X3: Recursive grammar: alternative container parses substitution issue

[Xeverous]

I would like to parse such text:

config {
	foo: 0
	bar: 1 {
		bar_child: 11
		bar_child2: 12
	}
	quux: 2
}

#include <boost/spirit/home/x3.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <string>
#include <vector>

namespace x3 = boost::spirit::x3;

namespace ast
{
	struct config_param
	{
		std::string name;
		int value;
		std::vector<config_param> child_params;
	};

	struct config
	{
		std::vector<config_param> params;
	};
}

BOOST_FUSION_ADAPT_STRUCT(
	ast::config_param,
	name, value, child_params)

BOOST_FUSION_ADAPT_STRUCT(
	ast::config,
	params)

using comment_type = x3::rule<class comment_class>;
BOOST_SPIRIT_DECLARE(comment_type)

using identifier_type = x3::rule<class identifier_class, std::string>;
BOOST_SPIRIT_DECLARE(identifier_type)

using whitespace_type = x3::rule<class whitespace_class>;
BOOST_SPIRIT_DECLARE(whitespace_type)

using config_param_type = x3::rule<class config_param_class, ast::config_param>;
BOOST_SPIRIT_DECLARE(config_param_type)

using config_type = x3::rule<class config_class, ast::config>;
BOOST_SPIRIT_DECLARE(config_type)

using grammar_type = x3::rule<class grammar_class, ast::config>;
BOOST_SPIRIT_DECLARE(grammar_type)

using skipper_type = whitespace_type;
using iterator_type = std::string::const_iterator;
using context_type = x3::phrase_parse_context<skipper_type>::type;

const comment_type comment = "comment";
const auto comment_def = x3::lexeme['#' >> *(x3::char_ - '\n')];
BOOST_SPIRIT_DEFINE(comment)

const identifier_type identifier = "identifier";
const auto identifier_def = x3::lexeme[(x3::alpha | '_') >> *(x3::alnum | '_')];
BOOST_SPIRIT_DEFINE(identifier)

const whitespace_type whitespace = "whitespace";
const auto whitespace_def = x3::space | comment;
BOOST_SPIRIT_DEFINE(whitespace)

const config_param_type config_param = "config param";
const auto config_param_def = identifier > ':' > x3::int_ > (('{' > *config_param > '}') /* | x3::attr(std::vector<ast::config_param>()) */ );
BOOST_SPIRIT_DEFINE(config_param)

const config_type config = "config";
const auto config_def = x3::lit("config") > '{' > *config_param > '}';
BOOST_SPIRIT_DEFINE(config)

const grammar_type grammar = "code";
const auto grammar_def = config;
BOOST_SPIRIT_DEFINE(grammar)

BOOST_SPIRIT_INSTANTIATE(grammar_type, iterator_type, context_type)

With comment enabled, every config param must have empty {} after it's value. I tried to remove this requirement by providing alternative that results in the same attribute (empty vector of childs). However, if you uncomment code, it does not compile.

Is this the same bug as #434 ? Any workaround?

[Kojoley]

I rechecked your example and found that I was wrong, I am sorry. Please provide MWE next time.

#include <boost/spirit/home/x3.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <vector>

namespace x3 = boost::spirit::x3;

struct Foo
{
    int value;
    std::vector<Foo> children;
};
BOOST_FUSION_ADAPT_STRUCT(Foo,
    value, children)

x3::rule<class foo_r, Foo> foo;
auto const foo_def = x3::int_ >> ('{' >> *foo >> '}' | '[' >> *foo >> ']');
BOOST_SPIRIT_DEFINE(foo)

BOOST_SPIRIT_INSTANTIATE(decltype(foo), char const*, x3::unused_type)

[Frkymhn]

i want to work on this issue please guide me

[Kojoley]

i want to work on this issue please guide me

For some reason, the specialization

spirit/include/boost/spirit/home/x3/support/traits/is_substitute.hpp

Lines 51 to 60 in b4c5ef7

	template <typename T, typename Attribute>
	struct is_substitute_impl<T, Attribute,
	typename enable_if<
	mpl::and_<
	fusion::traits::is_sequence<T>,
	fusion::traits::is_sequence<Attribute>,
	mpl::equal<T, Attribute, is_substitute<mpl::_1, mpl::_2>>
	>
	>::type>
	: mpl::true_ {};

is offending, if I comment it out - the repro from my previous post will compile. Try to identify the reason.