使用了C++20 module的项目生成的CMakeLists.txt不正确

[hghgthifg]

Xmake 版本

v2.9.5+HEAD.d30de52e9

操作系统版本和架构

Windows11 version 23H2

描述问题

src/main.cpp:

import Vec3;
import std;

int main(int argc, char** argv)
{
	auto point3 = vec3{0, 0, 0};

	int image_width = 256;
	int image_height = 256;

	std::cout << "P3\n"
			  << image_width << " " << image_height << "\n255\n";

	for (int j = 0; j < image_height; j++) {
		std::clog << "\rScanlines remaining: " << (image_height - j) << ' ' << std::flush;
		for (int i = 0; i < image_width; i++) {
			auto r = double(i) / double(image_width - 1);
			auto g = double(j) / double(image_height - 1);
			auto b = 0.0;

			int ir = int(255.999 * r);
			int ig = int(255.999 * g);
			int ib = int(255.999 * b);

			std::cout << ir << " " << ig << " " << ib << "\n";
		}
	}

	std::clog << "\rDone.                  \n";

	return 0;
}

src/vec3.cppm:

export module Vec3;
import std;

export class vec3
{
public:
	double e[3];

	vec3() : e{0, 0, 0} {}
	vec3(double e0, double e1, double e2) : e{e0, e1, e2} {}

	double x() const { return e[0]; }
	double y() const { return e[1]; }
	double z() const { return e[2]; }

	vec3 operator-() const { return vec3(-e[0], -e[1], -e[2]); }
	double operator[](int i) const { return e[i]; }
	double& operator[](int i) { return e[i]; }

	vec3& operator+=(const vec3& v)
	{
		e[0] += v.e[0];
		e[1] += v.e[1];
		e[2] += v.e[2];
		return *this;
	}

	vec3& operator*=(double t)
	{
		e[0] *= t;
		e[1] *= t;
		e[2] *= t;
		return *this;
	}

	vec3& operator/=(double t) { return *this *= 1 / t; }

	double length() const { return std::sqrt(length_squared()); }

	double length_squared() const
	{
		return e[0] * e[0] + e[1] * e[1] + e[2] * e[2];
	}
};

// point3 is just an alias for vec3, but useful for geometric clarity in the
// code.
export using point3 = vec3;

// Vector Utility Functions

export inline std::ostream& operator<<(std::ostream& out, const vec3& v)
{
	return out << v.e[0] << ' ' << v.e[1] << ' ' << v.e[2];
}

export inline vec3 operator+(const vec3& u, const vec3& v)
{
	return vec3(u.e[0] + v.e[0], u.e[1] + v.e[1], u.e[2] + v.e[2]);
}

export inline vec3 operator-(const vec3& u, const vec3& v)
{
	return vec3(u.e[0] - v.e[0], u.e[1] - v.e[1], u.e[2] - v.e[2]);
}

export inline vec3 operator*(const vec3& u, const vec3& v)
{
	return vec3(u.e[0] * v.e[0], u.e[1] * v.e[1], u.e[2] * v.e[2]);
}

export inline vec3 operator*(double t, const vec3& v)
{
	return vec3(t * v.e[0], t * v.e[1], t * v.e[2]);
}

export inline vec3 operator*(const vec3& v, double t) { return t * v; }

export inline vec3 operator/(const vec3& v, double t) { return (1 / t) * v; }

export inline double dot(const vec3& u, const vec3& v)
{
	return u.e[0] * v.e[0] + u.e[1] * v.e[1] + u.e[2] * v.e[2];
}

export inline vec3 cross(const vec3& u, const vec3& v)
{
	return vec3(u.e[1] * v.e[2] - u.e[2] * v.e[1],
				u.e[2] * v.e[0] - u.e[0] * v.e[2],
				u.e[0] * v.e[1] - u.e[1] * v.e[0]);
}

export inline vec3 unit_vector(const vec3& v) { return v / v.length(); }

xmake.lua:

add_rules("mode.debug", "mode.release")
set_policy("build.c++.modules", true)

set_languages("c++23")

target("RayTracing")
    set_kind("binary")
    add_files("src/*.cpp")
    add_files("src/*.cppm")

直接使用 xmake 进行构建是正常的，但是生成的 CMakeLists.txt 无法正常使用。

CMakeLists.txt:

# this is the build file for project 
# it is autogenerated by the xmake build system.
# do not edit by hand.

# project
cmake_minimum_required(VERSION 3.28.0)
cmake_policy(SET CMP0091 NEW)
project(RayTracing LANGUAGES CXX)
set(CMAKE_CXX_SCAN_FOR_MODULES ON)

# target
add_executable(RayTracing "")
set_target_properties(RayTracing PROPERTIES OUTPUT_NAME "RayTracing")
set_target_properties(RayTracing PROPERTIES RUNTIME_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/build/windows/x64/debug")
if(MSVC)
    target_compile_options(RayTracing PRIVATE /EHsc)
elseif(Clang)
    target_compile_options(RayTracing PRIVATE -fexceptions)
    target_compile_options(RayTracing PRIVATE -fcxx-exceptions)
elseif(Gcc)
    target_compile_options(RayTracing PRIVATE -fexceptions)
endif()
set_target_properties(RayTracing PROPERTIES CXX_EXTENSIONS OFF)
target_compile_features(RayTracing PRIVATE cxx_std_23)
if(MSVC)
    target_compile_options(RayTracing PRIVATE $<$<CONFIG:Debug>:-Od>)
else()
    target_compile_options(RayTracing PRIVATE -O0)
endif()
if(MSVC)
    target_compile_options(RayTracing PRIVATE -Zi)
else()
    target_compile_options(RayTracing PRIVATE -g)
endif()
if(MSVC)
    set_property(TARGET RayTracing PROPERTY
        MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")
endif()
target_sources(RayTracing PRIVATE
    src/main.cpp
    src/Vec3.cppm
)

用 CMake 构建得到的报错：

CMake Error: Output CMakeFiles\RayTracing.dir\src\Vec3.cppm.obj provides the `Vec3` module but it is not found in a `FILE_SET` of type `CXX_MODULES`
ninja: build stopped: subcommand failed.

期待的结果

期待生成的 CMakeLists.txt 能和用 xmake 一样成功构建

工程配置

add_rules("mode.debug", "mode.release")
set_policy("build.c++.modules", true)

set_languages("c++23")

target("RayTracing")
    set_kind("binary")
    add_files("src/*.cpp")
    add_files("src/*.cppm")

附加信息和错误日志

用 CMake 构建得到的报错：

CMake Error: Output CMakeFiles\RayTracing.dir\src\Vec3.cppm.obj provides the `Vec3` module but it is not found in a `FILE_SET` of type `CXX_MODULES`
ninja: build stopped: subcommand failed.

[Issues-translate-bot]

Bot detected the issue body's language is not English, translate it automatically.

---

Title: The CMakeLists.txt generated by projects using the C++20 module is incorrect

[waruqi]

你可以先自己调下 cmakelists.txt 看下哪里不对，xmake 能编译，不代表 cmake 一定也能很好支持 c++ modules。

[Issues-translate-bot]

Bot detected the issue body's language is not English, translate it automatically.

---

You can first adjust cmakelists.txt yourself to see what is wrong. If xmake can compile, it does not mean that cmake can also support c++ modules well.

[Tomcat-42]

Actually CMake support modules (with one exception, header units). But you should add sources like the following:

target_sources(foo
  PUBLIC
    FILE_SET CXX_MODULES FILES
      foo.cxx
)

Note the FILE_SET CXX_MODULES FILES annotation. This should be rather easy to implement in the XMake side.

Sources:

https://www.kitware.com/import-cmake-the-experiment-is-over/
https://www.kitware.com/import-std-in-cmake-3-30/

[waruqi]

Note the FILE_SET CXX_MODULES FILES annotation. This should be rather easy to implement in the XMake side.

You can try add it in generated CMakeLists.txt manually. Does it work?

I think cmake is able to automatically recognize and support .cppm files for compiling as modules. It works for me.

Only non-module file suffixes (.cxx) need to be set CXX_MODULES file type explicitly.

[whisper-bye]

Note the FILE_SET CXX_MODULES FILES annotation. This should be rather easy to implement in the XMake side.

You can try add it in generated CMakeLists.txt manually. Does it work?

I think cmake is able to automatically recognize and support .cppm files for compiling as modules. It works for me.

Only non-module file suffixes (.cxx) need to be set CXX_MODULES file type explicitly.

在我的环境下 windows + cmake 3.31.0 并使用 cppm 后缀无效，还是需要显式添加 PRIVATE FILE_SET CXX_MODULES FILES

[Chupakabra0]

You can try add it in generated CMakeLists.txt manually. Does it work?

I can confirm that this works for me only if I add to CMakeLists.txt:

target_sources(
    ${TARGET_NAME}
    PRIVATE Source.cpp
    PRIVATE FILE_SET cppHeaders TYPE HEADERS FILES Header.hpp
    PRIVATE FILE_SET cppModules TYPE CXX_MODULES FILES Module.cppm
)

I use cmake version 3.30.3

[Chupakabra0]

Also have to mention: if you wanna use import std; you must make more additions to CMakeLists.txt by yourself:

xmake.lua:

set_project("TestModules")
set_languages("c23", "c++23")
set_version("1.0.0")

add_rules("mode.debug", "mode.release")
set_policy("compatibility.version", "3.0")
set_warnings("all", "error")

if is_mode("debug") then
    set_symbols("debug")
    set_optimize("none")
else
    set_symbols("hidden")
    set_optimize("fastest")
    set_strip("all")
end

target("TestModules")
    set_kind("binary")
    add_files("Source.cpp", "Vec3.cppm")

CMakeLists.txt:

cmake_minimum_required(VERSION 3.28.0)
cmake_policy(SET CMP0091 NEW)
set(CMAKE_EXPERIMENTAL_CXX_IMPORT_STD "0e5b6991-d74f-4b3d-a41c-cf096e0b2508") # for import std
project(TestModules VERSION 1.0.0 LANGUAGES CXX)
# set(CMAKE_CXX_SCAN_FOR_MODULES ON) works for me without this line
set(CMAKE_CXX_MODULE_STD ON) # for import std

# target
add_executable(TestModules "")
set_target_properties(TestModules PROPERTIES OUTPUT_NAME "TestModules")
set_target_properties(TestModules PROPERTIES RUNTIME_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/build/windows/x64/debug")
if(MSVC)
    target_compile_options(TestModules PRIVATE -W3)
    target_compile_options(TestModules PRIVATE -WX)
elseif(Clang)
    target_compile_options(TestModules PRIVATE -Wall)
    target_compile_options(TestModules PRIVATE -Werror)
elseif(Gcc)
    target_compile_options(TestModules PRIVATE -Wall)
    target_compile_options(TestModules PRIVATE -Werror)
endif()
if(MSVC)
    target_compile_options(TestModules PRIVATE /EHsc)
elseif(Clang)
    target_compile_options(TestModules PRIVATE -fexceptions)
    target_compile_options(TestModules PRIVATE -fcxx-exceptions)
elseif(Gcc)
    target_compile_options(TestModules PRIVATE -fexceptions)
endif()
set_target_properties(TestModules PROPERTIES C_EXTENSIONS OFF)
target_compile_features(TestModules PRIVATE c_std_23)
set_target_properties(TestModules PROPERTIES CXX_EXTENSIONS OFF)
target_compile_features(TestModules PRIVATE cxx_std_23)
if(MSVC)
    target_compile_options(TestModules PRIVATE $<$<CONFIG:Debug>:-Od>)
else()
    target_compile_options(TestModules PRIVATE -O0)
endif()
if(MSVC)
    target_compile_options(TestModules PRIVATE -Zi)
else()
    target_compile_options(TestModules PRIVATE -g)
endif()
if(MSVC)
    set_property(TARGET TestModules PROPERTY
        MSVC_RUNTIME_LIBRARY "MultiThreadedDebugDLL")
endif()
target_sources(
    TestModules
    PRIVATE Source.cpp
    PRIVATE FILE_SET cppModules TYPE CXX_MODULES FILES Vec3.cppm
) # changed for CMake able to build C++20 modules support

Code of Source.cpp and Vec3.cppm same as @hghgthifg has. Tested this for the newest version of CMake 3.31.1. Works the same way like in 3.30.3.

If you use this CMakeLists.txt, you may encounter a warning after reloading the project. However, everything should work correctly, at least with the latest version of MSVC.

CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.31/Modules/Compiler/CMakeCommonCompilerMacros.cmake:248 (cmake_language):
  CMake's support for `import std;` in C++23 and newer is experimental.  It
  is meant only for experimentation and feedback to CMake developers.
Call Stack (most recent call first):
  C:/Program Files/CMake/share/cmake-3.31/Modules/CMakeDetermineCompilerSupport.cmake:113 (cmake_create_cxx_import_std)
  C:/Program Files/CMake/share/cmake-3.31/Modules/CMakeTestCXXCompiler.cmake:83 (CMAKE_DETERMINE_COMPILER_SUPPORT)
  CMakeLists.txt:9 (project)
This warning is for project developers.  Use -Wno-dev to suppress it.