Dear ROOT team,
after upgrading to macOS 26.4, I am encountering an issue when starting ROOT installed via Homebrew.
Environment
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OS: macOS 26.4 (Apple Silicon)
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ROOT: 6.38.04 (installed via Homebrew)
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Compiler: Apple clang 17.0.0
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Installation path:
/opt/homebrew/Cellar/root/6.38.04
Error message
Upon starting ROOT (root -l), I get:
/opt/homebrew/Cellar/root/6.38.04/etc/root/cling/std_darwin.modulemap:73:64: error: header '__type_traits/add_lvalue_reference.h' not found
module add_lvalue_reference { header "__type_traits/add_lvalue_reference.h" }
^
input_line_1:1:10: note: submodule of top-level module 'std' implicitly imported here
#include <new>
^
Warning in cling::IncrementalParser::CheckABICompatibility():
Failed to extract C++ standard library version.
Warning in cling::IncrementalParser::CheckABICompatibility():
Possible C++ standard library mismatch, compiled with _LIBCPP_ABI_VERSION '1'
Extraction of runtime standard library version was: ''
ROOT still starts, but the warnings suggest a mismatch between the compiled and runtime standard library.
Observations
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The missing header appears to belong to libc++ internal headers (
__type_traits/...) -
This suggests a possible change in the libc++ layout in macOS 26.4 / updated SDK
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The issue looks like a mismatch between ROOT expectations (as packaged by Homebrew) and the current system SDK / Command Line Tools
Important note
If I build ROOT manually from source (outside Homebrew) on the same system, the issue does not appear, and ROOT starts without errors.
This seems to indicate that the problem might be related specifically to the Homebrew build configuration rather than ROOT itself.
Is this a known incompatibility with macOS 26.4? Could this be due to how Homebrew builds ROOT against the system SDK? Would you recommend rebuilding ROOT locally as the preferred workaround for now?
Thanks in advance for your help.
Best regards,
Anna Marini