如何将编译选项添加到 CMake FetchContent 依赖项？

Question

我有一个 C/C++ 项目，我想在其中使用 CppUTest。因此，我将 CppUTest 的依赖项包含在以下内容中：

include(FetchContent)
FetchContent_Declare(
        CppUTest
        GIT_REPOSITORY      https://github.com/cpputest/cpputest.git
        GIT_TAG             latest-passing-build
        CONFIGURE_COMMAND   ""
        BUILD_COMMAND       ""
)
set(TESTS OFF CACHE BOOL "Switch off CppUTest Test build")
FetchContent_MakeAvailable(CppUTest)

这很好用。

在我的（汽车）项目中，我使用 C++20 标准，并且需要启用所有/大多数警告。但当我这样做时，CppUTest 给我带来了很多警告。因此，我想使用与项目代码不同的编译器选项来编译 CppUTest。

我如何在 CMake 中配置它？我用谷歌搜索了很多，但没有找到任何有用的东西。

谢谢，斯特凡

PS：我的简化CMake文件是：

cmake_minimum_required(VERSION 3.5)

project(projectName LANGUAGES CXX C)

set(CMAKE_C_STANDARD 99)
set(CMAKE_C_STANDARD_REQUIRED ON)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang")
    MESSAGE("Setting Clang flags:")
    SET(COMPILE_FLAGS_WARNINGS "-Weverything")
    SET(COMPILE_FLAGS_DEBUG    "-Og")
    SET(COMPILE_FLAGS_RELEASE  "-O2")
    SET(COMPILE_FLAGS_COVERAGE "--coverage")
elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "GNU")
    #more options here
elseif ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "MSVC")
    #more options here
endif()

MESSAGE("Debug: ${CMAKE_CXX_FLAGS} ${COMPILE_FLAGS_WARNINGS} ${COMPILE_FLAGS_DEBUG}")
MESSAGE("Release: ${CMAKE_CXX_FLAGS} ${COMPILE_FLAGS_WARNINGS} ${COMPILE_FLAGS_RELEASE}")
MESSAGE("Coverage: ${CMAKE_CXX_FLAGS} ${COMPILE_FLAGS_WARNINGS} ${COMPILE_FLAGS_DEBUG} ${COMPILE_FLAGS_COVERAGE}")

### Dependencies:

include(FetchContent)
FetchContent_Declare(
        CppUTest
        GIT_REPOSITORY      https://github.com/cpputest/cpputest.git
        GIT_TAG             latest-passing-build
        CONFIGURE_COMMAND   ""
        BUILD_COMMAND       ""
)    

set(TESTS OFF CACHE BOOL "Switch off CppUTest Test build")
FetchContent_MakeAvailable(CppUTest)

SET(CMAKE_CXX_FLAGS  "${CMAKE_CXX_FLAGS} ${COMPILE_FLAGS_WARNINGS}")
set(CMAKE_CXX_FLAGS_DEBUG "${COMPILE_FLAGS_DEBUG}")
set(CMAKE_CXX_FLAGS_RELEASE "${COMPILE_FLAGS_RELEASE}")
 
enable_testing()
    
### add tests
add_subdirectory(path/to/my/tests)

Answer 1

不使用set(CMAKE_<LANG>*。使用*target*接口。如果您不希望使用特定选项来编译所有内容，请不要全局设置它们。反而：

set_target_properties(mytests PROPERTY
    CXX_STANDARD 11
    etc.
)
target_compile_options(mytests PUBLIC -option1 -option2 ...)

无论如何，影响其后SET(CMAKE_<LANG>_*声明的目标。所以之后移动set(CMAKE_*FetchContent_MakeAvailable(CppUTest)