CMake 使用 Homebrew 公式安装 pybind11 绑定

Question

I would like to supply a Homebrew formula for a CMake project that builds and installs a C++ library along with its Python bindings written using pybind11.The formula should ideally work by running a plain

cmake --build . --target install

This installation flow works fine locally, but using a Homebrew formula introduces a problem in the installation directory for the Python bindings: while headers and libraries are installed in the proper directory in the Cellar identified by #{prefix}, the bindings need to be in a site-packages directory visible to Python. I am getting such directory within CMake using

install(TARGETS pyariadne DESTINATION ${Python_SITEARCH})

but the directory seem not to be writable by Homebrew, returning an Operation not permitted . Identifying the install directory by the following

execute_process(COMMAND python3 -m site --user-site OUTPUT_VARIABLE INSTALL_DIR)

does not work either since Homebrew identifies a temporary user site in /tmp and consequently any library installed there is subsequently removed.

How am I supposed to install everything from Homebrew, without resorting to changes of permissions to directories? I'd like to avoid packaging for pypi and using pip to install the bindings separately.

EDIT (example of the output, involved directories):

[109/110] Install the project...
-- Install configuration: "Release"
-- Installing: 

/usr/local/Cellar/python@3.9/3.9.2_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/pyariadne.so
CMake Error at cmake_install.cmake:49 (file):
  file INSTALL cannot copy file
  "/tmp/ariadne-20210305-1763-ggejxl/ariadne-2.1-rc2/build/pyariadne.so" to
  
"/usr/local/Cellar/python@3.9/3.9.2_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/pyariadne.so":
  Operation not permitted.

Directory /usr/local/Cellar/python@3.9/3.9.2_1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages links to /usr/local/lib/python3.9/site-packages . The former has user lgeretti:staff, the latter has user lgeretti:admin.

This issue not only happens on my machine, but I also verify it on a macos:latest GitHub Actions machine where the only required step is to brew install the package.

Answer 1

Found the solution from this post on Homebrew discussions, which relies on the libexec directory and pth file creation:

1. Use libexec as installation target in CMake, made it conditional on using Homebrew rather than local installation:

  if (HOMEBREW)
      install(TARGETS pyariadne DESTINATION libexec)
  else()
      find_package(Python)
      install(TARGETS pyariadne DESTINATION ${Python_SITEARCH})
  endif()

2. Set up the following in the formula, to create the.pth file:

  def install
    mkdir "build" do
      system "cmake -G \"Ninja\" .. -DCMAKE_BUILD_TYPE=Release -DHOMEBREW=1 -DCMAKE_INSTALL_PREFIX=#{prefix}"
      system "cmake", "--build", ".", "--target", "install", "--parallel"
    end

    python_version = Language::Python.major_minor_version Formula["python@3.9"].bin/"python3"
    (lib/"python#{python_version}/site-packages/homebrew-ariadne.pth").write <<~EOS
      import site; site.addsitedir('#{libexec}')
    EOS
  end

Answer 2

This is a better CMake implementation of Luca's good solution. One should introduce package customization points directly via a cache variable, rather than a packager-specific flag. This is the approach taken by the standard GNUInstallDirs module. See below:

find_package(Python)

set(MyProj_INSTALL_PYTHONDIR "${Python_SITEARCH}"
    CACHE STRING "Install destination for Python targets")
install(TARGETS pyariadne DESTINATION "${MyProj_INSTALL_PYTHONDIR}")

The default value of MyProj_INSTALL_PYTHONDIR is Python_SITEARCH , but it can be overridden in a package script:

def install
  mkdir "build" do
    system "cmake -G \"Ninja\" .. -DCMAKE_BUILD_TYPE=Release " \
           "-DMyProj_INSTALL_PYTHONDIR=libexec -DCMAKE_INSTALL_PREFIX=#{prefix}"
    system "cmake", "--build", ".", "--target", "install", "--parallel"
  end

  python_version = Language::Python.major_minor_version Formula["python@3.9"].bin/"python3"
  (lib/"python#{python_version}/site-packages/homebrew-ariadne.pth").write <<~EOS
    import site; site.addsitedir('#{libexec}')
  EOS
end

This way is significantly better because the CMake build no longer needs to know anything about Homebrew.