bpo-34170: Rework _PyCoreConfig_Read() to avoid side effect (GH-8353)

Rework _PyCoreConfig_Read() function which *reads* core configuration
to not *modify* the path configuration.

A new _PyCoreConfig_SetPathConfig() function now recreates the path
configuration from the core configuration. This function is now
called very late in _Py_InitializeCore(), just before calling
initimport().

Changes:

* Add _PyCoreConfig.dll_path
* Py_SetPath() now fails with a fatal python error on memory
   allocation failure.
* Rename _PyPathConfig_Calculate() to _PyPathConfig_Calculate_impl()
* Replace _PyPathConfig_Init() with _PyPathConfig_Calculate(): the
  function now requires a _PyPathConfig
* Add _PyPathConfig_SetGlobal() to set the _Py_path_config global
  variable.
* Add _PyCoreConfig_InitPathConfig(): compute the path configuration
* Add _PyCoreConfig_SetPathConfig(): set path configuration from core
  configuration
* Rename wstrlist_append() to _Py_wstrlist_append()
* _Py_wstrlist_append() now handles integer overflow.

1 files changed, 7 insertions, 0 deletions

diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 64fa1e5..325f423 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -759,6 +759,13 @@ _Py_InitializeCore(const _PyCoreConfig *core_config)
     if (!_PyContext_Init())
         return _Py_INIT_ERR("can't init context");
 
+    if (!core_config->_disable_importlib) {
+        err = _PyCoreConfig_SetPathConfig(core_config);
+        if (_Py_INIT_FAILED(err)) {
+            return err;
+        }
+    }
+
     /* This call sets up builtin and frozen import support */
     if (!interp->core_config._disable_importlib) {
         err = initimport(interp, sysmod);