[Rd] Detect UCRT-built R from within R sessions (and in configure.win)

[Tomas Kalibera]

On 9/8/21 2:08 PM, Hiroaki Yutani wrote:
> Hi,
>
> Are there any proper ways to know whether the session is running on
> the R that is built with the UCRT toolchain or not? Checking if the
> encoding is UTF-8 might do the trick, but I'm not sure if it's always
> reliable.

There in not such a mechanism, yet, but can be added, at least for 
diagnostics.

You are right that checking for UTF-8 encoding would not always be 
reliable. For example, the version of Windows may be too old to allow R 
use UTF-8 as native encoding (e.g. Windows server 2016), then R will use 
the native code page as it does today in the MSVCRT builds.

> Also, I'd like to know if there's any mechanism to detect the UCRT in
> configure.win. I know there are Makevars.ucrt and Makefile.ucrt, but
> one might want to do some feature test that is specific to the UCRT
> toolchain.

We could add support for configure.ucrt, which would take precedence 
over configure.win on the UCRT builds (like Makevars.ucrt takes 
precedence over Makevars.win). Would that work for you?

Best
Tomas

>
> Best,
> Hiroaki Yutani
>
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