Fix nondeterministic type checking caused by nonassociative of None joins#19158
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JukkaL merged 2 commits intopython:masterfrom May 28, 2025
Merged
Fix nondeterministic type checking caused by nonassociative of None joins#19158JukkaL merged 2 commits intopython:masterfrom
JukkaL merged 2 commits intopython:masterfrom
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
JukkaL
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May 28, 2025
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Nice! Making join associative would be the ultimate fix, but it will be a heavy lift due to backward compat. Incrementally making things more deterministic is a good way to deal with this in the shorter term.
| colors3: A[str] | B[str] | C[int] | D[None], | ||
| ) -> None: | ||
| for c1, c2, c3 in zip2(colors1, colors2, colors3): | ||
| # TODO: can't do reveal type because the union order is not deterministic |
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I wonder if there is a way to avoid non-deterministic union order altogether, e.g. by not putting types into sets?
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Nvm, you mention this in the issue description.
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Fixes #19121 (xarray case)
See #19147 for context
The ordering of the union is still nondeterministic. We could solve this by change the solver to use
dict[Type, Noneinstead ofset[Type]since dicts are ordered. But doing so could paper over further bad solving from nonassociativity or noncommutativity