also check plain '-fopenmp' for gcc (#6418)

* also check plain '-fopenmp' for gcc (closes #6409) * update NEWS * cite in NEWS --------- Co-authored-by: Michael Chirico <[email protected]>
Rdatatable · Aug 28, 2024 · 18f4ab6 · 18f4ab6
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diff --git a/NEWS.md b/NEWS.md
@@ -12,6 +12,8 @@
 
 2. Continued work to remove non-API C functions, [#6180](https://github.com/Rdatatable/data.table/issues/6180). Thanks Ivan Krylov for the PR and for writing a clear and concise guide about the R API: https://aitap.codeberg.page/R-api/.
 
+3. `data.table` again properly detects OpenMP support when built using `gcc` on macOS, [#6409](https://github.com/Rdatatable/data.table/issues/6409). Thanks @barracuda156 for the report and @kevinushey for the fix.
+
 # data.table [v1.16.0](https://github.com/Rdatatable/data.table/milestone/30)  (25 August 2024)
 
 ## BREAKING CHANGES

diff --git a/configure b/configure
@@ -121,6 +121,17 @@ detect_openmp () {
       echo "no"
     fi
 
+    # https://github.com/Rdatatable/data.table/issues/6409
+    printf "%s" "* checking if R installation supports OpenMP with \"-fopenmp\" ... "
+    if CPPFLAGS="${CPPFLAGS} -fopenmp" "${R_HOME}/bin/R" CMD SHLIB test-omp.c >> config.log 2>&1; then
+      echo "yes"
+      export PKG_CFLAGS="${PKG_CFLAGS} -fopenmp"
+      export R_OPENMP_ENABLED=1
+      return
+    else
+      echo "no"
+    fi
+
     if [ "$(uname -m)" = "arm64" ]; then
       HOMEBREW_PREFIX=/opt/homebrew
     else