Fix crash when inferring from tuple with middle rest and trailing variadic elements#63288
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ongjin wants to merge 1 commit intomicrosoft:mainfrom
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Fix crash when inferring from tuple with middle rest and trailing variadic elements#63288ongjin wants to merge 1 commit intomicrosoft:mainfrom
ongjin wants to merge 1 commit intomicrosoft:mainfrom
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…iadic elements When `getElementTypeOfSliceOfTupleType` returns `undefined` (because the implied arity from the variadic constraint consumes the entire source tuple), the result was passed directly to `inferFromTypes` via a non-null assertion, causing a `TypeError: Cannot read properties of undefined (reading 'aliasSymbol')` crash. Add null checks before calling `inferFromTypes` in both the `[...T, ...rest]` and `[...rest, ...T]` inference branches, consistent with the existing pattern used in the single-rest-element branch. Fixes microsoft#63005
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Summary
Fixes #63005
When inferring from a tuple type that has middle rest elements and trailing variadic elements (e.g.,
[...(infer C)[], ...infer B extends [any, any, any]]), the compiler crashes withTypeError: Cannot read properties of undefined (reading 'aliasSymbol').Root cause:
getElementTypeOfSliceOfTupleTypereturnsundefinedwhen the implied arity from the variadic constraint consumes the entire source tuple, but the result was passed toinferFromTypesvia a non-null assertion (!).Fix: Add null checks before calling
inferFromTypesin both the[...T, ...rest]and[...rest, ...T]inference branches, consistent with the existing pattern at the single-rest-element branch nearby.Test plan
inferTypesWithFixedTupleExtendsAtVariadicPosition.tsthat previously crashed