bpo-34523: Fix config_init_fs_encoding() for ASCII (GH-10232)

* bpo-34523, bpo-34403: Fix config_init_fs_encoding(): it now uses ASCII if _Py_GetForceASCII() is true. * Fix a regression of commit b2457ef. * Fix also a memory leak: get_locale_encoding() already allocates memory, no need to duplicate the string.

Author: vstinner

Include/coreconfig.h

@@ -75,6 +75,8 @@ typedef struct {
  highest priority;
  * PYTHONIOENCODING environment variable;
  * The UTF-8 Mode uses UTF-8/surrogateescape;
+ * If Python forces the usage of the ASCII encoding (ex: C locale
+ or POSIX locale on FreeBSD or HP-UX), use ASCII/surrogateescape;
  * locale encoding: ANSI code page on Windows, UTF-8 on Android,
  LC_CTYPE locale encoding on other platforms;
  * On Windows, "surrogateescape" error handler;

Python/coreconfig.c

@@ -1164,44 +1164,46 @@ config_init_fs_encoding(_PyCoreConfig *config)
  }
  }
 
- /* Windows defaults to utf-8/surrogatepass (PEP 529) */
+ /* Windows defaults to utf-8/surrogatepass (PEP 529).
+
+ Note: UTF-8 Mode takes the same code path and the Legacy Windows FS
+ encoding has the priortiy over UTF-8 Mode. */
  if (config->filesystem_encoding == NULL) {
  config->filesystem_encoding = _PyMem_RawStrdup("utf-8");
  if (config->filesystem_encoding == NULL) {
  return _Py_INIT_NO_MEMORY();
  }
  }
+
  if (config->filesystem_errors == NULL) {
  config->filesystem_errors = _PyMem_RawStrdup("surrogatepass");
  if (config->filesystem_errors == NULL) {
  return _Py_INIT_NO_MEMORY();
  }
  }
 #else
- if (config->utf8_mode) {
- /* UTF-8 Mode use: utf-8/surrogateescape */
- if (config->filesystem_encoding == NULL) {
+ if (config->filesystem_encoding == NULL) {
+ if (config->utf8_mode) {
+  /* UTF-8 Mode use: utf-8/surrogateescape */
  config->filesystem_encoding = _PyMem_RawStrdup("utf-8");
- if (config->filesystem_encoding == NULL) {
- return _Py_INIT_NO_MEMORY();
- }
+ /* errors defaults to surrogateescape above */
  }
- /* errors defaults to surrogateescape above */
- }
-
- if (config->filesystem_encoding == NULL) {
- /* macOS and Android use UTF-8, other platforms use
- the locale encoding. */
- char *locale_encoding;
+ else if (_Py_GetForceASCII()) {
+ config->filesystem_encoding = _PyMem_RawStrdup("ascii");
+ }
+ else {
+ /* macOS and Android use UTF-8,
+ other platforms use the locale encoding. */
 #if defined(__APPLE__) || defined(__ANDROID__)
- locale_encoding = "UTF-8";
+  config->filesystem_encoding = _PyMem_RawStrdup("utf-8");
 #else
- _PyInitError err = get_locale_encoding(&locale_encoding);
- if (_Py_INIT_FAILED(err)) {
- return err;
- }
+  _PyInitError err = get_locale_encoding(&config->filesystem_encoding);
+  if (_Py_INIT_FAILED(err)) {
+  return err;
+  }
 #endif
- config->filesystem_encoding = _PyMem_RawStrdup(locale_encoding);
+ }
+
  if (config->filesystem_encoding == NULL) {
  return _Py_INIT_NO_MEMORY();
  }