Update protobuf to 3.16.0

[pyup-bot]

This PR updates protobuf from 3.6.1 to 3.16.0.

Changelog

3.16.0

C++
* The ::pb namespace is no longer exposed due to conflicts.
* Allow MessageDifferencer::TreatAsSet() (and friends) to override previous
 calls instead of crashing.
* Reduce the size of generated proto headers for protos with `string` or
 `bytes` fields.
* Move arena() operation on uncommon path to out-of-line routine
* For iterator-pair function parameter types, take both iterators by value.
* Code-space savings and perhaps some modest performance improvements in
 RepeatedPtrField.
* Eliminate nullptr check from every tag parse.
* Remove unused _$name$_cached_byte_size_ fields.
* Serialize extension ranges together when not broken by a proto field in the
 middle.
* Do out-of-line allocation and deallocation of string object in ArenaString.
* Streamline ParseContext::ParseMessage<T> to avoid code bloat and improve
 performance.
* New member functions RepeatedField::Assign, RepeatedPtrField::{Add, Assign}.
* Fix undefined behavior warning due to innocuous uninitialization of value
 on an error path.
* Avoid expensive inlined code space for encoding message length for messages
 >= 128 bytes and instead do a procedure call to a shared out-of-line routine.
* util::DefaultFieldComparator will be final in a future version of protobuf.
 Subclasses should inherit from SimpleFieldComparator instead.

Java:
* Detect invalid overflow of byteLimit and return InvalidProtocolBufferException as documented.
* Exceptions thrown while reading from an InputStream in parseFrom are now
 included as causes.
* Support potentially more efficient proto parsing from RopeByteStrings.
* Clarify runtime of ByteString.Output.toStringBuffer().

Python
* Fixed a bug in text format where a trailing colon was printed for repeated field.
* When TextFormat encounters a duplicate message map key, replace the current
 one instead of merging.

JavaScript
* Make Any.pack() chainable.

2021-04-07 version 3.15.8 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Ruby
* Fixed memory leak of Ruby arena objects (8461)

2021-04-02 version 3.15.7 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C++
* Remove the ::pb namespace (alias) (8423)

Ruby
* Fix unbounded memory growth for Ruby <2.7 (8429)
* Fixed message equality in cases where the message type is different (8434)

2021-03-10 version 3.15.6 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Ruby
* Fixed bug in string comparison logic (8386)

2021-03-04 version 3.15.5 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Ruby
* Fixed quadratic memory use in array append (8379)

PHP
* Fixed quadratic memory use in array append (8379)

C++
* Do not disable RTTI by default in the CMake build (8377)

2021-03-02 version 3.15.4 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Ruby
* Fixed SEGV when users pass nil messages (8363)
* Fixed quadratic memory usage when appending to arrays (8364)

C++
* Create a CMake option to control whether or not RTTI is enabled (8361)

PHP
* read_property() handler is not supposed to return NULL (8362)

2021-02-25 version 3.15.3 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Ruby
* Ruby <2.7 now uses WeakMap too, which prevents memory leaks. (8341)

2021-02-23 version 3.15.2 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Ruby
* Fix for FieldDescriptor.get(msg) (8330)

C++
* Fix PROTOBUF_CONSTINIT macro redefinition (8323)

2021-02-05 version 3.15.1 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Ruby
* Bugfix for Message.[] for repeated or map fields (8313)

2021-02-05 version 3.15.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Protocol Compiler
* Optional fields for proto3 are enabled by default, and no longer require
 the --experimental_allow_proto3_optional flag.

C++
* MessageDifferencer: fixed bug when using custom ignore with multiple
 unknown fields
* Use init_seg in MSVC to push initialization to an earlier phase.
* Runtime no longer triggers -Wsign-compare warnings.
* Fixed -Wtautological-constant-out-of-range-compare warning.
* DynamicCastToGenerated works for nullptr input for even if RTTI is disabled
* Arena is refactored and optimized.
* Clarified/specified that the exact value of Arena::SpaceAllocated() is an
 implementation detail users must not rely on. It should not be used in
 unit tests.
* Change the signature of Any::PackFrom() to return false on error.
* Add fast reflection getter API for strings.
* Constant initialize the global message instances
* Avoid potential for missed wakeup in UnknownFieldSet
* Now Proto3 Oneof fields have "has" methods for checking their presence in
 C++.
* Bugfix for NVCC
* Return early in _InternalSerialize for empty maps.
* Adding functionality for outputting map key values in proto path logging
 output (does not affect comparison logic) and stop printing 'value' in the
 path. The modified print functionality is in the
 MessageDifferencer::StreamReporter.
* Fixed https://github.com/protocolbuffers/protobuf/issues/8129
* Ensure that null char symbol, package and file names do not result in a
 crash.
* Constant initialize the global message instances
* Pretty print 'max' instead of numeric values in reserved ranges.
* Removed remaining instances of std::is_pod, which is deprecated in C++20.
* Changes to reduce code size for unknown field handling by making uncommon
 cases out of line.
* Fix std::is_pod deprecated in C++20 (7180)
* Fix some -Wunused-parameter warnings (8053)
* Fix detecting file as directory on zOS issue 8051 (8052)
* Don't include sys/param.h for _BYTE_ORDER (8106)
* remove CMAKE_THREAD_LIBS_INIT from pkgconfig CFLAGS (8154)
* Fix TextFormatMapTest.DynamicMessage issue5136 (8159)
* Fix for compiler warning issue8145 (8160)
* fix: support deprecated enums for GCC < 6 (8164)
* Fix some warning when compiling with Visual Studio 2019 on x64 target (8125)

Python
* Provided an override for the reverse() method that will reverse the internal
 collection directly instead of using the other methods of the BaseContainer.
* MessageFactory.CreateProtoype can be overridden to customize class creation.
* Fix PyUnknownFields memory leak (7928)
* Add macOS big sur compatibility (8126)

JavaScript
* Generate `getDescriptor` methods with `*` as their `this` type.
* Enforce `let/const` for generated messages.
* js/binary/utils.js: Fix jspb.utils.joinUnsignedDecimalString to work with negative bitsLow and low but non-zero bitsHigh parameter. (8170)

PHP
* Added support for PHP 8. (8105)
* unregister INI entries and fix invalid read on shutdown (8042)
* Fix PhpDoc comments for message accessors to include "|null". (8136)
* fix: convert native PHP floats to single precision (8187)
* Fixed PHP to support field numbers >=2**28. (8235)
* feat: add support for deprecated fields to PHP compiler (8223)
* Protect against stack overflow if the user derives from Message. (8248)
* Fixed clone for Message, RepeatedField, and MapField. (8245)
* Updated upb to allow nonzero offset minutes in JSON timestamps. (8258)

Ruby
* Added support for Ruby 3. (8184)
* Rewrote the data storage layer to be based on upb_msg objects from the
 upb library. This should lead to much better parsing performance,
 particularly for large messages. (8184).
* Fill out JRuby support (7923)
* [Ruby] Fix: (SIGSEGV) gRPC-Ruby issue on Windows. memory alloc infinite
 recursion/run out of memory (8195)
* Fix jruby support to handle messages nested more than 1 level deep (8194)

Java
* Avoid possible UnsupportedOperationException when using CodedInputSteam
 with a direct ByteBuffer.
* Make Durations.comparator() and Timestamps.comparator() Serializable.
* Add more detailed error information for dynamic message field type
 validation failure
* Removed declarations of functions declared in java_names.h from
 java_helpers.h.
* Now Proto3 Oneof fields have "has" methods for checking their presence in
 Java.
* Annotates Java proto generated *_FIELD_NUMBER constants.
* Add -assumevalues to remove JvmMemoryAccessor on Android.

C
* Fix parsing negative Int32Value that crosses segment boundary (8035)
* Change ByteString to use memory and support unsafe create without copy (7645)
* Optimize MapField serialization by removing MessageAdapter (8143)
* Allow FileDescriptors to be parsed with extension registries (8220)
* Optimize writing small strings (8149)

2020-11-11 version 3.14.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

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.
* Add stack overflow protection for text format with unknown field values.
* FieldPath::FollowAll() now returns a bool to signal if an out-of-bounds
 error was encountered.
* Performance improvements for Map.
* Minor formatting fix when dumping a descriptor to .proto format with
 DebugString.
* UBSAN fix in RepeatedField (2073).
* 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.
* Fix segment fault for proto3 optional (7805)
* Adds a CMake option to build `libprotoc` separately (7949)

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;`.
* Adding forgotten duration.proto to the lite library (7738)

Python
* Print google.protobuf.NullValue as null instead of "NULL_VALUE" when it is
 used outside WKT Value/Struct.
* Fix bug occurring when attempting to deep copy an enum type in python 3.
* Add a setuptools extension for generating Python protobufs (7783)
* Remove uses of pkg_resources in non-namespace packages. (7902)
* [bazel/py] Omit google/__init__.py from the Protobuf runtime. (7908)
* Removed the unnecessary setuptools package dependency for Python package (7511)
* Fix PyUnknownFields memory leak (7928)

PHP
* Added support for "==" to the PHP C extension (7883)
* Added `==` operators for Map and Array. (7900)
* Native C well-known types (7944)
* Optimized away hex2bin() call in generated code (8006)
* New version of upb, and a new hash function wyhash in third_party. (8000)
* add missing hasOneof method to check presence of oneof fields (8003)

Go:
* Update go_package options to reference google.golang.org/protobuf module.

C:
* annotate ByteString.CopyFrom(ReadOnlySpan<byte>) as SecuritySafeCritical (7701)
* Fix C optional field reflection when there are regular fields too (7705)
* Fix parsing negative Int32Value that crosses segment boundary (8035)

Javascript:
* JS: parse (un)packed fields conditionally (7379)

2020-07-14 version 3.13.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

PHP:
* The C extension is completely rewritten. The new C extension has significantly
 better parsing performance and fixes a handful of conformance issues. It will
 also make it easier to add support for more features like proto2 and proto3 presence.
* The new C extension does not support PHP 5.x. PHP 5.x users can still use pure-PHP.

C++:
* Removed deprecated unsafe arena string accessors
* Enabled heterogeneous lookup for std::string keys in maps.
* Removed implicit conversion from StringPiece to std::string
* Fix use-after-destroy bug when the Map is allocated in the arena.
* Improved the randomness of map ordering
* Added stack overflow protection for text format with unknown fields
* Use std::hash for proto maps to help with portability.
* Added more Windows macros to proto whitelist.
* Arena constructors for map entry messages are now marked "explicit"
 (for regular messages they were already explicit).
* Fix subtle aliasing bug in RepeatedField::Add
* Fix mismatch between MapEntry ByteSize and Serialize with respect to unset
 fields.

Python:
* JSON format conformance fixes:
 * Reject lowercase t for Timestamp json format.
 * Print full_name directly for extensions (no camelCase).
 * Reject boolean values for integer fields.
 * Reject NaN, Infinity, -Infinity that is not quoted.
 * Base64 fixes for bytes fields: accept URL-safe base64 and missing padding.
* Bugfix for fields/files named "async" or "await".
* Improved the error message when AttributeError is returned from __getattr__
 in EnumTypeWrapper.

Java:
* Fixed a bug where setting optional proto3 enums with setFooValue() would
 not mark the value as present.
* Add Subtract function to FieldMaskUtil.

C:
* Dropped support for netstandard1.0 (replaced by support for netstandard1.1).
 This was required to modernize the parsing stack to use the `Span<byte>`
 type internally. (7351)
* Add `ParseFrom(ReadOnlySequence<byte>)` method to enable GC friendly
 parsing with reduced allocations and buffer copies. (7351)
* Add support for serialization directly to a `IBufferWriter<byte>` or
 to a `Span<byte>` to enable GC friendly serialization.
 The new API is available as extension methods on the `IMessage` type. (7576)
* Add `GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE` define to make
 generated code compatible with old C compilers (pre-roslyn compilers
 from .NET framework and old versions of mono) that do not support
 ref structs. Users that are still on a legacy stack that does
 not support C 7.2 compiler might need to use the new define
 in their projects to be able to build the newly generated code. (7490)
* Due to the major overhaul of parsing and serialization internals (7351 and 7576),
 it is recommended to regenerate your generated code to achieve the best
 performance (the legacy generated code will still work, but might incur
 a slight performance penalty).

2020-07-28 version 3.12.4 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

This release contains no significant changes, but exists because 3.12.3 was
mistakenly tagged at the wrong commit.

2020-06-01 version 3.12.3 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Objective-C
* Tweak the union used for Extensions to support old generated code. 7573

2020-05-26 version 3.12.2 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C++
* Simplified the template export macros to fix the build for mingw32. (7539)

Objective-C
* Fix for the :protobuf_objc target in the Bazel BUILD file. (7538)

2020-05-20 version 3.12.1 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Ruby
* Re-add binary gems for Ruby 2.3 and 2.4. These are EOL upstream, however
 many people still use them and dropping support will require more
 coordination.

2020-05-12 version 3.12.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

Protocol Compiler
* [experimental] Singular, non-message typed fields in proto3 now support
 presence tracking. This is enabled by adding the "optional" field label and
 passing the --experimental_allow_proto3_optional flag to protoc.
 * For usage info, see docs/field_presence.md.
 * During this experimental phase, code generators should update to support
   proto3 presence, see docs/implementing_proto3_presence.md for instructions.
* Allow duplicate symbol names when multiple descriptor sets are passed on
 the command-line, to match the behavior when multiple .proto files are passed.
* Deterministic `protoc --descriptor_set_out` (7175)

C++
* [experimental] Added proto3 presence support.
* New descriptor APIs to support proto3 presence.
* Enable Arenas by default on all .proto files.
* Documented that users are not allowed to subclass Message or MessageLite.
* Mark generated classes as final; inheriting from protos is strongly discouraged.
* Add stack overflow protection for text format with unknown fields.
* Add accessors for map key and value FieldDescriptors.
* Add FieldMaskUtil::FromFieldNumbers().
* MessageDifferencer: use ParsePartial() on Any fields so the diff does not
 fail when there are missing required fields.
* ReflectionOps::Merge(): lookup messages in the right factory, if it can.
* Added Descriptor::WellKnownTypes enum and Descriptor::well_known_type()
 accessor as an easier way of determining if a message is a Well-Known Type.
* Optimized RepeatedField::Add() when it is used in a loop.
* Made proto move/swap more efficient.
* De-virtualize the GetArena() method in MessageLite.
* Improves performance of json_stream_parser.cc by factor 1000 (7230)
* bug: 7076 undefine Windows OUT and OPTIONAL macros (7087)
* Fixed a bug in FieldDescriptor::DebugString() that would erroneously print
 an "optional" label for a field in a oneof.
* Fix bug in parsing bool extensions that assumed they are always 1 byte.
* Fix off-by-one error in FieldOptions::ByteSize() when extensions are present.
* Clarified the comments to show an example of the difference between
 Descriptor::extension and DescriptorPool::FindAllExtensions.
* Add a compiler option 'code_size' to force optimize_for=code_size on all
 protos where this is possible.

Java
* [experimental] Added proto3 presence support.
* Mark java enum _VALUE constants as Deprecated if the enum field is deprecated
* reduce <clinit> size for enums with allow_alias set to true.
* Sort map fields alphabetically by the field's key when printing textproto.
* Fixed a bug in map sorting that appeared in -rc1 and -rc2 (7508).
* TextFormat.merge() handles Any as top level type.
* Throw a descriptive IllegalArgumentException when calling
 getValueDescriptor() on enum special value UNRECOGNIZED instead of
 ArrayIndexOutOfBoundsException.
* Fixed an issue with JsonFormat.printer() where setting printingEnumsAsInts()
 would override the configuration passed into includingDefaultValueFields().
* Implement overrides of indexOf() and contains() on primitive lists returned
 for repeated fields to avoid autoboxing the list contents.
* Add overload to FieldMaskUtil.fromStringList that accepts a descriptor.
* [bazel] Move Java runtime/toolchains into //java (7190)

Python
* [experimental] Added proto3 presence support.
* [experimental] fast import protobuf module, only works with cpp generated code linked in.
* Truncate 'float' fields to 4 bytes of precision in setters for pure-Python
 implementation (C++ extension was already doing this).
* Fixed a memory leak in C++ bindings.
* Added a deprecation warning when code tries to create Descriptor objects
 directly.
* Fix unintended comparison between bytes and string in descriptor.py.
* Avoid printing excess digits for float fields in TextFormat.
* Remove Python 2.5 syntax compatibility from the proto compiler generated _pb2.py module code.
* Drop 3.3, 3.4 and use single version docker images for all python tests (7396)

JavaScript
* Fix js message pivot selection (6813)

PHP
* Persistent Descriptor Pool (6899)
* Implement lazy loading of php class for proto messages (6911)
* Correct return in Any.unpack docblock (7089)
* Ignore unknown enum value when ignore_unknown specified (7455)

Ruby
* [experimental] Implemented proto3 presence for Ruby. (7406)
* Stop building binary gems for ruby <2.5 (7453)
* Fix for wrappers with a zero value (7195)
* Fix for JSON serialization of 0/empty-valued wrapper types (7198)
* Call "Classnew" over rb_class_new_instance in decoding (7352)
* Build extensions for Ruby 2.7 (7027)
* assigning 'nil' to submessage should clear the field. (7397)

C
* [experimental] Add support for proto3 presence fields in C (7382)
* Mark GetOption API as obsolete and expose the "GetOptions()" method on descriptors instead (7491)
* Remove Has/Clear members for C message fields in proto2 (7429)
* Enforce recursion depth checking for unknown fields (7132)
* Fix conformance test failures for Google.Protobuf (6910)
* Cleanup various bits of Google.Protobuf (6674)
* Fix latest ArgumentException for C extensions (6938)
* Remove unnecessary branch from ReadTag (7289)

Objective-C
* [experimental] ObjC Proto3 optional support (7421)
* Block subclassing of generated classes (7124)
* Use references to Obj C classes instead of names in descriptors. (7026)
* Revisit how the WKTs are bundled with ObjC. (7173)

Other
* Add a proto_lang_toolchain for javalite (6882)
* [bazel] Update gtest and deprecate //external:{gtest,gtest_main} (7237)
* Add application note for explicit presence tracking. (7390)
* Howto doc for implementing proto3 presence in a code generator. (7407)


2020-02-14 version 3.11.4 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C
* Fix latest ArgumentException for C extensions (7188)
* Enforce recursion depth checking for unknown fields (7210)

Ruby
* Fix wrappers with a zero value (7195)
* Fix JSON serialization of 0/empty-valued wrapper types (7198)

2020-01-31 version 3.11.3 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C++
* Add OUT and OPTIONAL to windows portability files (7087)

PHP
* Refactored ulong to zend_ulong for php7.4 compatibility (7147)
* Call register_class before getClass from desc to fix segfault (7077)


2019-12-10 version 3.11.2 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

PHP
* Make c extension portable for php 7.4 (6968)


2019-12-02 version 3.11.1 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

PHP
* Extern declare protobuf_globals (6946)


2019-11-19 version 3.11.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C++
* Make serialization method naming consistent
* Make proto runtime + generated code free of deprecation warnings
* Moved ShutdownProtobufLibrary() to message_lite.h.  For backward compatibility a declaration is still available in stubs/common.h, but users should prefer message_lite.h
* Removed non-namespace macro EXPECT_OK()
* Removed mathlimits.h from stubs in favor of using std::numeric_limits from C++11
* Fixed bug in parser when ending on a group tag
* Add a helper function to UnknownFieldSet to deal with the changing return value of message::unknown_fields()
* Fix incorrect use of string_view iterators
* Support direct pickling of nested messages
* Skip extension tag validation for MessageSet if unknown dependencies are allowed
* Updated deprecation macros to annotate deprecated code (6612)
* Remove conversion warning in MapEntryFuncs::ByteSizeLong (6766)
* Revert "Make shared libraries be able to link to MSVC static runtime libraries, so that VC runtime is not required." (6914)

Java
* Remove the usage of MethodHandle, so that Android users prior to API version 26 can use protobuf-java
* Publish ProGuard config for javalite
* Fix for StrictMode disk read violation in ExtensionRegistryLite
* Include part of the ByteString's content in its toString().
* Include unknown fields when merging proto3 messages in Java lite builders

Python
* Add float_precision option in json format printer
* Optionally print bytes fields as messages in unknown fields, if possible
* FieldPath: fix testing IsSet on root path ''
* Experimental code gen (fast import protobuf module) which only work with cpp generated code linked in

JavaScript
* Remove guard for Symbol iterator for jspb.Map

PHP
* Avoid too much overhead in layout_init (6716)
* Lazily Create Singular Wrapper Message (6833)
* Implement lazy loading of php class for proto messages (6911)

Ruby
* Ruby lazy wrappers optimization (6797)

C
* (RepeatedField): Capacity property to resize the internal array (6530)
* Experimental proto2 support is now officially available (4642, 5183, 5350, 5936)
* Getting started doc: https://github.com/protocolbuffers/protobuf/blob/master/docs/csharp/proto2.md
* Add length checks to ExtensionCollection (6759)
* Optimize parsing of some primitive and wrapper types (6843)
* Use 3 parameter Encoding.GetString for default string values (6828)
* Change _Extensions property to normal body rather than expression (6856)

Objective C
* Fixed unaligned reads for 32bit arm with newer Xcode versions (6678)


2019-09-03 version 3.10.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C++
* Switch the proto parser to the faster MOMI parser.
* Properly escape Struct keys in the proto3 JSON serializer.
* Fix crash on uninitialized map entries.
* Informed the compiler of has-bit invariant to produce better code
* Unused imports of files defining descriptor extensions will now be reported
* Add proto2::util::RemoveSubranges to remove multiple subranges in linear time.
* Added BaseTextGenerator::GetCurrentIndentationSize()
* Made implicit weak fields compatible with the Apple linker
* Support 32 bit values for ProtoStreamObjectWriter to Struct.
* Removed the internal-only header coded_stream_inl.h and the internal-only methods defined there.
* Enforced no SWIG wrapping of descriptor_database.h (other headers already had this restriction).
* Implementation of the equivalent of the MOMI parser for serialization. This removes one of the two serialization routines, by making the fast array serialization routine completely general. SerializeToCodedStream can now be implemented in terms of the much much faster array serialization. The array serialization regresses slightly, but when array serialization is not possible this wins big. 
* Do not convert unknown field name to snake case to accurately report error.
* Fix a UBSAN warnings. (6333)
* Add podspec for C++ (6404)
* protoc: fix source code info location for missing label (6436)
* C++ Add move constructor for Reflection's SetString (6477)

Java
* Call loadDescriptor outside of synchronized block to remove one possible source of deadlock.
* Have oneof enums implement a separate interface (other than EnumLite) for clarity.
* Opensource Android Memory Accessors
* Update TextFormat to make use of the new TypeRegistry.
* Support getFieldBuilder and getRepeatedFieldBuilder in ExtendableBuilder
* Update JsonFormat to make use of the new TypeRegistry.
* Add proguard config generator for GmmBenchmarkSuiteLite.
* Change ProtobufArrayList to use Object[] instead of ArrayList for 5-10% faster parsing
* Implement ProtobufArrayList.add(E) for 20% (5%-40%) faster overall protolite2 parsing
* Make a copy of JsonFormat.TypeRegistry at the protobuf top level package. This will eventually replace JsonFormat.TypeRegistry.
* Fix javadoc warnings in generated files (6231)
* Java: Add Automatic-Module-Name entries to the Manifest (6568)

Python
* Add descriptor methods in descriptor_pool are deprecated.
* Uses explicit imports to prevent multithread test failures in py3.
* Added __delitem__ for Python extension dict
* Update six version to 1.12.0 and fix legacy_create_init issue (6391)

JavaScript
* Remove deprecated boolean option to getResultBase64String().
* Fix sint64 zig-zag encoding.
* Simplify hash64 string conversion to avoid DIGIT array. Should reduce overhead if these functions aren't used, and be more efficient by avoiding linear array searches.
* Change the parameter types of binaryReaderFn in ExtensionFieldBinaryInfo to (number, ?, ?).
* Create dates.ts and time_of_days.ts to mirror Java versions. This is a near-identical conversion of c.g.type.util.{Dates,TimeOfDays} respectively.
* Migrate moneys to TypeScript.

PHP
* Fix incorrect leap day for Timestamp (6696)
* Initialize well known type values (6713)

Ruby
* Fix scope resolution for Google namespace (5878)
* Support hashes for struct initializers (5716)
* Optimized away the creation of empty string objects. (6502)
* Roll forward Ruby upb changes now that protobuf Ruby build is fixed (5866)
* Optimized layout_mark() for Ruby (6521)
* Optimization for layout_init() (6547)
* Fix for GC of Ruby map frames. (6533)
* Fixed leap year handling by reworking upb_mktime() -> upb_timegm(). (6695)

Objective C
* Remove OSReadLittle* due to alignment requirements (6678)
* Don't use unions and instead use memcpy for the type swaps. (6672)

Other
* Override CocoaPods module to lowercase (6464)


2019-06-28 version 3.9.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C++
* Optimize and simplify implementation of RepeatedPtrFieldBase
* Don't create unnecessary unknown field sets.
* Remove branch from accessors to repeated field element array.
* Added delimited parse and serialize util.
* Reduce size by not emitting constants for fieldnumbers
* Fix a bug when comparing finite and infinite field values with explicit tolerances.
* TextFormat::Parser should use a custom Finder to look up extensions by number if one is provided.
* Add MessageLite::Utf8DebugString() to make MessageLite more compatible with Message.
* Fail fast for better performance in DescriptorPool::FindExtensionByNumber() if descriptor has no defined extensions.
* Adding the file name to help debug colliding extensions
* Added FieldDescriptor::PrintableNameForExtension() and DescriptorPool::FindExtensionByPrintableName().
 The latter will replace Reflection::FindKnownExtensionByName().
* Replace NULL with nullptr
* Created a new Add method in repeated field that allows adding a range of elements all at once.
* Enabled enum name-to-value mapping functions for C++ lite
* Avoid dynamic initialization in descriptor.proto generated code
* Move stream functions to MessageLite from Message.
* Move all zero_copy_stream functionality to io_lite.
* Do not create array of matched fields for simple repeated fields
* Enabling silent mode by default to reduce make compilation noise. (6237)

Java
* Expose TextFormat.Printer and make it configurable. Deprecate the static methods.
* Library for constructing google.protobuf.Struct and google.protobuf.Value
* Make OneofDescriptor extend GenericDescriptor.
* Expose streamingness of service methods from MethodDescriptor.
* Fix a bug where TextFormat fails to parse Any filed with > 1 embedded message sub-fields.
* Establish consistent JsonFormat behavior for nulls in oneofs, regardless of order.
* Update GSON version to 3.8.5. (6268)
* Add `protobuf_java_lite` Bazel target. (6177)

Python
* Change implementation of Name() for enums that allow aliases in proto2 in Python
 to be in line with claims in C++ implementation (to return first value).
* Explicitly say what field cannot be set when the new value fails a type check.
* Duplicate register in descriptor pool will raise errors
* Add __slots__ to all well_known_types classes, custom attributes are not allowed anymore.
* text_format only present 8 valid digits for float fields by default

JavaScript
* Add Oneof enum to the list of goog.provide

PHP
* Make php message class final to avoid mocking. (6277)
* Rename get/setXXXValue to get/setXXXWrapper. (6295)

Ruby
* Remove to_hash methods. (6166)


2019-04-29 version 3.8.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C++
* Use std::atomic<int32> in case of myriad2 platform
* Always declare enums to be int-sized
* Added DebugString() and ShortDebugString() methods on MessageLite
* Specialized different parse loop control flows
* Make hasbits potentially in register. The or's start forming an obstacle because it's a read modify store on the same mem address on each iteration.
* Move to an internal MACRO for parser validity checks.
* Improve map parsing performance.
* Make MergePartialFromCodedStream non virtual. This allows direct calls, potential inlining and is also a code health improvement
* Add an overall limit to parse_context to prevent reading past it. This allows to remove a annoying level of indirection.
* Fix a mistake, we shouldn't verify map key/value strings for utf8 in opt mode for proto2.
* Further improvements to cut binary size.
* Prepare to make MergePartialFromCodedStream non-virtual.
* A report on some interesting behavior change in python (caused by b/27494216) made me realize there is a check that needs to be done in case the parse ended on a end group tag.
* Add a note of caution to the comments around skip in CodedOutputStream.
* Simplify end check.
* Add overload for ParseMessage for MessageLite/Message types. If the explicit type is not known inlining won't help de-virtualizing the virtual call.
* Reduce linker input. It turns out that ParseMessage is not inlined, producing  template instantiations that are used only once and save nothing but cost more.
* Improve the parser.
* [c++17] Changed proto2::RepeatedPtrField iterators to no longer derive from the deprecated std::iterator class.
* Change the default value of case_insensitive_enum_parsing to false for JsonStringToMessage.
* Add a warning if a field name doesn't match the style guide.
* Fix TextFormat not round-trip correctly when float value is max float.
* Added locationed info for some errors at compiler
* Python reserved keywords are now working with getattr()/setattr() for most descriptors.
* Added AllowUnknownField() in text_format
* Append '_' to C++ reserved keywords for message, enum, extension
* Fix MSVC warning C4244 in protobuf's parse_context.h.
* Updating Iterators to be compatible with C++17 in MSVC.
* Use capability annotation in mutex.h
* Fix "UndefinedBehaviorSanitizer: cfi-bad-type"
* CriticalSectionLock class as a lightweight replacement for std::mutex on Windows platforms.
* Removed vestigial wire_format_lite_inl.h

C
* Added System.Memory dependency.

Java
* Make Java protoc code generator ignore optimize_for LITE_RUNTIME. Users should instead use the Java lite protoc plugin.
* Change Extension getMessageDefaultInstance() to return Message instead of MessageLite.
* Prevent malicious input streams from leaking buffers for ByteString or ByteBuffer parsing.
* Release new Javalite runtime.
* Show warning in case potential file name conflict.
* Allow Java reserved keywords to be used in extensions.
* Added setAllowUnknownFields() in text format
* Add memoization to ExtensionRegistryLite.getEmptyRegistry()
* Improve performance of CodedOutputStream.writeUInt32NoTag
* Add an optimized mismatch-finding algorithm to UnsafeUtil.
* When serializing uint32 varints, check that we have MAX_VARINT32_SIZE bytes left, not just MAX_VARINT_SIZE.
* Minor optimization to RopeByteString.PieceIterator

JavaScript
* Simplify generated toObject code when the default value is used.

Python
* Changes implementation of Name() for enums that allow aliases in proto2 in Python to be in line with claims in C++ implementation (to return first value).
* Added double_format option in text format printer.
* Added iter and __contains__ to extension dict
* Added allow_unknown_field option in python text format parser
* Fixed Timestamp.ToDatetime() loses precision issue
* Support unknown field in text format printer.
* Float field will be convert to inf if bigger than struct.unpack('f', b'\xff\xff\x7f\x7f')[0] which is about 3.4028234664e+38,
convert to -inf if smaller than -3.4028234664e+38
* Allowed casting str->bytes in Message.__setstate__

Ruby
* Helper methods to get enum name for Ruby.


2019-01-24 version 3.7.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C++
* Introduced new MOMI (maybe-outside-memory-interval) parser.
* Add an option to json_util to parse enum as case-insensitive. In the future, enum parsing in json_util will become case-sensitive.
* Added conformance test for enum aliases
* Added support for --cpp_out=speed:...
* Added use of C++ override keyword where appropriate
* Many other cleanups and fixes.

Java
* Fix illegal reflective access warning in JDK 9+
* Add BOM

Python
* Added Python 3.7 compatibility.
* Modified ParseFromString to return bytes parsed .
* Introduce Proto C API.
* FindFileContainingSymbol in descriptor pool is now able to find field and enum values.
* reflection.MakeClass()  and  reflection.ParseMessage() are deprecated.
* Added DescriptorPool.FindMethodByName() method in pure python (c extension already has it)
* Flipped proto3 to preserve unknown fields by default.
* Added support for memoryview in python3 proto message parsing.
* Added MergeFrom for repeated scalar fields in c extension (pure python already has it)
* Surrogates are now rejected at setters in python3.
* Added public unknown field API.
* RecursionLimit is also set to max if allow_oversize_protos is enabled.
* Disallow duplicate scalars in proto3 text_format parse.
* Fix some segment faults for c extension map field.

PHP
* Most issues for json encoding/decoding in the c extension have been fixed. There are still some edge cases not fixed. For more details, check conformance/failure_list_php_c.txt.
* Supports php 7.3
* Added helper methods to convert between enum values and names.
* Allow setting/getting wrapper message fields using primitive values.
* Various bug fixes.

Ruby
* Ruby 2.6 support.
* Drops support for ruby < 2.3.
* Most issues for json encoding/decoding in the c extension have been fixed. There are still some edge cases not fixed. For more details, check conformance/failure_list_ruby.txt.
* Json parsing can specify an option to ignore unknown fields: msg.decode_json(data, {ignore_unknown_fields: true}).
* Added support for proto2 syntax (partially).
* Various bug fixes.

Csharp
* More support for FieldMask include merge, intersect and more.
* Increasing the default recursion limit to 100.
* Support loading FileDescriptors dynamically.
* Provide access to comments from descriptors.
* Added Any.Is method.
* Compatible with C 6
* Added IComparable and comparison operators on Timestamp.

Objective C
* Add ability to introspect list of enum values (4678)
* Copy the value when setting message/data fields (5215)
* Support suppressing the objc package prefix checks on a list of files (5309)
* More complete keyword and NSObject method (via categories) checks for field names, can result in more fields being rename, but avoids the collisions at runtime (5289)
* Small fixes to TextFormat generation for extensions (5362)
* Provide more details/context in deprecation messages (5412)
* Array/Dictionary enumeration blocks NS_NOESCAPE annotation for Swift (5421)
* Properly annotate extensions for ARC when their names imply behaviors (5427)
* Enum alias name collision improvements (5480)


2018-07-27 version 3.6.1 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C++
* Introduced workaround for Windows issue with std::atomic and std::once_flag
 initialization (4777, 4773).

PHP
* Added compatibility with PHP 7.3 (4898).

Ruby
* Fixed Ruby crash involving Any encoding (4718).

2018-06-01 version 3.6.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)

C++
* Starting from this release, we now require C++11. For those we cannot yet
 upgrade to C++11, we will try to keep the 3.5.x branch updated with
 critical bug fixes only. If you have any concerns about this, please
 comment on issue 2780.
* Moved to C++11 types like std::atomic and std::unique_ptr and away from our
 old custom-built equivalents.
* Added support for repeated message fields in lite protos using implicit
 weak fields. This is an experimental feature that allows the linker to
 strip out more unused messages than previously was possible.
* Fixed SourceCodeInfo for interpreted options and extension range options.
* Fixed always_print_enums_as_ints option for JSON serialization.
* Added support for ignoring unknown enum values when parsing JSON.
* Create std::string in Arena memory.
* Fixed ValidateDateTime to correctly check the day.
* Fixed bug in ZeroCopyStreamByteSink.
* Various other cleanups and fixes.

Java
* Dropped support for Java 6.
* Added a UTF-8 decoder that uses Unsafe to directly decode a byte buffer.
* Added deprecation annotations to generated code for deprecated oneof
 fields.
* Fixed map field serialization in DynamicMessage.
* Cleanup and documentation for Java Lite runtime.
* Various other fixes and cleanups
* Fixed unboxed arraylists to handle an edge case
* Improved performance for copying between unboxed arraylists
* Fixed lite protobuf to avoid Java compiler warnings
* Improved test coverage for lite runtime
* Performance improvements for lite runtime

Python
* Fixed bytes/string map key incompatibility between C++ and pure-Python
 implementations (issue 4029)
* Added __init__.py files to compiler and util subpackages
* Use /MT for all Windows versions
* Fixed an issue affecting the Python-C++ implementation when used with
 Cython (issue 2896)
* Various text format fixes
* Various fixes to resolve behavior differences between the pure-Python and
 Python-C++ implementations

PHP
* Added php_metadata_namespace to control the file path of generated metadata
 file.
* Changed generated classes of nested message/enum. E.g., Foo.Bar, which
 previously generates Foo_Bar, now generates Foo/Bar
* Added array constructor. When creating a message, users can pass a php
 array whose content is field name to value pairs into constructor. The
 created message will be initialized according to the array. Note that
 message field should use a message value instead of a sub-array.
* Various bug fixes.

Objective-C
* We removed some helper class methods from GPBDictionary to shrink the size
 of the library, the functionary is still there, but you may need to do some
 specific +alloc / -init… methods instead.
* Minor improvements in the performance of object field getters/setters by
 avoiding some memory management overhead.
* Fix a memory leak during the raising of some errors.
* Make header importing completely order independent.
* Small code improvements for things the undefined behaviors compiler option
 was flagging.

Ruby
* Added ruby_package file option to control the module of generated class.
* Various bug fixes.

Javascript
* Allow setting string to int64 field.

Csharp
* Unknown fields are now parsed and then sent back on the wire. They can be
 discarded at parse time via a CodedInputStream option.
* Movement towards working with .NET 3.5 and Unity
* Expression trees are no longer used
* AOT generics issues in Unity/il2cpp have a workaround (see this commit for
 details)
* Floating point values are now compared bitwise (affects NaN value
 comparisons)
* The default size limit when parsing is now 2GB rather than 64MB
* MessageParser now supports parsing from a slice of a byte array
* JSON list parsing now accepts null values where the underlying proto
 representation does

2017-12-20 version 3.5.1 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)
Planned Future Changes
* Make C++ implementation C++11 only: we plan to require C++11 to build
 protobuf code starting from 3.6.0 release. Please join this github issue:
 https://github.com/protocolbuffers/protobuf/issues/2780 to provide your feedback.

protoc
* Fixed a bug introduced in 3.5.0 and protoc in Windows now accepts non-ascii
 characters in paths again.

C++
* Removed several usages of C++11 features in the code base.
* Fixed some compiler warnings.

PHP
* Fixed memory leak in C-extension implementation.
* Added discardUnknokwnFields API.
* Removed duplicated typedef in C-extension headers.
* Avoided calling private php methods (timelib_update_ts).
* Fixed Any.php to use fully-qualified name for DescriptorPool.

Ruby
* Added Google_Protobuf_discard_unknown for discarding unknown fields in
 messages.

C
* Unknown fields are now preserved by default.
* Floating point values are now bitwise compared, affecting message equality
 check and Contains() API in map and repeated fields.


2017-11-13 version 3.5.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)
Planned Future Changes
* Make C++ implementation C++11 only: we plan to require C++11 to build
 protobuf code starting from 3.6.0 release. Please join this github issue:
 https://github.com/protocolbuffers/protobuf/issues/2780 to provide your feedback.

General
* Unknown fields are now preserved in proto3 for most of the language
 implementations for proto3 by default. See the per-language section for
 details.
* reserve keyword are now supported in enums

C++
* Proto3 messages are now preserving unknown fields by default. If you rely on
 unknowns fields being dropped. Please use DiscardUnknownFields() explicitly.
* Deprecated the unsafe_arena_release_* and unsafe_arena_add_allocated_*
 methods for string fields.
* Added move constructor and move assignment to RepeatedField,
 RepeatedPtrField and google::protobuf::Any.
* Added perfect forwarding in Arena::CreateMessage
* In-progress experimental support for implicit weak fields with lite protos.
 This feature allows the linker to strip out more unused messages and reduce
 binary size.
* Various performance optimizations.

Java
* Proto3 messages are now preserving unknown fields by default. If you’d like
 to drop unknown fields, please use the DiscardUnknownFieldsParser API. For
 example:
   Parser<Foo> parser = DiscardUnknownFieldsParser.wrap(Foo.parser());
   Foo foo = parser.parseFrom(input);
* Added a new CodedInputStream decoder for Iterable<ByteBuffer> with direct
 ByteBuffers.
* TextFormat now prints unknown length-delimited fields as messages if
 possible.
* FieldMaskUtil.merge() no longer creates unnecessary empty messages when a
 message field is unset in both source message and destination message.
* Various performance optimizations.

Python
* Proto3 messages are now preserving unknown fields by default. Use
 message.DiscardUnknownFields() to drop unknown fields.
* Add FieldDescriptor.file in generated code.
* Add descriptor pool FindOneofByName in pure python.
* Change unknown enum values into unknown field set .
* Add more Python dict/list compatibility for Struct/ListValue.
* Add utf-8 support for text_format.Merge()/Parse().
* Support numeric unknown enum values for proto3 JSON format.
* Add warning for Unexpected end-group tag in cpp extension.

PHP
* Proto3 messages are now preserving unknown fields.
* Provide well known type messages in runtime.
* Add prefix ‘PB’ to generated class of reserved names.
* Fixed all conformance tests for encode/decode json in php runtime. C
 extension needs more work.

Objective-C
* Fixed some issues around copying of messages with unknown fields and then
 mutating the unknown fields in the copy.

C
* Added unknown field support in JsonParser.
* Fixed oneof message field merge.
* Simplify parsing messages from array slices.

Ruby
* Unknown fields are now preserved by default.
* Fixed several bugs for segment fault.

Javascript
* Decoder can handle both paced and unpacked data no matter how the proto is
 defined.
* Decoder now accept long varint for 32 bit integers.


2017-08-14 version 3.4.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)
Planned Future Changes
* There are some changes that are not included in this release but are planned
 for the near future
   - Preserve unknown fields in proto3: We are going to bring unknown fields
     back into proto3. In this release, some languages start to support
     preserving unknown fields in proto3, controlled by flags/options. Some
     languages also introduce explicit APIs to drop unknown fields for
     migration. Please read the change log sections by languages for details.
     For general timeline and plan:

       https://docs.google.com/document/d/1KMRX-G91Aa-Y2FkEaHeeviLRRNblgIahbsk4wA14gRk/view

     For issues and discussions:

       https://github.com/protocolbuffers/protobuf/issues/272

   - Make C++ implementation C++11 only: we plan to require C++11 to build
     protobuf code starting from 3.5.0 or 3.6.0 release, after unknown fields
     semantic changes are finished. Please join this
     github issue:

       https://github.com/protocolbuffers/protobuf/issues/2780

     to provide your feedback.

General
* Extension ranges now accept options and are customizable.
* "reserve" keyword now supports “max” in field number ranges,
 e.g.  reserve 1000 to max;

C++
* Proto3 messages are now able to preserve unknown fields. The default
 behavior is still to drop unknowns, which will be flipped in a future
 release. If you rely on unknowns fields being dropped. Please use
 Message::DiscardUnknownFields() explicitly.
* Packable proto3 fields are now packed by default in serialization.
* Following C++11 features are introduced when C++11 is available:
   - move-constructor and move-assignment are introduced to messages
   - Repeated fields constructor now takes std::initializer_list
   - rvalue setters are introduced for string fields
* Experimental Table-Driven parsing and serialization available to test. To
 enable it, pass in table_driven_parsing table_driven_serialization protoc
 generator flags for C++

   $ protoc --cpp_out=table_driven_parsing,table_driven_serialization:./ \
     test.proto

* lite generator parameter supported by the generator. Once set, all generated
 files, use lite runtime regardless of the optimizer_for setting in the
 .proto file.
* Various optimizations to make C++ code more performant on PowerPC platform
* Fixed maps data corruption when the maps are modified by both reflection API
 and generated API.
* Deterministic serialization on maps reflection now uses stable sort.
* file() accessors are introduced to various *Descriptor classes to make
 writing template function easier.
* ByteSize() and SpaceUsed() are deprecated.Use ByteSizeLong() and
 SpaceUsedLong() instead
* Consistent hash function is used for maps in DEBUG and NDEBUG build.
* "using namespace std" is removed from stubs/common.h
* Various performance optimizations and bug fixes

Java
* Introduced new parser API DiscardUnknownFieldsParser in preparation of
 proto3 unknown fields preservation change. Users who want to drop unknown
 fields should migrate to use this new parser API. For example:

   Parser<Foo> parser = DiscardUnknownFieldsParser.wrap(Foo.parser());
   Foo foo = parser.parseFrom(input);

* Introduced new TextFormat API printUnicodeFieldValue() that prints field
 value without escaping unicode characters.
* Added Durations.compare(Duration, Duration) and
 Timestamps.compare(Timestamp, Timestamp).
* JsonFormat now accepts base64url encoded bytes fields.
* Optimized CodedInputStream to do less copies when parsing large bytes
 fields.
* Optimized TextFormat to allocate less memory when printing.

Python
* SerializeToString API is changed to SerializeToString(self, **kwargs),
 deterministic parameter is accepted for deterministic serialization.
* Added sort_keys parameter in json format to make the output deterministic.
* Added indent parameter in json format.
* Added extension support in json format.
* Added __repr__ support for repeated field in cpp implementation.
* Added file in FieldDescriptor.
* Added pretty-print filter to text format.
* Services and method descriptors are always printed even if generic_service
 option is turned off.
* Note: AppEngine 2.5 is deprecated on June 2017 that AppEngine 2.5 will
 never update protobuf runtime. Users who depend on AppEngine 2.5 should use
 old protoc.

PHP
* Support PHP generic services. Specify file option php_generic_service=true
 to enable generating service interface.
* Message, repeated and map fields setters take value instead of reference.
* Added map iterator in c extension.
* Support json  encode/decode.
* Added more type info in getter/setter phpdoc
* Fixed the problem that c extension and php implementation cannot be used
 together.
* Added file option php_namespace to use custom php namespace instead of
 package.
* Added fluent setter.
* Added descriptor API in runtime for custom encode/decode.
* Various bug fixes.

Objective-C
* Fix for GPBExtensionRegistry copying and add tests.
* Optimize GPBDictionary.m codegen to reduce size of overall library by 46K
 per architecture.
* Fix some cases of reading of 64bit map values.
* Properly error on a tag with field number zero.
* Preserve unknown fields in proto3 syntax files.
* Document the exceptions on some of the writing apis.

C
* Implemented IReadOnlyDictionary<K,V> in MapField<K,V>
* Added TryUnpack method for Any message in addition to Unpack.
* Converted C projects to MSBuild (csproj) format.

Ruby
* Several bug fixes.

Javascript
* Added support of field option js_type. Now one can specify the JS type of a
 64-bit integer field to be string in the generated code by adding option
 [jstype = JS_STRING] on the field.

2017-04-05 version 3.3.0 (C++/Java/Python/PHP/Objective-C/C/Ruby/JavaScript)
Planned Future Changes
* There are some changes that are not included in this release but are
 planned for the near future:
   - Preserve unknown fields in proto3: please read this doc:

       https://docs.google.com/document/d/1KMRX-G91Aa-Y2FkEaHeeviLRRNblgIahbsk4wA14gRk/view

     for the timeline and follow up this github issue:

       https://github.com/protocolbuffers/protobuf/issues/272

     for discussion.
   - Make C++ implementation C++11 only: we plan to require C++11 to build
     protobuf code starting from 3.4.0 or 3.5.0 release. Please join this
     github issue:

       https://github.com/protocolbuffers/protobuf/issues/2780

     to provide your feedback.

C++
* Fixed map fields serialization of DynamicMessage to correctly serialize
 both key and value regardless of their presence.
* Parser now rejects field number 0 correctly.
* New API Message::SpaceUsedLong() that’s equivalent to
 Message::SpaceUsed() but returns the value in size_t.
* JSON support
 - New flag always_print_enums_as_ints in JsonPrintOptions.
 - New flag preserve_proto_field_names in JsonPrintOptions. It will instruct
   the JSON printer to use the original field name declared in the .proto
   file instead of converting them to lowerCamelCase when printing JSON.
 - JsonPrintOptions.always_print_primtive_fields now works for oneof message
   fields.
 - Fixed a bug that doesn’t allow different fields to set the same json_name
   value.
 - Fixed a performance bug that causes excessive memory copy when printing
   large messages.
* Various performance optimizations.

Java
* Map field setters eagerly validate inputs and throw NullPointerExceptions
 as appropriate.
* Added ByteBuffer overloads to the generated parsing methods and the Parser
 interface.
* proto3 enum's getNumber() method now throws on UNRECOGNIZED values.
* Output of JsonFormat is now locale independent.

Python
* Added FindServiceByName() in the pure-Python DescriptorPool. This works only
 for descriptors added with DescriptorPool.Add(). Generated descriptor_pool
 does not support this yet.
* Added a descriptor_pool parameter for parsing Any in text_format.Parse().
* descriptor_pool.FindFileContainingSymbol() now is able to find nested
 extensions.
* Extending empty [] to repeated field now sets parent message presence.

PHP
* Added file option php_class_prefix. The prefix will be prepended to all
 generated classes defined in the file.
* When encoding, negative int32 values are sign-extended to int64.
* Repeated/Map field setter accepts a regular PHP array. Type checking is
 done on the array elements.
* encode/decode are renamed to serializeToString/mergeFromString.
* Added mergeFrom, clear method on Message.
* Fixed a bug that oneof accessor didn’t return the field name that is
 actually set.
* C extension now works with php7.
* This is the first GA release of PHP. We guarantee that old generated code
 can always work with new runtime and new generated code.

Objective-C
* Fixed help for GPBTimestamp for dates before the epoch that contain
 fractional seconds.
* Added GPBMessageDropUnknownFieldsRecursively() to remove unknowns from a
 message and any sub messages.
* Addressed a threading race in extension registration/lookup.
* Increased the max message parsing depth to 100 to match the other languages.
* Removed some use of dispatch_once in favor of atomic compare/set since it
 needs to be heap based.
* Fixes for new Xcode 8.3 warnings.

C
* Fixed MapField.Values.CopyTo, which would throw an exception unnecessarily
 if provided exactly the right size of array to copy to.
* Fixed enum JSON formatting when multiple names mapped to the same numeric
 value.
* Added JSON formatting option to format enums as integers.
* Modified RepeatedField<T> to implement IReadOnlyList<T>.
* Introduced the start of custom option handling; it's not as pleasant as it
 might be, but the information is at least present. We expect to extend code
 generation to improve this in the future.
* Introduced ByteString.FromStream and ByteString.FromStreamAsync to
 efficiently create a ByteString from a stream.
* Added whole-message deprecation, which decorates the class with [Obsolete].

Ruby
* Fixed Messageto_h for messages with map fields.
* Fixed memcpy() in binary gems to work for old glibc, without breaking the
 build for non-glibc libc’s like musl.

Javascript
* Added compatibility tests for version 3.0.0.
* Added conformance tests.
* Fixed serialization of extensions: we need to emit a value even if it is
 falsy (like the number 0).
* Use closurebuilder.py in favor of calcdeps.py for compiling JavaScript.

2017-01-23 version 3.2.0 (C++/Java/Python/PHP/Ruby/Objective-C/C/JavaScript/Lite)
General
* Added protoc version number to protoc plugin protocol. It can be used by
 protoc plugin to detect which version of protoc is used with the plugin and
 mitigate known problems in certain version of protoc.

C++
* The default parsing byte size limit has been raised from 64MB to 2GB.
* Added rvalue setters for non-arena string fields.
* Enabled debug logging for Android.
* Fixed a double-free problem when using Reflection::SetAllocatedMessage()
 with extension fields.
* Fixed several deterministic serialization bugs:
 * MessageLite::SerializeAsString() now respects the global deterministic
   serialization flag.
 * Extension fields are serialized deterministically as well.  Fixed protocol
   compiler to correctly report importing-self as an error.
* Fixed FileDescriptor::DebugString() to print custom options correctly.
* Various performance/codesize optimizations and cleanups.

Java
* The default parsing byte size limit has been raised from 64MB to 2GB.
* Added recursion limit when parsing JSON.
* Fixed a bug that enumType.getDescriptor().getOptions() doesn't have custom
 options.
* Fixed generated code to support field numbers up to 2^29-1.

Python
* You can now assign NumPy scalars/arrays (np.int32, np.int64) to protobuf
 fields, and assigning other numeric types has been optimized for
 performance.
* Pure-Python: message types are now garbage-collectable.
* Python/C++: a lot of internal cleanup/refactoring.

PHP (Alpha)
* For 64-bit integers type (int64/uint64/sfixed64/fixed64/sint64), use PHP
 integer on 64-bit environment and PHP string on 32-bit environment.
* PHP generated code also conforms to PSR-4 now.
* Fixed ZTS build for c extension.
* Fixed c extension build on Mac.
* Fixed c extension build on 32-bit linux.
* Fixed the bug that message without namespace is not found in the descriptor
 pool. (2240)
* Fixed the bug that repeated field is not iterable in c extension.
* Message names Empty will be converted to GPBEmpty in generated code.
* Added phpdoc in generated files.
* The released API is almost stable. Unless there is large problem, we won't
 change it. See
 https://developers.google.com/protocol-buffers/docs/reference/php-generated
 for more details.

Objective-C
* Added support for push/pop of the stream limit on CodedInputStream for
 anyone doing manual parsing.

C
* No changes.

Ruby
* Message objects now support respond_to? for field getters/setters.
* You can now compare “message == non_message_object” and it will return false
 instead of throwing an exception.
* JRuby: fixed hashCode to properly reflect the values in the message.

Javascript
* Deserialization of repeated fields no longer has quadratic performance
 behavior.
* UTF-8 encoding/decoding now properly supports high codepoints.
* Added convenience methods for some well-known types: Any, Struct, and
 Timestamp. These make it easier to convert data between native JavaScript
 types and the well-known protobuf types.

2016-09-23 version 3.1.0 (C++/Java/Python/PHP/Ruby/Objective-C/C/JavaScript/Lite)
General
* Proto3 support in PHP (alpha).
* Various bug fixes.

C++
* Added MessageLite::ByteSizeLong() that’s equivalent to
 MessageLite::ByteSize() but returns the value in size_t. Useful to check
 whether a message is over the 2G size limit that protobuf can support.
* Moved default_instances to global variables. This allows default_instance
 addresses to be known at compile time.
* Adding missing generic gcc 64-bit atomicops.
* Restore New*Callback into google::protobuf namespace since these are used
 by the service stubs code
* JSON support.
 * Fixed some conformance issues.
* Fixed a JSON serialization bug for bytes fields.

Java
* Fixed a bug in TextFormat that doesn’t accept empty repeated fields (i.e.,
 “field: [ ]”).
* JSON support
 * Fixed JsonFormat to do correct snake_case-to-camelCase conversion for
   non-style-conforming field names.
 * Fixed JsonFormat to parse empty Any message correctly.
 * Added an option to JsonFormat.Parser to ignore unknown fields.
* Experimental API
 * Added UnsafeByteOperations.unsafeWrap(byte[]) to wrap a byte array into
   ByteString without copy.

Python
* JSON support
 * Fixed some conformance issues.

PHP (Alpha)
* We have added the proto3 support for PHP via both a pure PHP package and a
 native c extension. The pure PHP package is intended to provide usability
 to wider range of PHP platforms, while the c extension is intended to
 provide higher performance. Both implementations provide the same runtime
 APIs and share the same generated code. Users don’t need to re-generate
 code for the same proto definition when they want to switch the
 implementation later. The pure PHP package is included in the php/src
 directory, and the c extension is included in the php/ext directory.

 Both implementations provide idiomatic PHP APIs:
 * All messages and enums are defined as PHP cl

[pyup-bot]

Closing this in favor of #1578