Moving to C++20 required update of the protobuf to v22.x to pull in proto complier changes that handle C++20 reserved keywords correctly. protobuf v22 also underwent a massive refactor, which impacted a number of dependencies.

Impacted Envoy dependencies are failing to build with the protobuf v22.x because they used the internal guts (details) of previous protobuf.

List of affected dependencies:

• PGV and star validate
• gRPC-JSON transcoder (in progress)
• CEL (in progress)

C++20 mode is now enabled for the compile-time-options build. Moving forward an enabling it for the main build requires the following changes:

• Update GCC to version 11 for C++20 support comparable to clang
• Update Windows Visual Studio to 16.10 at least (currently at 16.9)
• May need to ditch clang with stdlib as the stdlib version bundled with clang does not support C++20 (at least in clang-14). Only clang with libc++ will be supported.