ASSERT that iterator is not .end() fails to compile in v2.0.0, VERIFY built with v1.2.2

[Hailios]

hey, I've updated libassert to 2.0.0 with conan from 1.2.2. some assertions that previously built, now fails to do so.

this is the offending code that now fails sto compile.

auto host_it = req.find(boost::beast::http::field::host);
ASSERT(host_it != req.end());

req is of type boost::beast::http::request<boost::beast::http::string_body>& from https://github.com/boostorg/beast/ using boost 1.84.

user/.conan2/p/b/libas3514cb9b8f850/p/include/libassert/assert.hpp: In instantiation of 'constexpr const bool libassert::detail::stringifiable<boost::beast::http::basic_fields<std::allocator<char> >::value_type>':
user/.conan2/p/b/libas3514cb9b8f850/p/include/libassert/assert.hpp:576:20:   required from 'constexpr bool libassert::detail::stringifiable_container() [with T = boost::beast::http::basic_fields<std::allocator<char> >::element]'
user/.conan2/p/b/libas3514cb9b8f850/p/include/libassert/assert.hpp:557:83:   required from 'constexpr const bool libassert::detail::stringifiable<boost::beast::http::basic_fields<std::allocator<char> >::element>'
user/.conan2/p/b/libas3514cb9b8f850/p/include/libassert/assert.hpp:576:20:   required from 'constexpr bool libassert::detail::stringifiable_container() [with T = boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::http::basic_fields<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, boost::intrusive::normal_link, boost::intrusive::dft_tag, 1>, true>]'
user/.conan2/p/b/libas3514cb9b8f850/p/include/libassert/assert.hpp:647:42:   required from 'std::string libassert::detail::generate_stringification(const T&) [with T = boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::http::basic_fields<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, boost::intrusive::normal_link, boost::intrusive::dft_tag, 1>, true>; std::string = std::__cxx11::basic_string<char>]'
user/.conan2/p/b/libas3514cb9b8f850/p/include/libassert/assert.hpp:1261:37:   required from 'libassert::binary_diagnostics_descriptor libassert::detail::generate_binary_diagnostic(const A&, const B&, std::string_view, std::string_view, std::string_view) [with A = boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::http::basic_fields<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, boost::intrusive::normal_link, boost::intrusive::dft_tag, 1>, true>; B = boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::http::basic_fields<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, boost::intrusive::normal_link, boost::intrusive::dft_tag, 1>, true>; std::string_view = std::basic_string_view<char>]'
user/.conan2/p/b/libas3514cb9b8f850/p/include/libassert/assert.hpp:1363:65:   required from 'void libassert::detail::process_assert_fail(expression_decomposer<A, B, C>&, const assert_static_parameters*, Args&& ...) [with A = boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::http::basic_fields<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, boost::intrusive::normal_link, boost::intrusive::dft_tag, 1>, true>&; B = boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::http::basic_fields<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, boost::intrusive::normal_link, boost::intrusive::dft_tag, 1>, true>; C = ops::neq; Args = {pretty_function_name_wrapper}]'
user/.conan2/p/b/libas3514cb9b8f850/p/include/libassert/assert.hpp:1416:28:   required from 'void libassert::detail::process_assert_fail_n(expression_decomposer<A, B, C>, const assert_static_parameters*, Args&& ...) [with A = boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::http::basic_fields<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, boost::intrusive::normal_link, boost::intrusive::dft_tag, 1>, true>&; B = boost::intrusive::list_iterator<boost::intrusive::bhtraits<boost::beast::http::basic_fields<std::allocator<char> >::element, boost::intrusive::list_node_traits<void*>, boost::intrusive::normal_link, boost::intrusive::dft_tag, 1>, true>; C = ops::neq; Args = {pretty_function_name_wrapper}]'
user/development/git/c++/HttpsSession.cpp:62:3:   required from here
user/.conan2/p/b/libas3514cb9b8f850/p/include/libassert/assert.hpp:560:38:   in 'constexpr' expansion of 'libassert::detail::stringifiable_container<boost::beast::http::basic_fields<std::allocator<char> >::value_type>()'
user/.conan2/p/b/libas3514cb9b8f850/p/include/libassert/assert.hpp:576:20: error: the value of 'libassert::detail::stringifiable<boost::beast::http::basic_fields<std::allocator<char> >::value_type>' is not usable in a constant expression
  576 |             return stringifiable<typename T::value_type>;
      |                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

built using

$ g++ --version
g++ (Ubuntu 13.2.0-4ubuntu3) 13.2.0

[jeremy-rifkin]

Thank you for reporting this, I’ll try to fix it tonight

[jeremy-rifkin]

I can reproduce for gcc 13.2, however it compiles fine in clang https://godbolt.org/z/bjqbEoGWj

[jeremy-rifkin]

I have found the problem.
note: 'libassert::detail::stringifiable<boost::beast::http::basic_fields<std::allocator<char> >::value_type>' used in its own initializer confused me a lot but the basic error boils down to

<source>: In instantiation of 'constexpr const bool stringifiable<boost::beast::http::basic_fields<std::allocator<char> >::value_type>':
<source>:60:16:   required from 'constexpr bool stringifiable_container() [with T = boost::beast::http::basic_fields<std::allocator<char> >::value_type]'
<source>:71:111:   required from here
<source>:44:34: error: 'constexpr bool stringifiable_container() [with T = boost::beast::http::basic_fields<std::allocator<char> >::value_type]' called in a constant expression before its definition is complete
   44 |     || stringifiable_container<T>();
      |        ~~~~~~~~~~~~~~~~~~~~~~~~~~^~

So... recursively checking T::value_type somehow leads back to T, which is a problem. It may be due to the basic_fields::value_type not being a using as is normal but a class named value_type instead. I'll have to try to better understand why this behaves as it does but for now it can be solved by checking std::is_same_v<typename T::value_type, T>. https://godbolt.org/z/vo6svn34W

Repro without boost: https://godbolt.org/z/1xf1hMdbd