setuptools: MANIFEST.in exclusion bypass in sdist via Unicode normalization collision (NFC/NFD) on macOS APFS/HFS+

Summary

When building a source distribution (python -m build --sdist / setup.py sdist), setuptools' FileList applies MANIFEST.in directives (exclude, global-exclude, recursive-exclude, prune) by matching a compiled glob against on-disk file names byte-for-byte, with no Unicode normalization. On normalization-preserving filesystems (notably macOS APFS and HFS+), a file written in NFD and a MANIFEST.in rule written in NFC refer to the same file but are byte-distinct, so the exclusion silently fails to match. A file the maintainer intended to exclude is then packed into the .tar.gz and, if published, uploaded to the public, immutable PyPI index.

Details

File names in FileList.files come from os.walk (setuptools/_distutils/filelist.py, _find_all_simple), so on APFS a file written NFD is offered to the matcher in NFD, while the MANIFEST.in pattern carries the author's editor form (typically NFC). The matching path performs no canonicalization:

# setuptools/command/egg_info.py  (FileList.global_exclude)
def global_exclude(self, pattern):
    match = translate_pattern(os.path.join('**', pattern))   # fnmatch.translate -> regex, no NFC/NFD
    return self._remove_files(match.match)                   # byte-level regex over raw os.walk names

A rule written NFC (café = 63 61 66 c3 a9) does not match an on-disk name written NFD (café = 63 61 66 65 cc 81), even though the filesystem treats the two as one file.

A unicodedata.normalize('NFD', ...) helper exists in setuptools/unicode_utils.py (decompose()), but it is never called in the manifest matching path, so neither the pattern nor the walked path is normalized before matching. The only normalization in this area, EggInfoCommand._manifest_normalize, uses filesys_decode (bytes→str decode only, no NFC/NFD) and runs when writing SOURCES.txt, after matching has already occurred.

Impact

MANIFEST.in exclusions are the documented mechanism maintainers use to keep secrets, local configs, and private fixtures out of the published sdist. A non-ASCII excluded file may be published to the public, immutable PyPI index despite the rule — an irreversible disclosure with no visual cue (NFC and NFD forms render identically). Exposure is filesystem-dependent and most relevant on macOS APFS/HFS+, where many maintainers build and publish. Pure-ASCII rules are unaffected.