Spread of two generic array types is misreported as having length 2

[dragomirtitian]

🔎 Search Terms

tuple spread any generic

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ

⏯ Playground Link

Playground Link

💻 Code

function join<T extends any[], P extends any[]>(): [...T, ...P] {
    let x: any[] = [];
    return x; // Target requires 2 element(s) but source may have fewer ❌❗❓
}

function join2<T extends any[], P extends any[]>(): [...T, ...P] {
    let x: [any, any] = null!
    return x; // Source provides no match for variadic element at position 0 in target ✅
}

🙁 Actual behavior

join errors on return with Target requires 2 element. There is nothing in the target type that suggests it requires two elements.

🙂 Expected behavior

Should error with a message similar to join2:

Source provides no match for variadic element at position 0 in target

Additional information about the issue

No response