gh-93103: Py_DecodeLocale() uses _PyRuntime.preconfig (#93187)

The Py_DecodeLocale() and Py_EncodeLocale() now use
_PyRuntime.preconfig, rather than Py_UTF8Mode and
Py_LegacyWindowsFSEncodingFlag global configuration varibles, to
decide if the UTF-8 encoding is used or not.

As documented, these functions must not be called before Python is
preinitialized. The new PyConfig API should now be used, rather than
using deprecated functions like Py_SetPath() or PySys_SetArgv().

Python/fileutils.c

@@ -603,9 +603,9 @@ _Py_DecodeLocaleEx(const char* arg, wchar_t **wstr, size_t *wlen,
     return _Py_DecodeUTF8Ex(arg, strlen(arg), wstr, wlen, reason,
                             errors);
 #else
-    int use_utf8 = (Py_UTF8Mode == 1);
+    int use_utf8 = (_PyRuntime.preconfig.utf8_mode >= 1);
 #ifdef MS_WINDOWS
-    use_utf8 |= !Py_LegacyWindowsFSEncodingFlag;
+    use_utf8 |= (_PyRuntime.preconfig.legacy_windows_fs_encoding == 0);
 #endif
     if (use_utf8) {
         return _Py_DecodeUTF8Ex(arg, strlen(arg), wstr, wlen, reason,
@@ -795,9 +795,9 @@ encode_locale_ex(const wchar_t *text, char **str, size_t *error_pos,
     return _Py_EncodeUTF8Ex(text, str, error_pos, reason,
                             raw_malloc, errors);
 #else
-    int use_utf8 = (Py_UTF8Mode == 1);
+    int use_utf8 = (_PyRuntime.preconfig.utf8_mode >= 1);
 #ifdef MS_WINDOWS
-    use_utf8 |= !Py_LegacyWindowsFSEncodingFlag;
+    use_utf8 |= (_PyRuntime.preconfig.legacy_windows_fs_encoding == 0);
 #endif
     if (use_utf8) {
         return _Py_EncodeUTF8Ex(text, str, error_pos, reason,

Python/preconfig.c

@@ -826,12 +826,10 @@ _PyPreConfig_Read(PyPreConfig *config, const _PyArgv *args)
         _Py_SetLocaleFromEnv(LC_CTYPE);
     }
 
-    _PyPreCmdline cmdline = _PyPreCmdline_INIT;
-    int init_utf8_mode = Py_UTF8Mode;
-#ifdef MS_WINDOWS
-    int init_legacy_encoding = Py_LegacyWindowsFSEncodingFlag;
-#endif
+    PyPreConfig save_runtime_config;
+    preconfig_copy(&save_runtime_config, &_PyRuntime.preconfig);
 
+    _PyPreCmdline cmdline = _PyPreCmdline_INIT;
     int locale_coerced = 0;
     int loops = 0;
 
@@ -847,11 +845,9 @@ _PyPreConfig_Read(PyPreConfig *config, const _PyArgv *args)
         }
 
         /* bpo-34207: Py_DecodeLocale() and Py_EncodeLocale() depend
-           on Py_UTF8Mode and Py_LegacyWindowsFSEncodingFlag. */
-        Py_UTF8Mode = config->utf8_mode;
-#ifdef MS_WINDOWS
-        Py_LegacyWindowsFSEncodingFlag = config->legacy_windows_fs_encoding;
-#endif
+           on the utf8_mode and legacy_windows_fs_encoding members
+           of _PyRuntime.preconfig. */
+        preconfig_copy(&_PyRuntime.preconfig, config);
 
         if (args) {
             // Set command line arguments at each iteration. If they are bytes
@@ -914,14 +910,10 @@ _PyPreConfig_Read(PyPreConfig *config, const _PyArgv *args)
     status = _PyStatus_OK();
 
 done:
-    if (init_ctype_locale != NULL) {
-        setlocale(LC_CTYPE, init_ctype_locale);
-        PyMem_RawFree(init_ctype_locale);
-    }
-    Py_UTF8Mode = init_utf8_mode ;
-#ifdef MS_WINDOWS
-    Py_LegacyWindowsFSEncodingFlag = init_legacy_encoding;
-#endif
+    // Revert side effects
+    setlocale(LC_CTYPE, init_ctype_locale);
+    PyMem_RawFree(init_ctype_locale);
+    preconfig_copy(&_PyRuntime.preconfig, &save_runtime_config);
     _PyPreCmdline_Clear(&cmdline);
     return status;
 }