[issue35883] Change invalid unicode characters to replacement characters in argv

[STINNER Victor]

STINNER Victor <vstinner at python.org> added the comment:

I wrote PR 24843 to fix this issue. With this fix, os.fsencode(sys.argv[1]) returns the original byte sequence as expected.

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I dislike the replace error handler since it loses information. The PEP 383 surrogateescape error handler exists to prevent losing information.

The root issue is that Py_DecodeLocale() creates wide characters outside Python Unicode valid range: [U+0000; U+10ffff].

On Linux, Py_DecodeLocale() usually calls mbstowcs() of the C library. The problem is that the the glibc UTF-8 decoder doesn't respect the RFC 3629, it doesn't reject characters outside [U+0000; U+10ffff] range. The following issue requests to change the glibc UTF-8 codec to respect the RFC 3629, but it's open since 2006:
https://sourceware.org/bugzilla/show_bug.cgi?id=2373

Even if the glibc changes, Python should behave the same on old glibc version.

My PEP modifies Py_DecodeLocale() to check if there are characters outside [U+0000; U+10ffff] range and use the surrogateescape error handler in that case.

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<https://bugs.python.org/issue35883>
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