通过 ExternalProject_Add 使用 pybind11 CMake 项目的智能方法

Question

我正在写使用Python模块pybind11与CMake3.9.4。因为它是方便，我想下载pybind11源文件中使用ExternalProject_Add我的CMakeLists.txt。

当我运行时cmake .，它不下载pybind11源文件，并引发错误。

CMake Error at CMakeLists.txt:21 (add_subdirectory):
  The source directory
    /Users/me/foo/pybind11_external-prefix/src/pybind11_external
  does not contain a CMakeLists.txt file.

CMake Error at CMakeLists.txt:22 (pybind11_add_module):
  Unknown CMake command "pybind11_add_module".

有一个解决方法：

1. 注释掉 CMakeLists.txt 中的最后 3 行
2. 跑 cmake .
3. 运行make（然后，它下载pybind11源文件）
4. 恢复 CMakeLists.txt 中的最后 3 行
5. 跑 cmake .
6. 跑 make

但是，这并不聪明......有没有办法下载pybind11使用ExternalProject_Add而不注释掉这些行并恢复它们（并且没有运行cmake和make两次）？

/Users/me/foo/CMakeLists.txt

cmake_minimum_required(VERSION 3.8)
project(foo)
set(CMAKE_CXX_STANDARD 14)

include(ExternalProject)
ExternalProject_Add(
        pybind11_external
        GIT_REPOSITORY https://github.com/pybind/pybind11.git
        GIT_TAG v2.2.1
        CONFIGURE_COMMAND ""
        BUILD_COMMAND ""
        INSTALL_COMMAND ""
)
set(PYBIND11_CPP_STANDARD -std=c++14)
ExternalProject_Get_Property(pybind11_external source_dir)
include_directories(${source_dir}/include)

add_subdirectory(${source_dir})             # comment out, then restore this line
pybind11_add_module(foo SHARED foo.cpp)     # comment out, then restore this line
add_dependencies(foo pybind11_external)     # comment out, then restore this line

/Users/me/foo/foo.hpp

CMake Error at CMakeLists.txt:21 (add_subdirectory):
  The source directory
    /Users/me/foo/pybind11_external-prefix/src/pybind11_external
  does not contain a CMakeLists.txt file.

CMake Error at CMakeLists.txt:22 (pybind11_add_module):
  Unknown CMake command "pybind11_add_module".

/Users/me/foo/foo.cpp

cmake_minimum_required(VERSION 3.8)
project(foo)
set(CMAKE_CXX_STANDARD 14)

include(ExternalProject)
ExternalProject_Add(
        pybind11_external
        GIT_REPOSITORY https://github.com/pybind/pybind11.git
        GIT_TAG v2.2.1
        CONFIGURE_COMMAND ""
        BUILD_COMMAND ""
        INSTALL_COMMAND ""
)
set(PYBIND11_CPP_STANDARD -std=c++14)
ExternalProject_Get_Property(pybind11_external source_dir)
include_directories(${source_dir}/include)

add_subdirectory(${source_dir})             # comment out, then restore this line
pybind11_add_module(foo SHARED foo.cpp)     # comment out, then restore this line
add_dependencies(foo pybind11_external)     # comment out, then restore this line

Answer 1

使用 CMake 的FetchContent模块（版本 3.11+），您可以执行以下操作：

include(FetchContent)
FetchContent_Declare(
    pybind11
    GIT_REPOSITORY https://github.com/pybind/pybind11
    GIT_TAG        v2.2.3
)

FetchContent_GetProperties(pybind11)
if(NOT pybind11_POPULATED)
    FetchContent_Populate(pybind11)
    add_subdirectory(${pybind11_SOURCE_DIR} ${pybind11_BINARY_DIR})
endif()

这将在配置时下载 pybind11 和add_subdirectory它。然后你就可以打电话了pybind11_add_module。