segfault with nested, adapted, structs

The following reduced test case segfaults when used with the spirit
version shipped with boost 1.64.

I'm using gcc 7.1.0: g++ test.cpp && ./a.out

If I remove BOOST_SPIRIT_X3_DEBUG the program does not segfault anymore.

As a workaround I found that the alternative definition of test prevents
the crash.

david

======================================================================
#define BOOST_SPIRIT_X3_DEBUG
#include <boost/fusion/adapted/struct/adapt_struct.hpp>
#include <boost/spirit/home/x3.hpp>
#include <string>

namespace x3 = boost::spirit::x3;

struct c8 {
	uint8_t x;
	uint8_t y;
};

struct c16 {
	uint16_t x;
	uint16_t y;
};

struct r {
	c8 a;
	c16 b;
};

BOOST_FUSION_ADAPT_STRUCT(c8, x, y)
BOOST_FUSION_ADAPT_STRUCT(c16, x, y)
BOOST_FUSION_ADAPT_STRUCT(r, a, b)

x3::rule<class c8_, c8> pc8 = "C8";
const auto pc8_def = x3::uint8 >> ',' >> x3::uint8;

x3::rule<class c16_, c16> pc16 = "C16";
const auto pc16_def = x3::uint16 >> ',' >> x3::uint16;

x3::rule<class test_, r> test = "TEST";
const auto test_def = "TEST" >> pc8 >> pc16;
// uncomment to workaround
//const auto test_def = "TEST" >> x3::lexeme[pc8] >> x3::lexeme[pc16];

BOOST_SPIRIT_DEFINE(pc8, pc16, test);

int main() {
	std::string input{"TEST 1,1 500,100"};
	r out;
	x3::phrase_parse(begin(input), end(input), test, x3::ascii::space, out);
}
======================================================================

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