docs: RFC on C++17 minimal standard support

[nilason]

Addresses #4040.

For reference:
GDAL RFC98
PDAL 2.4
GEOS#1144

[echoix]

Is there a way to write it such that the RFC doesn't have to be updated at each version? Such as the conditions that allow us to say: these are the supported ones without having to think more about it?

For Python, the case is quite easy.

[nilason]

Is there a way to write it such that the RFC doesn't have to be updated at each version? Such as the conditions that allow us to say: these are the supported ones without having to think more about it?

For Python, the case is quite easy.

I can only repeat what I said before on this matter: #4040 (comment).

[wenzeslaus]

@echoix I would prefer the Python way as well, but I'm afraid @nilason is right that it is just more complicated for C and C++. Maybe it will change it in the future, but the nature of the ecosystem is just very different now.

One thing which we could do differently is updating the same RFC instead of creating a new one. I don't know if that's a good idea here or in general. For things like release schedule it seems to make sense, though.

[nilason]

It is probable we will want to update C and C++ minimum standard only every 5–10 years, so a new RFC weighing in all factors is not such a big deal I think. The current standard should be mentioned in doc/development/style_guide.md.

For reference eg. GDAL RFCs work in the same way, without "updating". Each RFC is a document in itself, with its history and adoption procedure.

[wenzeslaus]

@nilason, do you want to make any changes to tested C and C++ version in relation to this? The gcc.yml workflow is already using gnu17 and c++17, but perhaps adding new versions? I don't know what GCC is there, but the underlying image is currently ubuntu-22.04. Related to that, do you want to run the CI with clang? macOS seems like a good image to do that right now.

[wenzeslaus]

I have some wording suggestions, but otherwise we are only testing C++17 in gcc.yml and our dependencies already require C++17, so I don't think there is much to discuss.

[nilason]

I have some wording suggestions, but otherwise we are only testing C++17 in gcc.yml and our dependencies already require C++17, so I don't think there is much to discuss.

Thanks for the good suggestions. In practice, also the mac runner is C++17, as that is the default with Clang 19.