[PATCH][libcxx] regex: Support capturing parens inside lookahead assertions

[William Fisher]

This patch fixes a bug where std::regex in ECMAScript mode was ignoring
capture groups inside lookahead assertions.

For example, matching /(?=(a))(a)/ to "a" should yield two captures: \1 =
"a", \2 = "a"

The test cases are in lookahead_capture.cpp.

Thanks,
Bill

#include <regex>
#include <cassert>

int main()
{
	{
		std::regex re{"^(?=(.))a$"};
		assert(re.mark_count() == 1);

		std::string s{"a"};
		std::smatch m;
		assert(std::regex_match(s, m, re));
		assert(m.size() == 2);
		assert(m[0] == "a");
		assert(m[1] == "a");
	}

	{
		std::regex re{"^(a)(?=(.))(b)$"};
		assert(re.mark_count() == 3);

		std::string s{"ab"};
		std::smatch m;
		assert(std::regex_match(s, m, re));
		assert(m.size() == 4);
		assert(m[0] == "ab");
		assert(m[1] == "a");
		assert(m[2] == "b");
		assert(m[3] == "b");
	}

	{
		std::regex re{"^(.)(?=(.)(?=.(.)))(...)$"};
		assert(re.mark_count() == 4);

		std::string s{"abcd"};
		std::smatch m;
		assert(std::regex_match(s, m, re));
		assert(m.size() == 5);
		assert(m[0] == "abcd");
		assert(m[1] == "a");
		assert(m[2] == "b");
		assert(m[3] == "d");
		assert(m[4] == "bcd");
	}

	{
		std::regex re{"^(a)(?!([^b]))(.c)$"};
		assert(re.mark_count() == 3);

		std::string s{"abc"};
		std::smatch m;
		assert(std::regex_match(s, m, re));
		assert(m.size() == 4);
		assert(m[0] == "abc");
		assert(m[1] == "a");
		assert(m[2] == "");
		assert(m[3] == "bc");
	}

	{
		std::regex re{"^(?!((b)))(?=(.))(?!(abc)).b$"};
		assert(re.mark_count() == 4);

		std::string s{"ab"};
		std::smatch m;
		assert(std::regex_match(s, m, re));
		assert(m.size() == 5);
		assert(m[0] == "ab");
		assert(m[1] == "");
		assert(m[2] == "");
		assert(m[3] == "a");
		assert(m[4] == "");
	}
}

lookahead_capture.patch
Description: Binary data

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