[ty] Prove TypedDict structural patterns exhaustive#26285
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Typing conformance resultsNo changes detected ✅Current numbersThe percentage of diagnostics emitted that were expected errors held steady at 94.47%. The percentage of expected errors that received a diagnostic held steady at 89.19%. The number of fully passing files held steady at 95/134. |
Memory usage reportMemory usage unchanged ✅ |
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Merging this PR will not alter performance
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dhruvmanila
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Jun 25, 2026
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Base automatically changed from
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June 25, 2026 11:35
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Summary
This is the third and final stacked PR split from #26010. It is based on #26284.
Prior to this change, we retained only whether a mapping pattern was empty or nonempty. That is enough to recognize
case {}as exhaustive for a mapping, but it cannot prove that a keyed pattern matches every value of aTypedDict. We also modelTypedDictstructurally rather than as a nominaldictsubtype, even though everyTypedDictvalue is a dictionary at runtime.This retains each mapping key and nested pattern for subject-aware exhaustiveness. A keyed mapping pattern is exhaustive for a
TypedDictonly when every key is a string literal naming a required field and every nested pattern exhausts that field's declared type. Optional, absent, and non-string keys remain refutable.The same runtime representation rule lets argumentless
dictandMappingclass patterns, along with the positionaldictmatch-self pattern, exhaust aTypedDictsubject. Negative narrowing reuses the resulting definite-match type instead of treating every nonempty mapping pattern as opaque.