C++20 consteval error in boost::pfr::names_as_array

[QuiteDiam0nd]

Problem

Hello! I get error with consteval function apply while using boost::pfr::names_as_array:

/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:112:20: 
error: constexpr variable 'fn' must be initialized by a constant expression
    constexpr auto fn = skip.apply(sv);

Actually, I found the same issue in fmt, but none of the fixes didn't help:

1. Using libc++ instead of libstdc++.
2. Setting set(CMAKE_CXX_STANDARD 17) instead of set(CMAKE_CXX_STANDARD 20).
3. Plenty of other CMake tricky fixes.

I'm using boost 1.85.0. Error occurs on boost 1.84.0 too. Thanks for any help or advice!

Environment

I'm using

clang++ --version

clang version 13.0.1
Target: x86_64-unknown-linux-gnu
Thread model: posix
Installed dir: /data2/clang-trunk/bin

add_compile_options("$<$<CONFIG:DEBUG>:-O0>")
  add_compile_options("$<$<CONFIG:RELEASE>:-O3>")
  add_compile_options("-Wall")
  add_compile_options("-Wextra")
  add_compile_options("-Werror")
  add_compile_options("-msse4.2")
  add_compile_options("-Werror=return-type")
  add_compile_options("-Wno-implicit-fallthrough")
  add_compile_options("-Wno-unused-parameter")
  add_compile_options("-pedantic")
  add_compile_options("-Wno-gnu-label-as-value")
  add_compile_options("-stdlib=libc++")

  add_link_options("-stdlib=libc++")
  add_link_options("-fuse-ld=lld")
  add_link_options("-ldl")

Full text of error:

In file included from /data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name.hpp:23:
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:112:20: error: constexpr variable 'fn' must be initialized by a constant expression
    constexpr auto fn = skip.apply(sv);
                   ^    ~~~~~~~~~~~~~~
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:180:20: note: in instantiation of function template specialization 'boost::pfr::detail::name_of_field_impl<..., {&do_not_use_PFR_with_local_types.value.timestamp}>' requested here
    return detail::name_of_field_impl<MsvcWorkaround, ptr>();
                   ^
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:188:54: note: in instantiation of function template specialization 'boost::pfr::detail::name_of_field<..., {&do_not_use_PFR_with_local_types.value.timestamp}>' requested here
inline constexpr auto stored_name_of_field = detail::name_of_field<T,
                                                     ^
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:200:73: note: in instantiation of variable template specialization 'boost::pfr::detail::stored_name_of_field' requested here
    return detail::sequence_tuple::make_sequence_tuple(std::string_view{stored_name_of_field<T, I>.data()}...);
                                                                        ^
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:236:20: note: in instantiation of function template specialization 'boost::pfr::detail::tie_as_names_tuple_impl<myclass::Options, 0UL, 1UL>' requested here
    return detail::tie_as_names_tuple_impl<T>(detail::make_index_sequence<detail::fields_count<T>()>{});
                   ^
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/core_name.hpp:79:17: note: in instantiation of function template specialization 'boost::pfr::detail::tie_as_names_tuple<myclass::Options>' requested here
        detail::tie_as_names_tuple<T>(),
                ^
/...my_project/: note: in instantiation of function template specialization 'boost::pfr::names_as_array<myclass::Options>' requested here
    auto names = boost::pfr::names_as_array<Options>();
                             ^
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:112:30: note: non-constexpr function 'apply' cannot be used in a constant expression
    constexpr auto fn = skip.apply(sv);
                             ^
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:35:32: note: declared here
    consteval std::string_view apply(std::string_view sv) const noexcept {
                               ^
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:114:9: error: static_assert expression is not an integral constant expression
        !fn.empty(),
        ^~~~~~~~~~~
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:114:13: note: initializer of 'fn' is not a constant expression
        !fn.empty(),
            ^
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:112:20: note: declared here
    constexpr auto fn = skip.apply(sv);
                   ^
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:120:33: error: non-type template argument is not a constant expression
    auto res = std::array<char, fn.size()+1>{};
                                ^~~~~~~~~~~
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:120:36: note: initializer of 'fn' is not a constant expression
    auto res = std::array<char, fn.size()+1>{};
                                   ^
/data2/eipulatov/.conan/data/boost/1.85.0/_/_/package/0458049ba3cdb8489beabfab45dd835a78ef307b/include/boost/pfr/detail/core_name20_static.hpp:112:20: note: declared here
    constexpr auto fn = skip.apply(sv);

[QuiteDiam0nd]

The problem fixed. The issue was with precompiled headers with boost headers.