通过ExternalProject_Add使用pybind11来实现CM项目的智能方法

Question

我正在使用pybind11和CMake 3.9.4编写python模块。 为方便起见，我希望在pybind11中使用ExternalProject_Add下载CMakeLists.txt源文件。

当我运行cmake .时，它不会下载pybind11源文件，并会抛出错误。

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".

有一种解决方法：

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

然而，这并不聪明......有没有办法使用pybind11下载ExternalProject_Add而不评论线路并恢复它们（并且没有运行cmake和{{1两次）？

/Users/me/foo/CMakeLists.txt

make

/Users/me/foo/foo.hpp

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.cpp

#ifndef FOO_LIBRARY_H
#define FOO_LIBRARY_H

#include<pybind11/pybind11.h>

int add(int i, int j);

#endif