Describe the bug, including details regarding any error messages, version, and platform.
Libc++ has made a change to stop supporting std::char_traits (and thus, also, basic_string and basic_string_view) for non-character types: https://discourse.llvm.org/t/deprecating-std-string-t-for-non-character-t/66779
Apparently, such support was never required by the standard, and is considered a mistake.
The initial libc++ change made this a hard error, but after reports of breakage, it was downgraded to a deprecation warning. See review thread https://reviews.llvm.org/D138307. It is now expected to become a hard error again in LLVM 18.
One of the projects broken is Apache Arrow, due to the usage here:
| using View = util::basic_string_view<Word>; |
E.g.,
/usr/include/c++/v1/string_view:279:45: error: implicit instantiation of undefined template 'std::char_traits<unsigned long>'
static_assert((is_same<_CharT, typename traits_type::char_type>::value),
^
arrow/util/bitmap.h:153:16: note: in instantiation of template class 'std::basic_string_view<unsigned long>' requested here
View<Word> words[N];
^
arrow/compute/kernels/scalar_if_else.cc:1595:15: note: in instantiation of function template specialization 'arrow::internal::Bitmap::VisitWords<3UL, (lambda at arrow/compute/kernels/scalar_if_else.cc:1595:35), unsigned long>' requested here
Bitmap::VisitWords(bitmaps, [&](std::array<uint64_t, 3> words) {
^
arrow/compute/kernels/scalar_if_else.cc:1652:14: note: in instantiation of function template specialization 'arrow::compute::internal::(anonymous namespace)::ExecArrayCaseWhen<arrow::BooleanType>' requested here
return ExecArrayCaseWhen<Type>(ctx, batch, out);
^
arrow/compute/kernels/codegen_internal.h:1173:47: note: in instantiation of member function 'arrow::compute::internal::(anonymous namespace)::CaseWhenFunctor<arrow::BooleanType>::Exec' requested here
return Generator<BooleanType, Args...>::Exec;
^
arrow/compute/kernels/scalar_if_else.cc:2738:17: note: in instantiation of function template specialization 'arrow::compute::internal::GenerateTypeAgnosticPrimitive<arrow::compute::internal::(anonymous namespace)::CaseWhenFunctor>' requested here
auto exec = GenerateTypeAgnosticPrimitive<CaseWhenFunctor>(*type);
I suspect "View" needs to be changed to use some other type than std::basic_string_view (could be std::span if you required c++20, but you probably don't want to require c++20 yet.)
Component(s)
C++
Describe the bug, including details regarding any error messages, version, and platform.
Libc++ has made a change to stop supporting std::char_traits (and thus, also, basic_string and basic_string_view) for non-character types: https://discourse.llvm.org/t/deprecating-std-string-t-for-non-character-t/66779
Apparently, such support was never required by the standard, and is considered a mistake.
The initial libc++ change made this a hard error, but after reports of breakage, it was downgraded to a deprecation warning. See review thread https://reviews.llvm.org/D138307. It is now expected to become a hard error again in LLVM 18.
One of the projects broken is Apache Arrow, due to the usage here:
arrow/cpp/src/arrow/util/bitmap.h
Line 52 in 53752ad
E.g.,
I suspect "View" needs to be changed to use some other type than std::basic_string_view (could be std::span if you required c++20, but you probably don't want to require c++20 yet.)
Component(s)
C++