pybind11Tools.cmake

# tools/pybind11Tools.cmake -- Build system for the pybind11 modules
#
# Copyright (c) 2015 Wenzel Jakob <wenzel@inf.ethz.ch>
#
# All rights reserved. Use of this source code is governed by a
# BSD-style license that can be found in the LICENSE file.

# Add a CMake parameter for choosing a desired Python version
if(NOT PYBIND11_PYTHON_VERSION)
  set(PYBIND11_PYTHON_VERSION
      ""
      CACHE STRING "Python version to use for compiling modules")
endif()

# A user can set versions manually too
set(Python_ADDITIONAL_VERSIONS
    "3.9;3.8;3.7;3.6;3.5;3.4"
    CACHE INTERNAL "")

list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_LIST_DIR}")
find_package(PythonLibsNew ${PYBIND11_PYTHON_VERSION} MODULE REQUIRED)
list(REMOVE_AT CMAKE_MODULE_PATH -1)

include(CheckCXXCompilerFlag)

# Warn or error if old variable name used
if(PYBIND11_CPP_STANDARD)
  string(REGEX MATCH [[..$]] VAL "${PYBIND11_CPP_STANDARD}")
  if(CMAKE_CXX_STANDARD)
    if(NOT CMAKE_CXX_STANDARD STREQUAL VAL)
      message(WARNING "CMAKE_CXX_STANDARD=${CMAKE_CXX_STANDARD} does not match "
                      "PYBIND11_CPP_STANDARD=${PYBIND11_CPP_STANDARD}, "
                      "please remove PYBIND11_CPP_STANDARD from your cache")
    endif()
  else()
    set(supported_standards 11 14 17 20)
    if("${VAL}" IN_LIST supported_standards)
      message(WARNING "USE -DCMAKE_CXX_STANDARD=${VAL} instead of PYBIND11_PYTHON_VERSION")
      set(CMAKE_CXX_STANDARD
          ${VAL}
          CACHE STRING "From PYBIND11_CPP_STANDARD")
    else()
      message(FATAL_ERROR "PYBIND11_CPP_STANDARD should be replaced with CMAKE_CXX_STANDARD "
                          "(last two chars: ${VAL} not understood as a valid CXX std)")
    endif()
  endif()
endif()

# Checks whether the given CXX/linker flags can compile and link a cxx file.  cxxflags and
# linkerflags are lists of flags to use.  The result variable is a unique variable name for each set
# of flags: the compilation result will be cached base on the result variable.  If the flags work,
# sets them in cxxflags_out/linkerflags_out internal cache variables (in addition to ${result}).
function(_pybind11_return_if_cxx_and_linker_flags_work result cxxflags linkerflags cxxflags_out
         linkerflags_out)
  set(CMAKE_REQUIRED_LIBRARIES ${linkerflags})
  check_cxx_compiler_flag("${cxxflags}" ${result})
  if(${result})
    set(${cxxflags_out}
        "${cxxflags}"
        CACHE INTERNAL "" FORCE)
    set(${linkerflags_out}
        "${linkerflags}"
        CACHE INTERNAL "" FORCE)
  endif()
endfunction()

# Internal: find the appropriate link time optimization flags for this compiler
function(_pybind11_add_lto_flags target_name prefer_thin_lto)
  if(NOT DEFINED PYBIND11_LTO_CXX_FLAGS)
    set(PYBIND11_LTO_CXX_FLAGS
        ""
        CACHE INTERNAL "")
    set(PYBIND11_LTO_LINKER_FLAGS
        ""
        CACHE INTERNAL "")

    if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
      set(cxx_append "")
      set(linker_append "")
      if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND NOT APPLE)
        # Clang Gold plugin does not support -Os; append -O3 to MinSizeRel builds to override it
        set(linker_append ";$<$<CONFIG:MinSizeRel>:-O3>")
      elseif(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
        set(cxx_append ";-fno-fat-lto-objects")
      endif()

      if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND prefer_thin_lto)
        _pybind11_return_if_cxx_and_linker_flags_work(
          HAS_FLTO_THIN "-flto=thin${cxx_append}" "-flto=thin${linker_append}"
          PYBIND11_LTO_CXX_FLAGS PYBIND11_LTO_LINKER_FLAGS)
      endif()

      if(NOT HAS_FLTO_THIN)
        _pybind11_return_if_cxx_and_linker_flags_work(
          HAS_FLTO "-flto${cxx_append}" "-flto${linker_append}" PYBIND11_LTO_CXX_FLAGS
          PYBIND11_LTO_LINKER_FLAGS)
      endif()
    elseif(CMAKE_CXX_COMPILER_ID MATCHES "Intel")
      # Intel equivalent to LTO is called IPO
      _pybind11_return_if_cxx_and_linker_flags_work(
        HAS_INTEL_IPO "-ipo" "-ipo" PYBIND11_LTO_CXX_FLAGS PYBIND11_LTO_LINKER_FLAGS)
    elseif(MSVC)
      # cmake only interprets libraries as linker flags when they start with a - (otherwise it
      # converts /LTCG to \LTCG as if it was a Windows path).  Luckily MSVC supports passing flags
      # with - instead of /, even if it is a bit non-standard:
      _pybind11_return_if_cxx_and_linker_flags_work(
        HAS_MSVC_GL_LTCG "/GL" "-LTCG" PYBIND11_LTO_CXX_FLAGS PYBIND11_LTO_LINKER_FLAGS)
    endif()

    if(PYBIND11_LTO_CXX_FLAGS)
      message(STATUS "LTO enabled")
    else()
      message(STATUS "LTO disabled (not supported by the compiler and/or linker)")
    endif()
  endif()

  # Enable LTO flags if found, except for Debug builds
  if(PYBIND11_LTO_CXX_FLAGS)
    set(not_debug "$<NOT:$<CONFIG:Debug>>")
    set(cxx_lang "$<COMPILE_LANGUAGE:CXX>")
    target_compile_options(${target_name}
                           PRIVATE "$<$<AND:${not_debug},${cxx_lang}>:${PYBIND11_LTO_CXX_FLAGS}>")
  endif()
  if(PYBIND11_LTO_LINKER_FLAGS)
    target_link_libraries(${target_name} PRIVATE "$<${not_debug}:${PYBIND11_LTO_LINKER_FLAGS}>")
  endif()
endfunction()

# Build a Python extension module:
# pybind11_add_module(<name> [MODULE | SHARED] [EXCLUDE_FROM_ALL]
#                     [NO_EXTRAS] [THIN_LTO] source1 [source2 ...])
#
function(pybind11_add_module target_name)
  set(options MODULE SHARED EXCLUDE_FROM_ALL NO_EXTRAS SYSTEM THIN_LTO)
  cmake_parse_arguments(PARSE_ARGV 1 ARG "${options}" "" "")

  if(ARG_MODULE AND ARG_SHARED)
    message(FATAL_ERROR "Can't be both MODULE and SHARED")
  elseif(ARG_SHARED)
    set(lib_type SHARED)
  else()
    set(lib_type MODULE)
  endif()

  if(ARG_EXCLUDE_FROM_ALL)
    set(exclude_from_all EXCLUDE_FROM_ALL)
  else()
    set(exclude_from_all "")
  endif()

  add_library(${target_name} ${lib_type} ${exclude_from_all} ${ARG_UNPARSED_ARGUMENTS})

  target_link_libraries(${target_name} PRIVATE pybind11::module)

  if(ARG_SYSTEM)
    message(
      STATUS
        "Warning: this does not have an effect - use NO_SYSTEM_FROM_IMPORTED if using imported targets"
    )
  endif()

  # Python debug libraries expose slightly different objects before 3.8
  # https://docs.python.org/3.6/c-api/intro.html#debugging-builds
  # https://stackoverflow.com/questions/39161202/how-to-work-around-missing-pymodule-create2-in-amd64-win-python35-d-lib
  if(PYTHON_IS_DEBUG)
    target_compile_definitions(${target_name} PRIVATE Py_DEBUG)
  endif()

  # The prefix and extension are provided by FindPythonLibsNew.cmake
  set_target_properties(${target_name} PROPERTIES PREFIX "${PYTHON_MODULE_PREFIX}")
  set_target_properties(${target_name} PROPERTIES SUFFIX "${PYTHON_MODULE_EXTENSION}")

  # -fvisibility=hidden is required to allow multiple modules compiled against
  # different pybind versions to work properly, and for some features (e.g.
  # py::module_local).  We force it on everything inside the `pybind11`
  # namespace; also turning it on for a pybind module compilation here avoids
  # potential warnings or issues from having mixed hidden/non-hidden types.
  set_target_properties(${target_name} PROPERTIES CXX_VISIBILITY_PRESET "hidden")
  set_target_properties(${target_name} PROPERTIES CUDA_VISIBILITY_PRESET "hidden")

  if(ARG_NO_EXTRAS)
    return()
  endif()

  if(CMAKE_VERSION VERSION_LESS 3.9 OR PYBIND11_CLASSIC_LTO)
    _pybind11_add_lto_flags(${target_name} ${ARG_THIN_LTO})
  else()
    include(CheckIPOSupported)
    check_ipo_supported(
      RESULT supported
      OUTPUT error
      LANGUAGES CXX)
    if(supported)
      set_property(TARGET ${target_name} PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
    else()
      message(WARNING "IPO is not supported: ${output}")
    endif()
  endif()

  if(NOT MSVC AND NOT ${CMAKE_BUILD_TYPE} MATCHES Debug|RelWithDebInfo)
    # Strip unnecessary sections of the binary on Linux/Mac OS
    if(CMAKE_STRIP)
      if(APPLE)
        add_custom_command(
          TARGET ${target_name}
          POST_BUILD
          COMMAND ${CMAKE_STRIP} -x $<TARGET_FILE:${target_name}>)
      else()
        add_custom_command(
          TARGET ${target_name}
          POST_BUILD
          COMMAND ${CMAKE_STRIP} $<TARGET_FILE:${target_name}>)
      endif()
    endif()
  endif()

  if(MSVC)
    # /MP enables multithreaded builds (relevant when there are many files), /bigobj is
    # needed for bigger binding projects due to the limit to 64k addressable sections
    target_compile_options(${target_name} PRIVATE /bigobj)
    if(CMAKE_VERSION VERSION_LESS 3.11)
      target_compile_options(${target_name} PRIVATE $<$<NOT:$<CONFIG:Debug>>:/MP>)
    else()
      # Only set these options for C++ files.  This is important so that, for
      # instance, projects that include other types of source files like CUDA
      # .cu files don't get these options propagated to nvcc since that would
      # cause the build to fail.
      target_compile_options(${target_name}
                             PRIVATE $<$<NOT:$<CONFIG:Debug>>:$<$<COMPILE_LANGUAGE:CXX>:/MP>>)
    endif()
  endif()
endfunction()