R-core member Tomas Kalibera has started experimenting with building R to target the new Windows Universal C Runtime (UCRT). The main motivation is that recent updates to Windows 10 and Windows Server 2019 have made it possible to set the native encoding to UTF-8 on software built for UCRT.
Native UTF-8 on Windows makes it easier for R to support certain system functionality on machines with non-western languages, for example copy-pasting Chineese text to the R terminal, or opening file with a Chineese filename (though the latter already works well in most cases). Tomas as written a few of blog posts with more detailed information: https://developer.r-project.org/Blog/public/
On Windows systems with a European language or from before 2019 the UCRT probably makes no difference to the R user.
Recent builds of rtools4 include a ucrt64 toolchain to test packages with Windows UCRT. To compile your own packages you need:
- A recent version of ucrt3 R-devel.exe build: https://www.r-project.org/nosvn/winutf8/ucrt3/
- A recent version of rtools4: https://cran.r-project.org/bin/windows/Rtools/
Unlike the regular R, the experimental R-devel builds look for gcc on the PATH, so you need to add e.g. c:/rtools40/ucrt64/bin to the PATH, in addition to the regular make tools from c:/rtools40/usr/bin.
A safe way to do this is to create a file C:/Program Files/R/R-devel/etc/Renviron.site containing:
PATH="${RTOOLS40_HOME}\ucrt64\bin;${RTOOLS40_HOME}\usr\bin;${PATH}"
Alternatively could also add this line to your regular ~/Renviron file as described in the rtools40 homepage. Now restart R and try installing a package from source:
install.packages("jsonlite", type = "source")Also note that the experimental UCRT version of R has a hack to automatically download and apply custom patches from Tomas Kalibera for certain packages. To disable this behavior you can add the following line to your Renviron file:
_R_INSTALL_TIME_PATCHES_=no
Building software for Windows UCRT requires a toolchain that is configured to target the UCRT, but other than that, everything works exactly the same. Binaries for UCRT and MSVCRT are typically incompatible, hence all system libraries and R packages need to be built with a UCRT toolchain to work in a UCRT version of R.
Recent versions of msys2 and rtools40 include such a ucrt64 toolchain, as well as ucrt64 binaries for all system libraries. Pacman packages are prefixed with mingw-w64-ucrt-x86_64 (as opposed to mingw-w64-x86_64 for regular msvcrt mingw64 binaries). For example to install imagemagick:
pacman -Sy mingw-w64-ucrt-x86_64-imagemagick
Pacman installs the ucrt-x86_64 toolchains and libaries are under c:/rtools40/ucrt64/ or c:/msys64/ucrt64/ so they do not conflict with the regular x86_64 toolchains and libraries which are in c:/rtools40/mingw64/ or c:/msys64/mingw64/.
Tomas has been using an alternative environment based on mxe to run his experiments, which you can read about in this blog posts. He has published a 6gb archive bundle of his local environment which uses cross-compilation from Linux. This toolchain is fully compatible and interchangable with the ucrt compilers from rtools4.