From f0c286b5759f5328a5d7db536ab5d056411163f6 Mon Sep 17 00:00:00 2001
From: Silvio Traversaro <silvio.traversaro@iit.it>
Date: Thu, 24 Oct 2024 17:10:19 +0200
Subject: [PATCH] Fix loading of Python bindings on Windows when installed in
 arbitrary directory

---
 bindings/CMakeLists.txt | 24 +++++++++++++++++++++---
 1 file changed, 21 insertions(+), 3 deletions(-)

diff --git a/bindings/CMakeLists.txt b/bindings/CMakeLists.txt
index 554769769b..bb45ae5250 100644
--- a/bindings/CMakeLists.txt
+++ b/bindings/CMakeLists.txt
@@ -50,9 +50,27 @@ if(FRAMEWORK_COMPILE_PYTHON_BINDINGS)
     add_subdirectory(python)
 
     # Create the __init__.py file
-    file(GENERATE
-         OUTPUT "${BLF_PYTHON_PACKAGE}/__init__.py"
-         CONTENT "from .bindings import *${NEW_LINE}from . import utils${NEW_LINE}")
+    file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/__init__.py "")
+
+    # If we are on Windows and BUILD_SHARED_LIBS is ON, handle the fact that
+    # the Python interpreter does not look into PATH to find dll (see https://docs.python.org/3.8/library/os.html#os.add_dll_directory)
+    if(WIN32 AND BUILD_SHARED_LIBS)
+        if(IS_ABSOLUTE PYTHON_INSTDIR)
+            set(PYTHON_FULL_INSTDIR "${PYTHON_INSTDIR}")
+        else()
+            set(PYTHON_FULL_INSTDIR "${CMAKE_INSTALL_PREFIX}/${PYTHON_INSTDIR}")
+        endif()
+        file(RELATIVE_PATH RELATIVE_PATH_BETWEEN_INIT_PY_AND_DLL_DIRECTORY ${PYTHON_FULL_INSTDIR} ${CMAKE_INSTALL_FULL_BINDIR})
+        file(APPEND "${BLF_PYTHON_PACKAGE}/__init__.py" "import os${NEW_LINE}")
+        file(APPEND "${BLF_PYTHON_PACKAGE}/__init__.py" "library_dll_path = os.path.join(os.path.dirname(__file__),'${RELATIVE_PATH_BETWEEN_INIT_PY_AND_DLL_DIRECTORY}')${NEW_LINE}")
+        file(APPEND "${BLF_PYTHON_PACKAGE}/__init__.py" "# Avoid to call add_dll_directory if not necessary,${NEW_LINE}")
+        file(APPEND "${BLF_PYTHON_PACKAGE}/__init__.py" "# for example if the library to find are already found in the proper location in a conda environment${NEW_LINE}")
+        file(APPEND "${BLF_PYTHON_PACKAGE}/__init__.py" "if(library_dll_path != os.path.join(os.environ.get('CONDA_PREFIX', ''),'Library','bin') and library_dll_path != os.path.join(os.environ.get('CONDA_PREFIX', ''),'bin')):${NEW_LINE}")
+        file(APPEND "${BLF_PYTHON_PACKAGE}/__init__.py" "    if(os.path.exists(library_dll_path)):${NEW_LINE}")
+        file(APPEND "${BLF_PYTHON_PACKAGE}/__init__.py" "        os.add_dll_directory(library_dll_path)${NEW_LINE}")
+    endif()
+    
+    file(APPEND "${BLF_PYTHON_PACKAGE}/__init__.py" "from .bindings import *${NEW_LINE}from . import utils${NEW_LINE}")
 
     # Install the __init__.py file
     install(FILES "${BLF_PYTHON_PACKAGE}/__init__.py"