Bug Report

🔎 Search Terms

Variadic tuple mapped type keyof

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

type Keys<O extends unknown[]> = { [K in keyof O]: K };

type A = Keys<[string, ...string[]]>;
type B = Keys<[string, ...string[], number]>;

🙁 Actual behavior

A and B both have the variadic part typed as ..."1"[], which is wrong. B is further wrong because the number part becomes "2", while in practice it would rarely be "2".

🙂 Expected behavior

A should be ["0", ...number[]]; B should be ["0", ...number[], number]