LibC: Implement getopt_long{,_only}

Few ports attempt to use this so lets add them :D

userspace/libraries/LibC/getopt.cpp

@@ -0,0 +1,194 @@
+#include <assert.h>
+#include <getopt.h>
+#include <stdio.h>
+#include <string.h>
+
+char* optarg = nullptr;
+int opterr = 1;
+int optind = 1;
+int optopt = 0;
+
+static int s_idx_in_arg = -1;
+static int s_old_optind = 1;
+
+static int getopt_long_impl(int argc, char* const argv[], const char* optstring, const struct option* longopts, int* longindex, bool need_double_hyphen)
+{
+	if (optind >= argc)
+		return -1;
+
+	if (optind == 0)
+	{
+		s_old_optind = -1;
+		s_idx_in_arg = -1;
+		optind = 1;
+	}
+
+	const char* curr = argv[optind];
+	if (curr == nullptr || curr[0] != '-' || curr[1] == '\0')
+		return -1;
+
+	if (curr[1] == '-' && curr[2] == '\0')
+	{
+		optind++;
+		return -1;
+	}
+
+	if (s_old_optind != optind)
+		s_idx_in_arg = -1;
+	struct dummy { ~dummy() { s_old_optind = optind; }} _;
+
+	if (s_idx_in_arg == -1 && (!need_double_hyphen || curr[1] == '-'))
+	{
+		for (size_t i = 0; longopts[i].name; i++)
+		{
+			const auto& opt = longopts[i];
+			const size_t name_len = strlen(opt.name);
+			if (strncmp(curr + 2, opt.name, name_len) != 0)
+				continue;
+			if (curr[2 + name_len] != '=' && curr[2 + name_len] != '\0')
+				continue;
+
+			bool has_argument;
+			switch (opt.has_arg)
+			{
+				case no_argument:
+					has_argument = false;
+					break;
+				case required_argument:
+					has_argument = true;
+					break;
+				case optional_argument:
+					has_argument = (curr[2 + name_len] == '=')
+						|| (optind + 1 < argc && argv[optind + 1][0] != '-');
+					break;
+				default:
+					assert(false);
+			}
+
+			if (!has_argument)
+			{
+				if (curr[2 + name_len] == '=')
+				{
+					if (opterr && optstring[0] != ':')
+						fprintf(stderr, "%s: option takes no argument -- %.*s\n", argv[0], static_cast<int>(name_len), curr + 2);
+					optind++;
+					return (optstring[0] == ':') ? ':' : '?';
+				}
+				optarg = nullptr;
+				optind++;
+			}
+			else
+			{
+				if (curr[2 + name_len] == '=')
+				{
+					optarg = const_cast<char*>(curr + 2 + name_len + 1);
+					optind++;
+				}
+				else
+				{
+					if (optind + 1 >= argc)
+					{
+						if (opterr && optstring[0] != ':')
+							fprintf(stderr, "%s: option requires an argument -- %.*s\n", argv[0], static_cast<int>(name_len), curr + 2);
+						optind++;
+						return (optstring[0] == ':') ? ':' : '?';
+					}
+					optarg = argv[optind + 1];
+					optind += 2;
+				}
+			}
+
+			if (longindex != nullptr)
+				*longindex = i;
+
+			if (opt.flag == nullptr)
+				return opt.val;
+			*opt.flag = opt.val;
+			return 0;
+		}
+
+		if (curr[1] == '-')
+		{
+			if (opterr && optstring[0] != ':')
+				fprintf(stderr, "%s: illegal option -- %s\n", argv[0], curr + 2);
+			optind++;
+			return '?';
+		}
+	}
+
+	if (s_idx_in_arg == -1)
+		s_idx_in_arg = 1;
+
+	for (size_t i = 0; optstring[i]; i++)
+	{
+		if (optstring[i] == ':')
+			continue;
+		if (curr[s_idx_in_arg] != optstring[i])
+			continue;
+
+		const bool has_argument = (optstring[i + 1] == ':');
+		if (!has_argument)
+		{
+			s_idx_in_arg++;
+			if (curr[s_idx_in_arg] == '\0')
+			{
+				s_idx_in_arg = -1;
+				optind++;
+			}
+		}
+		else
+		{
+			if (curr[s_idx_in_arg + 1] != '\0')
+			{
+				optarg = const_cast<char*>(curr + s_idx_in_arg + 1);
+				optind++;
+				s_idx_in_arg = -1;
+			}
+			else
+			{
+				if (optind + 1 >= argc)
+				{
+					if (opterr && optstring[0] != ':')
+						fprintf(stderr, "%s: option requires an argument -- %c\n", argv[0], optstring[i]);
+					optopt = optstring[i];
+					optind++;
+					return optstring[0] == ':' ? ':' : '?';
+				}
+				optarg = const_cast<char*>(argv[optind + 1]);
+				optind += 2;
+				s_idx_in_arg = -1;
+			}
+		}
+
+		return optstring[i];
+	}
+
+	if (opterr && optstring[0] != ':')
+		fprintf(stderr, "%s: illegal option -- %c\n", argv[0], curr[s_idx_in_arg]);
+	optopt = curr[s_idx_in_arg];
+
+	s_idx_in_arg++;
+	if (curr[s_idx_in_arg] == '\0')
+	{
+		s_idx_in_arg = -1;
+		optind++;
+	}
+
+	return '?';
+}
+
+int getopt(int argc, char* const argv[], const char* optstring)
+{
+	struct option option {};
+	return getopt_long_impl(argc, argv, optstring, &option, nullptr, true);
+}
+
+int getopt_long(int argc, char* argv[], const char* optstring, const struct option* longopts, int* longindex)
+{
+	return getopt_long_impl(argc, argv, optstring, longopts, longindex, true);
+}
+
+int getopt_long_only(int argc, char* argv[], const char* optstring, const struct option* longopts, int* longindex)
+{
+	return getopt_long_impl(argc, argv, optstring, longopts, longindex, false);
+}