cmdline: Add a command-line parser and tests for it

This parser accepts a command-line in a format similar to Linux's:
"foo bar=baz qux=12".

include/frg/cmdline.hpp

@@ -0,0 +1,126 @@
+#ifndef FRG_CMDLINE_HPP
+#define FRG_CMDLINE_HPP
+
+#include <frg/macros.hpp>
+#include <frg/string.hpp>
+#include <frg/tuple.hpp>
+
+#include <concepts>
+
+namespace frg FRG_VISIBILITY {
+
+struct option {
+	struct fn_type {
+		void (*ptr)(frg::string_view, void *);
+		void *ctx;
+		bool has_arg;
+	};
+
+	frg::string_view opt;
+	fn_type fn;
+
+	void apply(frg::string_view value) {
+		if (fn.ptr)
+			fn.ptr(value, fn.ctx);
+	}
+};
+
+template <typename T>
+auto as_number(T &here) {
+	return option::fn_type{
+		[] (frg::string_view value, void *ctx) {
+			auto n = value.to_number<T>();
+			if (n)
+				*static_cast<T *>(ctx) = n.value();
+		},
+		&here,
+		true
+	};
+}
+
+inline auto as_string_view(frg::string_view &here) {
+	return option::fn_type{
+		[] (frg::string_view value, void *ctx) {
+			*static_cast<frg::string_view *>(ctx) = value;
+		},
+		&here,
+		true
+	};
+}
+
+inline auto store_true(bool &here) {
+	return option::fn_type{
+		[] (frg::string_view value, void *ctx) {
+			*static_cast<bool *>(ctx) = true;
+		},
+		&here,
+		false
+	};
+}
+
+template <typename T>
+concept option_span = requires (T t) {
+	{ t.data() } -> std::convertible_to<option *>;
+	{ t.size() } -> std::convertible_to<size_t>;
+};
+
+
+template <option_span ...Ts>
+inline void parse_arguments(frg::string_view cmdline, Ts &&...args) {
+	auto try_apply_arg = [&] (frg::string_view arg, option opt) -> bool {
+		auto eq = arg.find_first('=');
+
+		if (eq == size_t(-1)) {
+			if (opt.fn.has_arg)
+				return false;
+
+			if (opt.opt != arg)
+				return false;
+
+			opt.apply({});
+		} else {
+			if (!opt.fn.has_arg)
+				return false;
+
+			auto name = arg.sub_string(0, eq);
+			auto val = arg.sub_string(eq + 1, arg.size() - eq -1);
+
+			if (opt.opt != name)
+				return false;
+
+			opt.apply(val);
+		}
+
+		return true;
+	};
+
+	auto try_arg_span = [&] (frg::string_view arg, auto span) -> bool {
+		for (size_t i = 0; i < span.size(); i++) {
+			if (try_apply_arg(arg, span.data()[i]))
+				return true;
+		}
+
+		return false;
+	};
+
+	while (true) {
+		size_t spc = cmdline.find_first(' ');
+		size_t split_on = spc;
+		if (spc == size_t(-1))
+			split_on = cmdline.size();
+
+		auto arg = cmdline.sub_string(0, split_on);
+
+		(try_arg_span(arg, args) || ...);
+
+		if (spc != size_t(-1)) {
+			cmdline = cmdline.sub_string(spc + 1, cmdline.size() - spc - 1);
+		} else {
+			break;
+		}
+	}
+}
+
+} // namespace frg
+
+#endif // FRG_CMDLINE_HPP

tests/tests.cpp

@@ -319,3 +319,44 @@ TEST(bitset, count) {
 	EXPECT_FALSE(a.all());
 	EXPECT_FALSE(a.none());
 }
+
+#include <frg/array.hpp>
+#include <frg/cmdline.hpp>
+
+TEST(cmdline, basic_cmdline) {
+	bool foo = false, bar = false;
+	frg::string_view v1{};
+	uint32_t v2 = 0;
+
+	frg::array args = {
+		frg::option{"foo", frg::store_true(foo)},
+		frg::option{"bar", frg::store_true(bar)},
+		frg::option{"baz", frg::as_string_view(v1)},
+		frg::option{"qux", frg::as_number(v2)},
+	};
+
+	frg::parse_arguments("foo baz=yoo qux=1234", args);
+
+	ASSERT_TRUE(foo);
+	ASSERT_FALSE(bar);
+	ASSERT_EQ(v1, "yoo");
+	ASSERT_EQ(v2, 1234);
+}
+
+TEST(cmdline, multiple_option_spans) {
+	bool nosmp = false;
+	frg::string_view init_exec{};
+
+	frg::array cpu_args = {
+		frg::option{"x86.nosmp", frg::store_true(nosmp)}
+	};
+
+	frg::array init_args = {
+		frg::option{"init.exec", frg::as_string_view(init_exec)}
+	};
+
+	frg::parse_arguments("x86.nosmp init.exec=/sbin/posix-subsystem", init_args, cpu_args);
+
+	ASSERT_TRUE(nosmp);
+	ASSERT_EQ(init_exec, "/sbin/posix-subsystem");
+}