PYBIND11_FINDPYTHON=ON (#738)

Reuse our `find_package(Python ...)` call and use new CMake logic in
pybind11.
https://pybind11.readthedocs.io/en/stable/compiling.html#modules-with-cmake
https://cmake.org/cmake/help/latest/command/find_package.html#config-mode-version-selection

Signed-off-by: Axel Huebl <axel.huebl@plasma.ninja>

CMakeLists.txt

@@ -136,7 +136,7 @@ impactx_make_third_party_includes_system(WarpX::ablastr_3d ablastr_3d)
 
 # Python
 if(ImpactX_PYTHON)
-    find_package(Python COMPONENTS Interpreter Development.Module REQUIRED)
+    find_package(Python 3.8 COMPONENTS Interpreter Development.Module REQUIRED)
 
     # default installation directories: Python
     impactx_set_default_install_dirs_python()

cmake/dependencies/pybind11.cmake

@@ -10,6 +10,11 @@ function(find_pybind11)
         message(STATUS "pybind11 repository: ${ImpactX_pybind11_repo} (${ImpactX_pybind11_branch})")
         include(FetchContent)
     endif()
+
+    # rely on our find_package(Python ...) call
+    # https://pybind11.readthedocs.io/en/stable/compiling.html#modules-with-cmake
+    set(PYBIND11_FINDPYTHON ON)
+
     if(ImpactX_pybind11_internal OR ImpactX_pybind11_src)
         set(CMAKE_POLICY_DEFAULT_CMP0077 NEW)
 

setup.py

@@ -74,11 +74,18 @@ def build_extension(self, ext):
         if not extdir.endswith(os.path.sep):
             extdir += os.path.sep
 
+        pyv = sys.version_info
         cmake_args = [
+            # Python: use the calling interpreter in CMake
+            # https://cmake.org/cmake/help/latest/module/FindPython.html#hints
+            # https://cmake.org/cmake/help/latest/command/find_package.html#config-mode-version-selection
+            f"-DPython_ROOT_DIR={sys.prefix}",
+            f"-DPython_FIND_VERSION={pyv.major}.{pyv.minor}.{pyv.micro}",
+            "-DPython_FIND_VERSION_EXACT=TRUE",
+            "-DPython_FIND_STRATEGY=LOCATION",
             "-DCMAKE_LIBRARY_OUTPUT_DIRECTORY=" + os.path.join(extdir, "impactx"),
             "-DCMAKE_VERBOSE_MAKEFILE=ON",
             "-DCMAKE_PYTHON_OUTPUT_DIRECTORY=" + extdir,
-            "-DPython_EXECUTABLE=" + sys.executable,
             ## variants
             "-DImpactX_COMPUTE=" + ImpactX_COMPUTE,
             "-DImpactX_FFT:BOOL=" + ImpactX_FFT,