Protocol Buffers v21.0-rc1

Versions

• Versioning scheme is changing to decouple major versions for languages
• Minor and patch versions will remain coupled
• Compilers and releases will refer to the version as just the minor and micro versions (i.e. 21.0)
• See here for more information on this change

C++

• Rename main cmake/CMakeLists.txt to CMakeLists.txt (#9603)
• avoid allocating memory if all extension are cleared (#9345)
• cmake: Call get_filename_component() with DIRECTORY mode instead of PATH mode (#9614)
• Escape GetObject macro inside protoc-generated code (#9739)
• Update CMake configuration to add a dependency on Abseil (#9793)
• Use __constinit only in GCC 12.2 and up (#9936)
• Refactor generated message class layout
• Optimize tokenizer ParseInteger by removing division
• Reserve exactly the right amount of capacity in ExtensionSet::MergeFrom
• Parse FLT_MAX correctly when represented in JSON

Java

• Update protobuf_version.bzl to separate protoc and per-language java … (#9900)
• 6x speedup in ArrayEncoder.writeUInt32NotTag

Python

• Increment python major version to 4 in version.json for python upb (#9926)
• The C extension module for Python has been rewritten to use the upb library.
  This is expected to deliver significant performance benefits, especially when
  parsing large payloads. There are some minor breaking changes, but these
  should not impact most users. For more information see:
  https://developers.google.com/protocol-buffers/docs/news/2022-05-06#python-updates
• Due to the breaking changes for Python, the major version number for Python
  has been incremented.
• The binary wheel for macOS now supports Apple silicon.

PHP

• chore: [PHP] fix phpdoc for MapField keys (#9536)
• [PHP] Remove unnecessary zval initialization (#9600)
• [PHP] fix PHP build system (#9571)
• Fix building packaged PHP extension (#9727)
• fix: reserve "ReadOnly" keyword for PHP 8.1 and add compatibility (#9633)
• fix: phpdoc syntax for repeatedfield parameters (#9784)
• fix: phpdoc for repeatedfield (#9783)
• Change enum string name for reserved words (#9780)
• Fixed composer.json to only advertise compatibility with PHP 7.0+. (#9819)

Ruby

• Allow pre-compiled binaries for ruby 3.1.0 (#9566)
• Implement respond_to? in RubyMessage (#9677)
• [Ruby] Fix RepeatedField#last, #first inconsistencies (#9722)
• Do not use range based UTF-8 validation in truffleruby (#9769)
• Improve range handling logic of RepeatedField (#9799)
• Disable the aarch64 build on macOS until it can be fixed. (#9816)

Compiler

• Protoc outputs the list of suggested field numbers when invalid field
  numbers are specified in the .proto file.
• Require package names to be less than 512 bytes in length

Other

• [Kotlin] remove redundant public modifiers for compiled code (#9642)
• [C#] Update GetExtension to support getting typed value (#9655)
• Fix invalid dependency manifest when using descriptor_set_out (#9647)
• Fix C# generator handling of a field named "none" in a oneof (#9636)
• Add initial version.json file for 21-dev (#9840)
• Remove duplicate java generated code (#9909)
• Fix versioning issues in 3.20.0