TS2769 : Function.bind

Bug Report

🔎 Search Terms

function bind

🕗 Version & Regression Information

TypeScript 4.1 & 4.2-beta

⏯ Playground Link

playground

💻 Code

type Funcs = {
    first (value: string): void;
    second (value: number): void;
}

type Store = {
    commit <Name extends keyof Funcs> (
        name: Name,
        ...args: Parameters<Funcs[Name]>
    ): void;
}

type Func <Name extends keyof Funcs> = (
    ...args: Parameters<Funcs[Name]>
) => void;

declare const store: Store;

function commit<Name extends keyof Funcs> (name: Name): Func<Name> {
    // error
    return store.commit.bind(undefined, name);
}

function commit2<Name extends keyof Funcs> (name: Name): Func<Name> {
    return function (...args: Parameters<Func<Name>>) {
        // correct
        store.commit(name, ...args);
    }
}

🙁 Actual behavior

(method) commit<Name extends keyof Funcs>(name: Name, ...args: Parameters<Funcs[Name]>): void
No overload matches this call.
  Overload 1 of 6, '(this: (this: undefined, arg0: Name, ...args: [value: string] | [value: number]) => void, thisArg: undefined, arg0: Name): (...args: [value: string] | [value: number]) => void', gave the following error.
    The 'this' context of type '<Name extends keyof Funcs>(name: Name, ...args: Parameters<Funcs[Name]>) => void' is not assignable to method's 'this' of type '(this: undefined, arg0: Name, ...args: [value: string] | [value: number]) => void'.
      Types of parameters 'args' and 'args' are incompatible.
        Type '[value: string] | [value: number]' is not assignable to type 'Parameters<Funcs[Name]>'.
          Type '[value: string]' is not assignable to type 'Parameters<Funcs[Name]>'.
  Overload 2 of 6, '(this: (this: undefined, ...args: Name[]) => void, thisArg: undefined, ...args: Name[]): (...args: Name[]) => void', gave the following error.
    The 'this' context of type '<Name extends keyof Funcs>(name: Name, ...args: Parameters<Funcs[Name]>) => void' is not assignable to method's 'this' of type '(this: undefined, ...args: Name[]) => void'.
      Types of parameters 'name' and 'args' are incompatible.
        Type 'Name[]' is not assignable to type '[name: Name, ...args: Parameters<Funcs[Name]>]'.
          Target requires 2 element(s) but source may have fewer.(2769)

🙂 Expected behavior

The function commit works correctly as the function commit2. I'm a bit confused and sorry if this bug has been reported.

リンク先の TypeScript Playground から始め、TypeScript 4.1 または 4.2-beta で、ジェネリックな commit と store.commit.bind の例を使って TS2769 エラーを再現します。リポジトリのファイルもテストも指定されていないため、Function.bind とジェネリックなパラメータタプルをコンパイラが処理する方法を追跡します。commit が commit2 と同じ挙動で型チェックを通れば完了です。