Is R 4.0 necessary?

[renkun-ken]

It DESCRIPTION it says

Depends:
    R (>= 4.0.0)

I checked the dependencies, none of the packages we depend on requires R >= 4.0.

I wonder which part of the package requires R 4.0? It would be nice if we could also support R 3.6 perhaps?

[renkun-ken]

From the dependencies, it looks like we only need R >= 3.2.0 (required by https://github.com/r-lib/systemfonts/blob/master/DESCRIPTION#L36). I tried on a machine with R 3.6.1 and everything seems to work properly.

[nx10]

The reason for R 4.0 is the updated C++ compiler under Windows. Belle depends on the C++17 standard which is only available in Rtools40 on windows.

I am quite busy at the moment, but will evaluate how much work it is to Backport Belle to C++14 soon.

[renkun-ken]

I see, looks like it is a Windows-only issue. I'm curious if it is possible to require different versions of R on different platforms as it seems to work properly on Linux and macOS without such problem.

[nx10]

Yes this is a windows only issue. I think the only way (other than backporting) would be to conditionally disable parts of the code during compile time depending on compiler features. (Disable webserver functionality for windows with R < 4.0)

[renkun-ken]

Yes this is a windows only issue. I think the only way (other than backporting) would be to conditionally disable parts of the code during compile time depending on compiler features. (Disable webserver functionality for windows with R < 4.0)

I think this makes good sense.

[nx10]

I just experimented with backporting Belle:

It turned out that windows R < 4.0 uses GCC 4.9 and actually only supports C++11 without having users manually edit a file in their home directory.

So I backported to C++11 which was easier then expected, but compiling Boost/Beast led to "internal compiler errors" with GCC 4.9. This is known and will not be fixed.

I have now set the minimum R version to >= 3.2 in the DESCRIPTION (5bccb5a). For windows users the installation will fail for anything < 4.0, but now Linux and macOS users can install it for earlier versions. We will have to see whether CRAN allows this in the next release, but I am optimistic, as we do specify C++17 in the SystemRequirements field.