bpo-38234: Py_Initialize() sets global path configuration (GH-16421)

* Py_InitializeFromConfig() now writes PyConfig path configuration to
  the global path configuration (_Py_path_config).
* Add test_embed.test_get_pathconfig().
* Fix typo in _PyWideStringList_Join().

Include/internal/pycore_pathconfig.h

@@ -66,7 +66,7 @@ extern int _Py_FindEnvConfigValue(
 extern wchar_t* _Py_GetDLLPath(void);
 #endif
 
-extern PyStatus _PyPathConfig_Init(void);
+extern PyStatus _PyConfig_WritePathConfig(const PyConfig *config);
 extern void _Py_DumpPathConfig(PyThreadState *tstate);
 
 #ifdef __cplusplus

Lib/test/test_embed.py

@@ -1230,6 +1230,44 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
                                    api=API_COMPAT, env=env,
                                    ignore_stderr=True, cwd=tmpdir)
 
+    def test_global_pathconfig(self):
+        # Test C API functions getting the path configuration:
+        #
+        # - Py_GetExecPrefix()
+        # - Py_GetPath()
+        # - Py_GetPrefix()
+        # - Py_GetProgramFullPath()
+        # - Py_GetProgramName()
+        # - Py_GetPythonHome()
+        #
+        # The global path configuration (_Py_path_config) must be a copy
+        # of the path configuration of PyInterpreter.config (PyConfig).
+        ctypes = support.import_module('ctypes')
+        _testinternalcapi = support.import_module('_testinternalcapi')
+
+        def get_func(name):
+            func = getattr(ctypes.pythonapi, name)
+            func.argtypes = ()
+            func.restype = ctypes.c_wchar_p
+            return func
+
+        Py_GetPath = get_func('Py_GetPath')
+        Py_GetPrefix = get_func('Py_GetPrefix')
+        Py_GetExecPrefix = get_func('Py_GetExecPrefix')
+        Py_GetProgramName = get_func('Py_GetProgramName')
+        Py_GetProgramFullPath = get_func('Py_GetProgramFullPath')
+        Py_GetPythonHome = get_func('Py_GetPythonHome')
+
+        config = _testinternalcapi.get_configs()['config']
+
+        self.assertEqual(Py_GetPath().split(os.path.pathsep),
+                         config['module_search_paths'])
+        self.assertEqual(Py_GetPrefix(), config['prefix'])
+        self.assertEqual(Py_GetExecPrefix(), config['exec_prefix'])
+        self.assertEqual(Py_GetProgramName(), config['program_name'])
+        self.assertEqual(Py_GetProgramFullPath(), config['executable'])
+        self.assertEqual(Py_GetPythonHome(), config['home'])
+
 
 class AuditingTests(EmbeddingTestsMixin, unittest.TestCase):
     def test_open_code_hook(self):

Python/pathconfig.c

@@ -133,7 +133,7 @@ _PyWideStringList_Join(const PyWideStringList *list, wchar_t sep)
     for (Py_ssize_t i=0; i < list->length; i++) {
         wchar_t *path = list->items[i];
         if (i != 0) {
-            *str++ = SEP;
+            *str++ = sep;
         }
         len = wcslen(path);
         memcpy(str, path, len * sizeof(wchar_t));
@@ -145,11 +145,11 @@ _PyWideStringList_Join(const PyWideStringList *list, wchar_t sep)
 }
 
 
+#ifdef MS_WINDOWS
 /* Initialize _Py_dll_path on Windows. Do nothing on other platforms. */
-PyStatus
-_PyPathConfig_Init(void)
+static PyStatus
+_PyPathConfig_InitDLLPath(void)
 {
-#ifdef MS_WINDOWS
     if (_Py_dll_path == NULL) {
         /* Already set: nothing to do */
         return _PyStatus_OK();
@@ -165,9 +165,9 @@ _PyPathConfig_Init(void)
     if (_Py_dll_path == NULL) {
         return _PyStatus_NO_MEMORY();
     }
-#endif
     return _PyStatus_OK();
 }
+#endif
 
 
 static PyStatus
@@ -217,6 +217,20 @@ done:
 }
 
 
+PyStatus
+_PyConfig_WritePathConfig(const PyConfig *config)
+{
+#ifdef MS_WINDOWS
+    PyStatus status = _PyPathConfig_InitDLLPath();
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
+#endif
+
+    return pathconfig_set_from_config(&_Py_path_config, config);
+}
+
+
 static PyStatus
 config_init_module_search_paths(PyConfig *config, _PyPathConfig *pathconfig)
 {
@@ -441,11 +455,12 @@ pathconfig_global_init(void)
 {
     PyStatus status;
 
-    /* Initialize _Py_dll_path if needed */
-    status = _PyPathConfig_Init();
+#ifdef MS_WINDOWS
+    status = _PyPathConfig_InitDLLPath();
     if (_PyStatus_EXCEPTION(status)) {
         Py_ExitStatusException(status);
     }
+#endif
 
     if (_Py_path_config.module_search_path == NULL) {
         status = pathconfig_global_read(&_Py_path_config);

Python/pylifecycle.c

@@ -475,7 +475,7 @@ pyinit_core_reconfigure(_PyRuntimeState *runtime,
     config = &interp->config;
 
     if (config->_install_importlib) {
-        status = _PyPathConfig_Init();
+        status = _PyConfig_WritePathConfig(config);
         if (_PyStatus_EXCEPTION(status)) {
             return status;
         }
@@ -646,7 +646,7 @@ pycore_init_import_warnings(PyThreadState *tstate, PyObject *sysmod)
     }
 
     if (config->_install_importlib) {
-        status = _PyPathConfig_Init();
+        status = _PyConfig_WritePathConfig(config);
         if (_PyStatus_EXCEPTION(status)) {
             return status;
         }