Status: current.
BATCHLAS_API is generated into <build>/include/batchlas/export.hh by generate_export_header() against batchlas_core_obj. The entities below carry it where it looks arbitrary. That placement is required.
GCC and Clang give an instantiation the minimum visibility of its template and its arguments. Backend and MatrixFormat are template parameters across the public surface (207 template <Backend ...> declarations). An unannotated enum hides those instantiations, and BATCHLAS_API on the function does nothing.
Annotate every enum in include/batchlas/blas/enums.hh that becomes a template argument.
batchlas::linalg::BinaryOp (include/batchlas/blas/linalg-ops.hh) is annotated for the same reason. Without it, all four elementwise_into<float, BinaryOp::*> specialisations stay hidden.
BATCHLAS_API is on the class templates Matrix, MatrixView and VectorView, not on the 313 explicit instantiations in src/matrix.cc. Only 22 of those lines are template class ...;. The other 291 instantiate member templates (factories, convert_to, to_row_major / to_column_major, MatrixView members), which a whole-class instantiation does not reach. A class-level attribute covers all 313.
Do not put the attribute on an explicit instantiation. g++ 13 rejects template class __attribute__((visibility("default"))) F<double,1>;; clang accepts it.
Every class in include/batchlas/error.hh carries BATCHLAS_API, including detail::exception_bridge. None has an out-of-line member, so vtables and typeinfo have vague linkage. Catch-by-type works only because every copy has default visibility and the linker merges them. Under -fvisibility=hidden a consumer's catch (const batchlas::error&) stops matching a throw from the library, and the exception calls std::terminate. BATCHLAS_API forces default visibility. This is rule 1 of Error model reached another way. detail::exception_bridge is on the catch-time upcast path, so its typeinfo must merge too.
Note: A throw/catch test cannot check this on x86-64. This DPC++ emits typeinfo names without the leading *, so libstdc++ falls back to strcmp and duplicate typeinfos still compare equal. The test passes with or without the annotation. Only reading the annotations discriminates.
WorkspaceLease is annotated on the class, not its members, because inline public members call the private release_(bool). Without the class annotation a consumer gets an unresolved reference to it. _ZN8batchlas14WorkspaceLease8release_Eb is among the 1,083 symbols the in-tree tests need.
Event is struct [[nodiscard]] Event, with BATCHLAS_API on each of its ten out-of-line members. g++ 13 rejects a class-key with both a C++11 and a GNU attribute, in either order (-std=c++20), so the class-level form does not compile there. Clang accepts both. Event has no virtual member, so per-member annotation is equivalent.
[[nodiscard]] is on the type, not on the roughly 279 functions returning it, because the operations are generated forwarders. It is a warning. Dropping an Event is harmless on the default in-order Queue, but it is a silent race on an out-of-order Queue, a second Queue sharing the context, or a hand-off to raw SYCL. In-tree discards are written (void).
Queue::attach_to_current_thread() and Queue::native_handle() carry BATCHLAS_API on the member, even though the class is annotated. Both are [[gnu::used]] inline in src/queue.hh (BATCHLAS_QUEUE_EXPORTED_INLINE). used keeps the symbol but does not set visibility, and -fvisibility-inlines-hidden hides inline members whatever the class says.
1.18.0
