bpo-29240: PyUnicode_DecodeLocale() uses UTF-8 on Android (#5272)

PyUnicode_DecodeLocaleAndSize(), PyUnicode_DecodeLocale() and
PyUnicode_EncodeLocale() now use always use the UTF-8 encoding on
Android, instead of the current locale encoding.

On Android API 19, mbstowcs() and wcstombs() are broken and cannot be
used.

Doc/c-api/unicode.rst

@@ -760,7 +760,8 @@ system.
                                                         Py_ssize_t len, \
                                                         const char *errors)
 
-   Decode a string from the current locale encoding. The supported
+   Decode a string from UTF-8 on Android, or from the current locale encoding
+   on other platforms. The supported
    error handlers are ``"strict"`` and ``"surrogateescape"``
    (:pep:`383`). The decoder uses ``"strict"`` error handler if
    *errors* is ``NULL``.  *str* must end with a null character but
@@ -780,7 +781,7 @@ system.
 
    .. versionchanged:: 3.7
       The function now also uses the current locale encoding for the
-      ``surrogateescape`` error handler. Previously, :c:func:`Py_DecodeLocale`
+      ``surrogateescape`` error handler, except on Android. Previously, :c:func:`Py_DecodeLocale`
       was used for the ``surrogateescape``, and the current locale encoding was
       used for ``strict``.
 
@@ -795,7 +796,8 @@ system.
 
 .. c:function:: PyObject* PyUnicode_EncodeLocale(PyObject *unicode, const char *errors)
 
-   Encode a Unicode object to the current locale encoding. The
+   Encode a Unicode object to UTF-8 on Android, or to the current locale
+   encoding on other platforms. The
    supported error handlers are ``"strict"`` and ``"surrogateescape"``
    (:pep:`383`). The encoder uses ``"strict"`` error handler if
    *errors* is ``NULL``. Return a :class:`bytes` object. *unicode* cannot
@@ -815,7 +817,8 @@ system.
 
    .. versionchanged:: 3.7
       The function now also uses the current locale encoding for the
-      ``surrogateescape`` error handler. Previously, :c:func:`Py_EncodeLocale`
+      ``surrogateescape`` error handler, except on Android. Previously,
+      :c:func:`Py_EncodeLocale`
       was used for the ``surrogateescape``, and the current locale encoding was
       used for ``strict``.
 

Python/fileutils.c

@@ -449,7 +449,12 @@ _Py_DecodeLocaleEx(const char* arg, wchar_t **wstr, size_t *wlen,
                    int current_locale, int surrogateescape)
 {
     if (current_locale) {
+#ifdef __ANDROID__
+        return _Py_DecodeUTF8Ex(arg, strlen(arg), wstr, wlen, reason,
+                                surrogateescape);
+#else
         return decode_current_locale(arg, wstr, wlen, reason, surrogateescape);
+#endif
     }
 
 #if defined(__APPLE__) || defined(__ANDROID__)
@@ -605,8 +610,13 @@ encode_locale_ex(const wchar_t *text, char **str, size_t *error_pos,
                  int raw_malloc, int current_locale, int surrogateescape)
 {
     if (current_locale) {
+#ifdef __ANDROID__
+        return _Py_EncodeUTF8Ex(text, str, error_pos, reason,
+                                raw_malloc, surrogateescape);
+#else
         return encode_current_locale(text, str, error_pos, reason,
                                      raw_malloc, surrogateescape);
+#endif
     }
 
 #if defined(__APPLE__) || defined(__ANDROID__)