Sequence + optional rule yields unexpected results

[anarthal]

The following program

#include <boost/parser/parser.hpp>

#include <optional>

namespace bp = boost::parser;

constexpr auto print_repl_field = [](auto& ctx) {
    const std::optional<unsigned short>& val = bp::_attr(ctx);
    if (val)
    {
        std::cout << "Found integer: " << *val << std::endl;
    }
    else
    {
        std::cout << "No integer found\n";
    }
};

constexpr auto replacement_field_def = bp::lit('{') >> -bp::ushort_;

constexpr bp::rule<struct replacement_field_rule, std::optional<unsigned short>>
    replacement_field = "replacement_field";

BOOST_PARSER_DEFINE_RULES(replacement_field)

int main(int argc, char** argv) { bp::parse(argv[1], replacement_field[print_repl_field]); }

Yields the following

./build/main '{9'
Found integer: 9 // correct

./build/main '{'
Found integer: 0 // incorrect

Doesn't happen if I remove the rule and make it a regular parser.

Compiler: gcc-12, debug, under Linux.

[tzlaine]

Interesting. Thanks for reporting this! I'll investigate.