compilation error with boost-1.90 and clang 21 #306
Description
I have a project that was working fine with boost-1.87. I updated my system and got boost-1.90. Now it is failing to compile. I did a git bisect and found that the change that broke things is
commit 821d1d4c084ae9d6ab9a1d83a5113701c934b22c
Author: Zach Laine <whatwasthataddress@gmail.com>
Date: Thu Feb 20 23:15:30 2025 -0600
Fix longstanding mysterious ill-formedness in
detail::static_assert_merge_attributes. It was down to unavailabilty of a
default ctor for certain parser types.
When I revert this change on top of boost-1.90, the code compiles again.
I don't know how much difference this makes, but it is a system running fedora 43 with clang++ 21.1.7
The error messages I see are like this:
clang++ -Isrc/libcommon.a.p -Isrc/ -I../src -I. -I.. -Isrc -I/usr/local/boost -flto -fdiagnostics-color=always -D_GLIBCXX_ASSERTIONS=1 -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Wpedantic -Werror -std=c++23 -O0 -g -DUSE_MPFR_BACKEND -Wcast-align -Wdouble-promotion -Wformat=2 -Wmisleading-indentation -Wno-reorder -Wnon-virtual-dtor -Woverloaded-virtual -Wno-deprecated-literal-operator -Wunused-but-set-parameter -Wunused-but-set-variable -Wunused-function -Wunused-label -Wunused-local-typedefs -Wunused-macros -Wno-unused-result -Wunused-value -Wno-unused-variable -Wno-unused-parameter -Wno-double-promotion -DHAVE_READLINE -DBOOST_ASIO_DISABLE_THREADS -DBOOST_ERROR_CODE_HEADER_ONLY -DBOOST_NO_RTTI -DBOOST_NO_TYPEID -DBOOST_SYSTEM_NO_DEPRECATED -fPIC -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=600 -DBOOST_ALL_NO_LIB -MD -MQ src/libcommon.a.p/parser.cpp.o -MF src/libcommon.a.p/parser.cpp.o.d -o src/libcommon.a.p/parser.cpp.o -c ../src/parser.cpp
../src/parser.cpp:635:11: error: non-const lvalue reference to type 'conditional_t<...>' cannot bind to a temporary of type 'conditional_t<...>'
635 | auto& val = _val(ctx);
| ^ ~~~~~~~~~
/usr/local/boost/boost/parser/parser.hpp:4732:51: note: in instantiation of function template specialization 'smrty::parser::(anonymous namespace)::(anonymous class)::operator()<const boost::parser::detail::parse_context<false, false, const char *, const char *, boost::parser::default_error_handler, const boost::parser::detail::nope, boost::parser::detail::nope, std::basic_string<char>, boost::parser::detail::nope, void, boost::parser::detail::nope, boost::parser::detail::nope, std::ranges::subrange<const char *>>>' requested here
4732 | decltype(action_(action_context)),
| ^
/usr/local/boost/boost/parser/parser.hpp:4683:13: note: in instantiation of function template specialization 'boost::parser::action_parser<boost::parser::seq_parser<std::tuple<boost::parser::digit_parser, boost::parser::digit_parser, boost::parser::digit_parser, boost::parser::digit_parser>, std::tuple<std::integral_constant<bool, true>, std::integral_constant<bool, true>, std::integral_constant<bool, true>, std::integral_constant<bool, true>>, std::tuple<std::integral_constant<long long, 0>, std::integral_constant<long long, 0>, std::integral_constant<long long, 0>, std::integral_constant<long long, 0>>>, smrty::parser::(anonymous namespace)::(lambda at ../src/parser.cpp:633:24)>::call<const char *, const char *, boost::parser::detail::parse_context<false, false, const char *, const char *, boost::parser::default_error_handler>, boost::parser::parser_interface<boost::parser::ws_parser<false, false>>, boost::parser::detail::nope>' requested here
4683 | call(first, last, context, skip, flags, success, retval);
| ^
/usr/local/boost/boost/parser/parser.hpp:3873:31: note: in instantiation of function template specialization 'boost::parser::action_parser<boost::parser::seq_parser<std::tuple<boost::parser::digit_parser, boost::parser::digit_parser, boost::parser::digit_parser, boost::parser::digit_parser>, std::tuple<std::integral_constant<bool, true>, std::integral_constant<bool, true>, std::integral_constant<bool, true>, std::integral_constant<bool, true>>, std::tuple<std::integral_constant<long long, 0>, std::integral_constant<long long, 0>, std::integral_constant<long long, 0>, std::integral_constant<long long, 0>>>, smrty::parser::(anonymous namespace)::(lambda at ../src/parser.cpp:633:24)>::call<const char *, const char *, boost::parser::detail::parse_context<false, false, const char *, const char *, boost::parser::default_error_handler>, boost::parser::parser_interface<boost::parser::ws_parser<false, false>>>' requested here
3873 | return parser.call(
| ^
The code in question:
struct time_parts
{
time_parts() :
absolute(false), year(), month(), day(), h(), m(), s(), sub(), tz(),
duration(), suffix(), full()
{
}
// amended ISO8601 format: // yyyy-mm-dd[Thh:mm:ss[.sub]][Z|([+-]hh:mm)]
bool absolute;
std::string year;
std::string month;
std::string day;
std::string h;
std::string m;
std::string s;
std::string sub;
std::string tz;
single_number_parts duration;
std::string suffix;
std::string full;
};
bp::rule<class time, time_parts> const time = "time";
auto const save_year = [](auto& ctx) {
const auto& attr = _attr(ctx);
auto& val = _val(ctx);
val.year = attr;
val.absolute = true;
};
// iso 8601 date format
auto const time_def = bp::lexeme
[bp::merge[(bp::digit >> bp::digit >> bp::digit >> bp::digit)[save_year] >>
bp::string("-") >> (bp::digit >> bp::digit)[save_month] >>
bp::string("-") >> (bp::digit >> bp::digit)[save_day] >>
bp::omit[-(
bp::string("T") >> (bp::digit >> bp::digit)[save_hour] >>
bp::string(":") >> (bp::digit >> bp::digit)[save_minute] >>
bp::string(":") >> (bp::digit >> bp::digit)[save_second] >>
-(bp::char_(".") >> +bp::digit)[save_sub_second] >>
-(bp::char_("+-") >>
(bp::digit >> bp::digit >> bp::char_(":") >> bp::digit >>
bp::digit))[save_timezone])]][save_full_time]];
Any help here would be great. I am not sure if I am doing something wrong here or if the change I reverted really is the problem.