Parameters and readonly tuples

Bug Report

I've encountered a wrong type inference regarding the Parameters generic when the rest operator and the union of readonly tuples are used together.

🔎 Search Terms

infer, Parameters, readonly.

🕗 Version & Regression Information

I have only tested this on TypeScript 4.3.5.

⏯ Playground Link

Playground link with relevant code

In this example, P1 is correctly inferred, whereas P2 is not.

💻 Code

type F = (...args: readonly [number, string] | readonly [string, number]) => void;
type P = Parameters<F>;

🙁 Actual behavior

The type P is never.

🙂 Expected behavior

One would expect P to be of type readonly [number, string] | readonly [string, number].

Inizia con l'esempio collegato di TypeScript Playground e riproduci l'inferenza di Parameters per l'unione di tuple readonly. Traccia la gestione da parte del compilatore dei parametri rest, delle tuple union e di Parameters, quindi verifica che P venga inferito come readonly [number, string] | readonly [string, number] anziché come never.