fix: preserve array and tuple structure in mapped types#2515
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Mar 30, 2026
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When a mapped type like `{ [K in keyof T]: F<T[K]> }` operates on an
array or tuple, TypeScript preserves the array/tuple structure. The
schema generator was instead producing objects with numeric string keys.
- Detect `keyof` constraint resolving to `number` (array) and produce ArrayType
- Detect `keyof` constraint resolving to numeric literal union (tuple) and
produce TupleType
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Rebased on next and ran tests. |
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@puckey CI is failing |
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Fixed the |
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Summary
{ [K in keyof T]: F<T[K]> }operates on an array or tuple, TypeScript preserves the array/tuple structure, but the schema generator produced objects with numeric string keyskeyofconstraint resolving tonumber(array) and produceArrayTypekeyofconstraint resolving to numeric literal union (tuple) and produceTupleTypeTest plan
type-immutable-array—Immutable<Bar[]>produces array schema,Immutable<[string, number]>produces tuple schema,Immutable<Bar>with Map/Set branches resolves correctly