[ty] Improve exhaustiveness analysis for type variables with bounds or constraints #21172
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Diagnostic diff on typing conformance testsNo changes detected when running ty on typing conformance tests ✅ |
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AlexWaygood
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carljm,
dcreager and
sharkdp
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Summary
Fixes astral-sh/ty#1456.
This PR backs out the changes made in #21130 and replaces them with a more generalised implementation of exhaustiveness checking for
matches over type variables with upper bounds or constraints. The approach in #21130 works for type variables with an enum upper bound, and could have been adapted to work for type variables with aboolupper bound. But it would not work for a type variable with a union upper bound, because of the fact that we distribute over a union (to create a union of intersections) when adding a union type to an intersection.Instead, the approach this PR takes is to speculatively solve all type variables in the positive part of an intersection to their upper bound/constraints when finally building the intersection. If that speculative intersection simplifies to
Never, so must the original intersection.Test Plan
New mdtests added.