...args should not be readonly within function body

Bug Report

🔎 Search Terms

readonly parameter inferred tuple array args variadic

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground Link

💻 Code

declare function callFn<T extends readonly any[]>(args: T, fn: (...args: T) => void): void;

declare const input: readonly string[];

callFn(input, (...args) => {
    args; // readonly string[] ?
})

declare function callFnNonGeneric(args: readonly string[], fn: (...args: readonly string[]) => void): void;

callFnNonGeneric(input, (...args) => {
    args; // readonly string[] ?
})

🙁 Actual behavior

...args is readonly.

🙂 Expected behavior

...args is not readonly.

When this function is called, the input will be a brand new array which can be modified without affecting the caller:

> const fn = (...args) => { args[0] = "oops" }
undefined
> const arr = ["some", "values"]
undefined
> fn(...arr)
undefined
> arr
[ 'some', 'values' ]

Split out of https://github.com/microsoft/TypeScript/pull/53258#issuecomment-1470970487

The "fix" here is to strip readonly from variadic args (at the top level). This also means the fix in #53258 can be reverted (as the real fix can be more general).

Inizia con l'esempio Playground collegato per riprodurre il modo in cui vengono inferiti gli argomenti variadici readonly, quindi leggi la discussione in PR #53258 sulla correzione correlata. Verifica che i parametri rest del corpo della funzione siano mutabili, preservando al contempo l'array readonly del chiamante, e verifica il comportamento previsto con gli esempi di questa issue.