerator {
   void GenerateConstructorCode(io::Printer* printer) const;
   void GenerateCopyConstructorCode(io::Printer* printer) const;
   void GenerateDestructorCode(io::Printer* printer) const;
-  bool GenerateArenaDestructorCode(io::Printer* printer) const;
-  void GenerateDefaultInstanceAllocator(io::Printer* printer) const;
   void GenerateSerializeWithCachedSizesToArray(io::Printer* printer) const;
   void GenerateByteSize(io::Printer* printer) const;
-  uint32 CalculateFieldTag() const;
-  bool IsInlined() const { return inlined_; }
-
-  bool MergeFromCodedStreamNeedsArena() const;
-
- protected:
-  const bool lite_;
-  bool inlined_;
 
  private:
   GOOGLE_DISALLOW_EVIL_CONSTRUCTORS(StringFieldGenerator);

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

@@ -77,9 +77,10 @@ void EnumGenerator::Generate(io::Printer* printer) {
   WriteEnumDocComment(printer, descriptor_);
   MaybePrintGeneratedAnnotation(context_, printer, descriptor_, immutable_api_);
   printer->Print(
-      "public enum $classname$\n"
+      "$deprecation$public enum $classname$\n"
       "    implements com.google.protobuf.ProtocolMessageEnum {\n",
-      "classname", descriptor_->name());
+      "classname", descriptor_->name(), "deprecation",
+      descriptor_->options().deprecated() ? "@java.lang.Deprecated " : "");
   printer->Annotate("classname", descriptor_);
   printer->Indent();
 

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

@@ -81,7 +81,7 @@ void SetEnumVariables(const FieldDescriptor* descriptor, int messageBitIndex,
   // with v2.5.0/v2.6.1, and remove the @SuppressWarnings annotations.
   (*variables)["for_number"] = "valueOf";
 
-  if (SupportFieldPresence(descriptor)) {
+  if (HasHasbit(descriptor)) {
     // For singular messages and builders, one bit is used for the hasField bit.
     (*variables)["get_has_field_bit_message"] = GenerateGetBit(messageBitIndex);
     (*variables)["get_has_field_bit_builder"] = GenerateGetBit(builderBitIndex);
@@ -145,7 +145,7 @@ ImmutableEnumFieldGenerator::ImmutableEnumFieldGenerator(
 ImmutableEnumFieldGenerator::~ImmutableEnumFieldGenerator() {}
 
 int ImmutableEnumFieldGenerator::GetNumBitsForMessage() const {
-  return SupportFieldPresence(descriptor_) ? 1 : 0;
+  return HasHasbit(descriptor_) ? 1 : 0;
 }
 
 int ImmutableEnumFieldGenerator::GetNumBitsForBuilder() const {

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

@@ -83,7 +83,7 @@ void SetEnumVariables(const FieldDescriptor* descriptor, int messageBitIndex,
       descriptor->options().deprecated() ? "@java.lang.Deprecated " : "";
   (*variables)["required"] = descriptor->is_required() ? "true" : "false";
 
-  if (SupportFieldPresence(descriptor)) {
+  if (HasHasbit(descriptor)) {
     // For singular messages and builders, one bit is used for the hasField bit.
     (*variables)["get_has_field_bit_message"] = GenerateGetBit(messageBitIndex);
 
@@ -137,7 +137,7 @@ ImmutableEnumFieldLiteGenerator::ImmutableEnumFieldLiteGenerator(
 ImmutableEnumFieldLiteGenerator::~ImmutableEnumFieldLiteGenerator() {}
 
 int ImmutableEnumFieldLiteGenerator::GetNumBitsForMessage() const {
-  return SupportFieldPresence(descriptor_) ? 1 : 0;
+  return HasHasbit(descriptor_) ? 1 : 0;
 }
 
 void ImmutableEnumFieldLiteGenerator::GenerateInterfaceMembers(

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

@@ -78,9 +78,10 @@ void EnumLiteGenerator::Generate(io::Printer* printer) {
   WriteEnumDocComment(printer, descriptor_);
   MaybePrintGeneratedAnnotation(context_, printer, descriptor_, immutable_api_);
   printer->Print(
-      "public enum $classname$\n"
+      "$deprecation$public enum $classname$\n"
       "    implements com.google.protobuf.Internal.EnumLite {\n",
-      "classname", descriptor_->name());
+      "classname", descriptor_->name(), "deprecation",
+      descriptor_->options().deprecated() ? "@java.lang.Deprecated " : "");
   printer->Annotate("classname", descriptor_);
   printer->Indent();
 

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

@@ -76,7 +76,6 @@ struct FieldDescriptorCompare {
 typedef std::set<const FieldDescriptor*, FieldDescriptorCompare>
     FieldDescriptorSet;
 
-
 // Recursively searches the given message to collect extensions.
 // Returns true if all the extensions can be recognized. The extensions will be
 // appended in to the extensions parameter.
@@ -86,9 +85,7 @@ bool CollectExtensions(const Message& message, FieldDescriptorSet* extensions) {
   const Reflection* reflection = message.GetReflection();
 
   // There are unknown fields that could be extensions, thus this call fails.
-  UnknownFieldSet unknown_fields;
-  unknown_fields.MergeFrom(reflection->GetUnknownFields(message));
-  if (unknown_fields.field_count() > 0) return false;
+  if (reflection->GetUnknownFields(message).field_count() > 0) return false;
 
   std::vector<const FieldDescriptor*> fields;
   reflection->ListFields(message, &fields);
@@ -390,6 +387,7 @@ void FileGenerator::Generate(io::Printer* printer) {
   printer->Print("}\n");
 }
 
+
 void FileGenerator::GenerateDescriptorInitializationCodeForImmutable(
     io::Printer* printer) {
   printer->Print(

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

@@ -78,6 +78,7 @@ class FileGenerator {
 
   void Generate(io::Printer* printer);
 
+
   // If we aren't putting everything into one file, this will write all the
   // files other than the outer file (i.e. one for each message, enum, and
   // service type).

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

@@ -1355,7 +1355,6 @@ void ImmutableMessageGenerator::GenerateInitializers(io::Printer* printer) {
   }
 }
 
-
 void ImmutableMessageGenerator::GenerateAnyMethods(io::Printer* printer) {
   printer->Print(
       "private static String getTypeUrl(\n"

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

@@ -160,7 +160,14 @@ std::string ClassNameResolver::GetFileImmutableClassName(
 
 std::string ClassNameResolver::GetFileClassName(const FileDescriptor* file,
                                                 bool immutable) {
-  if (immutable) {
+  return GetFileClassName(file, immutable, false);
+}
+
+std::string ClassNameResolver::GetFileClassName(const FileDescriptor* file,
+                                                bool immutable, bool kotlin) {
+  if (kotlin) {
+    return GetFileImmutableClassName(file) + "Kt";
+  } else if (immutable) {
     return GetFileImmutableClassName(file);
   } else {
     return "Mutable" + GetFileImmutableClassName(file);
@@ -200,9 +207,14 @@ std::string ClassNameResolver::GetDescriptorClassName(
 
 std::string ClassNameResolver::GetClassName(const FileDescriptor* descriptor,
                                             bool immutable) {
+  return GetClassName(descriptor, immutable, false);
+}
+
+std::string ClassNameResolver::GetClassName(const FileDescriptor* descriptor,
+                                            bool immutable, bool kotlin) {
   std::string result = FileJavaPackage(descriptor, immutable);
   if (!result.empty()) result += '.';
-  result += GetFileClassName(descriptor, immutable);
+  result += GetFileClassName(descriptor, immutable, kotlin);
   return result;
 }
 
@@ -211,50 +223,79 @@ std::string ClassNameResolver::GetClassName(const FileDescriptor* descriptor,
 std::string ClassNameResolver::GetClassFullName(
     const std::string& name_without_package, const FileDescriptor* file,
     bool immutable, bool is_own_file) {
+  return GetClassFullName(name_without_package, file, immutable, is_own_file,
+                          false);
+}
+
+std::string ClassNameResolver::GetClassFullName(
+    const std::string& name_without_package, const FileDescriptor* file,
+    bool immutable, bool is_own_file, bool kotlin) {
   std::string result;
   if (is_own_file) {
     result = FileJavaPackage(file, immutable);
   } else {
-    result = GetClassName(file, immutable);
+    result = GetClassName(file, immutable, kotlin);
   }
   if (!result.empty()) {
     result += '.';
   }
   result += name_without_package;
+  if (kotlin) result += "Kt";
   return result;
 }
 
 std::string ClassNameResolver::GetClassName(const Descriptor* descriptor,
                                             bool immutable) {
-  return GetClassFullName(ClassNameWithoutPackage(descriptor, immutable),
-                          descriptor->file(), immutable,
-                          MultipleJavaFiles(descriptor->file(), immutable));
+  return GetClassName(descriptor, immutable, false);
+}
+
+std::string ClassNameResolver::GetClassName(const Descriptor* descriptor,
+                                            bool immutable, bool kotlin) {
+  return GetClassFullName(
+      ClassNameWithoutPackage(descriptor, immutable), descriptor->file(),
+      immutable, MultipleJavaFiles(descriptor->file(), immutable), kotlin);
 }
 
 std::string ClassNameResolver::GetClassName(const EnumDescriptor* descriptor,
                                             bool immutable) {
-  return GetClassFullName(ClassNameWithoutPackage(descriptor, immutable),
-                          descriptor->file(), immutable,
-                          MultipleJavaFiles(descriptor->file(), immutable));
+  return GetClassName(descriptor, immutable, false);
+}
+
+std::string ClassNameResolver::GetClassName(const EnumDescriptor* descriptor,
+                                            bool immutable, bool kotlin) {
+  return GetClassFullName(
+      ClassNameWithoutPackage(descriptor, immutable), descriptor->file(),
+      immutable, MultipleJavaFiles(descriptor->file(), immutable), kotlin);
 }
 
 std::string ClassNameResolver::GetClassName(const ServiceDescriptor* descriptor,
                                             bool immutable) {
+  return GetClassName(descriptor, immutable, false);
+}
+
+std::string ClassNameResolver::GetClassName(const ServiceDescriptor* descriptor,
+                                            bool immutable, bool kotlin) {
   return GetClassFullName(ClassNameWithoutPackage(descriptor, immutable),
                           descriptor->file(), immutable,
-                          IsOwnFile(descriptor, immutable));
+                          IsOwnFile(descriptor, immutable), kotlin);
 }
 
 // Get the Java Class style full name of a message.
 std::string ClassNameResolver::GetJavaClassFullName(
     const std::string& name_without_package, const FileDescriptor* file,
     bool immutable) {
+  return GetJavaClassFullName(name_without_package, file, immutable, false);
+}
+
+std::string ClassNameResolver::GetJavaClassFullName(
+    const std::string& name_without_package, const FileDescriptor* file,
+    bool immutable, bool kotlin) {
   std::string result;
   if (MultipleJavaFiles(file, immutable)) {
     result = FileJavaPackage(file, immutable);
     if (!result.empty()) result += '.';
   } else {
-    result = GetClassName(file, immutable);
+    result = GetClassName(file, immutable, kotlin);
     if (!result.empty()) result += '$';
   }
   result += StringReplace(name_without_package, ".", "$", true);
@@ -263,7 +304,12 @@ std::string ClassNameResolver::GetJavaClassFullName(
 
 std::string ClassNameResolver::GetExtensionIdentifierName(
     const FieldDescriptor* descriptor, bool immutable) {
-  return GetClassName(descriptor->containing_type(), immutable) + "." +
+  return GetExtensionIdentifierName(descriptor, immutable, false);
+}
+
+std::string ClassNameResolver::GetExtensionIdentifierName(
+    const FieldDescriptor* descriptor, bool immutable, bool kotlin) {
+  return GetClassName(descriptor->containing_type(), immutable, kotlin) + "." +
          descriptor->name();
 }