[R-package] use C++17 in the CRAN package

.github/workflows/r_package.yml

@@ -335,13 +335,7 @@ jobs:
           Rscript -e "install.packages(c('R6', 'data.table', 'jsonlite', 'knitr', 'Matrix', 'RhpcBLASctl', 'rmarkdown', 'testthat'), repos = 'https://cran.rstudio.com', Ncpus = parallel::detectCores())"
           sh build-cran-package.sh
           R CMD check --as-cran --run-donttest lightgbm_*.tar.gz || exit -1
-          # ignoring the following NOTE:
-          #
-          # * checking C++ specification ... NOTE
-          #   Specified C++11: please update to current default of C++17
-          #
-          # until it's resolved (see https://github.com/microsoft/LightGBM/pull/5690)
-          if $(grep -v "C++ specification" "$LOG_FILE_NAME" | grep -v "1 NOTE" | grep -E "NOTE|WARNING|ERROR"); then
+          if grep -q -E "NOTE|WARNING|ERROR" lightgbm.Rcheck/00check.log; then
               echo "NOTEs, WARNINGs, or ERRORs have been found by R CMD check"
               exit -1
           fi

R-package/DESCRIPTION

@@ -62,5 +62,5 @@ Imports:
     parallel,
     utils
 SystemRequirements:
-    C++11
+    ~~CXXSTD~~
 RoxygenNote: 7.2.3

R-package/configure

@@ -1735,11 +1735,11 @@ if test -z "${R_HOME}"; then
     echo "could not determine R_HOME"
     exit 1
 fi
-CXX11=`"${R_HOME}/bin/R" CMD config CXX11`
-CXX11STD=`"${R_HOME}/bin/R" CMD config CXX11STD`
-CXX="${CXX11} ${CXX11STD}"
+CXX17=`"${R_HOME}/bin/R" CMD config CXX17`
+CXX17STD=`"${R_HOME}/bin/R" CMD config CXX17STD`
+CXX="${CXX17} ${CXX17STD}"
 CPPFLAGS=`"${R_HOME}/bin/R" CMD config CPPFLAGS`
-CXXFLAGS=`"${R_HOME}/bin/R" CMD config CXX11FLAGS`
+CXXFLAGS=`"${R_HOME}/bin/R" CMD config CXX17FLAGS`
 LDFLAGS=`"${R_HOME}/bin/R" CMD config LDFLAGS`
 ac_ext=cpp
 ac_cpp='$CXXCPP $CPPFLAGS'

R-package/configure.ac

@@ -20,11 +20,11 @@ if test -z "${R_HOME}"; then
     echo "could not determine R_HOME"
     exit 1
 fi
-CXX11=`"${R_HOME}/bin/R" CMD config CXX11`
-CXX11STD=`"${R_HOME}/bin/R" CMD config CXX11STD`
-CXX="${CXX11} ${CXX11STD}"
+CXX17=`"${R_HOME}/bin/R" CMD config CXX17`
+CXX17STD=`"${R_HOME}/bin/R" CMD config CXX17STD`
+CXX="${CXX17} ${CXX17STD}"
 CPPFLAGS=`"${R_HOME}/bin/R" CMD config CPPFLAGS`
-CXXFLAGS=`"${R_HOME}/bin/R" CMD config CXX11FLAGS`
+CXXFLAGS=`"${R_HOME}/bin/R" CMD config CXX17FLAGS`
 LDFLAGS=`"${R_HOME}/bin/R" CMD config LDFLAGS`
 AC_LANG(C++)
 

R-package/configure.win

@@ -6,10 +6,31 @@
 ###########################
 
 R_EXE="${R_HOME}/bin${R_ARCH_BIN}/R"
-CXX11=`"${R_EXE}" CMD config CXX11`
-CXX11STD=`"${R_EXE}" CMD config CXX11STD`
-CXX="${CXX11} ${CXX11STD}"
-CXXFLAGS=`"${R_EXE}" CMD config CXX11FLAGS`
+
+# As described in "Using C++ code" in "Writing R Extensions",
+# Rtools35 shipped with g++ 4.9, which didn't support C++17.
+#
+# Testing here for C++17 support, to account for that possibility
+# and to continue supporting R 3.6.
+#
+CXX17=`"${R_EXE}" CMD config CXX17`
+CXX17STD=`"${R_EXE}" CMD config CXX17STD`
+CXX="${CXX17} ${CXX17STD}"
+CXXFLAGS=`"${R_EXE}" CMD config CXX17FLAGS`
+CXX_STD="CXX17"
+
+cpp17_supported="yes"
+if test "${CXX17}" = "";
+then
+    cpp17_supported="no"
+    CXX11=`"${R_EXE}" CMD config CXX11`
+    CXX11STD=`"${R_EXE}" CMD config CXX11STD`
+    CXX="${CXX11} ${CXX11STD}"
+    CXXFLAGS=`"${R_EXE}" CMD config CXX11FLAGS`
+    CXX_STD="CXX11"
+fi
+echo "checking whether C++17 is supported...${cpp17_supported}"
+
 CPPFLAGS=`"${R_EXE}" CMD config CPPFLAGS`
 
 # LightGBM-specific flags
@@ -96,6 +117,9 @@ then
 fi
 
 # Generate Makevars.win from Makevars.win.in
+sed -e \
+    "s/@CXX_STD@/$CXX_STD/" \
+    < src/Makevars.win.in > src/Makevars.win
 sed -e \
     "s/@LGB_CPPFLAGS@/$LGB_CPPFLAGS/" \
     < src/Makevars.win.in > src/Makevars.win

R-package/src/Makevars.in

@@ -1,4 +1,4 @@
-CXX_STD = CXX11
+CXX_STD = CXX17
 
 PKGROOT=.
 

R-package/src/Makevars.win.in

@@ -1,4 +1,4 @@
-CXX_STD = CXX11
+CXX_STD = @CXX_STD@
 
 PKGROOT=.
 

build-cran-package.sh

@@ -127,6 +127,16 @@ cd "${TEMP_R_DIR}"
     sed -i.bak -e "s/~~VERSION~~/${LGB_VERSION}/" DESCRIPTION
     sed -i.bak -e "s/~~DATE~~/${CURRENT_DATE}/" DESCRIPTION
 
+    # Rtools35 (used with R 3.6 on Windows) doesn't support C++17
+    LGB_CXX_STD="C++17"
+    using_windows_and_r3=$(
+        Rscript -e 'cat(.Platform$OS.type == "windows" && R.version[["major"]] < 4)'
+    )
+    if [[ ${using_windows_and_r3} == "TRUE" ]]; then
+        LGB_CXX_STD="C++11"
+    fi
+    sed -i.bak -e "s/~~CXXSTD~~/${LGB_CXX_STD}/" DESCRIPTION
+
     # Remove 'region', 'endregion', and 'warning' pragmas.
     # This won't change the correctness of the code. CRAN does
     # not allow you to use compiler flag '-Wno-unknown-pragmas' or

build_r.R

@@ -390,6 +390,12 @@ description_contents <- gsub(
   , x = description_contents
   , fixed = TRUE
 )
+description_contents <- gsub(
+  pattern = "~~CXXSTD~~"
+  , replacement = "C++11"
+  , x = description_contents
+  , fixed = TRUE
+)
 writeLines(description_contents, DESCRIPTION_FILE)
 
 # CMake-based builds can't currently use R's builtin routine registration,