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build: Disable libstdc++ TBB backend to avoid unnecessary dependency #14509

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Merged
Ericson2314 merged 1 commit into from
Nov 7, 2025
Merged

build: Disable libstdc++ TBB backend to avoid unnecessary dependency #14509

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20 changes: 20 additions & 0 deletions nix-meson-build-support/common/meson.build
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,26 @@ if cxx.get_id() == 'clang'
add_project_arguments('-fpch-instantiate-templates', language : 'cpp')
endif

# Detect if we're using libstdc++ (GCC's standard library)
# libstdc++ uses Intel TBB as backend for C++17 parallel algorithms when <execution> is included.
# boost::concurrent_flat_map includes <execution>, which would require linking against TBB.
# Since we don't actually use parallel algorithms, disable the TBB backend to avoid the dependency.
# TBB is a dependency of blake3 and leaking into our build environment.
is_using_libstdcxx = cxx.compiles(
'''
#include <ciso646>
#ifndef __GLIBCXX__
#error "not libstdc++"
#endif
int main() { return 0; }
''',
name : 'using libstdc++',
)

if is_using_libstdcxx
add_project_arguments('-D_GLIBCXX_USE_TBB_PAR_BACKEND=0', language : 'cpp')
endif

# Darwin ld doesn't like "X.Y.ZpreABCD+W"
nix_soversion = meson.project_version().split('+')[0].split('pre')[0]

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