add xmake support for easier C++20 module compilation and testing

xmake.lua

@@ -0,0 +1,91 @@
+set_xmakever("2.8.2")
+set_project("argparse")
+
+set_version("2.9.0", { build = "%Y%m%d%H%M" })
+
+option("enable_module")
+option("enable_tests")
+option("enable_samples")
+
+add_cxxflags(
+	"-Wall",
+	"-Wno-long-long",
+	"-pedantic",
+	"-Wsign-conversion",
+	"-Wshadow",
+	"-Wconversion",
+	{ toolsets = { "clang", "gcc" } }
+)
+add_cxxflags("cl::/W4")
+
+if is_plat("windows") then
+	add_defines("_CRT_SECURE_NO_WARNINGS")
+end
+
+target("argparse")
+do
+	if get_config("enable_module") then
+		set_languages("c++20")
+		set_kind("object")
+	else
+		set_languages("c++17")
+		set_kind("headeronly")
+	end
+
+	add_includedirs("include", { public = true })
+	add_headerfiles("include/argparse/argparse.hpp")
+	if get_config("enable_module") then
+		add_files("module/argparse.cppm", { install = true })
+	end
+end
+
+if get_config("enable_tests") then
+	target("argparse_tests")
+	do
+		set_kind("binary")
+		set_languages("c++17")
+		set_basename("module_tests")
+
+		add_includedirs("test")
+
+		add_files("test/main.cpp", { defines = { "DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN" } })
+		add_files("test/**.cpp")
+
+		add_deps("argparse")
+	end
+
+	if get_config("enable_module") then
+		target("argparse_module_tests")
+		do
+			set_kind("binary")
+			set_languages("c++20")
+			set_basename("module_tests")
+
+			add_defines("WITH_MODULE")
+
+			add_includedirs("test")
+
+			add_files("test/main.cpp", { defines = { "DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN" } })
+			add_files("test/**.cpp")
+			add_files("test/argparse_details.cppm")
+
+			add_deps("argparse")
+		end
+	end
+end
+
+if get_config("enable_samples") then
+	for _, sample_file in ipairs(os.files("samples/*.cpp")) do
+			target(path.basename(sample_file))
+			do
+				set_kind("binary")
+				set_languages("c++17")
+
+				add_files(sample_file)
+
+        set_policy("build.c++.modules", false)
+
+				add_deps("argparse")
+			end
+	end
+end