[R-package] Add support for R 4.0 (fixes #3064, fixes #3024) (#3065)

* [R-package] replaced gendef.exe with R code to create R.def (fixes #3064)

* fix broken things

* trying to add R4.0 docs

* changed make

* fixing make paths

* update notes on environment variables

* fix linting

* fixes to CI

* fixing build_cmd and other stuff

* fix bad substitution

* fix Azure Linux builds

* I am bad at bash

* simplifying

* only testing R

* getting better logs

* mingw32

* docs

* toolchain

* using msys

* fix visual studio condition

* toolchain test

* full CI

* fix if-elses

* bump allowed NOTEs

* search for Rscript

* updates to docs

* use processx

* fix mismatched arguments

* move CI to GitHub Actions

* minor changes

* fix workflow file

* fix templating

* fix Azure DevOps

* debugging windows builds

* dont shQuote file name

* all GitHub Actions jobs

* Apply suggestions from code review
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* minor cleanup

* remove objdump printing

* make file.remove() invisible

* Apply suggestions from code review
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* reduce duplicated paths in docs
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

.appveyor.yml

@@ -15,8 +15,12 @@ environment:
   matrix:
     - COMPILER: MINGW
       TASK: r-package
-    - COMPILER: MSVC
+      R_VERSION: 3.6
+      TOOLCHAIN: MINGW
+    - COMPILER: MSVC 
       TASK: r-package
+      R_VERSION: 4.0
+      TOOLCHAIN: MSVC
       APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
     - COMPILER: MSVC
       TASK: python

.ci/test_r_package.sh

@@ -7,6 +7,26 @@ mkdir -p $R_LIB_PATH
 echo "R_LIBS=$R_LIB_PATH" > ${HOME}/.Renviron
 export PATH="$R_LIB_PATH/R/bin:$PATH"
 
+# Get details needed for installing R components
+#
+# NOTES:
+#    * Linux builds on Azure use a container and don't need these details
+if ! { [[ $AZURE == "true" ]] && [[ $OS_NAME == "linux" ]]; }; then
+    R_MAJOR_VERSION=( ${R_VERSION//./ } )
+    if [[ "${R_MAJOR_VERSION}" == "3" ]]; then
+        export R_MAC_VERSION=3.6.3
+        export R_LINUX_VERSION="3.6.3-1bionic"
+        export R_APT_REPO="bionic-cran35/"
+    elif [[ "${R_MAJOR_VERSION}" == "4" ]]; then
+        export R_MAC_VERSION=4.0.0
+        export R_LINUX_VERSION="4.0.0-1.1804.0"
+        export R_APT_REPO="bionic-cran40/"
+    else
+        echo "Unrecognized R version: ${R_VERSION}"
+        exit -1
+    fi
+fi
+
 # installing precompiled R for Ubuntu
 # https://cran.r-project.org/bin/linux/ubuntu/#installation
 # adding steps from https://stackoverflow.com/a/56378217/3986677 to get latest version
@@ -18,7 +38,7 @@ if [[ $AZURE != "true" ]] && [[ $OS_NAME == "linux" ]]; then
         --keyserver keyserver.ubuntu.com \
         --recv-keys E298A3A825C0D65DFD57CBB651716619E084DAB9
     sudo add-apt-repository \
-        "deb https://cloud.r-project.org/bin/linux/ubuntu bionic-cran35/"
+        "deb https://cloud.r-project.org/bin/linux/ubuntu ${R_APT_REPO}"
     sudo apt-get update
     sudo apt-get install \
         --no-install-recommends \

.ci/test_r_package_windows.ps1

@@ -29,34 +29,60 @@ function Download-Miktex-Setup {
     Download-File-With-Retries $FileToDownload $destfile
 }
 
-$env:R_WINDOWS_VERSION = "3.6.3"
 $env:R_LIB_PATH = "$env:BUILD_SOURCESDIRECTORY/RLibrary" -replace '[\\]', '/'
 $env:R_LIBS = "$env:R_LIB_PATH"
-$env:PATH = "$env:R_LIB_PATH/Rtools/bin;" + "$env:R_LIB_PATH/R/bin/x64;" + "$env:R_LIB_PATH/miktex/texmfs/install/miktex/bin/x64;" + $env:PATH
+$env:PATH = "$env:R_LIB_PATH/Rtools/bin;" + "$env:R_LIB_PATH/Rtools/usr/bin;" + "$env:R_LIB_PATH/R/bin/x64;" + "$env:R_LIB_PATH/miktex/texmfs/install/miktex/bin/x64;" + $env:PATH
 $env:CRAN_MIRROR = "https://cloud.r-project.org/"
 $env:CTAN_MIRROR = "https://ctan.math.illinois.edu/systems/win32/miktex"
 $env:CTAN_MIKTEX_ARCHIVE = "$env:CTAN_MIRROR/setup/windows-x64/"
 $env:CTAN_PACKAGE_ARCHIVE = "$env:CTAN_MIRROR/tm/packages/"
 
+# Get details needed for installing R components
+#
+# NOTES:
+#    * some paths and file names are different on R4.0
+$env:R_MAJOR_VERSION = $env:R_VERSION.split('.')[0]
+if ($env:R_MAJOR_VERSION -eq "3") {
+  $env:RTOOLS_MINGW_BIN = "$env:R_LIB_PATH/Rtools/mingw_64/bin"
+  $env:RTOOLS_EXE_FILE = "Rtools35.exe"
+  $env:R_WINDOWS_VERSION = "3.6.3"
+} elseif ($env:R_MAJOR_VERSION -eq "4") {
+  $env:RTOOLS_MINGW_BIN = "$env:R_LIB_PATH/Rtools/mingw64/bin"
+  $env:RTOOLS_EXE_FILE = "rtools40-x86_64.exe"
+  $env:R_WINDOWS_VERSION = "4.0.0"
+} else {
+  Write-Output "[ERROR] Unrecognized R version: $env:R_VERSION"
+  Check-Output $false
+}
+
 if ($env:COMPILER -eq "MINGW") {
-  $env:CXX = "$env:R_LIB_PATH/Rtools/mingw_64/bin/g++.exe"
-  $env:CC = "$env:R_LIB_PATH/Rtools/mingw_64/bin/gcc.exe"
+  $env:CXX = "$env:RTOOLS_MINGW_BIN/g++.exe"
+  $env:CC = "$env:RTOOLS_MINGW_BIN/gcc.exe"
 }
 
 cd $env:BUILD_SOURCESDIRECTORY
 tzutil /s "GMT Standard Time"
 [Void][System.IO.Directory]::CreateDirectory($env:R_LIB_PATH)
 
-if ($env:COMPILER -eq "MINGW") {
+if ($env:TOOLCHAIN -eq "MINGW") {
   Write-Output "Telling R to use MinGW"
   $install_libs = "$env:BUILD_SOURCESDIRECTORY/R-package/src/install.libs.R"
-  ((Get-Content -path $install_libs -Raw) -replace 'use_mingw <- FALSE','use_mingw <- TRUE') | Set-Content -Path $install_libs
+  ((Get-Content -Path $install_libs -Raw) -Replace 'use_mingw <- FALSE','use_mingw <- TRUE') | Set-Content -Path $install_libs
+} elseif ($env:TOOLCHAIN -eq "MSYS") {
+  Write-Output "Telling R to use MSYS"
+  $install_libs = "$env:BUILD_SOURCESDIRECTORY/R-package/src/install.libs.R"
+  ((Get-Content -Path $install_libs -Raw) -Replace 'use_msys2 <- FALSE','use_msys2 <- TRUE') | Set-Content -Path $install_libs
+} elseif ($env:TOOLCHAIN -eq "MSVC") {
+  # no customization for MSVC
+} else {
+  Write-Output "[ERROR] Unrecognized compiler: $env:TOOLCHAIN"
+  Check-Output $false
 }
 
 # download R and RTools
 Write-Output "Downloading R and Rtools"
 Download-File-With-Retries -url "https://cloud.r-project.org/bin/windows/base/old/$env:R_WINDOWS_VERSION/R-$env:R_WINDOWS_VERSION-win.exe" -destfile "R-win.exe"
-Download-File-With-Retries -url "https://cloud.r-project.org/bin/windows/Rtools/Rtools35.exe" -destfile "Rtools.exe"
+Download-File-With-Retries -url "https://cloud.r-project.org/bin/windows/Rtools/$env:RTOOLS_EXE_FILE" -destfile "Rtools.exe"
 
 # Install R
 Write-Output "Installing R"
@@ -67,9 +93,9 @@ Write-Output "Installing Rtools"
 Start-Process -FilePath Rtools.exe -NoNewWindow -Wait -ArgumentList "/VERYSILENT /DIR=$env:R_LIB_PATH/Rtools" ; Check-Output $?
 Write-Output "Done installing Rtools"
 
-# MiKTeX and pandoc can be skipped on non-MINGW builds, since we don't
+# MiKTeX and pandoc can be skipped on MSVC builds, since we don't
 # build the package documentation for those
-if ($env:COMPILER -eq "MINGW") {
+if ($env:COMPILER -ne "MSVC") {
     Download-Miktex-Setup "$env:CTAN_MIKTEX_ARCHIVE" "miktexsetup-x64.zip"
     Add-Type -AssemblyName System.IO.Compression.FileSystem
     [System.IO.Compression.ZipFile]::ExtractToDirectory("miktexsetup-x64.zip", "miktex")
@@ -115,7 +141,7 @@ if ($env:COMPILER -ne "MSVC") {
   $note_str = Get-Content "${LOG_FILE_NAME}" | Select-String -Pattern ' NOTE' | Out-String ; Check-Output $?
   $relevant_line = $note_str -match '.*Status: (\d+) NOTE.*'
   $NUM_CHECK_NOTES = $matches[1]
-  $ALLOWED_CHECK_NOTES = 3
+  $ALLOWED_CHECK_NOTES = 4
   if ([int]$NUM_CHECK_NOTES -gt $ALLOWED_CHECK_NOTES) {
       Write-Output "Found ${NUM_CHECK_NOTES} NOTEs from R CMD check. Only ${ALLOWED_CHECK_NOTES} are allowed"
       Check-Output $False
@@ -139,6 +165,16 @@ if ($checks.Matches.length -eq 0) {
   Check-Output $False
 }
 
+# Checking that we got the right toolchain for MinGW. If using MinGW, both
+# MinGW and MSYS toolchains are supported
+if ($env:COMPILER -eq "MINGW") {
+  $checks = Select-String -Path "${INSTALL_LOG_FILE_NAME}" -Pattern "Trying to build with.*$env:TOOLCHAIN"
+  if ($checks.Matches.length -eq 0) {
+    Write-Output "The wrong toolchain was used. Check the build logs."
+    Check-Output $False
+  }
+}
+
 if ($env:COMPILER -eq "MSVC") {
   Write-Output "Running tests with testthat.R"
   cd R-package/tests

.github/workflows/main.yml

@@ -10,7 +10,7 @@ on:
 
 jobs:
   test:
-    name: ${{ matrix.task }} (${{ matrix.os }}, ${{ matrix.compiler }})
+    name: ${{ matrix.task }} (${{ matrix.os }}, ${{ matrix.compiler }}, R ${{ matrix.r_version }})
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
@@ -19,15 +19,35 @@ jobs:
           - os: ubuntu-latest
             task: r-package
             compiler: gcc
+            r_version: 3.6
+          - os: ubuntu-latest
+            task: r-package
+            compiler: gcc
+            r_version: 4.0
+          - os: ubuntu-latest
+            task: r-package
+            compiler: clang
+            r_version: 3.6
           - os: ubuntu-latest
             task: r-package
             compiler: clang
+            r_version: 4.0
           - os: macOS-latest
             task: r-package
             compiler: gcc
+            r_version: 3.6
+          - os: macOS-latest
+            task: r-package
+            compiler: gcc
+            r_version: 4.0
+          - os: macOS-latest
+            task: r-package
+            compiler: clang
+            r_version: 3.6
           - os: macOS-latest
             task: r-package
             compiler: clang
+            r_version: 4.0
     steps:
       - name: Checkout repository
         uses: actions/checkout@v1
@@ -53,5 +73,6 @@ jobs:
           export CONDA="$HOME/miniconda"
           export PATH="$CONDA/bin:${HOME}/.local/bin:$PATH"
           export LGB_VER=$(head -n 1 VERSION.txt)
+          export R_VERSION="${{ matrix.r_version }}"
           $GITHUB_WORKSPACE/.ci/setup.sh
           $GITHUB_WORKSPACE/.ci/test.sh

.gitignore

@@ -406,6 +406,7 @@ R-package/src-i386
 lightgbm_r/*
 lightgbm*.tar.gz
 lightgbm.Rcheck/
+*.def
 
 # Files created by R examples and tests
 **/lgb-Dataset.data

.vsts-ci.yml

@@ -109,11 +109,18 @@ jobs:
   pool:
     vmImage: 'vs2017-win2016'
   strategy:
-    maxParallel: 4
+    maxParallel: 5
     matrix:
-      r_package:
+      r_package_msvc:
         TASK: r-package
         COMPILER: MSVC
+        R_VERSION: 3.6
+        TOOLCHAIN: MSVC
+      r_package_msys:
+        TASK: r-package
+        COMPILER: MINGW
+        R_VERSION: 4.0
+        TOOLCHAIN: MSYS
       regular:
         TASK: regular
         PYTHON_VERSION: 3.6

R-package/README.md

@@ -20,14 +20,53 @@ Note: 32-bit (i386) R/Rtools is currently not supported.
 
 #### Windows Preparation
 
-Installing [Rtools](https://cran.r-project.org/bin/windows/Rtools/) is mandatory, and only support the 64-bit version. It requires to add to PATH the Rtools MinGW64 folder, if it was not done automatically during installation.
+Installing a 64-bit version of [Rtools](https://cran.r-project.org/bin/windows/Rtools/) is mandatory.
 
-The default compiler is Visual Studio (or [VS Build Tools](https://visualstudio.microsoft.com/downloads/)) in Windows, with an automatic fallback to Rtools or any [MinGW64](https://sourceforge.net/projects/mingw-w64/files/Toolchains%20targetting%20Win64/Personal%20Builds/mingw-builds/) (x86_64-posix-seh) available (this means if you have only Rtools and CMake, it will compile fine).
+After installing `Rtools` and `CMake`, be sure the following paths are added to the environment variable `PATH`. These may have been automatically added when installing other software.
 
-To force the usage of Rtools / MinGW, you can set `use_mingw` to `TRUE` in `R-package/src/install.libs.R`.
+* `Rtools`
+    - If you have `Rtools` 3.x, example:
+        - `C:\Rtools\mingw_64\bin`
+    - If you have `Rtools` 4.0, example:
+        - `C:\rtools40\mingw64\bin`
+        - `C:\rtools40\usr\bin`
+* `CMake`
+    - example: `C:\Program Files\CMake\bin`
+* `R`
+    - example: `C:\Program Files\R\R-3.6.1\bin`
+
+NOTE: Two `Rtools` paths are required from `Rtools` 4.0 onwards because paths and the list of included software was changed in `Rtools` 4.0.
+
+#### Windows Toolchain Options
+
+A "toolchain" refers to the collection of software used to build the library. The R package can be built with three different toolchains.
 
 **Warning for Windows users**: it is recommended to use *Visual Studio* for its better multi-threading efficiency in Windows for many core systems. For very simple systems (dual core computers or worse), MinGW64 is recommended for maximum performance. If you do not know what to choose, it is recommended to use [Visual Studio](https://visualstudio.microsoft.com/downloads/), the default compiler. **Do not try using MinGW in Windows on many core systems. It may result in 10x slower results than Visual Studio.**
 
+**Visual Studio (default)**
+
+By default, the package will be built with [Visual Studio Build Tools](https://visualstudio.microsoft.com/downloads/).
+
+**MinGW (R 3.x)**
+
+If you are using R 3.x and installation fails with Visual Studio, `LightGBM` will fall back to using [MinGW](http://mingw-w64.org/doku.php) bundled with `Rtools`.
+
+If you want to force `LightGBM` to use MinGW (for any R version), open `R-package/src/install.libs.R` and change `use_mingw`:
+
+```r
+use_mingw <- TRUE
+```
+
+**MSYS2 (R 4.x)**
+
+If you are using R 4.x and installation fails with Visual Studio, `LightGBM` will fall back to using [MSYS2](https://www.msys2.org/). This should work with the tools already bundled in `Rtools` 4.0.
+
+If you want to force `LightGBM` to use MSYS2 (for any R version), open `R-package/src/install.libs.R` and change `use_msys2`:
+
+```r
+use_msys2 <- TRUE
+```
+
 #### Mac OS Preparation
 
 You can perform installation either with **Apple Clang** or **gcc**. In case you prefer **Apple Clang**, you should install **OpenMP** (details for installation can be found in [Installation Guide](https://github.com/microsoft/LightGBM/blob/master/docs/Installation-Guide.rst#apple-clang)) first and **CMake** version 3.16 or higher is required. In case you prefer **gcc**, you need to install it (details for installation can be found in [Installation Guide](https://github.com/microsoft/LightGBM/blob/master/docs/Installation-Guide.rst#gcc)) and set some environment variables to tell R to use `gcc` and `g++`. If you install these from Homebrew, your versions of `g++` and `gcc` are most likely in `/usr/local/bin`, as shown below.

R-package/inst/make-r-def.R

+# [description]
+#     Create a definition file (.def) from a .dll file, using objdump.
+#
+# [usage]
+#
+#     Rscript make-r-def.R something.dll something.def
+#
+# [references]
+#    * https://www.cs.colorado.edu/~main/cs1300/doc/mingwfaq.html
+
+args <- commandArgs(trailingOnly = TRUE)
+
+IN_DLL_FILE <- args[[1L]]
+OUT_DEF_FILE <- args[[2L]]
+DLL_BASE_NAME <- basename(IN_DLL_FILE)
+
+message(sprintf("Creating '%s' from '%s'", OUT_DEF_FILE, IN_DLL_FILE))
+
+# system() will not raise an R exception if the process called
+# fails. Wrapping it here to get that behavior.
+#
+# system() introduces a lot of overhead, at least on Windows,
+# so trying processx if it is available
+.pipe_shell_command_to_stdout <- function(command, args, out_file) {
+    has_processx <- suppressMessages({
+      suppressWarnings({
+        require("processx")  # nolint
+      })
+    })
+    if (has_processx) {
+        p <- processx::process$new(
+            command = command
+            , args = args
+            , stdout = out_file
+            , windows_verbatim_args = FALSE
+        )
+        invisible(p$wait())
+    } else {
+        message(paste0(
+          "Using system2() to run shell commands. Installing "
+          , "'processx' with install.packages('processx') might "
+          , "make this faster."
+        ))
+        # shQuote() is necessary here since one of the arguments
+        # is a file-path to R.dll, which may have spaces. processx
+        # does such quoting but system2() does not
+        exit_code <- system2(
+            command = command
+            , args = shoQuote(args)
+            , stdout = out_file
+        )
+        if (exit_code != 0L) {
+            stop(paste0("Command failed with exit code: ", exit_code))
+        }
+    }
+    return(invisible(NULL))
+}
+
+# use objdump to dump all the symbols
+OBJDUMP_FILE <- "objdump-out.txt"
+.pipe_shell_command_to_stdout(
+    command = "objdump"
+    , args = c("-p", IN_DLL_FILE)
+    , out_file = OBJDUMP_FILE
+)
+
+objdump_results <- readLines(OBJDUMP_FILE)
+invisible(file.remove(OBJDUMP_FILE))
+
+# Only one table in the objdump results matters for our purposes,
+# see https://www.cs.colorado.edu/~main/cs1300/doc/mingwfaq.html
+start_index <- which(
+    grepl(
+        pattern = "[Ordinal/Name Pointer] Table"
+        , x = objdump_results
+        , fixed = TRUE
+    )
+)
+empty_lines <- which(objdump_results == "")
+end_of_table <- empty_lines[empty_lines > start_index][1L]
+
+# Read the contents of the table
+exported_symbols <- objdump_results[(start_index + 1L):end_of_table]
+exported_symbols <- gsub("\t", "", exported_symbols)
+exported_symbols <- gsub(".*\\] ", "", exported_symbols)
+exported_symbols <- gsub(" ", "", exported_symbols)
+
+# Write R.def file
+writeLines(
+    text = c(
+        paste0("LIBRARY \"", DLL_BASE_NAME, "\"")
+        , "EXPORTS"
+        , exported_symbols
+    )
+    , con = OUT_DEF_FILE
+    , sep = "\n"
+)
+message(sprintf("Successfully created '%s'", OUT_DEF_FILE))

R-package/src/cmake/modules/FindLibR.cmake

@@ -41,20 +41,26 @@ function(create_rlib_for_msvc)
     message(FATAL_ERROR "LIBR_CORE_LIBRARY, '${LIBR_CORE_LIBRARY}', not found")
   endif()
 
-  find_program(GENDEF_EXE gendef)
   find_program(DLLTOOL_EXE dlltool)
 
-  if(NOT GENDEF_EXE OR NOT DLLTOOL_EXE)
-    message(FATAL_ERROR "Either gendef.exe or dlltool.exe not found!\
+  if(NOT DLLTOOL_EXE)
+    message(FATAL_ERROR "dlltool.exe not found!\
       \nDo you have Rtools installed with its MinGW's bin/ in PATH?")
   endif()
 
   set(LIBR_MSVC_CORE_LIBRARY "${CMAKE_CURRENT_BINARY_DIR}/R.lib" CACHE PATH "R.lib filepath")
 
-  # extract symbols from R.dll into R.def and R.lib import library
-  execute_process(COMMAND ${GENDEF_EXE}
-    "-" "${LIBR_CORE_LIBRARY}"
-    OUTPUT_FILE "${CMAKE_CURRENT_BINARY_DIR}/R.def"
+  get_filename_component(
+    LIBR_RSCRIPT_EXECUTABLE_DIR
+    ${LIBR_EXECUTABLE}
+    DIRECTORY
+  )
+  set(LIBR_RSCRIPT_EXECUTABLE "${LIBR_RSCRIPT_EXECUTABLE_DIR}/Rscript")
+
+  execute_process(
+    COMMAND ${LIBR_RSCRIPT_EXECUTABLE}
+    "${CMAKE_CURRENT_BINARY_DIR}/make-r-def.R"
+    "${LIBR_CORE_LIBRARY}" "${CMAKE_CURRENT_BINARY_DIR}/R.def"
   )
   execute_process(COMMAND ${DLLTOOL_EXE}
     "--input-def" "${CMAKE_CURRENT_BINARY_DIR}/R.def"

R-package/src/install.libs.R

 # User options
 use_precompile <- FALSE
 use_gpu <- FALSE
+
+# For Windows, the package will be built with Visual Studio
+# unless you set one of these to TRUE
 use_mingw <- FALSE
+use_msys2 <- FALSE
+
+if (use_mingw && use_msys2) {
+  stop("Cannot use both MinGW and MSYS2. Please choose only one.")
+}
 
 if (.Machine$sizeof.pointer != 8L) {
   stop("LightGBM only supports 64-bit R, please check the version of R and Rtools.")
@@ -110,12 +118,55 @@ if (!use_precompile) {
   )
   setwd(build_dir)
 
+  use_visual_studio <- !(use_mingw || use_msys2)
+
+  # If using MSVC to build, pull in the script used
+  # to create R.def from R.dll
+  if (WINDOWS && use_visual_studio) {
+    write_succeeded <- file.copy(
+      "../../inst/make-r-def.R"
+      , file.path(build_dir, "make-r-def.R")
+      , overwrite = TRUE
+    )
+    if (!write_succeeded) {
+      stop("Copying make-r-def.R failed")
+    }
+  }
+
   # Prepare installation steps
   cmake_args <- NULL
   build_cmd <- "make"
   build_args <- "_lightgbm"
   lib_folder <- file.path(source_dir, fsep = "/")
 
+  WINDOWS_BUILD_TOOLS <- list(
+    "MinGW" = c(
+      build_tool = "mingw32-make.exe"
+      , makefile_generator = "MinGW Makefiles"
+    )
+    , "MSYS2" = c(
+      build_tool = "make.exe"
+      , makefile_generator = "MSYS Makefiles"
+    )
+  )
+
+  if (use_mingw) {
+    windows_toolchain <- "MinGW"
+  } else if (use_msys2) {
+    windows_toolchain <- "MSYS2"
+  } else {
+    # Rtools 4.0 moved from MinGW to MSYS toolchain. If user tries
+    # Visual Studio install but that fails, fall back to the toolchain
+    # supported in Rtools
+    if (R_ver >= 4.0) {
+      windows_toolchain <- "MSYS2"
+    } else {
+      windows_toolchain <- "MinGW"
+    }
+  }
+  windows_build_tool <- WINDOWS_BUILD_TOOLS[[windows_toolchain]][["build_tool"]]
+  windows_makefile_generator <- WINDOWS_BUILD_TOOLS[[windows_toolchain]][["makefile_generator"]]
+
   if (use_gpu) {
     cmake_args <- c(cmake_args, "-DUSE_GPU=ON")
   }
@@ -139,21 +190,21 @@ if (!use_precompile) {
 
   # Check if Windows installation (for gcc vs Visual Studio)
   if (WINDOWS) {
-    if (use_mingw) {
-      message("Trying to build with MinGW")
+    if (!use_visual_studio) {
+      message(sprintf("Trying to build with %s", windows_toolchain))
       # Must build twice for Windows due sh.exe in Rtools
-      cmake_args <- c(cmake_args, "-G", shQuote("MinGW Makefiles"))
+      cmake_args <- c(cmake_args, "-G", shQuote(windows_makefile_generator))
       .run_shell_command("cmake", c(cmake_args, ".."), strict = FALSE)
-      build_cmd <- "mingw32-make.exe"
+      build_cmd <- windows_build_tool
       build_args <- "_lightgbm"
     } else {
       visual_studio_succeeded <- .generate_vs_makefiles(cmake_args)
       if (!isTRUE(visual_studio_succeeded)) {
-        warning("Building with Visual Studio failed. Attempting with MinGW")
+        warning(sprintf("Building with Visual Studio failed. Attempting with %s", windows_toolchain))
         # Must build twice for Windows due sh.exe in Rtools
-        cmake_args <- c(cmake_args, "-G", shQuote("MinGW Makefiles"))
+        cmake_args <- c(cmake_args, "-G", shQuote(windows_makefile_generator))
         .run_shell_command("cmake", c(cmake_args, ".."), strict = FALSE)
-        build_cmd <- "mingw32-make.exe"
+        build_cmd <- windows_build_tool
         build_args <- "_lightgbm"
       } else {
         build_cmd <- "cmake"
@@ -196,6 +247,7 @@ if (!use_precompile) {
   }
 
   # build the library
+  message("Building lib_lightgbm")
   .run_shell_command(build_cmd, build_args)
   src <- file.path(lib_folder, paste0("lib_lightgbm", SHLIB_EXT), fsep = "/")
 

build_r.R

@@ -115,6 +115,13 @@ for (src_file in c("lightgbm_R.cpp", "lightgbm_R.h", "R_object_helper.h")) {
   .handle_result(result)
 }
 
+result <- file.copy(
+  from = file.path("R-package", "inst", "make-r-def.R")
+  , to = file.path(TEMP_R_DIR, "inst", "bin/")
+  , overwrite = TRUE
+)
+.handle_result(result)
+
 # NOTE: --keep-empty-dirs is necessary to keep the deep paths expected
 #       by CMake while also meeting the CRAN req to create object files
 #       on demand

docs/GPU-Windows.rst

@@ -135,7 +135,7 @@ To check whether you need 32-bit or 64-bit MinGW for R, install LightGBM as usua
 If it says ``mingw_64`` then you need the 64-bit version (PATH with ``c:\Rtools\bin;c:\Rtools\mingw_64\bin``),
 otherwise you need the 32-bit version (``c:\Rtools\bin;c:\Rtools\mingw_32\bin``), the latter being a very rare and untested case.
 
---------------
+NOTE: If you are using `Rtools` 4.0 or later, the path will have `mingw64` instead of `mingw_64` (PATH with `C:\rtools40\mingw64\bin`), and `mingw32` instead of `mingw_32` (`C:\rtools40\mingw32\bin`). The 32-bit version remains an unsupported solution under Rtools 4.0.
 
 Download the prebuilt Boost
 ---------------------------