Make rprotobuf compatible with protobuf >= 22.x

[TeoGiane]

This should close #92

Still a WIP.

I tried to manage both cases introducing a preprocessor directive checking the version of protobuf. I tried to preserve as much as possible the existing code. Maybe we can improve src/RSourceTree.h/src/RSourceTree.cpp, since a lot of code is re-used.

On my machine (Arch Linux, gcc 13.1.1, protobuf 23.4-1) now the compilation is successfull. I have also tested compilation on Ubuntu 20.04 with protobuf 3.14.0, which relies on the old API.

[eddelbuettel]

Thanks for this! It looks pretty promising and we would get by without even a configure check.

I presume you have all the relevant piece (incl Abseil) on Arch?

[TeoGiane]

Thanks for this! It looks pretty promising and we would get by without even a configure check.

I think so. Looking at the Protocol Buffers C++ installation instruction, abseil is a requirement for installation. Hence, in case a user would prefer to build protobuf and protoc from source needs to install abseil as well, starting from version 22.0. In case user would prefer to rely on a binary version in its own package repository, abseil would be installed as well as dependency (that is what has happened to me, too).

I presume you have all the relevant piece (incl Abseil) on Arch?

On Arch, abseil is installed as a dependency of the protobuf package, with the name of abseil-cpp (see here). Having a quick look in case of Ubuntu/Debian users, I guess the corresponding name is libabsl-dev (see here).

Question: What about Windows users? Do we need some extra effort for them?

I'll soon revise my changes in the code to reduce/avoid redundancy. All suggestions are appreciated!
Thanks a lot.

[eddelbuettel]

What about Windows users?

They usually get the package as a binary from CRAN, and CRAN relies on the ProtoBuf library it has prepared. Those tend to 'stick' for a while. With your #ifdef it still build, they will simply have an older ProtoBuf library powering it (not unlike Linux using a distro-supplied older one).

[bastistician]

Just ran into the same issue (#95) on Alpine 3.19 that ships protobuf 24.4. I can confirm that this PR also fixes #95.

[eddelbuettel]

Ok, ball in my court, with my head hanging slightly in shame for having sat on this for so long. I will add a yaml file to run an action with this utilising Alpine 3.19 while Debian / Ubuntu take their time to update to newer Protocol Buffer library versions.

[eddelbuettel]

As for the older questions "but what about Windows users": someone would need to assist @kalibera to get to a newer / current Protocol Buffers library for the setup at CRAN. Ditto for macOS and @s-u.

[eddelbuettel]

Thank you both -- the @TeoGiane for the rather nice and clean PR, and to @bastistician for the wake-up call and demo of how to actually test this. CI has been added so I merged this now.

[kalibera]

As for the older questions "but what about Windows users": someone would need to assist @kalibera to get to a newer / current Protocol Buffers library for the setup at CRAN. Ditto for macOS and @s-u.

I've updated protobuf in development version of Rtools and rprotobuf passes its checks. Pending further testing, it should be available in the next release of Rtools. Ideally, anyone wanting a major update (like in this case) or addition of a library would first contribute such change upstream to MXE and then ping the Rtools maintainer via R bugzilla to include it in Rtools.