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

[Tomas Kalibera]

On 9/20/21 11:03 AM, Hiroaki Yutani wrote:
> I tried to use configure.ucrt, and found it results in the following
> NOTE on the released version of R, unfortunately.
>
>      * checking top-level files ... NOTE
>      Non-standard file/directory found at top level:
>      'configure.ucrt'
>
> Will this be accepted by CRAN if I submit a package that contains
> configure.ucrt? Or, is it too early to use it in a CRAN package?

Thanks, that's right, so I've ported this part to R-devel and R-patched, 
configure.ucrt and cleanup.ucrt will be treated as "standard". There is 
nothing we can do about already released versions, the NOTE will appear.

You can also use configure.win and branch on R.version$crt, e.g.

!is.null(R.version$crt) && R.version$crt == "ucrt"

or

identical(R.version$crt, "ucrt")

> In either case, while I don't have a strong opinion here, I'm starting
> to feel that it might be preferable to provide an environmental
> variable rather than creating ".ucrt" versions of files. In my
> understanding, the plan is to switch all the Windows R to UCRT at some
> point in future. But, it's not clear to me how to unify these ".win"
> files and ".ucrt" files smoothly.

With R.version$crt, you can already get a make (or even environment) 
variable. Writing R Extensions has examples how to invoke R in make 
files to get "R CMD config" values, so here you would invoke "Rscript" 
instead with one of the conditions above.

Either is fine. With .ucrt files, you can avoid copy pasting of common 
code using "include" directives. With the variable, you can use make 
conditionals. As you found now, with the variable you have the advantage 
of not getting a NOTE with already released versions of R. The .ucrt 
files are easier to maintain in hot-patches, but that is not an 
advantage for package authors.

Once a package depends on a version of R that will already use UCRT, one 
either would refactor/remove the conditionals, or integrate the ".ucrt" 
files back into the ".win". So, in the long term, there should be no 
conditionals on R.version$crt nor ".ucrt" files.

Best
Tomas
> Best,
> Hiroaki Yutani
>
> 2021年9月14日(火) 23:44 Hiroaki Yutani <yutani.ini using gmail.com>:
>
>> Thanks for both, I'll try these features.
>>
>> 2021年9月14日(火) 22:40 Tomas Kalibera <tomas.kalibera using gmail.com>:
>>
>>>
>>> On 9/9/21 5:54 AM, Hiroaki Yutani wrote:
>>>
>>> Thank you for the prompt reply.
>>>
>>>> There in not such a mechanism, yet, but can be added, at least for
>>>> diagnostics.
>>> For example, can R.version somehow contain the information?
>>>
>>> Yes, now added to the experimental builds. R.version$crt contains "ucrt" (and would contain "msvcrt" if R was built against MSVCRT).
>>>
>>>
>>>> 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?
>>> Yes, configure.ucrt should work for me. There might be someone who prefers to switch by some envvar rather than creating another file, but I don't have a strong opinion here.
>>>
>>> The experimental builds now support configure.ucrt and cleanup.ucrt files.
>>>
>>> Best
>>> Tomas
>>>
>>>
>>> Best,
>>> Hiroaki Yutani
>>>
>>> 2021年9月9日(木) 0:48 Tomas Kalibera <tomas.kalibera using gmail.com>:
>>>>
>>>> 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
>>>>>
>>>>> ______________________________________________
>>>>> R-devel using r-project.org mailing list
>>>>> https://stat.ethz.ch/mailman/listinfo/r-devel