bpo-29240: Fix locale encodings in UTF-8 Mode (#5170)

Modify locale.localeconv(), time.tzname, os.strerror() and other
functions to ignore the UTF-8 Mode: always use the current locale
encoding.

Changes:

* Add _Py_DecodeLocaleEx() and _Py_EncodeLocaleEx(). On decoding or
  encoding error, they return the position of the error and an error
  message which are used to raise Unicode errors in
  PyUnicode_DecodeLocale() and PyUnicode_EncodeLocale().
* Replace _Py_DecodeCurrentLocale() with _Py_DecodeLocaleEx().
* PyUnicode_DecodeLocale() now uses _Py_DecodeLocaleEx() for all
  cases, especially for the strict error handler.
* Add _Py_DecodeUTF8Ex(): return more information on decoding error
  and supports the strict error handler.
* Rename _Py_EncodeUTF8_surrogateescape() to _Py_EncodeUTF8Ex().
* Replace _Py_EncodeCurrentLocale() with _Py_EncodeLocaleEx().
* Ignore the UTF-8 mode to encode/decode localeconv(), strerror()
  and time zone name.
* Remove PyUnicode_DecodeLocale(), PyUnicode_DecodeLocaleAndSize()
  and PyUnicode_EncodeLocale() now ignore the UTF-8 mode: always use
  the "current" locale.
* Remove _PyUnicode_DecodeCurrentLocale(),
  _PyUnicode_DecodeCurrentLocaleAndSize() and
  _PyUnicode_EncodeCurrentLocale().

Doc/c-api/sys.rst

@@ -106,6 +106,16 @@ Operating System Utilities
    surrogate character, escape the bytes using the surrogateescape error
    handler instead of decoding them.
 
+   Encoding, highest priority to lowest priority:
+
+   * ``UTF-8`` on macOS and Android;
+   * ``UTF-8`` if the Python UTF-8 mode is enabled;
+   * ``ASCII`` if the ``LC_CTYPE`` locale is ``"C"``,
+     ``nl_langinfo(CODESET)`` returns the ``ASCII`` encoding (or an alias),
+     and :c:func:`mbstowcs` and :c:func:`wcstombs` functions uses the
+     ``ISO-8859-1`` encoding.
+   * the current locale encoding.
+
    Return a pointer to a newly allocated wide character string, use
    :c:func:`PyMem_RawFree` to free the memory. If size is not ``NULL``, write
    the number of wide characters excluding the null character into ``*size``
@@ -137,6 +147,18 @@ Operating System Utilities
    :ref:`surrogateescape error handler <surrogateescape>`: surrogate characters
    in the range U+DC80..U+DCFF are converted to bytes 0x80..0xFF.
 
+   Encoding, highest priority to lowest priority:
+
+   * ``UTF-8`` on macOS and Android;
+   * ``UTF-8`` if the Python UTF-8 mode is enabled;
+   * ``ASCII`` if the ``LC_CTYPE`` locale is ``"C"``,
+     ``nl_langinfo(CODESET)`` returns the ``ASCII`` encoding (or an alias),
+     and :c:func:`mbstowcs` and :c:func:`wcstombs` functions uses the
+     ``ISO-8859-1`` encoding.
+   * the current locale encoding.
+
+   The function uses the UTF-8 encoding in the Python UTF-8 mode.
+
    Return a pointer to a newly allocated byte string, use :c:func:`PyMem_Free`
    to free the memory. Return ``NULL`` on encoding error or memory allocation
    error

Doc/c-api/unicode.rst

@@ -770,12 +770,20 @@ system.
    :c:data:`Py_FileSystemDefaultEncoding` (the locale encoding read at
    Python startup).
 
+   This function ignores the Python UTF-8 mode.
+
    .. seealso::
 
       The :c:func:`Py_DecodeLocale` function.
 
    .. versionadded:: 3.3
 
+   .. versionchanged:: 3.7
+      The function now also uses the current locale encoding for the
+      ``surrogateescape`` error handler. Previously, :c:func:`Py_DecodeLocale`
+      was used for the ``surrogateescape``, and the current locale encoding was
+      used for ``strict``.
+
 
 .. c:function:: PyObject* PyUnicode_DecodeLocale(const char *str, const char *errors)
 
@@ -797,12 +805,20 @@ system.
    :c:data:`Py_FileSystemDefaultEncoding` (the locale encoding read at
    Python startup).
 
+   This function ignores the Python UTF-8 mode.
+
    .. seealso::
 
       The :c:func:`Py_EncodeLocale` function.
 
    .. versionadded:: 3.3
 
+   .. versionchanged:: 3.7
+      The function now also uses the current locale encoding for the
+      ``surrogateescape`` error handler. Previously, :c:func:`Py_EncodeLocale`
+      was used for the ``surrogateescape``, and the current locale encoding was
+      used for ``strict``.
+
 
 File System Encoding
 """"""""""""""""""""

Include/fileutils.h

@@ -20,18 +20,41 @@ PyAPI_FUNC(char*) _Py_EncodeLocaleRaw(
 #endif
 
 #ifdef Py_BUILD_CORE
+PyAPI_FUNC(int) _Py_DecodeUTF8Ex(
+    const char *arg,
+    Py_ssize_t arglen,
+    wchar_t **wstr,
+    size_t *wlen,
+    const char **reason,
+    int surrogateescape);
+
+PyAPI_FUNC(int) _Py_EncodeUTF8Ex(
+    const wchar_t *text,
+    char **str,
+    size_t *error_pos,
+    const char **reason,
+    int raw_malloc,
+    int surrogateescape);
+
 PyAPI_FUNC(wchar_t*) _Py_DecodeUTF8_surrogateescape(
-    const char *s,
-    Py_ssize_t size,
-    size_t *p_wlen);
+    const char *arg,
+    Py_ssize_t arglen);
 
-PyAPI_FUNC(wchar_t *) _Py_DecodeCurrentLocale(
+PyAPI_FUNC(int) _Py_DecodeLocaleEx(
     const char *arg,
-    size_t *size);
+    wchar_t **wstr,
+    size_t *wlen,
+    const char **reason,
+    int current_locale,
+    int surrogateescape);
 
-PyAPI_FUNC(char*) _Py_EncodeCurrentLocale(
+PyAPI_FUNC(int) _Py_EncodeLocaleEx(
     const wchar_t *text,
-    size_t *error_pos);
+    char **str,
+    size_t *error_pos,
+    const char **reason,
+    int current_locale,
+    int surrogateescape);
 #endif
 
 #ifndef Py_LIMITED_API

Include/unicodeobject.h

@@ -1810,20 +1810,6 @@ PyAPI_FUNC(PyObject*) PyUnicode_EncodeLocale(
     PyObject *unicode,
     const char *errors
     );
-
-PyAPI_FUNC(PyObject*) _PyUnicode_DecodeCurrentLocale(
-    const char *str,
-    const char *errors);
-
-PyAPI_FUNC(PyObject*) _PyUnicode_DecodeCurrentLocaleAndSize(
-    const char *str,
-    Py_ssize_t len,
-    const char *errors);
-
-PyAPI_FUNC(PyObject*) _PyUnicode_EncodeCurrentLocale(
-    PyObject *unicode,
-    const char *errors
-    );
 #endif
 
 /* --- File system encoding ---------------------------------------------- */

Modules/_datetimemodule.c

@@ -696,7 +696,7 @@ static int parse_isoformat_date(const char *dtstr,
     if (NULL == p) {
         return -1;
     }
-    
+
     if (*(p++) != '-') {
         return -2;
     }

Modules/_localemodule.c

@@ -572,8 +572,9 @@ PyIntl_bind_textdomain_codeset(PyObject* self,PyObject*args)
     if (!PyArg_ParseTuple(args, "sz", &domain, &codeset))
         return NULL;
     codeset = bind_textdomain_codeset(domain, codeset);
-    if (codeset)
+    if (codeset) {
         return PyUnicode_DecodeLocale(codeset, NULL);
+    }
     Py_RETURN_NONE;
 }
 #endif

Modules/getpath.c

@@ -449,8 +449,8 @@ search_for_exec_prefix(const _PyCoreConfig *core_config,
             n = fread(buf, 1, MAXPATHLEN, f);
             buf[n] = '\0';
             fclose(f);
-            rel_builddir_path = _Py_DecodeUTF8_surrogateescape(buf, n, NULL);
-            if (rel_builddir_path != NULL) {
+            rel_builddir_path = _Py_DecodeUTF8_surrogateescape(buf, n);
+            if (rel_builddir_path) {
                 wcsncpy(exec_prefix, calculate->argv0_path, MAXPATHLEN);
                 exec_prefix[MAXPATHLEN] = L'\0';
                 joinpath(exec_prefix, rel_builddir_path);

Modules/readline.c

@@ -132,13 +132,13 @@ static PyModuleDef readlinemodule;
 static PyObject *
 encode(PyObject *b)
 {
-    return _PyUnicode_EncodeCurrentLocale(b, "surrogateescape");
+    return PyUnicode_EncodeLocale(b, "surrogateescape");
 }
 
 static PyObject *
 decode(const char *s)
 {
-    return _PyUnicode_DecodeCurrentLocale(s, "surrogateescape");
+    return PyUnicode_DecodeLocale(s, "surrogateescape");
 }
 
 

Modules/timemodule.c

@@ -418,11 +418,11 @@ tmtotuple(struct tm *p
     SET(8, p->tm_isdst);
 #ifdef HAVE_STRUCT_TM_TM_ZONE
     PyStructSequence_SET_ITEM(v, 9,
-        _PyUnicode_DecodeCurrentLocale(p->tm_zone, "surrogateescape"));
+        PyUnicode_DecodeLocale(p->tm_zone, "surrogateescape"));
     SET(10, p->tm_gmtoff);
 #else
     PyStructSequence_SET_ITEM(v, 9,
-        _PyUnicode_DecodeCurrentLocale(zone, "surrogateescape"));
+        PyUnicode_DecodeLocale(zone, "surrogateescape"));
     PyStructSequence_SET_ITEM(v, 10, _PyLong_FromTime_t(gmtoff));
 #endif /* HAVE_STRUCT_TM_TM_ZONE */
 #undef SET
@@ -809,8 +809,7 @@ time_strftime(PyObject *self, PyObject *args)
 #ifdef HAVE_WCSFTIME
             ret = PyUnicode_FromWideChar(outbuf, buflen);
 #else
-            ret = _PyUnicode_DecodeCurrentLocaleAndSize(outbuf, buflen,
-                                                        "surrogateescape");
+            ret = PyUnicode_DecodeLocaleAndSize(outbuf, buflen, "surrogateescape");
 #endif
             PyMem_Free(outbuf);
             break;
@@ -1541,8 +1540,8 @@ PyInit_timezone(PyObject *m) {
     PyModule_AddIntConstant(m, "altzone", timezone-3600);
 #endif
     PyModule_AddIntConstant(m, "daylight", daylight);
-    otz0 = _PyUnicode_DecodeCurrentLocale(tzname[0], "surrogateescape");
-    otz1 = _PyUnicode_DecodeCurrentLocale(tzname[1], "surrogateescape");
+    otz0 = PyUnicode_DecodeLocale(tzname[0], "surrogateescape");
+    otz1 = PyUnicode_DecodeLocale(tzname[1], "surrogateescape");
     PyModule_AddObject(m, "tzname", Py_BuildValue("(NN)", otz0, otz1));
 #else /* !HAVE_TZNAME || __GLIBC__ || __CYGWIN__*/
     {