These R package checks are run on Windows using an experimental (patched)
version of R-devel and an experimental version of Rtools, currently of
Rtools43. The purpose of these checks is testing updates and new versions
of Rtools and mostly related changes needed for R [2].  This experimental
setup is referred to as "ucrt3" in other documents.  I has been used in the
past to experiment with transition to UCRT and UTF-8 as the native encoding
on Windows, but this has been already merged into R.

How much these results correspond to R-devel and released Rtools43 depends
on how substantial experimental patches are applied, which can be found
using the information below. Particularly intermittent compilation failures
not present in other checks for Windows should be safe to ignore by package
authors.

See [1] for the necessary components to reproduce these checks 

  R-devel-win-*.exe .......... is a binary installer of (patched) R-devel
  R-devel-win-dbg*.exe ....... a debug build of the same
  
  CRAN/bin, BIOC/bin ......... binary CRAN packages and several of their
                               BIOC dependencies, some patched, built for
                               UCRT, automatically used by the patched R

  gcc13_ucrt3_full_*.tar.zst . the toolchain and libraries

  gcc13_ucrt3_base_*.tar.zst . the toolchain and subset of libraries,
                               enough to build R and recommended packages,
                               but probably also many other CRAN packages

  gcc13_ucrt3_cross_*.tar.zst
                             . the cross-compilation toolchain, so be used
                               on Linux with the "base" or "full" bundle
                               of libraries (currently only used to build
                               Tcl/Tk bundle)

  Tcl-*.zip .................. Tcl/Tk bundle, needed to build R from source


  rtools43-*.exe ............. preview version of Rtools43 with the toolchain
                               and libraries

  R-devel-*.diff ............. patches for R
  patches .................... patches for R packages

  *.stamp .................... stamp files informing about versioning

These components are rebuilt automatically.  In some cases the R installer
or R binary builds may be newer than those used for the check results.  The
exact versions can be identified with the help of stamp files:

  r_packages_4413_built_by_R-devel-win-79975-4413-4413.exe.stamp
  r_packages_4413_checked_by_R-devel-win-79975-4413-4413.exe.stamp

These give the full name of the R installer: R-devel-win-79975-4413-4413.exe

For reference, the relation of the version numbers in different components
is as follows:

  R devel patch R-devel-79975-4413.diff ........ R-devel 79975, R patches 4413
  R toolchain gcc13_ucrt3_full_4413.tar.zst..... toolchain 4413
  Rtools43 rtools43-4413-4741.exe .............. toolchain 4413, R tools 4741

  R installer R-devel-win-79975-4413-4413.exe .. R-devel 79975, toolchain 4413,
                                                 R patches 4413

  Tcl/Tk bundle Tcl-4413-4415.zip .............. toolchain 4413, tcl/tk 4415

  R package patches 4413 (the first number after "r_packages_" in the .stamp)

The 4413 in the example is SVN revision from R-dev-web [3], which hosts the
toolchain, R patches, R package patches and scripts.  It is sampled when the
different sub-components are taken, hence many subcomponents may have the
same version.

The checks are run on Windows Server 2022 with UTF-8 as the current native
and system encoding. 

When the R-devel-*.diff file(s) are empty, this is a vanilla R-devel build
of the corresponding version.

To find out the changes in the Rtools used, one can find out the current
version of the toolchain in RTools43 from [4] (e.g. file
rtools43-5038-5046.exe means version 5038) and compare with the version from
[1] (e.g.  file rtools43-5111-5107.exe, so toolchain version 5111):

svn diff -r 5038:5111 https://svn.r-project.org/R-dev-web/trunk/WindowsBuilds/winutf8/ucrt3/toolchain_libs

which in this case means that only cmake has been added to Rtools43, which
would very unlikely break anything.

[1] https://www.r-project.org/nosvn/winutf8/ucrt3
[2] https://svn.r-project.org/R-dev-web/trunk/WindowsBuilds/winutf8/ucrt3/howto.html
[3] https://svn.r-project.org/R-dev-web/trunk/WindowsBuilds/winutf8/ucrt3
[4] https://cran.r-project.org/bin/windows/Rtools/rtools43/files/