How can I use precompiled headers with nanobind?

[petrasvestartas]

Hi,

When I work with C++ I tend use precompiled headers to reduced compilation time.
But with nanobind setup and command pip install -e . -v the stdafx.h precompiled header is recompiled every single time.

How can I use precompiled headers with nanobind?

Below is my CMakeLists.txt

cmake_minimum_required(VERSION 3.15...3.26)

project(cgal_wrapper LANGUAGES CXX)
set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

# =====================================================================
# Dependencies
# =====================================================================
include(ExternalProject)

# Define source directories for external dependencies
set(EXTERNAL_DIR "${CMAKE_CURRENT_SOURCE_DIR}/external")
set(CGAL_SOURCE_DIR "${EXTERNAL_DIR}/cgal")
set(BOOST_SOURCE_DIR "${EXTERNAL_DIR}/boost")
set(EIGEN_SOURCE_DIR "${EXTERNAL_DIR}/eigen")

# Create a custom target for all external dependencies
add_custom_target(external_downloads ALL)

# ========================================================================
# CGAL
# ========================================================================
if(NOT EXISTS "${CGAL_SOURCE_DIR}")
    message(STATUS "Downloading CGAL...")
    ExternalProject_Add(
        cgal_download
        URL https://github.com/CGAL/cgal/releases/download/v6.0.1/CGAL-6.0.1.zip
        SOURCE_DIR       "${CGAL_SOURCE_DIR}"
        CONFIGURE_COMMAND ""
        BUILD_COMMAND     ""
        INSTALL_COMMAND   ""
        LOG_DOWNLOAD ON
        UPDATE_COMMAND    ""
        PATCH_COMMAND     ""
        TLS_VERIFY       ON
    )
    add_dependencies(external_downloads cgal_download)
endif()

# ========================================================================
# BOOST
# ========================================================================
if(NOT EXISTS "${BOOST_SOURCE_DIR}")
  message(STATUS "Configuring Boost...")
  ExternalProject_Add(boost_download
      URL https://archives.boost.io/release/1.82.0/source/boost_1_82_0.tar.gz
      SOURCE_DIR "${BOOST_SOURCE_DIR}"
      CONFIGURE_COMMAND ""
      BUILD_COMMAND ""
      INSTALL_COMMAND ${CMAKE_COMMAND} -E copy_directory <SOURCE_DIR>/boost ${BOOST_SOURCE_DIR}/boost
      LOG_DOWNLOAD 
      ON
  )
  
  add_dependencies(external_downloads boost_download)
endif()

# ========================================================================
# EIGEN
# ========================================================================
if(NOT EXISTS "${EIGEN_SOURCE_DIR}")
    message(STATUS "Downloading Eigen...")
    ExternalProject_Add(
        eigen_download
        URL https://gitlab.com/libeigen/eigen/-/archive/3.4.0/eigen-3.4.0.tar.gz
        SOURCE_DIR       "${EIGEN_SOURCE_DIR}"
        CONFIGURE_COMMAND ""
        BUILD_COMMAND     ""
        INSTALL_COMMAND   ""
        LOG_DOWNLOAD ON
        UPDATE_COMMAND    ""
        PATCH_COMMAND     ""
    )
    add_dependencies(external_downloads eigen_download)
endif()

# Add include directories
set(CGAL_INCLUDE_DIR "${CGAL_SOURCE_DIR}/include")
set(BOOST_INCLUDE_DIR "${BOOST_SOURCE_DIR}")
set(EIGEN_INCLUDE_DIR "${EIGEN_SOURCE_DIR}")

# Print include directories for verification
message(STATUS "====================================================")
message(STATUS "CGAL INCLUDE DIRECTORY: ${CGAL_INCLUDE_DIR}")
message(STATUS "BOOST INCLUDE DIRECTORY: ${BOOST_INCLUDE_DIR}")
message(STATUS "EIGEN INCLUDE DIRECTORY: ${EIGEN_INCLUDE_DIR}")
message(STATUS "====================================================")

include_directories(
    ${CGAL_INCLUDE_DIR}
    ${BOOST_INCLUDE_DIR}
    ${EIGEN_INCLUDE_DIR}
)

# Incase linking is not working check the includes
#  add_compile_options(/showIncludes)

# Define libraries as header only
add_definitions(
    -DCGAL_HEADER_ONLY
    -DBOOST_ALL_NO_LIB 
    -DBOOST_ALL_DYN_LINK=0
    -DCGAL_DISABLE_GMP
    -DCGAL_USE_BOOST_MP
)

# =====================================================================
# BOOST and CGAL flags to configure multiprecision
# =====================================================================
set(CGAL_DO_NOT_USE_MPZF ON CACHE BOOL "Do not use MPZF")
set(CGAL_USE_GMPXX OFF CACHE BOOL "Disable GMPXX")
set(CGAL_DISABLE_GMP ON CACHE BOOL "Disable GMP in CGAL")
set(CMAKE_DISABLE_FIND_PACKAGE_GMP ON CACHE BOOL "Disable CMake find package for GMP")
set(CMAKE_DISABLE_FIND_PACKAGE_MPFR ON CACHE BOOL "Disable CMake find package for MPFR")
set(CGAL_NT_USE_BOOST_MP ON CACHE BOOL "Use Boost Multiprecision")

# Eigen is header-only by default, no special defines needed

# =====================================================================
# Binding
# =====================================================================

if (NOT SKBUILD)
  message(WARNING "\
  This CMake file is meant to be executed using 'scikit-build'. Running
  it directly will almost certainly not produce the desired result. If
  you are a user trying to install this package, please use the command
  below, which will install all necessary build dependencies, compile
  the package in an isolated environment, and then install it.
  =====================================================================
   $ pip install .
  =====================================================================
  If you are a software developer, and this is your own package, then
  it is usually much more efficient to install the build dependencies
  in your environment once and use the following command that avoids
  a costly creation of a new virtual environment at every compilation:
  =====================================================================
   $ pip install nanobind scikit-build-core[pyproject]
   $ conda install cmake
   $ pip install --no-build-isolation -ve .
   $ pip install --no-build-isolation -ve . -Ceditable.rebuild=true
  =====================================================================
  You may optionally add -Ceditable.rebuild=true to auto-rebuild when
  the package is imported. Otherwise, you need to re-run the above
  after editing C++ files.")
endif()

# Try to import all Python components potentially needed by nanobind
find_package(Python 3.8
  REQUIRED COMPONENTS Interpreter Development.Module
  OPTIONAL_COMPONENTS Development.SABIModule)

# Import nanobind through CMake's find_package mechanism
find_package(nanobind CONFIG REQUIRED)

# We are now ready to compile the actual extension module
nanobind_add_module(
  compas_cgal_ext
  STABLE_ABI
  NB_STATIC
  src/compas_cgal.cpp
  src/meshing.cpp
)

# Set include directories for the extension
target_include_directories(compas_cgal_ext PRIVATE 
    ${CGAL_INCLUDE_DIR}
    ${BOOST_INCLUDE_DIR}
    ${EIGEN_INCLUDE_DIR}
)

# Simple precompiled header setup
target_precompile_headers(compas_cgal_ext PRIVATE src/stdafx.h)

# Make sure external dependencies are downloaded before building the extension
add_dependencies(compas_cgal_ext external_downloads)

# Install directive for scikit-build-core
install(TARGETS compas_cgal_ext LIBRARY DESTINATION compas_cgal)

###############################################################################
# PCH support
###############################################################################
set(CMAKE_PCH_INSTANTIATE_TEMPLATES ON)

[wjakob]

Precompiled headers is not a topic that I am familiar with. If you do find a solution, could you share it here in case others run into the same problem?

[petrasvestartas]

Using the above cmakelist last 4 commands and the code below, helps to reduce build time in my code more than twice:

  $ pip install nanobind scikit-build-core[pyproject]
  $ conda install cmake
  $ pip install --no-build-isolation -ve .
  $ pip install --no-build-isolation -ve . -Ceditable.rebuild=true

I see that stdafx.h is compiled only when code is changed in that file.

More about this topic and why it is relevant:
https://youtu.be/eSI4wctZUto?feature=shared

[wjakob]

Ok, so just to clarify: what is explained in the CMakeLists.txt warning message actually corresponds to the right commands to get PCH to work? (So we don't need to change the instructions?)

Edit: Plus

set(CMAKE_PCH_INSTANTIATE_TEMPLATES ON)

[petrasvestartas]

Exactly:)