X3: Should eps or other literal parsers compile with an actual attribute

[Kojoley]

#include <boost/spirit/home/x3.hpp>
#include <boost/fusion/include/vector.hpp>
int main()
{
    using boost::spirit::x3::eps;
    using boost::spirit::x3::lit;
    char const* const it = "";
    int i;
    char c;
    boost::fusion::vector<> v;

    parse(it, it, eps, i);
    parse(it, it, eps, c);

    parse(it, it, lit('x'), i);
    parse(it, it, lit('x'), c);

    parse(it, it, eps >> eps, i);
    parse(it, it, eps >> eps, c);
    parse(it, it, eps >> eps, v);

    parse(it, it, lit('x') >> lit('x'), i);
    parse(it, it, lit('x') >> lit('x'), c);
    parse(it, it, lit('x') >> lit('x'), v);
}

From my point of view all those cases are wrong and ideally should not compile by firing a static assert.

[Kojoley]

608 made think about opposite issue in optional parser which has a sibling in alternative parser:

#include <boost/spirit/home/x3.hpp>
int main()
{
    using boost::spirit::x3::eps;
    using boost::spirit::x3::int_;
    char const* const it = "";
    int i;
    parse(it, it, int_ | eps, i); // equivalent of -int_ which also should not compile
}