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| og:image:alt | Previously we considered the else branch unreachable in the testNarrowingAnyUnion test case. It's also nice that the new code is more obviously correct
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Feb 3, 2026
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Better narrowing
#20564
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Check #20728
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Improve narrowing with numeric types
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[1.18 regression] Negative type narrowing of TypeIs of Union with TypeVar not working
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