Locale-encoded text is corrupted on FreeBSD, NetBSD, DragonFly BSD and macOS in non-UTF-8 locales

Bug report

On FreeBSD, NetBSD and DragonFly BSD, wchar_t values are not Unicode code points in non-UTF-8 locales: mbstowcs() and wcstombs() keep the raw locale values (e.g. the KOI8-U byte 0xD0 becomes 0x00D0, and the EUC-JP byte pair 0xB7 0xEE becomes 0xB7EE). CPython assumes that wchar_t is Unicode, so every interface which passes locale-encoded text through wchar_t produces mojibake.

For example, in the uk_UA.KOI8-U locale, time.strftime('%A') returns 'ÐÏÎÅĦÌÏË' instead of 'понеділок'. The same applies to locale.nl_langinfo(), locale.localeconv(), format(n, 'n'), localized OSError and ctypes error messages, sys.argv and readline history.

I propose to use iconv() in _Py_DecodeLocaleEx() and _Py_EncodeLocaleEx() on these platforms. Unlike the codec machinery, iconv() is usable in early interpreter startup (e.g. for decoding the command line arguments), and the C library's iconv() supports all encodings used by its own locales. wcsftime() also cannot be used, so time.strftime() should use strftime() and decode its result. If iconv() is not functional for the locale encoding, the current behavior is kept.

Related: gh-93251 (localized gai_strerror() and hstrerror() messages are decoded as UTF-8 — affects all platforms, fixed separately).

Linked PRs

• gh-154722

檢視 _Py_DecodeLocaleEx() 和 _Py_EncodeLocaleEx()，然後檢查報告中描述的 time.strftime() 路徑。比較所列 BSD 和 macOS 非 UTF-8 locale 中的行為，包括 iconv() 無法運作時的 fallback。當受影響的 locale 相關介面不再產生報告中的亂碼時，即視為完成。