Handle unreadable configuration files - #4035
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gaborbernat merged 2 commits intoAug 20, 2026
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Fixes tox-dev#4031. The three source-loading paths in tox.config.source.discover translate ValueError into HandledError, but reading a file can also raise an OSError subclass. A config file that exists and cannot be read - wrong permissions, a directory where a file was expected - lets PermissionError escape, and the CLI prints a full traceback instead of the one-line error it uses for malformed files. Catches OSError alongside ValueError in all three paths: the directory branch of discover_source, _locate_source, and _load_exact_source. Affects the named file, automatic discovery, and -c <directory> equally. The regression test exercises discover_source directly rather than going through the tox_project fixture. The fixture converts exceptions on its own, so through it both the fixed and unfixed code produce the same output and the test cannot tell them apart.
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Fixes #4031.
The problem
The three source-loading paths in
tox.config.source.discovertranslateValueErrorintoHandledError, but reading a file can also raise anOSErrorsubclass. So a config file that exists and cannot be read letsPermissionErrorescape:After:
The change
OSErroris caught alongsideValueErrorin all three paths — the directory branch ofdiscover_source,_locate_source, and_load_exact_source— so the named file, automatic discovery, and-c <directory>all behave the same. Verified all three by hand.A note on the test
The regression test exercises
discover_sourcedirectly rather than going through thetox_projectfixture.I wrote it through the fixture first, and it passed against unfixed code. The fixture converts exceptions on its own, so from the outside both versions produce the same
HandledError| ToxIni failed loadingline and the test cannot tell them apart. Testing the function where the bug lives does distinguish them: unfixed it raisesPermissionError, fixed it raisesHandledError.The test is skipped on Windows and when running as root, since neither can make a file unreadable this way.
tests/config/source/: 200 passed.