Fix DLL search: use AddDllDirectory without SetDefaultDllDirectories for bundled Python

Author: akenmorris

Libs/Application/Job/PythonWorker.cpp

@@ -237,23 +237,32 @@ bool PythonWorker::init() {
 
 #ifdef _WIN32
   if (using_bundled) {
-    // Prepend Python DLL directories to PATH so the embedded interpreter can
-    // find .pyd extension dependencies (e.g. _ctypes.pyd -> libffi-8.dll).
-    // We use PATH instead of SetDefaultDllDirectories/AddDllDirectory because
-    // those restrict DLL search process-wide, which breaks the build tree
-    // where DLLs are spread across conda, deps, and build directories.
+    // Register DLL directories via AddDllDirectory BEFORE Python init.
+    // We do NOT call SetDefaultDllDirectories here — Python 3.8+ calls
+    // SetDefaultDllDirectories(LOAD_LIBRARY_SEARCH_DEFAULT_DIRS) internally
+    // during Py_Initialize(), which enables LOAD_LIBRARY_SEARCH_USER_DIRS.
+    // Directories registered via AddDllDirectory before that point will then
+    // be searched for implicit DLL dependencies of .pyd extensions.
     QString dlls_dir = python_home + "/DLLs";
     QString app_dir = QCoreApplication::applicationDirPath();
-    QString current_path = qgetenv("PATH");
-    QString new_path = dlls_dir + ";" + python_home + ";" + app_dir;
+    AddDllDirectory(dlls_dir.toStdWString().c_str());
+    AddDllDirectory(python_home.toStdWString().c_str());
+    AddDllDirectory(app_dir.toStdWString().c_str());
 
     // In the build tree, PYTHONHOME points to conda's prefix. Conda's .pyd
     // files need DLLs from conda's Library/bin/ (e.g. libexpat.dll for pyexpat).
     QString conda_library_bin = python_home + "/Library/bin";
     if (QDir(conda_library_bin).exists()) {
-      new_path += ";" + conda_library_bin;
+      AddDllDirectory(conda_library_bin.toStdWString().c_str());
     }
 
+    // Also prepend to PATH for any DLL loading that happens before Python's
+    // SetDefaultDllDirectories takes effect.
+    QString current_path = qgetenv("PATH");
+    QString new_path = dlls_dir + ";" + python_home + ";" + app_dir;
+    if (QDir(conda_library_bin).exists()) {
+      new_path += ";" + conda_library_bin;
+    }
     new_path += ";" + current_path;
     qputenv("PATH", new_path.toUtf8());