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 +1,133 @@
+#ifndef FRG_CMDLINE_HPP
+#define FRG_CMDLINE_HPP
+
+#include <frg/macros.hpp>
+#include <frg/string.hpp>
+#include <frg/tuple.hpp>
+
+#include <ranges>
+
+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) {
+		FRG_ASSERT(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
+	};
+}
+
+template<typename T, T value>
+auto store_const(T &here) {
+	return option::fn_type{
+		[] (frg::string_view, void *ctx) {
+			*static_cast<T *>(ctx) = value;
+		},
+		&here,
+		false
+	};
+}
+
+inline auto store_true(bool &here) {
+	return store_const<bool, true>(here);
+}
+
+inline auto store_false(bool &here) {
+	return store_const<bool, false>(here);
+}
+
+
+inline void parse_arguments(frg::string_view cmdline, std::ranges::range auto 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;
+	};
+
+	while (true) {
+		size_t spc = cmdline.find_first(' ');
+		size_t opening_quote = cmdline.find_first('\"');
+		size_t closing_quote = size_t(-1);
+		bool quoted = false;
+
+		if(opening_quote < spc) {
+			quoted = true;
+
+			closing_quote = opening_quote + 1 + cmdline.sub_string(opening_quote + 1, cmdline.size() - opening_quote - 1).find_first('\"');
+			spc = closing_quote + 1 + cmdline.sub_string(closing_quote + 1, cmdline.size() - closing_quote - 1).find_first(' ');
+		}
+
+		size_t split_on = spc;
+		if (spc == size_t(-1))
+			split_on = cmdline.size();
+
+		auto arg = cmdline.sub_string(quoted ? (opening_quote + 1) : 0, quoted ? (closing_quote - opening_quote - 1) : split_on);
+
+		for (const option &opt : args) {
+			if (try_apply_arg(arg, opt))
+				break;
+		}
+
+		if (spc != size_t(-1)) {
+			cmdline = cmdline.sub_string(spc + 1, cmdline.size() - spc - 1);
+		} else {
+			break;
+		}
+	}
+}
+
+} // namespace frg
+
+#endif // FRG_CMDLINE_HPP

meson.build

@@ -8,6 +8,7 @@ if not get_option('frigg_no_install')
 		'include/frg/algorithm.hpp',
 		'include/frg/allocation.hpp',
 		'include/frg/array.hpp',
+		'include/frg/cmdline.hpp',
 		'include/frg/container_of.hpp',
 		'include/frg/detection.hpp',
 		'include/frg/dyn_array.hpp',

tests/tests.cpp

@@ -525,3 +525,52 @@ 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::string_view v3{};
+	frg::string_view v4{};
+
+	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::option{"path1", frg::as_string_view(v3)},
+		frg::option{"path2", frg::as_string_view(v4)},
+	};
+
+	frg::parse_arguments("\"path1=a space/nospace\" foo baz=yoo qux=1234 \"path2=/a/b c/d\"", args);
+
+	ASSERT_TRUE(foo);
+	ASSERT_FALSE(bar);
+	ASSERT_EQ(v1, "yoo");
+	ASSERT_EQ(v2, 1234);
+	ASSERT_EQ(v3, "a space/nospace");
+	ASSERT_EQ(v4, "/a/b c/d");
+}
+
+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::array combined = { init_args, cpu_args };
+
+	frg::parse_arguments("x86.nosmp init.exec=/sbin/posix-subsystem", std::views::join(combined));
+
+	ASSERT_TRUE(nosmp);
+	ASSERT_EQ(init_exec, "/sbin/posix-subsystem");
+}