Overloaded function args not inferred correctly

Bug Report

🔎 Search Terms

overload functions

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about overloading and different function arguments behavior

⏯ Playground Link

Playground link with relevant code

💻 Code

function a1(arg1: unknown): 1;
function a1(arg1: unknown, arg2: unknown): 2;
function a1(...args: ([arg1: unknown] | [arg1: unknown, arg2: unknown])): 1 | 2 {
    return args.length;
}

const b1: typeof a1 = function f1(...args) {
    return a1(...args);
}

even simpler is using an interface

interface a1 {
    (arg1: unknown): 1;
    (arg1: unknown, arg2: unknown): 2;
}

// errors
const b1: a1 = function f1(...args) {
    return args.length;
}

🙁 Actual behavior

Error: Target signature provides too few arguments. Expected 2 or more, but got one., given the single signature of b1 above is variadic, and in fact matches the implementation signature of a1, one would assume the two functions are equivalent (from a signature perspective)

🙂 Expected behavior

The type of args in b1 should be inferred as the union of all overloads of a1 since it is the only way the variadic args would satisfy the assigned typeof a1 requirement.

リンクされた TypeScript Playground と 2 つの overload の例から始めて、diagnostic を再現します。割り当てられた関数の rest parameter が overload に対してどのように推論されるかを追跡し、その後、args が必要な overload union を受け取り、報告されたエラーなしで代入が受け入れられることを確認します。