Indexing tuple intersection type beyond length produces unexpected type

Bug Report

🔎 Search Terms

tuple intersection index type

⏯ Playground Link

Playground Link

💻 Code

type T = [number, boolean] & { x: string };
declare const t: T;
const a = t[0]; // number
const b = t[1]; // boolean
const c = t[2]; // number | boolean !?

🙁 Actual behavior

c is typed as number | boolean

🙂 Expected behavior

c should be typed as undefined

I'm not sure if this is a bug, or intended behavior. But it was surprising. If the type is just a tuple, indexing beyond its length produced undefined. But if it is part of an intersection, the element type is changed to number | boolean, as if it is no longer a tuple, but an array. However, indexing 0 or 1 still produces the correct type for those element positions.

Commencez par le TypeScript Playground lié et reproduisez l'accès indexé à une intersection de tuples présenté dans l'issue. Suivez le chemin de vérification des types du compilateur pour l'indexation de tuples hors limites lorsqu'une intersection est présente, puis ajoutez des tests montrant que t[2] est typé comme undefined, tandis que t[0] et t[1] conservent leurs types d'élément.