Setuptools extensions for CMake: Seamless integration of Cmake build system to setuptools

This Python package provides an extension to setuptools to integrate CMake into setuptools workflow. CMake build tool is tasked to build/install a complete Python distribution package with binary extensions and necessary data files. Then, setuptools follows to package up the bundled files for binary distribution (bdist_wheel/bdist_egg/etc.) or the CMake source directory for source distribution (sdist).

Features

• setup() Wrapper: cmaketools.setup() wraps setuptools.setup() to provide one-stop setup() call for both CMake and setupstools.
• Source Distributable: cmaketools let you create a pip-installable source distribution via Setuptools' sdist command. This enables the use of tox to perform multi-environment testing.
• Automatic Source Content Detection: By taking advantage of the source directory structure imposed by CMake project, setup.py's critical keywords: package_dir, packages, package_data, ext_modules, and cmdclass.
• Source File Protection: Neither CMake nor Python setuptools will modify any content of the source directory under any command. It will not be cluttered by __pycache__ or other runtime artifacts.
• Git Submodule Aware: If a project contains git submodules, the submodules will be automatically cloned during pip installation, and the pinned commit of each submodule will be checked out before build.
• Support for CMake Command-Line Options: The most of the CMake command line options are made available as the build_ext command options. For example, python setup.py build_ext -GNinja will build the CMake project with Ninja build system.
• Integaration of Native Code Tests: CMake ships with a test driver program, called ctest. It could be called to run the CMake build tests from Python via cmaketools.cmakeutil.ctest().

Usage Examples

You can experiment cmaketools with different Python/native interfaces availeble from following GitHub templates:

• CPython: https://github.com/python-cmaketools/cpython-example
• Pybind11: https://github.com/python-cmaketools/pybind-example
• Boost-Python: https://github.com/python-cmaketools/boost-python-example

Package Authoring Guide

Source Directory Structure

The structure of the source directory and placements of CMakeLists.txt must adhere to the requirements below for cmaketools to detect the package structure correctly. Here are some key tips in structuring the source directory:

• Source Directory (src) corresponds to the root package (or Lib\site-packages in Python directory). It could be named arbitrarily so long as it is assigned to src_dir attribute of CMakeBuilder.
• Package Directory Source subdirectories with __init__.py file are included in packages setup argument.
• Pure Python Modules Place all .py module files where they belong within the package structure.
• Binary Extension Module To define a binary module, create a directory under a package directory it belongs to. In the example, src/mypkg/example_module is one such directory then we expect mypkg.example_module binary module. Make sure the directory name matches the module name defined in C/C++ source file. Each binary module directory should contain CMakeLists.txt file which defines the library target. For example, the CMakeLists.txt file in module directory shall call pybind11_add_module to include a pybind11-based module to the build project. This is a requirement for the auto-configuration of ext_modules setup argument.
• Additional Files Any "owned" additional data files needed to build the binary modules or to be used by the package shall be placed somewhere in src as it is the directory packaged by sdist.
• 3rd-Pary Files If downloadable or git-clonable, place them outside of src to keep sdist package small. Script CMake to install them to their final in-package location to keep your package platform agnostic. This can be done via git submodules or CMake file(DOWNLOAD <url> <file> ...) command, then build it if necessary and install the files relative to CMAKE_INSTALL_PREFIX. Only if they must be distributed in sdist package, place them inside src.

CMakeLists.txt Authoring Tips

First, to learn how to author CMake scripts, visit Official CMake Tutorial.

The CMake integration relies on CMake's ability to traverse directory hierarchies, i.e., to encapsulate the build process of each directory via its CMakeLists.txt script and traverse directries. Some script snippets are repetitive and reusable as described below.

Here are general tips:

• In general, CMakeLists.txt is expected in the source directory and its (sub)directories (possibly excluding resource/asset directories). Parent CMakeLists.txt must call add_subdirectory() for each of its subdirectories.

• Base Source Directory shall define a SRC_DIR variable by

  set(SRC_DIR ${CMAKE_CURRENT_SOURCE_DIR})

  so relative paths of subdirectories can be evaluated later.

• Package Directories with pure Python modules must contain install(FILES <file>...) command to copy all .py files to the install target folder (typically dist/<package_name>):

  file(RELATIVE_PATH DST_DIR ${SRC_DIR} ${CMAKE_CURRENT_SOURCE_DIR})
  file(GLOB PYFILES LIST_DIRECTORIES false RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} "*.py")
  install(FILES ${PYFILES} DESTINATION ${DST_DIR} COMPONENT "PY")

  Note COMPONENT "PY" designation in install. This lets setuptools's build_py to run CMake to install these files (and package_data files).

• External Module Directories runs add_library(<name> SHARED | MODULE ...) command either directly or indirectly. Here, it is imperative to set name of the library target to match its directory name. Then the target is copied to the final destination with install(TARGETS <target>...) command.

  # match target name to folder name
  get_filename_component(TARGET ${CMAKE_CURRENT_SOURCE_DIR} NAME)
  
  # build commands
  add_library(${TARGET} ...) # typically Python3_add_library or pybind11_add_module
  set_target_properties(${TARGET} PROPERTIES PREFIX "${PYTHON_MODULE_PREFIX}")
  set_target_properties(${TARGET} PROPERTIES SUFFIX "${PYTHON_MODULE_EXTENSION}")
  
  # ... more build commands to follow
  
  # install commands
  get_filename_component(CURRENT_SRC_DIR ${CMAKE_CURRENT_SOURCE_DIR} DIRECTORY)
  if(${SRC_DIR} STREQUAL ${CURRENT_SRC_DIR})
  set(DST_DIR ".") # if parent is the base source folder
  else()
  file(RELATIVE_PATH DST_DIR ${SRC_DIR} ${CURRENT_SRC_DIR})
  endif()
  install(TARGETS ${TARGET} DESTINATION ${DST_DIR} COMPONENT "EXT")

  Here we register the install as EXT component so build_ext will only copy external modules to their final locations.

• Own Package Data Files are handled in a similar fashion as the pure Python modules with install(FILES <file>...) command as PY component.

  # to install a package data file 'data.txt'
  file(RELATIVE_PATH DST_DIR ${SRC_DIR} ${CMAKE_CURRENT_SOURCE_DIR})
  install(FILES "data.txt" DESTINATION ${DST_DIR} COMPONENT "PY")

• 3rd-Party Package Data Files are a bit trickier. The most intuitive way perhaps is to call the install command from the source folder, which matches the folder where the 3rd-party file is placed in the package. For example, suppose this skeletal directory model:

  # After 'cmake --install build'
  project-root/
  ├── build/
  |   └── lib/
  |       └── 3rd-party-tool/
  |           └── libtool.dll # <=original
  ├── dist/
  |   └── mypkg/
  |       └── lib/
  |           └── libtool.dll # <=distro-ready file (the install destination)
  ├── lib/
  |   └── 3rd-party-tool/ # lib source files in here to be built
  └── src/
    └── mypkg/
        └── lib/
            └── CMakeLists.txt # <=issue install command in this file

  The source files of a 3rd-party library is included to the project via git submodule in lib/3rd-party-tool/ and when built let's assume its DLL (assuming Windows) file will be found at build/lib/3rd-party-tool/libtool.dll. We want this DLL file to be placed in lib folder of the Python package, which means CMake must install (copy) libtool.dll to dist/mypkg/lib/libtool.dll. The install command shall be issued by src/mypkg/lib/CMakeLists.txt even if src/mypkg/lib/ would otherwise be empty.

  # to install a package data file
  SET(DLL_NAME "libtool.dll")
  SET(DLL_PATH "${CMAKE_BINARY_DIR}/lib/3rd-party-tool/${DLL_NAME}")
  file(RELATIVE_PATH DST_DIR ${SRC_DIR} ${CMAKE_CURRENT_SOURCE_DIR})
  install(FILES ${DLL_PATH} DESTINATION ${DST_DIR} COMPONENT "PY")

  Note: Typically you can construct CMake variable via libarary's CMake variables rather than hard-coding the DLL_PATH as done above.

• Project Root CMakeLists.txt defines general configurations (such as finding dependent libraries and setting up tests) of the build project. There are a couple things could be configured here to improve the CMake/Setuptools co-operation.

• Set default install path to be dist so CMake by default installs to the same dist directory location as setuptools:

  if (CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
  set (CMAKE_INSTALL_PREFIX "${CMAKE_SOURCE_DIR}/dist" CACHE PATH "default install path" FORCE )
  endif()

setup() Arguments

cmaketools.setup() call wraps setuptools.setup() so to initialize CMakeBuilder and auto-generate setuptools.setup() arguments. As such, it accepts most of setuptools.setup() arguments with additional arguments to configure CMake build. Also, it may overwrite user-provided setuptools arguments in order to integrate CMake.

List of New Arguments for CMake

Overriden setuptools arguments

• cmdclass (partial override, overrides egg_info, build_py, build_ext, sdist, and install_data commands)
• data_files
• ext_modules
• package_dir
• package_data
• packages

build_ext Command Options for cmaketools-based setup.py

The build_ext command options are completely changed to accomodate CMake command-line options. Here is the output of python setup.py --help build_ext

Common commands: (see '--help-commands'  for more)
setup.py build will build the package underneath 'build/'
setup.py install will install the package

Global options:
--verbose (-v) run verbosely (default)
--quiet (-q) run quietly (turns verbosity off)
--dry-run (-n) don't actually do anything
--help (-h) show detailed help message
--no-user-cfg ignore pydistutils.cfg in your home directory

Options for 'build_ext' command:
--cmake-path Name/path of the CMake executable to use, overriding
default auto-detection.
--build-lib (-b) directory for compiled extension modules
--inplace (-i) ignore build-lib and put compiled extensions into the
source directory alongside your pure Python modules
--force (-f) forcibly build everything (delete existing
CMakeCache.txt)
--cache (-C) Pre-load a CMake script to populate the cache.
--define (-D) Create or update a CMake CACHE entry (separated by
';')
--undef (-U) Remove matching entries from CMake CACHE.
--generator (-G) Specify a build system generator.
--toolset (-T) Toolset specification for the generator, if supported.
--platform (-A) Specify platform name if supported by generator.
--Wno-dev Suppress developer warnings.
--Wdev Enable developer warnings.
--Werror Make specified warnings into errors: dev or
deprecated.
--Wno-error Make specified warnings not errors.
--Wdeprecated Enable deprecated functionality warnings.
--Wno-deprecated Suppress deprecated functionality warnings.
--log-level Set the log level to one of: ERROR, WARNING, NOTICE,
STATUS, VERBOSE, DEBUG, TRACE
--log-context Enable the message() command outputting context
attached to each message.
--debug-trycompile Do not delete the try_compile() build tree. Only
useful on one try_compile() at a time.
--debug-output Put cmake in a debug mode.
--debug-find Put cmake find commands in a debug mode.
--trace Put cmake in trace mode.
--trace-expand Put cmake in trace mode with variables expanded.
--trace-format Put cmake in trace mode and sets the trace output
format.
--trace-source Put cmake in trace mode, but output only lines of a
specified file.
--trace-redirect Put cmake in trace mode and redirect trace output to a
file instead of stderr.
--warn-uninitialized Specify a build system generator.
--warn-unused-vars Warn about unused variables.
--no-warn-unused-cli Don’t warn about command line options.
--check-system-vars Find problems with variable usage in system files.
--parallel (-j) The maximum number of concurrent processes to use when
building.
--config For multi-configuration tools, choose this
configuration.
--clean-first Build target clean first, then build.
--verbose (-v) Enable verbose output - if supported - including the
build commands to be executed.
--strip Strip before installing.
--help-generator list available compilers

usage: setup.py [global_opts] cmd1 [cmd1_opts] [cmd2 [cmd2_opts] ...]
or: setup.py --help [cmd1 cmd2 ...]
or: setup.py --help-commands
or: setup.py cmd --help