bpo-34403: Fix initfsencoding() for ASCII (GH-10233)

* Add _Py_GetForceASCII(): check if Python forces the usage of ASCII in Py_DecodeLocale() and Py_EncodeLocale(). * initfsencoding() now uses ASCII if _Py_GetForceASCII() is true.

Author: vstinner

Include/fileutils.h

@@ -183,6 +183,10 @@ PyAPI_FUNC(int) _Py_GetLocaleconvNumeric(
 
 #endif /* Py_LIMITED_API */
 
+#ifdef Py_BUILD_CORE
+PyAPI_FUNC(int) _Py_GetForceASCII(void);
+#endif
+
 #ifdef __cplusplus
 }
 #endif

Python/fileutils.c

@@ -180,6 +180,18 @@ check_force_ascii(void)
  return 1;
 }
 
+
+int
+_Py_GetForceASCII(void)
+{
+ if (force_ascii == -1) {
+ force_ascii = check_force_ascii();
+ }
+ return force_ascii;
+}
+
+
+
 static int
 encode_ascii(const wchar_t *text, char **str,
  size_t *error_pos, const char **reason,

Python/pylifecycle.c

@@ -1615,6 +1615,10 @@ initfsencoding(PyInterpreterState *interp)
  Py_FileSystemDefaultEncoding = "utf-8";
  Py_HasFileSystemDefaultEncoding = 1;
  }
+ else if (_Py_GetForceASCII()) {
+ Py_FileSystemDefaultEncoding = "ascii";
+ Py_HasFileSystemDefaultEncoding = 1;
+ }
  else if (Py_FileSystemDefaultEncoding == NULL) {
  Py_FileSystemDefaultEncoding = get_locale_encoding();
  if (Py_FileSystemDefaultEncoding == NULL) {