Fix matching against union of tuples #19600
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Inspired by @Copilot in 35ae089
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
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This is now ready for review. |
This was referenced Aug 7, 2025
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This pull request fixes handling of union types containing tuples in match statements. Previously, when a tuple was part of a union, all its items would be unioned together and treated as a homogeneous tuple of that union type, which was incorrect.
It still fallbacks on this behavior if we there are multiple tuples in the union with Unpack in them, but otherwise now it should be handled correctly.
I attempted to keep as much of the existing semantics the same besides for this change. I also tried to keep the performance roughly similar, not unioning types more than needed.
Closes #19599