This is a demonstration of the use of github actions for checking packages on Windows using an experimental "ucrt3" build of R using a development version of Rtools (since Rtools42). More information about the experimental builds is available in this howto.
r-install installs the "ucrt3" build of R.
See codetools for an example how to use it. The codetools package does not include native code, so it does not have to install the toolchain.
toolchain-install installs the toolchain. One may choose the "full" version or just "base", which only has libraries needed to build R and recommended packages, so it is smaller in size.
See pkg-check-test (tiff) for an example how to use it for checking a package. This example builds the tiff package and is based on Simon Urbanek's pkg-check-test, with a patch applied to support the UCRT builds. This package depends on two other packages, png and jpeg and requires at least the "base" toolchain to build its native code.
Both actions use an action for checking R packages by Simon Urbanek (original version here), currently in a slightly modified version R-actions.
Please check release notes for each individual github release of the toolchain and the included diff file. Some releases include R builds which automatically apply patches to packages at installation time. They also typically use binary builds of dependent packages (patched the same way, of CRAN and Bioconductor packages). The check action in R-actions now disable the patching explicitly for the package being checked, while it is being checked, but the patching still applies during installation of dependencies (and first round of installing the package itself). So, checks for a package may provide surprising results when there is a patch for the package (e.g. installation passes but then check fails, or there are messages about issues applying a patch). On the other hand, the benefit is that one may test changes to a package even when CRAN versions of dependent packages have not yet been fixed.