From e09a25c6219788bcfa25c628789444c6216b887a Mon Sep 17 00:00:00 2001
From: Vincenzo Eduardo Padulano <vincenzo.eduardo.padulano@cern.ch>
Date: Thu, 22 Jan 2026 18:00:07 +0100
Subject: [PATCH] [build] Unify retrieval of MacOS SDK path

Use `xcrun --show-sdk-path` only once to set the CMAKE_OSX_SYSROOT variable and then reuse it also for the modulemap fix on Darwin.

Since the modulemap fix needed the `xcrun` command to work anyway, turn the warning previously issued if CMake couldn't find this command to an error.
---
 CMakeLists.txt                            |  4 ++--
 cmake/scripts/std_modulemap_darwin_fix.py | 18 +++++-------------
 core/clingutils/CMakeLists.txt            |  2 +-
 3 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 21600976447d6..3a1a84fa25403 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -34,8 +34,8 @@ if(CMAKE_HOST_APPLE AND (NOT CMAKE_OSX_SYSROOT OR CMAKE_OSX_SYSROOT STREQUAL "")
 
     set(CMAKE_OSX_SYSROOT "${SDK_PATH}" CACHE PATH "SDK path" FORCE)
   else()
-    message(WARNING "The CMAKE_OSX_SYSROOT variable is not set and the 'xcrun' executable is not available. "
-                    "This build of ROOT might not be able to find the correct MacOS SDK.")
+    message(FATAL_ERROR "The CMAKE_OSX_SYSROOT variable is not set and the 'xcrun' executable is not available. "
+                        "This build of ROOT cannot find the correct MacOS SDK.")
   endif()
 endif()
 
diff --git a/cmake/scripts/std_modulemap_darwin_fix.py b/cmake/scripts/std_modulemap_darwin_fix.py
index bfa322003039b..d610a7a8c5030 100644
--- a/cmake/scripts/std_modulemap_darwin_fix.py
+++ b/cmake/scripts/std_modulemap_darwin_fix.py
@@ -4,14 +4,6 @@
 import subprocess
 import sys
 
-
-def get_sdk_path():
-    result = subprocess.run(["xcrun", "--show-sdk-path"], capture_output=True, text=True)
-    if result.returncode != 0:
-        raise RuntimeError("Could not resolve SDK path")
-    return os.path.realpath(result.stdout.strip())
-
-
 def remove_ctype_module(content):
     # Break cyclic module dependencies
     # See: https://github.com/root-project/root/commit/8045591a17125b49c1007787c586868dea764479
@@ -20,11 +12,11 @@ def remove_ctype_module(content):
 
 
 def main():
-    if len(sys.argv) < 2:
-        raise ValueError("Usage: std_modulemap_darwin_fix.py <output_path>")
-    output_path = sys.argv[1]
-    sdk = get_sdk_path()
-    cpp_modulemap = os.path.join(sdk, "usr/include/c++/v1/module.modulemap")
+    if len(sys.argv) < 3:
+        raise ValueError("Usage: std_modulemap_darwin_fix.py <sdk_path> <output_path>")
+    sdk_path = sys.argv[1]
+    output_path = sys.argv[2]
+    cpp_modulemap = os.path.join(sdk_path, "usr/include/c++/v1/module.modulemap")
     if not os.path.exists(cpp_modulemap):
         # Try again if we are running a conda build. conda-forge ships the MacOS SDK stripped of libc++.
         # Instead, the standard libraries are shipped as a separate package which must be declared as a build
diff --git a/core/clingutils/CMakeLists.txt b/core/clingutils/CMakeLists.txt
index 2a74a10eb0703..b0ca97cf06262 100644
--- a/core/clingutils/CMakeLists.txt
+++ b/core/clingutils/CMakeLists.txt
@@ -133,7 +133,7 @@ if (runtime_cxxmodules)
 
       add_custom_command(
         OUTPUT ${GENERATED_MODULEMAP}
-        COMMAND ${Python3_EXECUTABLE} ${PROJECT_SOURCE_DIR}/cmake/scripts/std_modulemap_darwin_fix.py ${GENERATED_MODULEMAP}
+        COMMAND ${Python3_EXECUTABLE} ${PROJECT_SOURCE_DIR}/cmake/scripts/std_modulemap_darwin_fix.py ${CMAKE_OSX_SYSROOT} ${GENERATED_MODULEMAP}
         DEPENDS ${PROJECT_SOURCE_DIR}/cmake/scripts/std_modulemap_darwin_fix.py
         COMMENT "Generating wrapped std modulemap for macOS SDK"
       )