[ty] Avoid quadratic enum comparison narrowing#25789
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Typing conformance resultsNo changes detected ✅Current numbersThe percentage of diagnostics emitted that were expected errors held steady at 92.23%. The percentage of expected errors that received a diagnostic held steady at 87.42%. The number of fully passing files held steady at 92/134. |
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Merging this PR will not alter performance
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Summary
Stacks on #25788.
The equality evaluator introduced in #25788 expands enum types into member literals before narrowing. When both operands contain enum types, recursively expanding one side causes the other side to be expanded and compared again for every member, making
==and!=quadratic. Mixed enum and open-ended unions can trigger the same repeated work without producing useful narrowing.This expands each finite operand once, then compares the resulting finite sets directly. It has fast paths for identical and disjoint sets, and it avoids expansion when the other operand includes an open-ended union arm. Narrowing with an identity singleton such as
Nonestill works.The regression coverage compares same-enum, optional-enum, and different-enum operands with 250-member enums and enforces a 10-second upper bound.