x3 error handler shows error location on the new line if an expected item is missing before the line end

[maximiliank]

If an expected item is missing before a line end, the location of the detailed error message is moved to the next line if there is a line end. Lets say you want to parse two integers separated by comma per line, then the following results in an error message on the wrong line:

1
3,4
+++++++++++++++++++++++
In line 2:
Error! Expecting: delimiter ',' here:
3,4
^_

Instead I would expect:

In line 1:
Error! Expecting: delimiter ',' here:
1
_^_

The reason is that the error_handler::skip_whitespace (which is called from error_handler::operator()) eats the '\n' and moves the position to the next line.

An example can be found here.

[Kojoley]

Reduced:

#include <boost/spirit/home/x3.hpp>
#include <boost/spirit/home/x3/support/utility/annotate_on_success.hpp>
#include <boost/spirit/home/x3/support/utility/error_reporting.hpp>
#include <iostream>

namespace x3 = boost::spirit::x3;

struct error_handler {
  template <typename Iterator, typename Exception, typename Context>
  x3::error_handler_result on_error(Iterator& first, Iterator const& last,
                                    Exception const& x,
                                    Context const& context) {
    auto& error_handler = x3::get<x3::error_handler_tag>(context).get();
    std::string message = "Error! Expecting: " + x.which() + " here:";
    error_handler(x.where(), message);
    return x3::error_handler_result::fail;
  }
};

namespace boost::spirit::x3 {
template <>
struct get_info<int_type> {
  std::string operator()(int_type const&) const { return "integral number"; }
};
}  // namespace boost::spirit::x3

struct Line : error_handler, x3::annotate_on_success {};

int main() {
  std::string_view input = "x\nx456";
  auto iter = input.cbegin();
  auto const end = input.cend();

  const auto line = x3::rule<struct Line>{"line"} = 'x' > x3::int_;
  x3::error_handler<decltype(iter)> error_handler(iter, end, std::cout);
  parse(iter, end, x3::with<x3::error_handler_tag>(std::ref(error_handler))[line % x3::eol]);
}