cmake - 使用 CMake 下载预构建的库

Question

我正在尝试使用 FetchContent下载 SDL2 的预构建开发库。

因此它们随后可以被 FindSDL2.cmake 拾取模块。

但是，目前我发现 find_package 在库下载之前正在执行，导致第一个干净的 CMake 构建在定位 SDL2 时失败。

但是，在第二次运行时，因为预构建库已经被缓存，所以SDL2在第二次运行时被定位。

关于如何确保在调用 find_package 之前已下载这些预建库有什么建议吗？

我的 CMakeLists.txt 文件。

cmake_minimum_required(VERSION 3.19.2)

project(racer VERSION 0.1.0)

# Racer
file(GLOB SOURCES src/*.cpp)
add_executable(${PROJECT_NAME} ${SOURCES})

# OpenGL
find_package(OpenGL REQUIRED)
target_include_directories(${PROJECT_NAME} PRIVATE ${OPENGL_INCLUDE_DIRS})
target_link_libraries(${PROJECT_NAME} ${OPENGL_LIBRARIES})

# FindSDL2 Modules
list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake/sdl2)

# Fetch Content Module
include(FetchContent)

# Visual C++
## SDL2
FetchContent_Declare(
  SDL2
  URL     https://www.libsdl.org/release/SDL2-devel-2.0.14-VC.zip
  URL_MD5 2b521c5ec247955dc342235d06ebd874
)
FetchContent_MakeAvailable(SDL2)
set(SDL2_PATH ${sdl2_SOURCE_DIR})
find_package(SDL2 REQUIRED)
target_include_directories(${PROJECT_NAME} PRIVATE ${SDL2_INCLUDE_DIRS})
target_link_libraries(${PROJECT_NAME} ${SDL2_LIBRARIES})
add_custom_command(TARGET racer POST_BUILD
    COMMAND ${CMAKE_COMMAND} -E copy_directory
        ${sdl2_SOURCE_DIR}/lib/x64
        $<TARGET_FILE_DIR:racer>)

首次运行日志。

[main] Configuring folder: racer 
[proc] Executing command: "C:\Program Files\CMake\bin\cmake.EXE" --no-warn-unused-cli -DCMAKE_EXPORT_COMPILE_COMMANDS:BOOL=TRUE -DCMAKE_BUILD_TYPE:STRING=Debug "-DCMAKE_C_COMPILER:FILEPATH=C:\Program Files\LLVM\bin\clang.exe" "-DCMAKE_CXX_COMPILER:FILEPATH=C:\Program Files\LLVM\bin\clang++.exe" -Hc:/Users/Josh/projects/racer -Bc:/Users/Josh/projects/racer/build -G "Unix Makefiles"
[cmake] Not searching for unused variables given on the command line.
[cmake] -- The C compiler identification is Clang 12.0.0 with GNU-like command-line
[cmake] -- The CXX compiler identification is Clang 12.0.0 with GNU-like command-line
[cmake] -- Detecting C compiler ABI info
[cmake] -- Detecting C compiler ABI info - done
[cmake] -- Check for working C compiler: C:/Program Files/LLVM/bin/clang.exe - skipped
[cmake] -- Detecting C compile features
[cmake] -- Detecting C compile features - done
[cmake] -- Detecting CXX compiler ABI info
[cmake] -- Detecting CXX compiler ABI info - done
[cmake] -- Check for working CXX compiler: C:/Program Files/LLVM/bin/clang++.exe - skipped
[cmake] -- Detecting CXX compile features
[cmake] -- Detecting CXX compile features - done
[cmake] -- Found OpenGL: opengl32   
[cmake] CMake Error at C:/Program Files/CMake/share/cmake-3.19/Modules/FindPackageHandleStandardArgs.cmake:218 (message):
[cmake]   Could NOT find SDL2 (missing: SDL2_LIBRARY SDL2_INCLUDE_DIR)
[cmake] Call Stack (most recent call first):
[cmake]   C:/Program Files/CMake/share/cmake-3.19/Modules/FindPackageHandleStandardArgs.cmake:582 (_FPHSA_FAILURE_MESSAGE)
[cmake]   cmake/sdl2/FindSDL2.cmake:313 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
[cmake]   CMakeLists.txt:29 (find_package)
[cmake] 
[cmake] 
[cmake] -- Configuring incomplete, errors occurred!
[cmake] See also "C:/Users/Josh/projects/racer/build/CMakeFiles/CMakeOutput.log".
[cmake] See also "C:/Users/Josh/projects/racer/build/CMakeFiles/CMakeError.log".

第二次运行日志(没有清理 build 目录)。

[main] Configuring folder: racer 
[proc] Executing command: "C:\Program Files\CMake\bin\cmake.EXE" --no-warn-unused-cli -DCMAKE_EXPORT_COMPILE_COMMANDS:BOOL=TRUE -DCMAKE_BUILD_TYPE:STRING=Debug "-DCMAKE_C_COMPILER:FILEPATH=C:\Program Files\LLVM\bin\clang.exe" "-DCMAKE_CXX_COMPILER:FILEPATH=C:\Program Files\LLVM\bin\clang++.exe" -Hc:/Users/Josh/projects/racer -Bc:/Users/Josh/projects/racer/build -G "Unix Makefiles"
[cmake] Not searching for unused variables given on the command line.
[cmake] -- Found SDL2: C:/Users/Josh/projects/racer/build/_deps/sdl2-src/lib/x64/SDL2.lib (found version "2.0.14") 
[cmake] CMake Warning (dev) at C:/Program Files/CMake/share/cmake-3.19/Modules/FindPackageHandleStandardArgs.cmake:426 (message):
[cmake]   The package name passed to `find_package_handle_standard_args` (SDL2main)
[cmake]   does not match the name of the calling package (SDL2).  This can lead to
[cmake]   problems in calling code that expects `find_package` result variables
[cmake]   (e.g., `_FOUND`) to follow a certain pattern.
[cmake] Call Stack (most recent call first):
[cmake]   cmake/sdl2/FindSDL2.cmake:318 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
[cmake]   CMakeLists.txt:29 (find_package)
[cmake] This warning is for project developers.  Use -Wno-dev to suppress it.
[cmake] 
[cmake] -- Found SDL2main: C:/Users/Josh/projects/racer/build/_deps/sdl2-src/lib/x64/SDL2main.lib (found version "2.0.14") 
[cmake] -- Configuring done
[cmake] -- Generating done
[cmake] -- Build files have been written to: C:/Users/Josh/projects/racer/build

Answer 1

我认为您需要在第一次调用 project() 之前完成所有的 FetchContent 操作。然后在调用 project() 之后调用 find_package()。

它没有在文档中明确涵盖，但有一个指定使用工具链文件的示例，即使该工具链文件是通过 FetchContent 下载的:https://cmake.org/cmake/help/latest/module/FetchContent.html#examples

未经测试但可能:

cmake_minimum_required(VERSION 3.19.2)

# Fetch Content Module
include(FetchContent)

# Visual C++
## SDL2
FetchContent_Declare(
SDL2
URL     https://www.libsdl.org/release/SDL2-devel-2.0.14-VC.zip
URL_MD5 2b521c5ec247955dc342235d06ebd874
)
FetchContent_MakeAvailable(SDL2)
set(SDL2_PATH ${sdl2_SOURCE_DIR})

project(racer VERSION 0.1.0)

# Racer
file(GLOB SOURCES src/*.cpp)
add_executable(${PROJECT_NAME} ${SOURCES})

# OpenGL
find_package(OpenGL REQUIRED)
target_include_directories(${PROJECT_NAME} PRIVATE ${OPENGL_INCLUDE_DIRS})
target_link_libraries(${PROJECT_NAME} ${OPENGL_LIBRARIES})

# FindSDL2 Modules
list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake/sdl2)

find_package(SDL2 REQUIRED)
target_include_directories(${PROJECT_NAME} PRIVATE ${SDL2_INCLUDE_DIRS})
target_link_libraries(${PROJECT_NAME} ${SDL2_LIBRARIES})
add_custom_command(TARGET racer POST_BUILD
    COMMAND ${CMAKE_COMMAND} -E copy_directory
        ${sdl2_SOURCE_DIR}/lib/x64
        $<TARGET_FILE_DIR:racer>)