Do not put a concept in an exported template parameter list - #260
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GCC 14 does not encode a template parameter type-constraint in the mangled name; Clang 18+ does. On an explicitly instantiated template the two compilers therefore produce different symbols: GCC _ZN13tensorwrapper8generate21generate_eigen_systemIdEE... Clang _ZN13tensorwrapper8generate21generate_eigen_systemITkN3wtf8concepts13FloatingPointEdEE... The wheels are built by GCC, so a Clang consumer of the C++ SDK asks for a symbol the library never exports. SCF test_cmake_build (ubuntu-latest, clang-18) failed with 8 undefined references to generate_eigen_system<float> and <double> from its Catch2 template tests, while the gcc-14 leg linked fine -- the giveaway that this is a mangling divergence and not a missing instantiation. Fix: declare the five exported templates with `typename T` and enforce the requirement with a static_assert in each definition. Internal helpers that are never exported (add_noise_impl, the *_spacing helpers, sort_eigenvalues) keep their constraints. Verified by compiling each patched TU with BOTH g++-14 and clang++-18: the emitted manglings are now identical. Reduced repro confirmed the mechanism (a GCC-built .so links against a GCC consumer and fails against a Clang one; clang -fclang-abi-compat=17 also links, confirming Clang 18 introduced the constrained mangling). Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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🚀 [bumpr] Bumped! |
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Fixes the 8 undefined references that fail SCF
test_cmake_build (ubuntu-latest, clang-18).Root cause
GCC 14 does not encode a template parameter’s type-constraint in the mangled name. Clang 18+ does. On an explicitly instantiated template the two produce different symbols:
The wheels are built by GCC, so a Clang consumer of the C++ SDK asks for a symbol the library never exports. The gcc-14 leg links fine — that asymmetry is the giveaway that this is a mangling divergence, not a missing instantiation.
The call sites are SCF’s own Catch2 template tests (
eigen_normal.cpp,jacobi_normal.cpp), which instantiate over<float>and<double>.Reduced repro (confirms the mechanism)
A constrained template +
extern template+ explicit instantiation, library built by g++-14:_ZN2tw3genIdEE..._ZN2tw3genITkN3wtf8concepts13FloatingPointEdEE...-fclang-abi-compat=17_ZN2tw3genIdEE...The
-fclang-abi-compat=17row confirms Clang 18 introduced the constrained mangling. That flag is not a usable fix here — these are public wheels, and third-party Clang consumers cannot be required to pass a compatibility flag.The fix
Declare the five exported templates with
typename Tand enforce the requirement with astatic_assertin each definition. Internal helpers that are never exported (add_noise_impl, the*_spacinghelpers,sort_eigenvalues) keep their concept constraints.Affected:
add_noise(×2),generate_eigen_system,generate_eigenvalues,random_orthogonal_matrix. A scan of the other ten ecosystem repos found no other constrained-and-explicitly-instantiated templates.Verification
Each patched TU compiled with both g++-14 and clang++-18; the emitted manglings are now identical in all four files.
Behaviour note
Misuse moves from a call-site constraint error to a
static_assertin the definition. In practice these templates are explicitly instantiated forfloat/doubleonly, so any otherTwas already a link error.🤖 Generated with Claude Code