Ninja生成器是否支持C++20模块分区？CMake构建报错求助

问题概述 #

使用Visual Studio 2022生成器可正常构建的CMake项目，切换到Ninja生成器时构建失败，询问Ninja生成器是否支持C++20模块分区。

报错信息 #

C:\cmake\bin\ninja\cl : Command line warning D9025: overriding '/std:c20' with '/std:clatest'
[3/8] Generating CXX dyndep file Common\Collector\CMakeFiles\Collector.dir\CXX.dd
FAILED: Common/Collector/CMakeFiles/Collector.dir/CXX.dd C:/cmake/bin/ninja/Common/Collector/CMakeFiles/Collector.dir/CXXModules.json Common/Collector/CMakeFiles/Collector.dir/MetricAgent.cpp.obj.modmap Common/Collector/CMakeFiles/Collector.dir/MetricCollector.cpp.obj.modmap Common/Collector/CMakeFiles/Collector.dir/MetricAgent.ixx.obj.modmap Common/Collector/CMakeFiles/Collector.dir/MetricCollector.ixx.obj.modmap
"C:\Program Files\Microsoft Visual Studio\2022\Enterprise\Common7\IDE\CommonExtensions\Microsoft\CMake\CMake\bin\cmake.exe" -E cmake_ninja_dyndep --tdi=Common\Collector\CMakeFiles\Collector.dir\CXXDependInfo.json --lang=CXX --modmapfmt=msvc --dd=Common\Collector\CMakeFiles\Collector.dir\CXX.dd @Common\Collector\CMakeFiles\Collector.dir\CXX.dd.rsp
C:\cmake\bin\ninja\EXEC : CMake error : Output Common\Collector\CMakeFiles\Collector.dir\MetricAgent.cpp.obj provides the MetricCollector:Agent module but it is not found in a FILE_SET of type CXX_MODULES
ninja: build stopped: subcommand failed.

Build failed.

CMake配置 #

顶层CMakeLists.txt #

cmake_minimum_required(VERSION 3.29)
project(Agent LANGUAGES CXX)
# Set the C++ standard to C++20
set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_EXPERIMENTAL_CXX_MODULE_DYNDEP 1)
set(CXX_SCAN_FOR_MODULES ON)
set(CMAKE_CXX_SCAN_FOR_MODULES ON)

项目级CMakeLists.txt #

project(Collector CXX)
set(CODE_SOURCES MetricAgent.cpp MetricCollector.cpp )
set(INTERF_SOURCES MetricAgent.ixx MetricCollector.ixx )
add_library(${PROJECT_NAME} STATIC ${CODE_SOURCES} ${INTERF_SOURCES})
target_sources(${PROJECT_NAME}
    PRIVATE 
        ${CODE_SOURCES}
    PUBLIC
        FILE_SET CXX_MODULES
    BASE_DIRS
        ${CMAKE_SOURCE_DIR}/Common/Collector
    FILES
        ${INTERF_SOURCES}
    )

模块代码 #

MatricCollector.ixx（注意：存在拼写错误，应为MetricCollector.ixx） #

module;
export module MetricCollector;
export import : Agent;

MatricCollector.cpp（注意：存在拼写错误，应为MetricCollector.cpp） #

module;
module MetricCollector;

MetricAgent.ixx #

module;
export module MetricCollector : Agent;

MetricAgent.cpp #

module;
module MetricCollector : Agent;

解决方案 #

Ninja生成器支持C++20模块分区，报错源于CMake配置问题：MetricAgent.cpp作为MetricCollector:Agent模块分区的实现文件，未被纳入CXX_MODULES文件集，导致动态依赖扫描无法识别其归属。

修复步骤：

1. 修正文件拼写错误：将MatricCollector.ixx和MatricCollector.cpp重命名为MetricCollector.ixx和MetricCollector.cpp，避免模块名称匹配失败。
2. 调整CMake配置：将模块实现文件（.cpp）加入CXX_MODULES文件集，确保CMake正确追踪模块依赖。修改后的项目级CMakeLists.txt如下：

project(Collector CXX)
set(CODE_SOURCES MetricAgent.cpp MetricCollector.cpp )
set(INTERF_SOURCES MetricAgent.ixx MetricCollector.ixx )
add_library(${PROJECT_NAME} STATIC)
target_sources(${PROJECT_NAME}
    PRIVATE 
        ${CODE_SOURCES}
    PUBLIC
        FILE_SET CXX_MODULES
            BASE_DIRS
                ${CMAKE_SOURCE_DIR}/Common/Collector
            FILES
                ${INTERF_SOURCES}
                ${CODE_SOURCES}
    )

3. 确保target_sources的语法缩进正确，BASE_DIRS和FILES需对齐在FILE_SET CXX_MODULES下方，避免CMake解析错误。

内容的提问来源于stack exchange，提问作者Uriel