From da6266a59923f28116714a1171a3736b4a57db4e Mon Sep 17 00:00:00 2001
From: Kevin Ushey <kevinushey@gmail.com>
Date: Mon, 1 Dec 2025 16:08:38 -0800
Subject: [PATCH 1/2] alternate openmp plugin changes

---
 ChangeLog      |  4 ++++
 R/Attributes.R | 63 +++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 64 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index b08ef1f73..4f11ca684 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+2025-12-01  Kevin Ushey <kevinushey@gmail.com>
+
+	* R/Attributes.R: Update OpenMP plugin for macOS
+
 2025-11-24  Dirk Eddelbuettel  <edd@debian.org>
 
 	* inst/include/Rcpp/r/check_r_headers.h: Add RCPP_NO_R_HEADERS_CHECK
diff --git a/R/Attributes.R b/R/Attributes.R
index 53e9f0a61..500fd60fd 100644
--- a/R/Attributes.R
+++ b/R/Attributes.R
@@ -586,10 +586,67 @@ compileAttributes <- function(pkgdir = ".", verbose = getOption("verbose")) {
     list(env = list(PKG_CXXFLAGS ="-std=c++2b"))
 }
 
+.openmpPluginDefault <- function() {
+    list(env = list(PKG_CXXFLAGS = "-fopenmp", PKG_LIBS = "-fopenmp"))
+}
+
+.openmpPluginDarwin <- function() {
+
+    # get the C++ compiler from R
+    r <- file.path(R.home("bin"), "R")
+    cxx <- tryCatch(
+        system2(r, c("CMD", "config", "CXX"), stdout = TRUE),
+        condition = identity
+    )
+    if (inherits(cxx, "condition"))
+        return(.openmpPluginDefault())
+
+    # check the compiler version
+    command <- paste(cxx, "--version")
+    version <- tryCatch(
+        system(command, intern = TRUE),
+        condition = identity
+    )
+    if (inherits(version, "condition"))
+        return(.openmpPluginDefault())
+
+    # if we're using Apple clang, use alternate flags
+    # assume libomp was installed following https://mac.r-project.org/openmp/
+    if (any(grepl("Apple clang", version))) {
+
+        cxxflags <- "-Xclang -fopenmp"
+        libs <- "-lomp"
+
+    }
+
+    # if we're using Homebrew clang, add in libomp include paths
+    else if (any(grepl("Homebrew clang", version))) {
+
+        # ensure Homebrew paths are included during compilation
+        machine <- Sys.info()[["machine"]]
+        prefix <- if (machine == "arm64") "/opt/homebrew" else "/usr/local"
+
+        # build flags
+        cxxflags <- sprintf("-I%s/opt/libomp/include -fopenmp", prefix)
+        libs <- sprintf("-L%s/opt/libomp/lib -fopenmp", prefix)
+
+    # otherwise, use default -fopenmp flags for other compilers (LLVM clang; gcc)
+    } else {
+
+        cxxflags <- "-fopenmp"
+        libs <- "-fopenmp"
+
+    }
+
+    list(env = list(PKG_CXXFLAGS = cxxflags, PKG_LIBS = libs))
+
+}
+
 ## built-in OpenMP plugin
-.plugins[["openmp"]] <- function() {
-    list(env = list(PKG_CXXFLAGS="-fopenmp",
-                    PKG_LIBS="-fopenmp"))
+.plugins[["openmp"]] <- if (Sys.info()[["sysname"]] == "Darwin") {
+    .openmpPluginDarwin
+} else {
+    .openmpPluginDefault
 }
 
 .plugins[["unwindProtect"]] <- function() { # nocov start

From 9ad19e6c259ef65f06cf65873426bcb40c37c8c2 Mon Sep 17 00:00:00 2001
From: Kevin Ushey <kevinushey@gmail.com>
Date: Mon, 1 Dec 2025 16:32:44 -0800
Subject: [PATCH 2/2] alternative using R CMD SHLIB

---
 R/Attributes.R | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/R/Attributes.R b/R/Attributes.R
index 500fd60fd..a6019b1fe 100644
--- a/R/Attributes.R
+++ b/R/Attributes.R
@@ -592,15 +592,30 @@ compileAttributes <- function(pkgdir = ".", verbose = getOption("verbose")) {
 
 .openmpPluginDarwin <- function() {
 
+    # generate a test script for compilation
+    script <- tempfile("openmp-detect-", fileext = ".cpp")
+    writeLines("", con = script)
+    on.exit(unlink(script, force = TRUE), add = TRUE)
+
     # get the C++ compiler from R
     r <- file.path(R.home("bin"), "R")
-    cxx <- tryCatch(
-        system2(r, c("CMD", "config", "CXX"), stdout = TRUE),
+    output <- tryCatch(
+        system2(r, c("CMD", "SHLIB", "--dry-run", shQuote(script)), stdout = TRUE),
         condition = identity
     )
-    if (inherits(cxx, "condition"))
+    if (inherits(output, "condition"))
         return(.openmpPluginDefault())
 
+    # extract the compiler invocation from the shlib output
+    # use some heuristics here...
+    index <- grep("make would use", output)
+    compile <- output[[index + 1L]]
+
+    # use everything up to the first include flag, which is normally
+    # the R headers from CPPFLAGS
+    idx <- regexpr(" -I", compile, fixed = TRUE)
+    cxx <- substring(compile, 1L, idx - 1L)
+
     # check the compiler version
     command <- paste(cxx, "--version")
     version <- tryCatch(
@@ -613,29 +628,21 @@ compileAttributes <- function(pkgdir = ".", verbose = getOption("verbose")) {
     # if we're using Apple clang, use alternate flags
     # assume libomp was installed following https://mac.r-project.org/openmp/
     if (any(grepl("Apple clang", version))) {
-
         cxxflags <- "-Xclang -fopenmp"
         libs <- "-lomp"
-
     }
 
     # if we're using Homebrew clang, add in libomp include paths
     else if (any(grepl("Homebrew clang", version))) {
-
-        # ensure Homebrew paths are included during compilation
         machine <- Sys.info()[["machine"]]
         prefix <- if (machine == "arm64") "/opt/homebrew" else "/usr/local"
-
-        # build flags
         cxxflags <- sprintf("-I%s/opt/libomp/include -fopenmp", prefix)
         libs <- sprintf("-L%s/opt/libomp/lib -fopenmp", prefix)
 
     # otherwise, use default -fopenmp flags for other compilers (LLVM clang; gcc)
     } else {
-
         cxxflags <- "-fopenmp"
         libs <- "-fopenmp"
-
     }
 
     list(env = list(PKG_CXXFLAGS = cxxflags, PKG_LIBS = libs))