From 95b4b49fc77dbdcc64621db63203279e1c9e6719 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Stefan=20Br=C3=BCns?= <stefan.bruens@rwth-aachen.de>
Date: Wed, 6 Jul 2022 17:20:53 +0200
Subject: [PATCH] Optionally prefer system wide pybind11

Linux distributions typically prefer system provided libraries, so
optionally use it when found.

(This also allows to use the github provided tarball, which omits the
pybind11 submodule).

Fix the PYBIND_INCLUDE_DIR usage:
- remove misleading find_path invocation, which may point to the system
  wide pybind11
- use pybind11_INCLUDE_DIR	which is provided by both find_package(pybind11)
  and bundled pybind11/CMakeLists.txt
- pybind11_INCLUDE_DIR is used by pybind11_add_module, use it also for
  ngcore (core/register_archive.hpp)
---
 CMakeLists.txt | 30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b7662035..20c01740 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -5,10 +5,12 @@ endif(NOT CMAKE_BUILD_TYPE)
 cmake_minimum_required(VERSION 3.13)
 cmake_policy(VERSION 3.13)
 
+include (CMakeDependentOption)
 option( USE_NATIVE_ARCH  "build for native cpu architecture" ON)
 
 option( USE_GUI     "build with GUI" ON )
 option( USE_PYTHON  "build with python interface" ON )
+cmake_dependent_option( PREFER_SYSTEM_PYBIND11  "Use system wide PyBind11" ON "USE_PYTHON" OFF)
 option( USE_MPI     "enable mpi parallelization" OFF )
 option( USE_MPI4PY  "enable mpi4py interface" ON )
 option( USE_OCC     "build with OpenCascade geometry kernel interface" OFF)
@@ -302,24 +304,30 @@ else()
 endif()
 
 if (USE_PYTHON)
-    add_subdirectory(external_dependencies/pybind11)
-    find_path(PYBIND_INCLUDE_DIR pybind11/pybind11.h HINTS ${PYTHON_INCLUDE_DIR})
-    if( PYBIND_INCLUDE_DIR )
-        message(STATUS "Found Pybind11: ${PYBIND_INCLUDE_DIR}")
-    else( PYBIND_INCLUDE_DIR )
-        message(FATAL_ERROR "Could NOT find pybind11!")
-    endif( PYBIND_INCLUDE_DIR )
+    if (PREFER_SYSTEM_PYBIND11)
+      find_package(pybind11 CONFIG)
+    endif()
+    if (pybind11_FOUND)
+      set(NG_INSTALL_PYBIND OFF)
+    else()
+      add_subdirectory(external_dependencies/pybind11)
+      if (pybind11_INCLUDE_DIR)
+          message(STATUS "Found Pybind11: ${pybind11_INCLUDE_DIR}")
+      else()
+          message(FATAL_ERROR "Could NOT find pybind11!")
+      endif()
+    endif()
 
-    target_include_directories(netgen_python INTERFACE ${PYBIND_INCLUDE_DIR} ${PYTHON_INCLUDE_DIRS})
-    target_include_directories(nglib PRIVATE ${PYBIND_INCLUDE_DIR} ${PYTHON_INCLUDE_DIRS})
+    target_include_directories(netgen_python INTERFACE ${pybind11_INCLUDE_DIR} ${PYTHON_INCLUDE_DIRS})
+    target_include_directories(nglib PRIVATE ${pybind11_INCLUDE_DIR} ${PYTHON_INCLUDE_DIRS})
     if(NOT ${BUILD_FOR_CONDA} OR WIN32)
         # Don't link python libraries in conda environments
         target_link_libraries(netgen_python INTERFACE ${PYTHON_LIBRARIES})
     endif()
 
     if(NG_INSTALL_PYBIND)
-      install(DIRECTORY ${PYBIND_INCLUDE_DIR}/pybind11 DESTINATION ${NG_INSTALL_DIR_INCLUDE} COMPONENT netgen_devel)
-      install(FILES ${PYBIND_INCLUDE_DIR}/../LICENSE DESTINATION ${NG_INSTALL_DIR_INCLUDE}/pybind11 COMPONENT netgen_devel)
+      install(DIRECTORY ${pybind11_INCLUDE_DIR}/pybind11 DESTINATION ${NG_INSTALL_DIR_INCLUDE} COMPONENT netgen_devel)
+      install(FILES ${pybind11_INCLUDE_DIR}/../LICENSE DESTINATION ${NG_INSTALL_DIR_INCLUDE}/pybind11 COMPONENT netgen_devel)
     endif(NG_INSTALL_PYBIND)
 endif (USE_PYTHON)