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Update OpenMP plugin to detect and handle Apple clang on macOS #1409

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coatless wants to merge 4 commits into from
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Update OpenMP plugin to detect and handle Apple clang on macOS #1409

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3c2907d
Modified the openmp plugin to properly detect macOS and differentiate…
coatless Nov 18, 2025
8bc698c
Add ChangeLog entry
coatless Nov 18, 2025
6789a7f
Update OpenMP plugin scaffolding for macOS based on feedback
coatless Nov 24, 2025
c3fd7d4
Whitespace tweak after rebase to parentrepo main branch
eddelbuettel Nov 25, 2025
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4 changes: 4 additions & 0 deletions ChangeLog
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Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,10 @@
or related R headers were installed first
* inst/include/RcppCommon.h: Call new header as first thing

2025-11-18 James J Balamuta <[email protected]>

* R/Attributes.R: Updated OpenMP Plugin's flags on macOS

2025-11-04 Dirk Eddelbuettel <[email protected]>

* .github/workflows/macos.yaml (jobs): Roll macos-13 to macos-14
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48 changes: 46 additions & 2 deletions R/Attributes.R
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Expand Up @@ -588,8 +588,52 @@ compileAttributes <- function(pkgdir = ".", verbose = getOption("verbose")) {

## built-in OpenMP plugin
.plugins[["openmp"]] <- function() {
list(env = list(PKG_CXXFLAGS="-fopenmp",
PKG_LIBS="-fopenmp"))

# Default flags for non-macOS systems
cxxflags <- "-fopenmp"
libs <- "-fopenmp"

# Check if we're on macOS
if (Sys.info()[["sysname"]] == "Darwin") {
# Get the C++ compiler from R CMD config CXX
r_cmd <- file.path(R.home("bin"), "R")
cxx <- tryCatch({
system2(r_cmd, c("CMD", "config", "CXX"), stdout = TRUE, stderr = FALSE)
}, error = function(e) "")

if (length(cxx) > 0 && nzchar(cxx[1])) {
# Check compiler version using full command (this includes any flags)
compiler_version <- tryCatch({
system(paste(cxx[1], "--version"), intern = TRUE, ignore.stderr = TRUE)
}, error = function(e) character(0))

if (length(compiler_version) > 0) {
# Check for Apple clang
is_apple_clang <- any(grepl("Apple", compiler_version, ignore.case = TRUE))
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@kevinushey kevinushey Dec 1, 2025 •
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This check also succeeds (and is checked in the conditional) for Homebrew's build of clang, since it has

> writeLines(compiler_version)
Homebrew clang version 21.1.6
Target: arm64-apple-darwin25.1.0
Thread model: posix
InstalledDir: /opt/homebrew/Cellar/llvm/21.1.6/bin
Configuration file: /opt/homebrew/etc/clang/arm64-apple-darwin25.cfg

and so apple is picked up in the grep invocation from the target triple.

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Suggested change
is_apple_clang <- any(grepl("Apple", compiler_version, ignore.case = TRUE))
is_apple_clang <- any(grepl("Apple clang", compiler_version))

# Check for Homebrew clang
is_homebrew_clang <- any(grepl("Homebrew", compiler_version, ignore.case = TRUE))
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Suggested change
is_homebrew_clang <- any(grepl("Homebrew", compiler_version, ignore.case = TRUE))
is_homebrew_clang <- any(grepl("Homebrew clang", compiler_version))


if (is_apple_clang) {
# Apple clang requires -Xclang -fopenmp
cxxflags <- "-Xclang -fopenmp"
libs <- "-lomp"
} else if (is_homebrew_clang) {
# Homebrew clang needs include/lib paths for the added libomp formula
# Determine prefix based on architecture (arm64 vs x86_64)
arch <- Sys.info()[["machine"]]
brew_prefix <- if (arch == "arm64") "/opt/homebrew" else "/usr/local"

cxxflags <- paste("-Xclang -fopenmp",
paste0("-I", brew_prefix, "/opt/libomp/include"))
libs <- paste(paste0("-L", brew_prefix, "/opt/libomp/lib"), "-lomp")
}
# Otherwise it's gcc and regular -fopenmp works (defaults are fine)
}
}
}

list(env = list(PKG_CXXFLAGS = cxxflags,
PKG_LIBS = libs))
}

.plugins[["unwindProtect"]] <- function() { # nocov start
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